Biomonitoring coastal environments with transplanted macroalgae: A methodological review

The goose barnacle Pollicipes pollicipes as a tool for trace metal biomonitoring and health risk assessment for human consumers in northwestern Atlantic coast of Morocco

The bioaccumulation of trace metals Cd, Cr, Cu, Fe, and Zn in soft tissues of the barnacle Pollicipes pollicipes was investigated seasonally along the Atlantic coast of northwestern Morocco. Average concentrations (μg g-1 dry weight) exhibited a decreasing order: Fe (548.15 ± 132.43) > Zn (430.80 ± 181.68) > Cd (17.46 ± 9.99) > Cu (7.72 ± 1.26) > Cr (3.12 ± 0.80), with the highest levels during wet seasons. The "Metal Pollution Index" and "Individual Multimetal Bioaccumulation Index" revealed a substantial barnacle contamination in industrialized areas. Additionally, Cd and Zn concentrations surpassed permissible guideline limits. While the "Target Hazard Quotient" and "Hazard Index" unveiled no significant health risks associated with barnacle consumption for humans, Cd posed potential risks, particularly for children consuming barnacles from polluted locations. Regarding the "Maximum Safe Consumption", Cd demonstrated potential harm across all sex and age groups. These findings contribute valuable data on the safety of barnacle consumption, marking the initial assessment of such risks in Morocco. The study offers evidence of metal pollution occurrence and proposes the barnacle species as a reliable biomonitor of trace metal bioavailabilities in marine coastal areas. To our knowledge, this investigation is the first comprehensive report of metal contamination biomonitoring using barnacles from Moroccan Atlantic waters.

What dead seaweeds can tell us about metal uptake and their application to control marine pollution

The mechanisms of trace element uptake by seaweeds are still unknown, despite being key to understand the impact of pollution in coastal environments. This knowledge gap, in addition to the lack of standardization, have also hindered the use of seaweeds to monitor seawater pollution. To address these shortcomings, we tested the use of devitalization as a pre-exposure treatment for brown seaweed transplants, and we compared devitalized and fresh transplants to gain some insights into the mechanisms of element uptake. We exposed four types of Fucus vesiculosus transplants in 6 sites for 4, 8 and 20 days: fresh and devitalized (dried or boiled) algal segments held in mesh bags, and whole algal thalli imitating natural conditions. We then determined he concentrations of 11 trace elements in the algal tissues. The element concentrations were highest in the devitalized transplants, but the material lost consistency and weight throughout the exposure period, limiting their use to short periods. We proposed several factors that may contribute to the different accumulation patterns between treatments, and examined the implications for the uptake mechanisms, revealing that two of the most important are surface adsorption of sediment particles and chemical bounds to extracellular components.

Effects of anthropogenic pressures on the seagrass Halophila stipulacea and its associated macrozoobenthic communities in the northern Gulf of Aqaba

Halophila stipulacea is a tropical seagrass species, native to the Red Sea, Persian Gulf, and Indian Ocean, while invasive to the Mediterranean and Caribbean Seas. The benthic fauna assemblages associated with H. stipulacea in its native habitats and the potential effects of anthropogenic stressors on these assemblages remain unknown. We compared meadow characteristics, associated fauna assemblages and trophic niche structures of H. stipulacea from an impacted and a pristine site in the northern Red Sea. Seagrass cover and biomass were higher in the impacted site, however, the associated fauna community was more abundant and diverse in the pristine site. Both meadows showed comparable trophic niches based on stable isotope analysis. This study provides first insights into the macrozoobenthos associated with H. stipulacea in its native habitat and highlights the importance of better understanding the relationship between seagrasses and their associated biota and the potential effects of urbanization on this relationship.

