Impacts on the deep-sea ecosystem by a severe coastal storm

New insights into the migration, distribution and accumulation of micro-plastic in marine environment: A critical mechanism review

Microplastics (MPs) are widely distributed in the marine environment, posing a significant threat to marine biota. The contribution of anthropogenic and terrestrial sources to the aquatic ecosystem has led to an increase in MPs findings, and their abundance in aquatic biota has been reported to be of concern. MPs are formed mainly via photo degradation of macroplastics (large plastic debris), and their release into the environment is a result of the degradation of additives. Eco-toxicological risks are increasing for marine organisms, due to the ingestion of MPs, which cause damage to gastrointestinal (GI) tracts and stomach. Plastics with a size <5 mm are considered MPs, and they are commonly identified by Raman spectroscopy, Fourier transfer infrared (FTIR) spectroscopy, and Laser direct infrared (LDIR). The size, density and additives are the main factors influencing the abundance and bioavailability of MPs. The most abundant type of MPs found in fishes are fiber, polystyrenes, and fragments. These microscale pellets cause physiological stress and growth deformities by targeting the GI tracts of fishes and other biota. Approximately 80% MPs come from terrestrial sources, either primary, generated during different products such as skin care products, tires production and the use of MPs as carrier for pharmaceutical products, or secondary plastics, disposed of near coastal areas and water bodies. The issue of MPs and their potential effects on the marine ecosystem require proper attention. Therefore, this study conducted an extensive literature review on assessing MPs levels in fishes, sediments, seawater, their sources, and effects on marine biota (especially on fishes), chemo-physical behavior and the techniques used for their identification.

Nutrient conditions determine the strength of herbivore‐mediated stabilizing feedbacks in barrens

Abiotic environmental conditions can significantly influence the way species interact. In particular, plant–herbivore interactions can be substantially dependent on temperature and nutrients. The overall product of these relationships is critical for the fate and stability of vegetated ecosystems like marine forests. The last few decades have seen a rapid spread of barrens on temperate rocky reefs mainly as a result of overgrazing. The ecological feedbacks that characterize the barren state involve a different set of interactions than those occurring in vegetated habitats. Reversing these trends requires a proper understanding of the novel feedbacks and the conditions under which they operate. Here, we explored the role of a secondary herbivore in reinforcing the stability of barrens formed by sea urchin overgrazing under different nutrient conditions. Combining comparative and experimental studies in two Mediterranean regions characterized by contrasting nutrient conditions, we assessed: (i) if the creation of barren areas enhances limpet abundance, (ii) the size‐specific grazing impact by limpets, and (iii) the ability of limpets alone to maintain barrens. Our results show that urchin overgrazing enhanced limpet abundance. The effects of limpet grazing varied with nutrient conditions, being up to five times more intense under oligotrophic conditions. Limpets were able to maintain barrens in the absence of sea urchins only under low‐nutrient conditions, enhancing the stability of the depauperate state. Overall, our study suggests a greater vulnerability of subtidal forests in oligotrophic regions of the Mediterranean and demonstrates the importance of environment conditions in regulating feedbacks mediated by plant–herbivore interactions.

Contamination and ecological risk assessment of heavy metals, and relationship with organic matter sources in surface sediments of the Cross River Estuary and nearshore areas

Chemical speciation of heavy metals (Zn, Pb, Cu, and Cd) was studied to evaluate the contamination status and associated risks and to constrain the sources of heavy metals in relation to sedimentary organic matter (OM) sources in surface sediments of the Cross River Estuary (CRE) and nearshore areas surrounded by a degrading mangrove ecosystem (typical C₃ plants). The contamination factor (CF) and geo-accumulation (I_geo) indicated that Cd and Zn were the most polluted heavy metals. High percentages of Zn (63.78%), Pb (64.48%), Cd (76.72%) and the considerable amount of Cu (48.57%) in non-residual fractions indicated that these heavy metals are bioavailable. Cd showed moderate to high ecological and bioavailability risk based on the ecological risk (E_r) and risk assessment code (RAC). Significant positive correlations occurred among the heavy metals, fine-grained sediments, and sedimentary OM from terrestrial C₃ sources. These correlations, together with high percentages of heavy metals in the oxidizable fraction (~33-50%), indicated that the erosive washout of OM and fine sediments ladened with heavy metals from the adjoining degraded mangrove ecosystem contributed significantly to the increased contents of heavy metals in surface sediments of the study area.

