Seaweed Growth Monitoring with a Low-Cost Vision-Based System

In this paper, we introduce a method for automated seaweed growth monitoring by combining a low-cost RGB and stereo vision camera. While current vision-based seaweed growth monitoring techniques focus on laboratory measurements or above-ground seaweed, we investigate the feasibility of the underwater imaging of a vertical seaweed farm. We use deep learning-based image segmentation (DeeplabV3+) to determine the size of the seaweed in pixels from recorded RGB images. We convert this pixel size to meters squared by using the distance information from the stereo camera. We demonstrate the performance of our monitoring system using measurements in a seaweed farm in the River Scheldt estuary (in The Netherlands). Notwithstanding the poor visibility of the seaweed in the images, we are able to segment the seaweed with an intersection of the union (IoU) of 0.9, and we reach a repeatability of 6% and a precision of the seaweed size of 18%.

Leveraging the blue economy to transform marine forest restoration

The UN Decade of Ecosystem Restoration is a response to the urgent need to substantially accelerate and upscale ecological restoration to secure Earth's sustainable future. Globally, restoration commitments have focused overwhelmingly on terrestrial forests. In contrast, despite a strong value proposition, efforts to restore seaweed forests lag far behind other major ecosystems and continue to be dominated by small-scale, short-term academic experiments. However, seaweed forest restoration can match the scale of damage and threat if moved from academia into the hands of community groups, industry, and restoration practitioners. Connecting two rapidly growing sectors in the Blue Economy-seaweed cultivation and the restoration industry-can transform marine forest restoration into a commercial-scale enterprise that can make a significant contribution to global restoration efforts.

Assessment of intertidal seaweed biomass based on RGB imagery

The Above Ground Biomass (AGB) of seaweeds is the most fundamental ecological parameter as the material and energy basis of intertidal ecosystems. Therefore, there is a need to develop an efficient survey method that has less impact on the environment. With the advent of technology and the availability of popular filming devices such as smartphones and cameras, intertidal seaweed wet biomass can be surveyed by remote sensing using popular RGB imaging sensors. In this paper, 143 in situ sites of seaweed in the intertidal zone of GouQi Island, ShengSi County, Zhejiang Province, were sampled and biomass inversions were performed. The hyperspectral data of seaweed at different growth stages were analyzed, and it was found that the variation range was small (visible light range < 0.1). Through Principal Component Analysis (PCA), Most of the variance is explained in the first principal component, and the load allocated to the three kinds of seaweed is more than 90%. Through Pearson correlation analysis, 24 parameters of spectral features, 9 parameters of texture features (27 in total for the three RGB bands) and parameters of combined spectral and texture features of the images were selected for screening, and regression prediction was performed using two methods: Random Forest (RF), and Gradient Boosted Decision Tree (GBDT), combined with Pearson correlation coefficients. Compared with the other two models, GBDT has better fitting accuracy in the inversion of seaweed biomass, and the highest R² was obtained when the top 17, 17 and 11 parameters with strong correlation were selected for the regression prediction by Pearson’s correlation coefficient for Ulva australis, Sargassum thunbergii, and Sargassum fusiforme, and the R² for Ulva australis was 0.784, RMSE 156.129, MAE 50.691 and MAPE 28.201, the R² for Sargassum thunbergii was 0.854, RMSE 790.487, MAE 327.108 and MAPE 19.039, and the R² for Sargassum fusiforme was 0.808, RMSE 445.067 and MAPE 28.822. MAE was 180.172 and MAPE was 28.822. The study combines in situ survey with machine learning methods, which has the advantages of being popular, efficient and environmentally friendly, and can provide technical support for intertidal seaweed surveys.

Distinguishing the molecular diversity, nutrient content, and energetic potential of exometabolomes produced by macroalgae and reef-building corals

Metabolites exuded by primary producers comprise a significant fraction of marine dissolved organic matter, a poorly characterized, heterogenous mixture that dictates microbial metabolism and biogeochemical cycling. We present a foundational untargeted molecular analysis of exudates released by coral reef primary producers using liquid chromatography-tandem mass spectrometry to examine compounds produced by two coral species and three types of algae (macroalgae, turfing microalgae, and crustose coralline algae [CCA]) from Mo'orea, French Polynesia. Of 10,568 distinct ion features recovered from reef and mesocosm waters, 1,667 were exuded by producers; the majority (86%) were organism specific, reflecting a clear divide between coral and algal exometabolomes. These data allowed us to examine two tenets of coral reef ecology at the molecular level. First, stoichiometric analyses show a significantly reduced nominal carbon oxidation state of algal exometabolites than coral exometabolites, illustrating one ecological mechanism by which algal phase shifts engender fundamental changes in the biogeochemistry of reef biomes. Second, coral and algal exometabolomes were differentially enriched in organic macronutrients, revealing a mechanism for reef nutrient-recycling. Coral exometabolomes were enriched in diverse sources of nitrogen and phosphorus, including tyrosine derivatives, oleoyl-taurines, and acyl carnitines. Exometabolites of CCA and turf algae were significantly enriched in nitrogen with distinct signals from polyketide macrolactams and alkaloids, respectively. Macroalgal exometabolomes were dominated by nonnitrogenous compounds, including diverse prenol lipids and steroids. This study provides molecular-level insights into biogeochemical cycling on coral reefs and illustrates how changing benthic cover on reefs influences reef water chemistry with implications for microbial metabolism.

Highly restricted dispersal in habitat-forming seaweed may impede natural recovery of disturbed populations

Cystoseira sensu lato (Class Phaeophyceae, Order Fucales, Family Sargassaceae) forests play a central role in marine Mediterranean ecosystems. Over the last decades, Cystoseira s.l. suffered from a severe loss as a result of multiple anthropogenic stressors. In particular, Gongolaria barbata has faced multiple human-induced threats, and, despite its ecological importance in structuring rocky communities and hosting a large number of species, the natural recovery of G. barbata depleted populations is uncertain. Here, we used nine microsatellite loci specifically developed for G. barbata to assess the genetic diversity of this species and its genetic connectivity among fifteen sites located in the Ionian, the Adriatic and the Black Seas. In line with strong and significant heterozygosity deficiencies across loci, likely explained by Wahlund effect, high genetic structure was observed among the three seas (ENA corrected FST = 0.355, IC = [0.283, 0.440]), with an estimated dispersal distance per generation smaller than 600 m, both in the Adriatic and Black Sea. This strong genetic structure likely results from restricted gene flow driven by geographic distances and limited dispersal abilities, along with genetic drift within isolated populations. The presence of genetically disconnected populations at small spatial scales (< 10 km) has important implications for the identification of relevant conservation and management measures for G. barbata: each population should be considered as separated evolutionary units with dedicated conservation efforts.

On the Health Benefits vs. Risks of Seaweeds and Their Constituents: The Curious Case of the Polymer Paradigm

To exploit the nutraceutical and biomedical potential of selected seaweed-derived polymers in an economically viable way, it is necessary to analyze and understand their quality and yield fluctuations throughout the seasons. In this study, the seasonal polysaccharide yield and respective quality were evaluated in three selected seaweeds, namely the agarophyte Gracilaria gracilis, the carrageenophyte Calliblepharis jubata (both red seaweeds) and the alginophyte Sargassum muticum (brown seaweed). It was found that the agar synthesis of G. gracilis did not significantly differ with the seasons (27.04% seaweed dry weight (DW)). In contrast, the carrageenan content in C. jubata varied seasonally, being synthesized in higher concentrations during the summer (18.73% DW). Meanwhile, the alginate synthesis of S. muticum exhibited a higher concentration (36.88% DW) during the winter. Therefore, there is a need to assess the threshold at which seaweed-derived polymers may have positive effects or negative impacts on human nutrition. Furthermore, this study highlights the three polymers, along with their known thresholds, at which they can have positive and/or negative health impacts. Such knowledge is key to recognizing the paradigm governing their successful deployment and related beneficial applications in humans.