Macroalgae for biomonitoring of trace elements in relation to environmental parameters and seasonality in a sub-tropical mangrove estuary

Being a resourceful ecosystem, mangrove estuaries have always been subjected to trace elements (TEs) contamination, and therefore, the biomonitoring approach holds immense potential for surveilling the aquatic environment. To investigate the potentiality of mangrove macroalgae as biomonitors, estuarine water, intertidal-sediment, and macroalgal samples were collected from the Pasur River estuary of Sundarbans mangrove ecosystem, Bangladesh, and afterward studied through Atomic Absorption Spectrometer to quantify the levels of six concerned TEs (Fe, Mn, Zn, Cu, Pb, and Cd). This study utilized the geo-environmental and ecological indices and sediment characterization approaches (sediment quality guidelines-SQGs) for assessing the contamination scenario of the adjacent environment to macroalgae whereas the performance of studied algal groups was evaluated using Bio-contamination factor, Comprehensive bio-concentration index, and Metal accumulation index. Metal occurrence scheme in the water followed the order of Fe > Zn > Mn > Pb > Cd while Fe > Mn > Zn > Cu > Pb > Cd for both sediment and macroalgae. Both Pb and Cd exceeded the guideline limit in estuarine water and the indices approach manifested low to moderate contamination with enrichment from anthropogenic origin of Mn, Zn, and Cu in sediment. Moreover, the SQGs revealed rare biological effects of Cu on an aquatic community. Within algal samples, Chlorophyta contributed the highest biomass production, followed by Phaeophyta and Rhodophyta. Statistical relationship disclosed the influence of environmental variables on TE's accumulation in Chlorophyta. By contrast, hydrochemical's association showed prevalence over the TEs accumulation process for Phaeophyta and Rhodophyta. Bioaccumulation performance analysis revealed that the ability to accumulate TEs in macroalgal groups varied with seasons. Therefore, biomonitoring with macroalgae for the region of interest might require further temporal considerations.

Global decrease in heavy metal concentrations in brown algae in the last 90 years

In the current scenario of global change, heavy metal pollution is of major concern because of its associated toxic effects and the persistence of these pollutants in the environment. This study is the first to evaluate the changes in heavy metal concentrations worldwide in brown algae over the last 90 years (>15,700 data across the globe reported from 1933 to 2020). The study findings revealed significant decreases in the concentrations of Cd, Co, Cr, Cu, Fe, Hg, Mn, Pb and Zn of around 60-84% (ca. 2% annual) in brown algae tissues. The decreases were consistent across the different families considered (Dictyotaceae, Fucaceae, Laminariaceae, Sargassaceae and Others), and began between 1970 and 1990. In addition, strong relationships between these trends and pH, SST and heat content were detected. Although the observed metal declines could be partially explained by these strong correlations, or by adaptions in the algae, other evidences suggest an actual reduction in metal concentrations in oceans because of the implementation of environmental policies. In any case, this study shows a reduction in metal concentrations in brown algae over the last 50 years, which is important in itself, as brown algae form the basis of many marine food webs and are therefore potential distributors of pollutants.

Do we know the cellular location of heavy metals in seaweed? An up-to-date review of the techniques

Seaweeds are dominant organisms in coastal environments. However, in the context of global change, the integrity of these organisms is threatened by metal pollution. It is therefore important to understand how seaweeds are affected by metal concentrations in the water. Measuring the concentrations of metals in seaweed provides information about the effects of metal pollution on the seaweeds themselves and their ecosystems. Nonetheless, correct interpretation of this type of analysis requires knowledge of the cellular location of the pollutants, as the effects will differ depending on whether the metals are present in particles adhered to the surface, attached to external polysaccharides or dissolved in the cytoplasm. Thus, the objectives of this study were to compile the available information on the subcellular distribution of metals in seaweeds and to conduct a critical review of the information. We found that the existing studies provide contrasting, sometimes contradictory, results. Thus, metals have been detected entirely intracellularly and also mainly outside of the cells. In all of the studies reviewed, which used different techniques (mainly extracellular elution, X-ray microanalysis and centrifugation), methodological and/or conceptual problems were identified that raise questions about the effectiveness of each approach. To obtain reliable information about the distribution of metals in algal cells, further studies must be conducted that take into consideration the differences between elements and algal species and the limits of the methods used to measure the elements.

Impact of aquaculture and agriculture nutrient sources on macroalgae in a bioassay study

Eutrophication is a major threat to aquatic ecosystems, because excessive nutrient enrichment may result in the loss of ecosystem services. Fjord systems are specifically under pressure due to nutrient input from land (agriculture) and sea (aquaculture). In this bioassay study, we have analyzed the effect of different nutrient sources, as well as their combination, on growth, nutrient composition and recruitment of habitat-forming and ephemeral macrophytes. We found that agricultural fertilizer increased growth for all algae (except Fucus), while the fish farm effluents mainly increased growth of Ulva. The C:N ratio was hardly affected by the fish farm, but decreased significantly in all algae when agriculture fertilizer was added. Most interestingly, however, distance to the fish farm modulated the algal response to the fertilizer. Our results demonstrate the importance of studying effects of multiple stressors in aquatic ecosystems to sustainably manage the consequences of anthropogenic impacts.