Plastic as a Vector of Dispersion for Marine Species With Invasive Potential. A Review

Plastic debris constitutes up to 87% of marine litter and represents one of the most frequently studied vectors for marine alien species with invasive potential in the last 15 years. This review addresses an integrated analysis of the different factors involved in the impact of plastic as a vector for the dispersal of marine species. The sources of entry of plastic materials into the ocean are identified as well as how they move between different habitats affecting each trophic level and producing hot spots of plastic accumulation in the ocean. The characterization of plastic as a dispersal vector for marine species has provided information about the inherent properties of plastics which have led to its impact on the ocean: persistence, buoyancy, and variety in terms of chemical composition, all of which facilitate colonization by macro and microscopic species along with its dispersion throughout different oceans and ecosystems. The study of the differences in the biocolonization of plastic debris according to its chemical composition provided fundamental information regarding the invasion process mediated by plastic, and highlighted gaps of knowledge about this process. A wide range of species attached to plastic materials has been documented and the most recurrent phyla found on plastic have been identified from potentially invasive macrofauna to toxic microorganisms, which are capable of causing great damage in places far away from their origin. Plastic seems to be more efficient than the natural oceanic rafts carrying taxa such as Arthropoda, Annelida, and Mollusca. Although the differential colonization of different plastic polymers is not clear, the chemical composition might determine the community of microorganisms, where we can find both pathogens and virulent and antibiotic resistance genes. The properties of plastic allow it to be widely dispersed in practically all ocean compartments, making this material an effective means of transport for many species that could become invasive.

An ecotoxicological approach to microplastics on terrestrial and aquatic organisms: A systematic review in assessment, monitoring and biological impact

Marine and land plastic debris biodegrades at micro- and nanoscales through progressive fragmentation. Oceanographic model studies confirm the presence of up to ∼2.41 million tons of microplastics across the Atlantic, Pacific, and Indian subtropical gyres. Microplastics distribute from primary (e.g., exfoliating cleansers) and secondary (e.g., chemical deterioration) sources in the environment. This anthropogenic phenomenon poses a threat to the flora and fauna of terrestrial and aquatic ecosystems as ingestion and entanglement cases increase over time. This review focuses on the impact of microplastics across taxa at suggested environmentally relevant concentrations, and advances the groundwork for future ecotoxicological-based research on microplastics including the main points: (i) adhesion of chemical pollutants (e.g., PCBs); (ii) biological effects (e.g., bioaccumulation, biomagnification, biotransportation) in terrestrial and aquatic organisms; (iii) physico-chemical properties (e.g., polybrominated diphenyl ethers) and biodegradation pathways in the environment (e.g., chemical stress, heat stress); and (iv) an ecotoxicological prospect for optimized impact assessments.

Linking effects of microplastics to ecological impacts in marine environments

Recently, efforts to determine the ecological impacts of microplastic pollutants have increased because of plastic's accelerated contamination of the environment. The tiny size, variable surface topography, thermal properties, bioavailability and biological toxicity of microplastics all offer opportunities for these pollutants to negatively impact the environment. Additionally, various inorganic and organic chemicals sorbed on these particles may pose a greater threat to organisms than the microplastics themselves. However, there is still a big knowledge gap in the assessment of various toxicological effects of microplastics in the environment. Ecological risk assessment of microplastics has become more challenging with the current data gaps. Thus, a current literature review and identification of the areas where research on ecology of microplastics can be extended is necessary. We have provided an overview of various aspects of microplastics by which they interact negatively or positively with marine organisms. We hypothesize that biogeochemical interactions are critical to fully understand the ecological impacts, movement, and fate of microplastics in oceans. As microplastics are now ubiquitous in marine environments and impossible to remove, we recommend that it's not too late to converge research on plastic alternatives. In addition, strict actions should be taken promptly to prevent plastics from entering the environment.