Ocean acidification decreases grazing pressure but alters morphological structure in a dominant coastal seaweed

Ocean acidification driven by anthropogenic climate change is causing a global decrease in pH, which is projected to be 0.4 units lower in coastal shallow waters by the year 2100. Previous studies have shown that seaweeds grown under such conditions may alter their growth and photosynthetic capacity. It is not clear how such alterations might impact interactions between seaweed and herbivores, e.g. through changes in feeding rates, nutritional value, or defense levels. Changes in seaweeds are particularly important for coastal food webs, as they are key primary producers and often habitat-forming species. We cultured the habitat-forming brown seaweed Fucus vesiculosus for 30 days in projected future pCO2 (1100 μatm) with genetically identical controls in ambient pCO2 (400 μatm). Thereafter the macroalgae were exposed to grazing by Littorina littorea, acclimated to the relevant pCO2-treatment. We found increased growth (measured as surface area increase), decreased tissue strength in a tensile strength test, and decreased chemical defense (phlorotannins) levels in seaweeds exposed to high pCO2-levels. The herbivores exposed to elevated pCO2-levels showed improved condition index, decreased consumption, but no significant change in feeding preference. Fucoid seaweeds such as F. vesiculosus play important ecological roles in coastal habitats and are often foundation species, with a key role for ecosystem structure and function. The change in surface area and associated decrease in breaking force, as demonstrated by our results, indicate that F. vesiculosus grown under elevated levels of pCO2 may acquire an altered morphology and reduced tissue strength. This, together with increased wave energy in coastal ecosystems due to climate change, could have detrimental effects by reducing both habitat and food availability for herbivores.

Invasive Seaweeds in the Iberian Peninsula: A Contribution for Food Supply

The introduction of exotic organisms in marine ecosystems can lead to economic and ecological losses. Globally, seaweeds represent a significant part of these non-indigenous species (NIS), with 407 introduced algal species. Furthermore, the presence of NIS seaweeds has been reported as a major concern worldwide since the patterns of their potential invasion mechanisms and vectors are not yet fully understood. Currently, in the Iberian Peninsula, around 50 NIS seaweeds have been recorded. Some of these are also considered invasive due to their overgrowth characteristic and competition with other species. However, invasive seaweeds are suitable for industrial applications due to their high feedstock. Hence, seaweeds' historical use in daily food diet, allied to research findings, showed that macroalgae are a source of nutrients and bioactive compounds with nutraceutical properties. The main goal of this review is to evaluate the records of NIS seaweeds in the Iberian Peninsula and critically analyze the potential of invasive seaweeds application in the food industry.

Arctic coastal benthos long-term responses to perturbations under climate warming

Climate warming influences structure and function of Arctic benthic ecosystems. Assessing the response of these systems to perturbations requires long-term studies addressing key ecological processes related to recolonization and succession of species. Based on unique time-series (1980-2017), this study addresses successional patterns of hard-bottom benthos in two fjords in NW Svalbard after a pulse perturbation in 1980 and during a period of rapid climate warming. Analysis of seafloor photographs revealed different return rates of taxa, and variability in species densities, through time. It took 13 and 24 years for the community compositions of cleared and control transects to converge in the two fjords. Nearly two decades after the study initiation, an increase in filamentous and foliose macroalgae was observed with a subsequent reorganization in the invertebrate community. Trait analyses showed a decrease in body size and longevity of taxa in response to the pulse perturbation and a shift towards small/medium size and intermediate longevity following the macroalgae takeover. The observed slow recovery rates and abrupt shifts in community structure document the vulnerability of Arctic coastal ecosystems to perturbations and continued effects of climate warming. This article is part of the theme issue 'The changing Arctic Ocean: consequences for biological communities, biogeochemical processes and ecosystem functioning'.

Optimal number of Fucus vesiculosus samples to differentiate between sites affected by distinct levels of heavy metal contamination

The presence of trace elements in marine habitats is a serious environmental problem which increasingly affects ecosystem and human health. The use of macroalgae as contamination biomonitors represents a valuable alternative approach to traditional physicochemical methods. The present study was carried out to determine the optimal number of samples of Fucus vesiculosus needed to detect statistically significant differences in the mean concentrations of Al, As, Cd, Co Cr, Cu, Fe, Hg, Ni, Pb, Zn, N and δ15N between two sampling sites affected by different levels of contamination. For this purpose, we plotted the density distributions of the concentrations of the different elements and examined the local variability at three sites. For sites with mean concentrations differing by more than 30 %, 20 samples were sufficient to detect significant differences for all of the elements, except Cr. The proposed methodology could be used in other studies in the absence of specific research on each species and region.

Estimating intertidal seaweed biomass at larger scales from quadrat surveys

The amount of macroalgal biomass is an important ecosystem variable. Estimates can be made for a sampled area or values can be extrapolated to represent biomass over a larger region. Typically biomass is scaled-up using the area multiplied by the mean: a non-spatial method. Where algal biomass is patchy or shows gradients, non-spatial estimates for an area may be improved by spatial interpolation. A separate issue with scaling-up biomass estimates is that conventional confidence intervals based on the standard error (SE) of the sample may not be appropriate. The issues around interpolation and confidence intervals were examined for three fucoid species using data from 40 × 0.25 m-2 quadrats thrown in a 0.717 ha sampling plot on the shore of Galway Bay. Despite evidence of spatial autocorrelation, interpolation did not appear to improve estimates of the total plot biomass of Fucus serratus and F. vesiculosus. In contrast, interpolated estimates for Ascophyllum nodosum had less error than those based on the non-spatial method. Bootstrapped confidence intervals had several benefits over those based on the SE. These benefits include the avoidance of negative confidence limits at low sample sizes and no assumptions of normality in the data. If there is reason to expect strong patchiness or a gradient of biomass in the area of interest, interpolation is likely to produce more accurate estimates of biomass than non-spatial methods. Development of methodologies for biomass would benefit from more definition of local and regional gradients in biomass and their associated covariates.

Macroalgal germplasm banking for conservation, food security, and industry

Ex situ seed banking was first conceptualized and implemented in the early 20th century to maintain and protect crop lines. Today, ex situ seed banking is important for the preservation of heirloom strains, biodiversity conservation and ecosystem restoration, and diverse research applications. However, these efforts primarily target microalgae and terrestrial plants. Although some collections include macroalgae (i.e., seaweeds), they are relatively few and have yet to be connected via any international, coordinated initiative. In this piece, we provide a brief introduction to macroalgal germplasm banking and its application to conservation, industry, and mariculture. We argue that concerted effort should be made globally in germline preservation of marine algal species via germplasm banking with an overview of the technical advances for feasibility and ensured success.

Seaweed germplasm banking is an important resource for biodiversity conservation, human food security, and industry innovation. This Perspective article maintains that an international, coordinative initiative is needed to fully develop and capitalize on this resource.

Neoproterozoic origin and multiple transitions to macroscopic growth in green seaweeds

The Neoproterozoic Era records the transition from a largely bacterial to a predominantly eukaryotic phototrophic world, creating the foundation for the complex benthic ecosystems that have sustained Metazoa from the Ediacaran Period onward. This study focuses on the evolutionary origins of green seaweeds, which play an important ecological role in the benthos of modern sunlit oceans and likely played a crucial part in the evolution of early animals by structuring benthic habitats and providing novel niches. By applying a phylogenomic approach, we resolve deep relationships of the core Chlorophyta (Ulvophyceae or green seaweeds, and freshwater or terrestrial Chlorophyceae and Trebouxiophyceae) and unveil a rapid radiation of Chlorophyceae and the principal lineages of the Ulvophyceae late in the Neoproterozoic Era. Our time-calibrated tree points to an origin and early diversification of green seaweeds in the late Tonian and Cryogenian periods, an interval marked by two global glaciations with strong consequent changes in the amount of available marine benthic habitat. We hypothesize that unicellular and simple multicellular ancestors of green seaweeds survived these extreme climate events in isolated refugia, and diversified in benthic environments that became increasingly available as ice retreated. An increased supply of nutrients and biotic interactions, such as grazing pressure, likely triggered the independent evolution of macroscopic growth via different strategies, including true multicellularity, and multiple types of giant-celled forms.