Precision and cost-effectiveness of bioindicators to estimate nutrient regimes on coral reefs

Bioindicators are useful for determining nutrient regimes in marine environments, but their ability to evaluate corals reefs in different ecological states is poorly understood. The precision, availability and congruency of eight potential bioindicators (brown macroalgae, green macroalgae, turf algae, cyanobacteria, soft corals, zoanthids, sponges, and sediment) and their stable isotopic and elemental signatures (δ¹⁵N, δ¹³C, %N, %C, and C:N Ratio) were assessed across 21 reefs in the Inner Seychelles. The coefficient of variation (CoV) for δ¹⁵N showed that green and brown macroalgae were highly precise (2.47 ± 0.95, n = 11; 4.68 ± 1.33, n = 16, respectively), though were less common on coral-mortality reefs relative to macroalgal-dominated ones. Zoanthids were also highly precise for δ¹⁵N (2.98 ± 1.20), but were more readily available regardless of reef state (n = 18). Congruency was low among these indicators, suggesting that different physiological mechanisms for nutrient processing have a stronger influence on a bioindicator's effectiveness than reef state.

Isotopically labelled macroalgae: A new method for determining sources of excess nitrogen pollution

RATIONALE

Stable nitrogen isotope ratios (δ15 N) can be used to discern sources of excess nitrogen pollution in water. The δ15 N values of nitrate in water often do not reflect the true δ15 N source value owing to high temporal variation, and there are high analytical costs associated with obtaining δ15 N values from water nitrate. To find alternative solutions, we isotopically labelled macroalgae (i.e. seaweed) beyond natural variation as a new method for determining sources of excess nitrogen pollution in seawater.

METHODS

Fucus vesiculosus (bladder wrack) non-fertile tips were collected from Easington Colliery, County Durham, UK, and cultured in two isotopically enriched solutions containing ammonium sulphate with δ15 N values of 170 ± 5‰ and -60 ± 3‰ for a period of 19 days. The macroalgae were cultured in separate opened glass jars in an incubator with set temperature (11°C) and light (125 μmol photons m-2 s-2 on a light/dark rhythm of 16 h/8 h). The oven-dried tips were analysed for δ15 N over the 19-day experiment.

RESULTS

The macroalgal tips incorporated the isotopically enriched solutions rapidly, reaching 50% of the isotopically enriched seawater after ca 11 days for the 15 N-enriched solution and ca 15 days for the 14 N-enriched solution. δ15 N values were incorporated more into the torn base of the macroalgal tips than into the middle and apex regions.

CONCLUSIONS

F. vesiculosus rapidly incorporates the isotopic ratio of the artificial seawater solution to which it is translocated. The laboratory-developed isotopically labelled macroalgae can be manufactured to generate 'unnatural' δ15 N values for translocation into coastal environments. This approach can provide an efficient, low-cost alternative to current analytical methods for determining and monitoring nitrogen pollution.

δ15N in deployed macroalgae as a tool to monitor nutrient input driven by tourism activities in Mediterranean islands

Mediterranean Sea is among the world's leading tourist destinations; however, the sharp increase in tourists during the high season may affect coastal seawater. The main aim of this study was to evaluate the occurrence and temporal variation of anthropogenic nutrients in coastal seawater in relation to tourist flows in three Mediterranean islands (Cyprus, Sicily and Rhodes), through short-term macroalgae deployments, coupled with δ¹⁵N analysis and GIS mapping. In all islands, an overall increase in macroalgae δ¹⁵N occurred over the deployment carried out in August in the tourist sites, suggesting the presence of anthropogenic nutrients. Decreasing δ¹⁵N values occurred at increasing distance from the coastline in two out of the three islands (Cyprus and Sicily). This study revealed the usefulness of the approach used in the assessment of tourism impact in terms of trophic enrichment and its potential to support competent authorities for the development of sustainable coastal management plans.