Effects of a severe storm on seagrass meadows

Extreme environmental events can strongly affect coastal marine ecosystems but are typically unpredictable. Reliable data on benthic community conditions before such events are rarely available, making it difficult to measure their effects. At the end of October 2018, a severe storm hit the Ligurian coast (NW Mediterranean) producing damages to coastal infrastructures. Thanks to recent data collected just before the event on two Posidonia oceanica seagrass meadows hit by the storm, it has been possible to assess the impact of the event on one of the most valuable habitats of the Mediterranean Sea. By means of seagrass cover and depth data gathered along four depth transects positioned within the two meadows in areas differently exposed to the storm waves, and by using models (WW3® + SWAN + XBeach 1D) to evaluate wave height and bed shear stress, we showed that meadows experienced erosion and burial phenomena according to exposure. Paradoxically, meadows in good conditions suffered more damage as compared to those already suffering from previous local anthropogenic impacts. Besides the direct effect of waves in terms of plant uprooting, a major loss of P. oceanica was due to sediment burial in the deepest parts of the meadows. Overall, the loss of living P. oceanica cover amounted to about 50%. Considering that previous research showed that the loss of the original surface of P. oceanica meadows in 160 years due to anthropogenic pressures was similarly around 50%, the present study documented that an extreme environmental event can generate in a single day a loss of natural capital equal to that produced gradually by more than a century of human impact.

Spatiotemporal variations of biogenic elements and sources of sedimentary organic matter in the largest oyster mariculture bay (Maowei Sea), Southwest China

China is the largest mariculture producer in the world, but detailed information on the spatiotemporal variations of biogenic elements and sources of sedimentary organic matter (SOM) via mariculture is limited. The primary objective of this study was to assess the influence of mariculture on the origin of SOM in relation with biogenic elements and geochemical paramaters due to the importance of SOM as a potential source of nutrients and energy in coastal marine environments. Surface sediments from the Maowei Sea were collected in August (summer) and December (winter), 2016 for grain size, total organic carbon (TOC), total nitrogen (TN), organic phosphorus (OP), biogenic silica (BSi), δ¹³C and δ¹⁵N analyses. Significant correlation (p < 0.01) was observed between TOC and TN in summer and winter respectively, indicating that they have common source in both seasons. The spatiotemporal distributions of TOC, TN, OP and BSi were influenced by the sources and distribution of SOM, grain sizes and hydrodynamic conditions in the Maowei Sea. The overall ranges of δ¹³C (-26.86‰ to -23.01‰) and δ¹⁵N (2.54‰ to 9.82‰) and C/N ratio (5.83 to 18.67) showed that SOM is derived from mixed sources. The δ¹³C and δ¹⁵N-based three-end-member mixing model results revealed that >40% of the deposited SOM originates from terrestrial source during two seasons. The SOM from shellfish mariculture was seasonal, mainly deposited in the intensive mariculture areas, and its proportions were only higher than contributions from marine plankton in summer. Generally, this study indicates that shellfish biodepositions can significantly influence the cycle of carbon and other biogenic elements in the intensive mariculture areas. Nevertheless, the overall dominance of terrestrial and marine SOM suggests that the sources of SOM and factors influencing carbon cycling in the Maowei Sea do not exclusively depend on the intensity of mariculture activities.

Bulk sedimentary phosphorus in relation to organic carbon, sediment textural properties and hydrodynamics in the northern Beibu Gulf, South China Sea

Bulk sedimentary phosphorus (P) is studied to evaluate its source, distribution, preservation and enrichment in relation with organic carbon (OC), sediment textures and moisture contents in the northern Beibu Gulf. Approximately 80% of surface sediments in the investigated sites were composed of coarse sandy texture (>63 μm). Total P (TP), inorganic P (IP) and organic P (OP) contents were lower to medium range compared to the levels reported for other marginal seas. Sedimentary OC and P were derived from mixed sources, with high terrestrial influence in the coastal areas (molar OC/OP ratios >250:1). The distribution of P corroborated with the variation tendency of fine-grained sediments, moisture contents and OC. Both IP and OP may significantly influence the trophic state of seawater if released from surface sediments. Influenced by hydrodynamics, frequent resuspension and high abundance of sand, TP is less preserved, and shows low to moderate enrichment in surface sediments.