Socioeconomic prospects of a seaweed bioeconomy in Sweden

Seaweed cultivation is a large industry worldwide, but production in Europe is small compared to production in Asian countries. In the EU, the motivations for seaweed farming may be seen from two perspectives; one being economic growth through biomass production and the other being the provisioning of ecosystem services such as mitigating eutrophication. In this paper, we assess the economic potential of large-scale cultivation of kelp, Saccharina latissima, along the Swedish west coast, including the value of externalities. The findings suggest that seaweed farming has the potential of becoming a profitable industry in Sweden. Furthermore, large-scale seaweed farming can sequester a significant share of annual anthropogenic nitrogen and phosphorus inflows to the basins of the Swedish west coast (8% of N and 60% of P). Concerning the valuation of externalities, positive values generated from sequestration of nitrogen and phosphorus are potentially counteracted by negative values from interference with recreational values. Despite the large N and P uptake, the socioeconomic value of this sequestration is only a minor share of the potential financial value from biomass production. This suggests that e.g. payment schemes for nutrient uptake based on the socioeconomic values generated is not likely to be a tipping point for the industry. Additionally, seaweed cultivation is not a cost-efficient measure in itself to remove nutrients. Policy should thus be oriented towards industry development, as the market potential of the biomass will be the driver that may unlock these bioremediation opportunities.

Development of a suitability assessment model for the cultivation of intertidal macroalgae in the United States

The focus of this novel study was to determine the comparative suitability of intertidal macroalgae production along the coast of the contiguous United States and determine the optimal locations to consider commercial cultivation using geographic information systems (GIS) software. Intertidal macroalgae cultivation represents an immense opportunity in the United States. The market demand for macroalgae has been growing and is expected to continue with the discovery of new uses. Currently, the coastal waters of the United States are extremely underutilized, particularly for macroalgae production. This study considered economic and environmental factors at a national scale, finally assessing the viability in a representative body of water with in-situ water sampling. The results of this study suggest that intertidal macroalgae cultivation is most ideally suited for the southeastern United States, primarily due to lower costs of production and more hospitable coastlines. Based on a limited water quality samples, it is feasible for macroalgae cultivation. However, due to the informational deficits, as acknowledged in this study, more work is required to refine and enhance the assessment model. This paper identifies these gaps and lists recommendations to overcome these knowledge gaps.

The Unique Lipidomic Signatures of Saccharina latissima Can Be Used to Pinpoint Their Geographic Origin

The aquaculture of macroalgae for human consumption and other high-end applications is experiencing unprecedented development in European countries, with the brown algae Saccharina latissima being the flag species. However, environmental conditions in open sea culture sites are often unique, which may impact the biochemical composition of cultured macroalgae. The present study compared the elemental compositions (CHNS), fatty acid profiles, and lipidomes of S. latissima originating from three distinct locations (France, Norway, and the United Kingdom). Significant differences were found in the elemental composition, with Norwegian samples displaying twice the lipid content of the others, and significantly less protein (2.6%, while French and UK samples contained 6.3% and 9.1%, respectively). The fatty acid profiles also differed considerably, with UK samples displaying a lower content of n-3 fatty acids (21.6%), resulting in a higher n-6/n-3 ratio. Regarding the lipidomic profile, samples from France were enriched in lyso lipids, while those from Norway displayed a particular signature of phosphatidylglycerol, phosphatidylinositol, and phosphatidylcholine. Samples from the UK featured higher levels of phosphatidylethanolamine and, in general, a lower content of galactolipids. These differences highlight the influence of site-specific environmental conditions in the shaping of macroalgae biochemical phenotypes and nutritional value. It is also important to highlight that differences recorded in the lipidome of S. latissima make it possible to pinpoint specific lipid species that are likely to represent origin biomarkers. This finding is relevant for future applications in the field of geographic origin traceability and food control.

Transcriptome sequencing of Saccharina japonica sporophytes during whole developmental periods reveals regulatory networks underlying alginate and mannitol biosynthesis

BACKGROUND

Alginate is an important cell wall component and mannitol is a soluble storage carbon substance in the brown seaweed Saccharina japonica. Their contents vary with kelp developmental periods and harvesting time. Alginate and mannitol regulatory networks and molecular mechanisms are largely unknown.

RESULTS

With WGCNA and trend analysis of 20,940 known genes and 4264 new genes produced from transcriptome sequencing of 30 kelp samples from different stages and tissues, we deduced that ribosomal proteins, light harvesting complex proteins and "imm upregulated 3" gene family are closely associated with the meristematic growth and kelp maturity. Moreover, 134 and 6 genes directly involved in the alginate and mannitol metabolism were identified, respectively. Mannose-6-phosphate isomerase (MPI2), phosphomannomutase (PMM1), GDP-mannose 6-dehydrogenase (GMD3) and mannuronate C5-epimerase (MC5E70 and MC5E122) are closely related with the high content of alginate in the distal blade. Mannitol accumulation in the basal blade might be ascribed to high expression of mannitol-1-phosphate dehydrogenase (M1PDH1) and mannitol-1-phosphatase (M1Pase) (in biosynthesis direction) and low expression of mannitol-2-dehydrogenase (M2DH) and Fructokinase (FK) (in degradation direction). Oxidative phosphorylation and photosynthesis provide ATP and NADH for mannitol metabolism whereas glycosylated cycle and tricarboxylic acid (TCA) cycle produce GTP for alginate biosynthesis. RNA/protein synthesis and transportation might affect alginate complex polymerization and secretion processes. Cryptochrome (CRY-DASH), xanthophyll cycle, photosynthesis and carbon fixation influence the production of intermediate metabolite of fructose-6-phosphate, contributing to high content of mannitol in the basal blade.

CONCLUSIONS

The network of co-responsive DNA synthesis, repair and proteolysis are presumed to be involved in alginate polymerization and secretion, while upstream light-responsive reactions are important for mannitol accumulation in meristem of kelp. Our transcriptome analysis provides new insights into the transcriptional regulatory networks underlying the biosynthesis of alginate and mannitol during S. japonica developments.

Removal of an established invader can change gross primary production of native macroalgae and alter carbon flow in intertidal rock pools

The impact of invasive species on recipient communities can vary with environmental context and across levels of biological complexity. We investigated how an established invasive seaweed species affected the biomass, eco-physiology, carbon and nitrogen storage capacity of native seaweeds at sites with a different environmental setting due to a persistent upwelling in northern Spain. We removed the invasive Japanese wireweed Sargassum muticum from intertidal rock pools once every month during a one-year period and used an in-situ stable isotope pulse-chase labeling to estimate gross primary production (GPP), nitrogen uptake rate, 13C-carbon and 15N-nitrogen storage capacities. Following the addition of 13C-enriched bicarbonate and 15N-enriched nitrate to the seawater in the rock pools during the period of the low tide, we sampled macroalgal thalli at incoming tide to determine label uptake rate. After four days, we sampled macroalgal assemblages to determine both label storage capacity and biomass. After one year of removal there was no change in the macroalgal assemblage. However, both the GPP and 13C-carbon storage capacity were higher in the turf-forming Corallina spp. and, sometimes, in the canopy-forming Bifurcaria bifurcata. Nitrogen uptake rate followed similar, but more variable results. Although S. muticum inhibited carbon storage capacity of native species, the assemblage-level 13C-carbon storage was similar in the S. muticum-removed and control rock pools because the presence of the invasive species compensated for the functional loss of native species, particularly at sites where it was most abundant. No obvious effects were observed in relation to the environmental setting. Overall, the effect of the invasive S. muticum on carbon flow appeared to be mediated both by the effects on resource-use efficiency of native species and by its own biomass. Integrating physiological and assemblage-level responses can provide a broad understanding of how invasive species affect recipient communities and ecosystem functioning.