Long-term monitoring of temperate macroalgal assemblages inside and outside a No take marine reserve

Macroalgal communities have an essential role in the shallow benthic habitats of temperate seas, where changes in their composition can resonate through entire coastal ecosystems. As all major ecosystems on Earth, algal beds have already been affected by multiple disturbances. Passive conservation tools, such as marine protected areas or No-take zones, have the potential to reduce some of the anthropogenic impacts by limiting human activity. However, without a good knowledge of the natural community dynamics, it is not easy to discern between changes fruit of the intrinsic variability of biological communities and the ones caused by human-related stressors. In this study, we evaluated the natural variability of macroalgal communities' composition inside and outside a Mediterranean No-Take marine reserve during 15 years. We described their temporal dynamics considering their main drivers and we tested the effect of protection in seaweed beds. We did not find differences either in the composition of the macroalgal assemblages or the total algal cover between protected and non-protected locations over the fifteen years of study. Nevertheless, we observed a positive effect of the protection increasing the cover of some specific species, such as the canopy-forming Treptacantha elegans. Our results highlight the importance of obtaining long-term data in ecological studies to better understand the natural variability of marine communities. Accordingly, a robust understanding of the community dynamics would help us to avoid misinterpretations between 'impacted' or 'in-recovery' communities when recovery times are longer than the study periods.

Geochemical discrimination of bulk organic matter in surface sediments of the Cross River estuary system and adjacent shelf, South East Nigeria (West Africa)

Knowledge of the sources, distribution and fate of organic matter (OM) in estuarine and adjacent shelf sediments are important for the understanding of the global biogeochemical cycles. Bulk organic carbon (C-org), total nitrogen (TN), biogenic silica (BSi), stable carbon (δ¹³C-org) and nitrogen (δ¹⁵N) isotopes, and sediment grain sizes were measured to study the spatial distributions and sources of sediment OM in the Cross River estuary system (CRES) and adjacent shelf. Surface sediments in the CRES were composed of clayey silt and sandy silt, while the adjacent shelf sediments were mainly silty sand. The range of the studied parameters was -28.79‰ to -22.20‰ for δ¹³C-org, -1.32‰-6.31‰ for δ¹⁵N, 6.7-29.2 for C-org/N ratios, 0.08%-0.33% for TN, 0.24‰-0.74‰ for BSi, and 0.47%-5.28% for C-org, and their spatial distributions showed a general decreasing trend in both the terrestrial and estuarine OM from the riverine regions to the adjacent shelf. Based on the three-end-member mixing model using the δ¹³C and δ¹⁵N isotopic values, ~58.01 ± 15.32% of sediment OM are derived from terrestrial sources dominated by C₃ vascular plants, while ~26.34 ± 9.71% are attributed to estuarine sources dominated by aquatic macrophytes, and ~15.65 ± 12.37% for marine plankton source. Other sources of OM identified included soils underlain C₃ vascular plants and agricultural farms enriched with N, sewage, and petroleum hydrocarbons. The relationship between C-org vs. BSi, and the atomic BSi/Corg ratios suggested that diatoms also play an important role in OM sequestration in surface sediments of the CRES and adjacent shelf. The correlations of the δ¹³C-org and δ¹⁵N isotopic values vs. C-org/N ratios resulted in scatter plots, indicating that the distributions of sediment OM in the CRES and adjacent shelf are influenced by post depositional processes, fixed inorganic N adsorbed on fine-grained sediments, microbial degradation, as well as sediment grain size.

Beached microplastics in the Northwestern Mediterranean Sea

Microplastics are small (<5mm) fragments of plastic debris that are ubiquitous in coastal areas and in open ocean. We have investigated the occurrence and composition of microplastics in beach sediments from the micro-tidal Northwestern Mediterranean Sea. Samples were collected on two beaches (northern and southern site) of the western Gulf of Lion showing markedly different characteristics. Sampling was performed along depositional lower, mid and upper beaches and repeated after 1month. Concentrations of microplastics in the northern and southern site were highly variable, ranging from 33 to 798 and from 12 to 187 microplastics per kg of dry sediment, respectively. Highest concentrations were found at three specific locations: nearby a local river mouth, within an accretionary area and in a depositional upper beach. The spatial and temporal distribution of beached microplastics seems to be directly dependent on external forcing such as wind, swell, precipitation, outflow and river mouth proximity.