Underpinning the Development of Seaweed Biotechnology: Cryopreservation of Brown Algae (Saccharina latissima) Gametophytes

Sugar kelp (Saccharina latissima) is an economically important species, and natural populations provide diverse and productive habitats as well as important ecosystem services. For seaweed aquaculture to be successful in newly emerging industry in Europe and other Western countries, it will have to develop sustainable production management strategies. A key feature in this process is the capacity to conserve genetic diversity for breeding programs aimed at developing seed stock for onward cultivation, as well as in the management of wild populations, as potentially interesting genetic resources are predicted to disappear due to climate change. In this study, the cryopreservation of male and female gametophytes (haploid life stage) of S. latissima by different combinations of two-step cooling methods and cryoprotectants was explored. We report here that cryopreservation constitutes an attractive option for the long-term preservation of S. latissima gametophytes, with viable cells in all treatment combinations. The highest viabilities for both male and female gametophytes were found using controlled-rate cooling methods combined with dimethyl sulfoxide 10% (v/v). Morphological normal sporophytes were observed to develop from cryopreserved vegetative gametophytic cells, independent of treatment. This indicates that cryopreservation is a useful preservation method for male and female S. latissima gametophytes.

A unique life cycle transition in the red seaweed Pyropia yezoensis depends on apospory

Plant life cycles consist of two temporally separated stages: a haploid gametophyte and a diploid sporophyte. In plants employing a haploid-diploid sexual life cycle, the transition from sporophyte to gametophyte generally depends on meiosis. However, previous work has shown that in the red seaweed Pyropia yezoensis, this transition is independent of meiosis, though how and when it occurs is unknown. Here, we explored this question using transcriptomic profiling of P. yezoensis gametophytes, sporophytes, and conchosporangia parasitically produced on sporophytes. We identify a knotted-like homeobox gene that is predominately expressed in the conchosporangium and may determine its identity. We also find that spore-like single cells isolated from the conchosporangium develop directly into gametophytes, indicating that the gametophyte identity is established before the release of conchospores and prior to the onset of meiosis. Based on our findings, we propose a triphasic life cycle for P. yezoensis involving production of gametophytes by apospory.

Viability of combining microalgae and macroalgae cultures for treating anaerobically digested piggery effluent

Algal phytoremediation represents a practical green solution for treating anaerobically digested piggery effluent (ADPE). The potential and viability of combining microalgae and macroalgae cultivation for the efficient treatment of ADPE were evaluated in this study. Bioprospecting the ability of different locally isolated macroalgae species illustrated the potential of Cladophora sp. to successfully grow and treat ADPE with up to 150 mg/L NH₄⁺ with a biomass productivity of (0.13 ± 0.02) g/(L·day) and ammonium removal rate of (10.23 ± 0.18) mg/(L·day) NH₄⁺. When grown by itself, the microalgae consortium used in this study consisting of Chlorella sp. and Scenedesmus sp. was found to grow and treat undiluted ADPE (up to 525 mg/L NH₄⁺) with an average ammonium removal rate of 25 mg/(L·day) NH₄⁺ and biomass productivity of (0.012 ± 0.0001) g/(L·day). Nevertheless, when combined together, despite the different cultivation systems (attached and non-attached) evaluated, microalgae and macroalgae were unable to co-exist together and treat ADPE as their respective growth were inversely related to each other due to direct competition for nutrients and available resources as well as the negative physical interaction between both algal groups.

What nutrient sources support anomalous growth and the recent sargassum mass stranding on Caribbean beaches? A review

Since 2011, tropical beaches from Africa to Brazil, Central America, and the Caribbean have been inundated by tons of sargassum seaweed from a new equatorial source of pelagic sargassum in the Atlantic. In recent years the extraordinary accumulations of sargassum make this a nuisance algal bloom for tropical coasts. In 2018 satellite data indicated floating mats of sargassum that extended throughout the Caribbean to the northeast coast of Brazil with the highest percent coverage over the water yet recorded. A literature review suggests that Atlantic equatorial recirculation of seaweed mats combined with nutrients from several possible sources may be stimulating the growth and accumulations of sargassum. In the western equatorial recirculation area, new nutrient sources may include Amazon River floods and hurricanes; in the eastern equatorial recirculation area, nutrient sources that could sustain the sargassum blooms include coastal upwelling and Congo River freshwater and nutrients.

Enhanced nutrient loading and herbivory do not depress the resilience of subtidal canopy forests in Mediterranean oligotrophic waters

The interaction between top-down and bottom-up forces determines the recovery trajectory of macroalgal forests exposed to multiple stressors. In an oligotrophic system, we experimentally investigated how nutrient inputs affected the recovery of Cystoseira brachycarpa following physical disturbance of varying intensities, both inside forested areas and at the boundary with sea urchin barrens. Unexpectedly, Cystoseira forests were highly resilient to disturbance, as they were able to recover from any partial damage. In general, the addition of nutrients sped up the recovery of Cystoseira. Thus, only the total canopy removal, in combination with either low nutrient availability or intense grazing pressure, promoted the expansion of mat-forming algae or urchin barrens, respectively. Our study suggests that the effects of enhanced nutrient levels may vary according to the trophic characteristics of the waterbody, and hence, are likely to vary among regions of the Mediterranean basin.

On relaxation of the influences of treated sewage effluent on an adjacent seaweed farm in a tidal strait

An Eulerian passive tracer model coupled with a quadruple-nested 3D circulation model was used to assess the coastal dispersal of treated wastewater effluent from a sewage treatment plant and the associated impacts on an adjacent seaweed farm using three different operational scenarios. When the discharged volume and source effluent fluxes were decreased by ~16.7%, the accumulated effluent in the farm was reduced by ~25.4%. A tracer flux budget analysis revealed the apparent predominance of the transient component that accounts for the nonlinear interactions primarily from tidal currents and eddies. The transient flux promoted the effluent influx to impede effluent accumulation in the farm, whereas the mean flux contributed to the outgoing flux. A source flux reduction caused a remarkable decrease in the transient flux and thus an even greater effluent accumulation reduction. In turn, a modified source density scenario without total effluent volume change did not work as expected.

Salinity mediates the effects of nitrogen enrichment on the growth, photosynthesis, and biochemical composition of Ulva prolifera

To study the combined effects of multiple nitrogen (N) sources and salinity on the growth and physiology on macroalgae, we cultured Ulva prolifera under three N levels (N₀, 0.1235 mg L^-1; N₁, 0.6 mg L^-1; and N₂, 4.4 mg L^-1; the ratios were 18:74:8 for NH₄-N, NO₃-N, and NO₂-N, respectively) and three salinity conditions (15, 25, and 35). Then, the growth, pigment content, photosynthetic performance, superoxide dismutase (SOD) activity, and contents of soluble protein and carbohydrates were measured. The results showed the following: (1) Compared to that grown at salinity 25, the growth of U. prolifera decreased under salinity 35, especially under the N₀ and N₂ levels, but there were no significant effects of salinity 15 under any of the N levels. (2) There were no significant effects of salinity on the chlorophyll a (Chla) content, but compared to the content at salinity 25, the chlorophyll b (Chlb) content was enhanced by salinity 15 and 35; lower ratio values between Chla and carotenoids (Car) occurred under the salinity 25 treatment. Under each salinity condition, the pigments were enhanced by a high N level. (3) A relatively higher salinity level decreased the photosynthetic oxygen evolution rate, while a higher N level increased this value. Compared to the rate at salinity 25, the dark respiration rate (R_d) significantly increased at salinity 15 under the N₀ condition. (4) SOD activity was enhanced by a high N level, but no significant effects of salinity were observed. (5) The carbohydrate content was enhanced at salinity 35 under the N₀ and N₁ levels, and under salinity 15, this value increased with increasing N levels. In conclusion, although the growth of U. prolifera decreased at high N levels under high salinity conditions, a high N level induced an increase in photosynthesis, while no significant decrease in growth occurred. These findings indicate that low salinity and high N levels may be nonnegligible reasons why this species thrives, and low salinity was the better choice when this species was used for wastewater treatment.

Uncertainty in the optical remote estimation of the biomass of Ulva prolifera macroalgae using MODIS imagery in the Yellow Sea

A laboratory experiment was conducted to obtain a floating algae index (FAI) of the floating macroalgae (Ulva prolifera), corresponding to various values of biomass per unit area (BPA). A piecewise empirical model was used to fit the statistical relationships between BPA and FAI, corresponding to FAI ≤ 0.2 (BPA ≤ 1.81kg/m²) and FAI ˃ 0.2 (BPA ˃ 1.81 kg/m²). Spectral mixing derived results show that a linear relationship between FAI and BPA is maintained when the BPA of endmembers is less than 1.81 kg/m². However, when the BPA of the endmembers exceeds 1.81 kg/m², there is substantial uncertainty in the optical remote estimation of biomass. Although the MODIS-derived FAI of Ulva prolifera is often less than 0.2, it is very difficult to determine whether the FAI results from low BPA (≤ 1.81kg/m²) of the endmembers, or from a low area ratio including high BPA (˃ 1.81 kg/m²), due to pixel mixing. If it is assumed that the unit biomass distribution of pure endmembers is a standard Gaussian distribution, then the uncertainty in the biomass estimation of Ulva prolifera from MODIS data can be expressed. This results in the uncertainty of ~36% in total biomass estimation, ~43% of which was contributed by a few pixels (10% of total pixels) with high FAI (˃ 0.05). The uncertainty in BPA caused by high FAI (˃ 0.05) pixels is about 7.2 times that for low FAI (≤ 0.05) pixels. In future research, the spatial distribution characteristics of the FAI of pure endmembers need to be considered in order to improve the accuracy of optical remote estimation of floating Ulva prolifera.

Seagrass restoration in Gulf of Mannar, Tamil Nadu, Southeast India: a viable management tool

Seagrass beds are important marine ecosystems that provide significant ecological services. The global decline of seagrass beds is becoming severe due to the increasing pressure of human-induced factors and changing climatic conditions. Restoration of seagrasses is an evolving science that started in 1939. In this study, we report a remarkably successful restoration activity carried out in the Gulf of Mannar (GoM), Southeast India. This is the first wide-scale effort in Indian waters. After the initial experimentation, manual transplantation of seagrass sprigs was carried out near Vaan and Koswari islands in GoM. Transplantation was performed with PVC quadrats and jute twines in areas of 800 m² in both the islands during February to May 2014. An increase from 16.4 ± 0.3 to 32.3 ± 0.6% in Vaan and from 15.1 ± 0.2 to 35.1 ± 0.9% in Koswari was observed in seagrass percentage cover during the period from June 2014 to May 2016. Area cover, shoot density, macrofaunal density and fish density increased at the restoration sites after the transplantation. Bottom trawling was found to be the most serious threat to the seagrass beds in these islands. This method of transplantation can be replicated in other areas of degraded seagrass in India to carry out wide-scale restoration of seagrasses.

Climate change induced range shifts in seaweeds distributions in Europe

There are evidences of how climate change is affecting seaweeds distribution and the ecosystems services they provide. Therefore, it is necessary to consider these impacts when managing marine areas. One of the most applied tools in recent years to deal with this are species distribution models, however there are still some challenges to solve, such as the inclusion of hydrodynamic predictors and the application of effective, transferable and user-oriented methodologies. Five species (Saccorhiza polyschides, Gelidium spinosum, Sargassum muticum, Pelvetia canaliculata and Cystoseira baccata) in Europe and 15 variables were considered. Nine of them were projected to the RCPs 4.5 and 8.5 for the mid-term (2040-2069) and the long term (2070-2099). Algorithms for each species were applied to generate models that were assessed by comparison of probabilities and observations (area under the curve, true skill statistics, Boyce index, sensitivity, correct classification rate), niches overlap (Schoener's D, Hellinger's I), geographical similarity (interquartile range) and ecological realism. Models built demonstrated very good predictive accuracy and sensitivity, without overfitting risk. A medium overlap in the historical and RCPs environmental conditions were obtained, therefore the models can be considered transferable and results accurate because only some isolated points were detected as outliers, corresponding to low probabilities. The areas of S. polyschides and G. spinosum have been identified to be dramatically reduced, meanwhile S. muticum and C. baccata were predicted to expand their range. P. canaliculata was expected to keep its sites of presence but with a decrease in its probability of occurrence. For all species it was remarkable the importance of hydrodynamic variables and parameters representing extreme conditions. Spatially predictions of the potential species and areas at risk are decisive for defining management strategies and resource allocation. The performance and usefulness of the approach applied in this study have been demonstrated for algae with different ecological requirements (from upper littoral to subtidal) and distributional patterns (native and invasive), therefore results can be used by marine planners with different goals: marine protected areas designation, monitoring efforts guiding, invasions risk assessment or aquaculture facilities zonation.

Life Cycle Assessment of Seaweed Cultivation Systems

Life cycle assessment (LCA) is a holistic methodology that identifies the impacts of a production system on the environment. The results of an LCA are used to identify which processes can be improved to minimize impacts and optimize production.LCA is composed of four phases: (1) goal and scope definition, (2) life cycle inventory analysis, (3) life cycle impact assessment, and (4) interpretation.The goal and scope define the purpose of the analysis; describe the system and its function, establish a functional unit to collect data and present results, set the system boundaries, and explain the assumptions made and data quality requirements. Life cycle inventory analysis is the collection, processing and organization of data. Life cycle impact assessment associates the results from the inventory phase to one or multiple impacts on environment or human health. The interpretation evaluates the outcome of each phase of the analysis. In this phase the practitioner decides whether it is necessary to amend other phases, e.g., collection of more data or adjustments of goal of the analysis. In the interpretation, the practitioner draws conclusions, exposes the limitations, and provides recommendations to the readers.The quality of LCA of seaweed production and conversion is based on data availability and detail level. Performing an LCA at the initial stage of seaweed production in Europe is an advantage: the recommended design improvements can be implemented without significant economic investments. The quality of LCA will keep improving with the increase of scientific publications, data sharing, and public reports.

Coral reef systems of the Mexican Caribbean: Status, recent trends and conservation

Over the last four decades the Mexican Caribbean has experienced intensive coastal development, and change on the reef system condition has already been observed. This paper describes the reef system characteristics, at local and seascape scales, and discusses the current status and trends, considering the main research efforts from academia and Non-Governmental Organizations. To date, the coral cover of most reefs in the region is between 15 and 20%, following a slight recovery on mean coral cover over the last decade. During this same period, fleshy macroalgae and herbivorous fish biomass appear to have increased. At seascape scales, an increase of macroalgae and the loss of seagrass habitat have been observed. Considering that anthropogenic and environmental disturbances will most likely increase, the establishment of newly protected areas in the Mexican Caribbean is appropriate, but sufficient accompanying funding is required.