Sensitivity of Storm-Induced Hazards in a Highly Curvilinear Coastline to Changing Storm Directions. The Tordera Delta Case (NW Mediterranean)

Extreme coastal storms, especially when incident in areas with densely urbanized coastlines, are one of the most damaging forms of natural disasters. The main hazards originating from coastal storms are inundation and erosion, and their magnitude and extent needs to be accurately assessed for effective management of coastal risk. The use of state-of-art morphodynamic process-based models is becoming standard, with most being applied to straight coastlines with gentle slopes. In this study, the XBeach model is used to assess the coastal response of a curvilinear sensitive deltaic coast with coarse sediment and steep slopes (intermediate-reflective conditions). The tested hypothesis is that changes in wave direction may cause large variations in the magnitude of storm-induced hazards. The model is tested against field data available for the Sant Esteve Storm (December 2008), obtaining an overall BSS (Brier Skill Score) score on the emerged morphological response of 0.68. Later, the 2008 event is used as baseline scenario to create synthetic events covering the range from NE to S. The obtained results show that storm-induced hazards along a highly curvilinear coast are very sensitive to changes in wave direction. Therefore, even under climate scenarios of relatively steady storminess, a potential shift in wave direction may significantly change hazard conditions and thus, need to be accounted for in robust damage risk assessments.

Floating microplastics and aggregate formation in the Western Mediterranean Sea

Pollution by large-sized plastics and microplastic debris is widespread in all Earth environments, also threatening marine ecosystems worldwide. In this study we determine the load of microplastics in the Western Mediterranean Sea and evaluate their aggregation potential into marine aggregates. We report average microplastic abundances of 0.10 ± 0.09 items m^-2 (max: 0.50 items m^-2). Abundances and chemical composition of microplastics are subject to temporal changes as a function of human activities in the areas of influence and shifting meteorological and sea-state conditions. We find that microplastics were on average smaller in mass than other studies conducted in the Mediterranean Sea indicating longer exposure times in the environment. The microplastic aggregation potential was determined by inspecting formed biogenic aggregates either during sample collection or in the laboratory. Smaller and more angular microplastics dominated in marine aggregates, representing an average 40% in abundance and 25% in mass of microplastics.

No-take marine reserves control the recovery of sea urchin populations after mass mortality events

Understanding how no-take zones (NTZs) shape the population dynamics of key herbivores is crucial for the conservation and management of temperate benthic communities. Here, we examine the recovery patterns of sea urchin populations following a high-intensity storm under contrasting protection regimes in the NW Mediterranean Sea. We found significant differences in the recovery trends of Paracentrotus lividus abundance and biomass in the five years following the storm. The P. lividus populations outside the NTZ recovered faster than the populations inside the NTZ, revealing that predation was the main factor controlling the sea urchin populations inside the NTZ during the study period. Arbacia lixula reached the highest abundance and biomass values ever observed outside the NTZ in 2016. Our findings reveal that predation can control the establishment of new sea urchin populations and emphasize top-down control in NTZs, confirming the important role of fully protected areas in the structure of benthic communities.

The imprint of microfibres in southern European deep seas

Pollution of the marine environment by large and microscopic plastic fragments and their potential impacts on organisms has stimulated considerable research interest and has received widespread publicity. However, relatively little attention has been paid to the fate and effects of microplastic particles that are fibrous in shape, also referred as microfibres, which are mostly shed from synthetic textiles during production or washing. Here we assess composition and abundance of microfibres in seafloor sediments in southern European seas, filling gaps in the limited understanding of the long-range transport and magnitude of this type of microplastic pollution. We report abundances of 10–70 microfibres in 50 ml of sediment, including both natural and regenerated cellulose, and synthetic plastic (polyester, acrylic, polyamide, polyethylene, and polypropylene) fibres. Following a shelf-slope-deep basin continuum approach, based on the relative abundance of fibres it would appear that coastal seas retain around 33% of the sea floor microfibres, but greater quantities of the fibres are exported to the open sea, where they accumulate in sediments. Submarine canyons act as preferential conduits for downslope transport of microfibres, with 29% of the seafloor microfibres compared to 18% found on the open slope. Around 20% of the microfibres found had accumulated in the deep open sea beyond 2000m of water depth. The remoteness of the deep sea does not prevent the accumulation of microfibres, being available to become integrated into deep sea organisms.