Mechanical properties of the wave-swept kelp Egregia menziesii change with season, growth rate and herbivore wounds

The resistance of macroalgae to damage by hydrodynamic forces depends on the mechanical properties of their tissues. Although factors such as water-flow environment, algal growth rate and damage by herbivores have been shown to influence various material properties of macroalgal tissues, the interplay of these factors as they change seasonally and affect algal mechanical performance has not been worked out. We used the perennial kelp Egregia menziesii to study how the material properties of the rachis supporting a frond changed seasonally over a 2 year period, and how those changes correlated with seasonal patterns of the environment, growth rate and herbivore load. Rachis tissue became stiffer, stronger and less extensible with age (distance from the meristem). Thus, slowly growing rachises were stiffer, stronger and tougher than rapidly growing ones. Growth rates were highest in spring and summer when upwelling and long periods of daylight occurred. Therefore, rachis tissue was most resistant to damage in the winter, when waves were large as a result of seasonal storms. Herbivory was greatest during summer, when rachis growth rates were high. Unlike other macroalgae, E. menziesii did not respond to herbivore damage by increasing rachis tissue strength, but rather by growing in width so that the cross-sectional area of the wounded rachis was increased. The relative timing of environmental factors that affect growth rates (e.g. upwelling supply of nutrients, daylight duration) and of those that can damage macroalgae (e.g. winter storms, summer herbivore outbreaks) can influence the material properties and thus the mechanical performance of macroalgae.

A simple and effective method for monitoring floating green macroalgae blooms: a case study in the Yellow Sea

Several algorithms have been proposed to detect floating macroalgae blooms in the global ocean. However, some of them are difficult or even impossible to routinely apply by non-experts because of performing a sophisticated atmospheric correction scheme or due to the mismatch in spectral bands from one sensor to another. Here, a generic, simple and effective method, referred to as the Floating Green Tide Index (FGTI), was proposed to detect floating green macroalgae blooms (GMB). The FGTI was defined as the difference between greenness and wetness features extracted from digital number (DN) observation through Tasseled Cap Transformation analysis, providing the advantage of bypassing the atmospheric correction procedure. Through cross-index and cross-sensor comparisons, the FGTI showed similar performance to the existing VB-FAH (Virtual-Baseline Floating macroAlgae Height) and FAI (Floating Algae Index) algorithms but proved more robust than the traditional NDVI (Normalized Difference Vegetation Index) in terms of response to perturbations by environmental conditions, viewing geometry, sun glint, and thin cloud contamination. Given the requirement for spectral bands in the current and planned satellite sensors, the FGTI design can easily be extended to any satellite sensor, and therefore provide an excellent data resource for studying GMB in any part of the global ocean.

Macroalgae bloom decay decreases the sediment organic carbon sequestration potential in tropical seagrass meadows of the South China Sea

Seagrass meadows are experiencing worldwide declines mainly because of nutrient enrichment, which always result in macroalgae bloom and consequently periodic collapse and decomposition. However, effects of macroalgae decay on the sediment organic carbon (SOC) sequestration capacity remain unknown. Depending on the macroalgae biomass in eutrophic seagrass meadows of South China Sea, we carried out a laboratory chamber experiment to investigate the sediment labile organic carbon (OC) compositions and the influencing SOC transformation enzyme activity variations of seagrass meadows in response to common macroalgae bloom species (Cladophora spp.) decomposition. Although the dehydrogenase and β-glucosidase activities were not affected by macroalgae decomposition, the macroalgae decomposition significantly elevated the salt-extractable carbon (SEC) content, SEC/SOC, levels of invertase and polyphenol oxidase activities, and the CO₂ release. Overall, this study indicates that macroalgae decomposition stimulates the SOC transformation, and therefore, it is not benefit for SOC sequestration within seagrass meadows of the South China Sea.

Comparison of UVB effects on growth and induction of UVB screening compounds in isolates of metaphytic algae from temperate zone streams and ponds

Filaments in the surface layers of metaphytic mats are exposed to high photon flux densities of PAR and UVBR. We investigated the effect of UVBR exposure on growth of eight isolates of common metaphytic algae (Cladophora, Mougeotia, Oedogonium, Pithophora, Spirogyra, and Zygnema) acclimated to either high or low PAR levels prior to UVBR exposure. All isolates acclimated to low PAR exhibited significant reductions in growth rate caused by the UVBR exposure (P < 0.05). Acclimation to high PAR resulted in seven of the isolates being more tolerant of the UVB exposure. The two Zygnema isolates exhibited the most pronounced effect of high PAR acclimation with growth rates of UVB exposed treatments being equal to that of controls (P > 0.05). High PAR acclimation also protected chlorophyll a levels in the Zygnema isolates. Absorption of UVB by methanol extracts increased 322%-381% for the two Zygnema isolates when high PAR acclimated. The broad absorption peak at 270 nm suggests that phenolic compounds were responsible. Previous studies have shown that Zygnema isolates from extreme environments tolerate UVBR and contain UVB screening compounds, but our results extend these adaptions to Zygnema from typical temperate zone habitats. Although none of the other metaphytic algae produced UVB absorbing compounds, they all exhibited higher growth rates under UVBR exposure following high PAR acclimation. This suggests that the algae evaluated have inducible defenses against UVBR exposure that coupled with their mat structure would provide an adaption to the challenging light environment in shallow-water habitats.

Stable isotopic evidence of nitrogen sources and C4 metabolism driving the world's largest macroalgal green tides in the Yellow Sea

During recent years, rapid seasonal growth of macroalgae covered extensive areas within the Yellow Sea, developing the world's most spatially extensive "green tide". The remarkably fast accumulation of macroalgal biomass is the joint result of high nitrogen supplies in Yellow Sea waters, plus ability of the macroalgae to optionally use C4 photosynthetic pathways that facilitate rapid growth. Stable isotopic evidence shows that the high nitrogen supply is derived from anthropogenic sources, conveyed from watersheds via river discharges, and by direct atmospheric deposition. Wastewater and manures supply about half the nitrogen used by the macroalgae, fertiliser and atmospheric deposition each furnish about a quarter of the nitrogen in macroalgae. The massive green tides affecting the Yellow Sea are likely to increase, with significant current and future environmental and human consequences. Addressing these changing trajectories will demand concerted investment in new basic and applied research as the basis for developing management policies.

The impact of elevated atmospheric CO2 on cadmium toxicity in Pyropia haitanensis (Rhodophyta)

Cadmium is one of the major heavy metal pollutions in coastal waters, and it is well known that cadmium at trace concentration is toxic to macroalgae. Change in marine carbonate system and ocean acidification caused by elevated atmospheric CO₂ also alter physiological characteristics of macroalgae. However, less research is focused on the combined impacts of elevated CO₂ and cadmium pollution on the growth and physiology in macroalgae. In this study, the maricultivated macroalga Pyropia haitanensis (Rhodophyta) was cultured at three levels of Cd²⁺ (control, 4 and 12 mg L^-1) and two concentrations of CO₂, the ambient CO₂ (AC, 410 ppm) and elevated CO₂ (HC, 1100 ppm). The results showed that 12 mg L^-1 Cd²⁺ significantly suppressed the relative growth rate and superoxide dismutase activity in AC-grown P. haitanensis, while such inhibition extents by Cd²⁺ were alleviated in HC-grown algae. Cd²⁺ had no effects on efficiency of electron transport (α) and maximum electron transport rate (ETR_max), but α was increased by elevated CO₂. Cd²⁺ dramatically suppressed the maximum net photosynthesis oxygen evolution rate (NPR_m) and the minimum saturation irradiance (I_k) when the algal thalli were grown at AC, while such suppression of NPR_m by Cd²⁺ was much decreased when the thalli were grown at HC. Collectively, our results suggested that elevated CO₂ would alleviate Cd²⁺ toxicity on P. haitanensis.

A study of the environmental factors influencing the growth phases of Ulva prolifera in the southern Yellow Sea, China

Macroalgal blooms of U. prolifera in the southern Yellow Sea (SYS) have become an ecological disaster. In this study, we attempt to explore the influence of environmental factors and human activity on the annual development of U. prolifera during 2011-2016, combining geostationary ocean color imager images and monitored environmental factors. Blooms of U. prolifera were mainly distributed in the central SYS, drifting from the southern Yellow Sea Radial Sand Ridges. Three growth phases were defined (initial phase, outbreak phase and dissipation phase) to facilitate analysis of the relationship between the environmental factors and growth conditions of U. prolifera. Seaweed cultivation, sea surface temperature (SST) and available radiation influenced the algal biomass during the initial phase; the seawater transparency, precipitation and wind activity affected the algae during the outbreak phase; and SST, intense radiation and cleanup operations increased the rate of algal extinction in the dissipation phase.

Remote sensing of early-stage green tide in the Yellow Sea for floating-macroalgae collecting campaign

The world's largest green tide originated from the Jiangsu Shoal of the Yellow Sea was due to fast reproduction of floating green macroalgae (Ulva prolifera). It brought significant impacts on marine environment and ecosystem in the Yellow Sea. In this study, we examined the expansion of green tide from the Jiangsu Shoal during the period from 29 April to 25 June 2016. Using high-resolution satellite images, we revealed a declined growth rate during the northward drifting of early-stage green tide for the first time, i.e., the green tide had higher growth rate (up to 25% per day) in the turbid waters of the Jiangsu Shoal in May and a lower growth rate (low to 3% per day) in the relatively clear waters in the middle of the western Yellow Sea in June, which suggests that water clarity might not be the key factor controlling the growth rate of the floating macroalgae in the surface waters under natural conditions. The high growth rate led to shortened time windows for controlling the green tide by employing macroalgae collecting campaigns at the initial sites of the green tide, which was no more than 14 days in the 2016 case.

Investigation of broad scale implementation of integrated multitrophic aquaculture using a 3D model of an estuary

A 3D ecosystem model was used to quantify changes in water quality brought about by salmon aquaculture in the D'Entrecasteaux Channel and Huon Estuary in southeast Tasmania. Macroalgae-based integrated multitrophic aquaculture (IMTA) was simulated and showed that IMTA is capable of reducing the increased chlorophyll concentration attributable to fish farming by up to 10-15% in large areas of the region, during the season of highest production. Kelp farms (Macrocystis pyrifera) recovered between 6 and 11% of the dissolved inorganic nitrogen (DIN) input by salmon aquaculture over a nine month period, with DIN remediation increasing linearly with farm size. Under a ten-fold increase in aquaculture to very high loads, a much lower remediation effect was found for both chlorophyll and DIN. Model results indicate that IMTA could have an important impact on reducing negative effects of finfish aquaculture on water quality providing that stocking rates are not too high.

Vitamin D Content of Australian Native Food Plants and Australian-Grown Edible Seaweed

Vitamin D has previously been quantified in some plants and algae, particularly in leaves of the Solanaceae family. We measured the vitamin D content of Australian native food plants and Australian-grown edible seaweed. Using liquid chromatography with triple quadrupole mass spectrometry, 13 samples (including leaf, fruit, and seed) were analyzed in duplicate for vitamin D₂, vitamin D₃, 25-hydroxyvitamin D₂, and 25-hydroxyvitamin D₃. Five samples contained vitamin D₂: raw wattleseed (Acacia victoriae) (0.03 µg/100 g dry weight (DW)); fresh and dried lemon myrtle (Backhousia citriodora) leaves (0.03 and 0.24 µg/100 g DW, respectively); and dried leaves and berries of Tasmanian mountain pepper (Tasmannia lanceolata) (0.67 and 0.05 µg/100 g DW, respectively). Fresh kombu (Lessonia corrugata) contained vitamin D₃ (0.01 µg/100 g DW). Detected amounts were low; however, it is possible that exposure to ultraviolet radiation may increase the vitamin D content of plants and algae if vitamin D precursors are present.

Enhancement of Biochemical and Nutritional Contents of Some Cultivated Seaweeds Under Laboratory Conditions

Six species of macroalgae belonging to the Chlorophyta, Phaeophyta, and Rhodophyta divisions were cultivated in a closed system with Guillard's f/2, Walne's, Provasoli Enriched Seawater (PES) medium, and seawater (control) for 6 weeks. The growth rate and parameters of the tested seaweeds showed that all used media enhanced the growth rate and chemical content as compared with other seaweeds cultivated in seawater without addition of any nutrients. There are significant differences in the effect of the used media on the seaweed composition at p = .01; PES is more effective than the f/2 and Walne's media. The results indicate that the cultivation technique of some macroalgae was an efficient tool for increasing the seaweeds' biomass and increasing their chemical compounds, calories, and energy under laboratory conditions.

Effect of water motion and microhabitat preferences on spatio-temporal variation of epiphytic communities: a case study in an artificial rocky reef system, Laoshan Bay, China

Epiphytic fauna community structure is mainly determined by macro-scale environmental characteristics (e.g., water motion), whereas the influences of, and interaction with, micro-scale habitat-forming species are not well known. In order to explore the effects of water motion and functional macroalgal group on the community structure of epiphytic faunas, macroalgae and epiphytic faunas from four isolated artificial rocky reefs with different levels of hydrodynamic conditions were investigated in Laoshan Bay of China. A total of 32 macroalgal species and 22 faunal species were recorded on the surveys. The biomass and abundance of macroalgae and epiphytic faunas showed significant variations among stations and months. The biomass and abundance of epiphytic faunas were highest at outer Huangshankou station (H1) with medium hydrodynamic force. The lowest biomass of epiphytic faunas occurred at inner Huangshankou station (H3) with highest level of water motion, while the lowest abundance of epiphytic faunas occurred at Liepo station (L) with lowest level of water motion. Results showed that medium water motion level contributed to increasing biodiversity of epiphytic faunas. Epiphytic communities generally presented higher biomass and abundance in summer than in spring or autumn, which indicated temperature could be the ecological driver for temporal variation of epiphytic communities. The epiphytic faunas showed distinct preferences to structural morphology of macroalgae which forms suitable habitat for these organisms. This study suggests that artificial rocky reefs are of great significance to restore and maintain coastal biodiversity, and appropriate physical disturbance promote community reestablishment.

Transcriptomic study to understand thermal adaptation in a high temperature-tolerant strain of Pyropia haitanensis

Pyropia haitanensis, a high-yield commercial seaweed in China, is currently undergoing increasing levels of high-temperature stress due to gradual global warming. The mechanisms of plant responses to high temperature stress vary with not only plant type but also the degree and duration of high temperature. To understand the mechanism underlying thermal tolerance in P. haitanensis, gene expression and regulation in response to short- and long-term temperature stresses (SHS and LHS) was investigated by performing genome-wide high-throughput transcriptomic sequencing for a high temperature tolerant strain (HTT). A total of 14,164 differential expression genes were identified to be high temperature-responsive in at least one time point by high-temperature treatment, representing 41.10% of the total number of unigenes. The present data indicated a decrease in the photosynthetic and energy metabolic rates in HTT to reduce unnecessary energy consumption, which in turn facilitated in the rapid establishment of acclimatory homeostasis in its transcriptome during SHS. On the other hand, an increase in energy consumption and antioxidant substance activity was observed with LHS, which apparently facilitates in the development of resistance against severe oxidative stress. Meanwhile, ubiquitin-mediated proteolysis, brassinosteroids, and heat shock proteins also play a vital role in HTT. The effects of SHS and LHS on the mechanism of HTT to resist heat stress were relatively different. The findings may facilitate further studies on gene discovery and the molecular mechanisms underlying high-temperature tolerance in P. haitanensis, as well as allow improvement of breeding schemes for high temperature-tolerant macroalgae that can resist global warming.

Food selection of a generalist herbivore exposed to native and alien seaweeds

Understanding which factors influence the invasion of alien seaweed has become a central concern in ecology. Increasing evidence suggests that the feeding preferences of native herbivores influence the success of alien seaweeds in the new community. We investigated food selection of a generalist native grazer Paracentrotus lividus, in the presence of two alien seaweeds (Caulerpa cylindracea and Caulerpa taxifolia var. distichophylla) and two native seaweeds (Dictyopteris membranacea and Cystoseira compressa). Sea urchins were fed with six experimental food items: C. cylindracea, C. taxifolia var. distichophylla, a mixture of C. cylindracea and C. taxifolia var. distichophylla, D. membranacea, C. compressa and a mixture of D. membranacea and C. compressa. P. lividus ingested all the combinations of food offered, though it preferentially consumed the alien mixture, C. cylindracea and D. membranacea. The alien C. taxifolia var. distichophylla was consumed significantly less than the other food items and, interestingly, it was ingested in a greater amount when mixed with C. cylindracea than when on its own. This finding suggests that C. taxifolia var. distichophylla may become vulnerable to sea urchin grazing when it grows intermingled with C. cylindracea, which does not gain immediate protection from the presence of the very low palatable congeneric seaweed. The present study highlights the potential role of native grazers to indirectly affect the interspecific competition between the two alien seaweeds in the Mediterranean Sea.

Variations of dominant free-floating Ulva species in the source area for the world's largest macroalgal blooms, China: Differences of ecological tolerance

Species composition and seasonal variations of free-floating Ulva species were investigated in the source area of the world's largest macroalgal blooms during 2009-2015. Based on a combination of a morphological analysis and sequences of nuclear-encoded ITS and 5S rDNA spacer regions, the dominant species in the free-floating Ulva community at the early stage of green tides were Ulva compressa, Ulva flexuosa, and Ulva linza. The first appearance of Ulva prolifera on the sea surface was in mid-May and it dominated the floating Ulva community in June from 2009 to 2011. From 2012-2015, U. prolifera was not only the first species to appear on the sea surface but also the dominant species during the whole early stage of green tides. To explain the successional mechanism, the effects of environmental factors on the growth of four Ulva species were examined in the laboratory under different combinations of light intensity and temperature. It was found that the highest growth rate of U. prolifera was 44.9%/d, which was much higher than the other three Ulva species. The strong tolerance of U. prolifera to extreme conditions also helps it survive and bloom in the Yellow Sea.

ALEX index enables detection of alien macroalgae invasions across habitats within a marine protected area

A modified version of the ALien Biotic IndEX (ALEX) has been recently proposed to evaluate biological invasions in macroalgal assemblages. ALEX was applied in a Marine Protected Area where a recreational-fishing port is present testing the following hypotheses: ALEX increases with the distance from the port, it changes between the two directions off the port and it changes among three different habitats: Cystoseira beds, algal turf and dead matte of the seagrass Posidonia oceanica. A total of 78 native macroalgal taxa and 4 introduced species were found, the Chlorophyta Caulerpa cylindracea and the Rhodophyta Apoglossum gregarium, Acrothamnion preissii and Womersleyella setacea. All study sites were in high quality status highlighting that the assemblages investigated were at an early stage of NIS invasion. However, ALEX detected different values among conditions and habitats within the MPA, suggesting a local dynamics of NIS spread and different resistance to invasion of the investigated habitats.

Nutritional and bioactive compounds of commercialized algae powders used as food supplements

The main nutritional/bioactive compounds (protein; aminoacids, AA; fucose; minerals; vitamins B12 and C; and total phenolic content, TPC) of nine commercial algae powders, used as food supplements, were studied. Undaria pinnatifida showed the highest protein/aminoacid contents (51.6/54.4 g 100 g-1). Among brown macroalgae, Himanthalia elongata showed the highest fucose content (26.3 g kg-1) followed by Laminaria ochroleuca (22.5 g kg-1). Mineral contents of 15-24% were observed in the algae, being particularly excellent sources of iodine (69.0-472.0 mg kg-1). Porphyra spp. and Palmaria palmata showed the highest vitamin B12 contents (667-674 µg kg-1). Vitamin C ranged among 490.4-711.8 mg kg-1. H. elongata showed the highest total phenolic content (14.0 g kg-1). In conclusion, the studied algae are excellent sources of protein, AA, minerals, vitamin C and some of them presented particularly high vitamin B12 and fucose contents, which may have a potential use as food supplements.

Intertidal geothermal hot springs as a source of trace elements to the coastal zone: A case study from Bahía Concepción, Gulf of California

We investigated the influence of the intertidal geothermal hot spring (GHS) on the biogeochemistry of trace elements in Santispac Bight, Bahía Concepción (Gulf of California). The geothermal fluids were enriched in As and Hg mainly in ionic form. The suspended particulate matter of the GHS had elevated enrichment factor (EF) >1 of As, Bi, Cd, Co, Cu, Mn, Mo, Sb, Sn, Sr, Ti, U and Zn. The sediment core from GHS1 had high concentration of As, Hg, Corg, S, V, Mo, and U and the extremely high EF of these elements at 8cm of the core. The maximum bioaccumulation of As and Hg was in seaweeds Sargassum sinicola collected near the GHS2. The results confirm the input of trace elements to the coastal zone in Bahía Concepción from geothermal fluids and the evident modification of the chemical composition of the adjacent marine environment.

Widespread sewage pollution of the Indian River Lagoon system, Florida (USA) resolved by spatial analyses of macroalgal biogeochemistry

The Indian River Lagoon (IRL) system, a poorly flushed 240 km long estuary in east-central Florida (USA), previously received 200 MLD of point source municipal wastewater that was largely mitigated by the mid-1990's. Since then, non-point source loads, including septic tank effluent, have become more important. Seventy sites were sampled for bloom-forming macroalgae and analyzed for δ¹⁵N, % nitrogen, % phosphorus, carbon:nitrogen, carbon:phosphorus, and nitrogen:phosphorus ratios. Data were fitted to geospatial models showing elevated δ¹⁵N values (>+5‰), matching human wastewater in most of the IRL system, with elevated enrichment (δ¹⁵N ≥ +7‰ to +10‰) in urbanized portions of the central IRL and Banana River Lagoon. Results suggest increased mobilization of OSDS NH₄⁺ during the wetter 2014 season. Resource managers must improve municipal wastewater treatment infrastructure and commence significant septic-to-sewer conversion to mitigate nitrogen over-enrichment, water quality decline and habitat loss as mandated in the Tampa and Sarasota Bays and the Florida Keys.

Nutrient bioextraction and microalgae growth inhibition using submerged macrophyte Myriophyllum spicatum in a low salinity area of East China Sea

Myriophyllum spicatum was cultivated in a low salinity area of Hangzhou Bay (salinity 5.8-6.5), from August to October in 2016, to evaluate the abilities of its nutrient bioextraction and microalgae growth inhibition. During the 72-day cultivation period, M. spicatum had a specific growth rate (SGR) of 6.23%day^-1 and increased 20-fold in biomass (wet weight). Tissue C, N and P assimilation quantities of M. spicatum were found to be 3279.39kg, 360.61kg and 26.97kg, respectively. The concentration of NH₄-N, NO₃-N, NO₂-N and PO₄-P after M. spicatum cultivation was decreased by 47.92%, 58.28%, 36.40% and 55.57%, respectively. The phytoplankton density was decreased from 1064.60×10⁴cellsL^-1 to 12.85×10⁴cellsL^-1. These results indicated that cultivation of M. spicatum can help in nutrient bioextraction and microalgae growth inhibition in low salinity marine water bodies.