Extreme weather and climate events with ecological relevance: a review

Robust evidence exists that certain extreme weather and climate events, especially daily temperature and precipitation extremes, have changed in regard to intensity and frequency over recent decades. These changes have been linked to human-induced climate change, while the degree to which climate change impacts an individual extreme climate event (ECE) is more difficult to quantify. Rapid progress in event attribution has recently been made through improved understanding of observed and simulated climate variability, methods for event attribution and advances in numerical modelling. Attribution for extreme temperature events is stronger compared with other event types, notably those related to the hydrological cycle. Recent advances in the understanding of ECEs, both in observations and their representation in state-of-the-art climate models, open new opportunities for assessing their effect on human and natural systems. Improved spatial resolution in global climate models and advances in statistical and dynamical downscaling now provide climatic information at appropriate spatial and temporal scales. Together with the continued development of Earth System Models that simulate biogeochemical cycles and interactions with the biosphere at increasing complexity, these make it possible to develop a mechanistic understanding of how ECEs affect biological processes, ecosystem functioning and adaptation capabilities. Limitations in the observational network, both for physical climate system parameters and even more so for long-term ecological monitoring, have hampered progress in understanding bio-physical interactions across a range of scales. New opportunities for assessing how ECEs modulate ecosystem structure and functioning arise from better scientific understanding of ECEs coupled with technological advances in observing systems and instrumentation.This article is part of the themed issue 'Behavioural, ecological and evolutionary responses to extreme climatic events'.

Plastics and microplastics in the oceans: From emerging pollutants to emerged threat

Plastic production has increased dramatically worldwide over the last 60 years and it is nowadays recognized as a serious threat to the marine environment. Plastic pollution is ubiquitous, but quantitative estimates on the global abundance and weight of floating plastics are still limited, particularly for the Southern Hemisphere and the more remote regions. Some large-scale convergence zones of plastic debris have been identified, but there is the urgency to standardize common methodologies to measure and quantify plastics in seawater and sediments. Investigations on temporal trends, geographical distribution and global cycle of plastics have management implications when defining the origin, possible drifting tracks and ecological consequences of such pollution. An elevated number of marine species is known to be affected by plastic contamination, and a more integrated ecological risk assessment of these materials has become a research priority. Beside entanglement and ingestion of macro debris by large vertebrates, microplastics are accumulated by planktonic and invertebrate organisms, being transferred along food chains. Negative consequences include loss of nutritional value of diet, physical damages, exposure to pathogens and transport of alien species. In addition, plastics contain chemical additives and efficiently adsorb several environmental contaminants, thus representing a potential source of exposure to such compounds after ingestion. Complex ecotoxicological effects are increasingly reported, but the fate and impact of microplastics in the marine environment are still far to be fully clarified.

Ordinary and Extraordinary Movement Behaviour of Small Resident Fish within a Mediterranean Marine Protected Area

It is important to account for the movement behaviour of fishes when designing effective marine protected areas (MPAs). Fish movements occur across different spatial and temporal scales and understanding the variety of movements is essential to make correct management decisions. This study describes in detail the movement patterns of an economically and commercially important species, Diplodus sargus, within a well-enforced Mediterranean MPA. We monitored horizontal and vertical movements of 41 adult individuals using passive acoustic telemetry for up to one year. We applied novel analysis and visualization techniques to get a comprehensive view of a wide range of movements. D. sargus individuals were highly territorial, moving within small home ranges (< 1 km²), inside which they displayed repetitive diel activity patterns. Extraordinary movements beyond the ordinary home range were observed under two specific conditions. First, during stormy events D. sargus presented a sheltering behaviour, moving to more protected places to avoid the disturbance. Second, during the spawning season they made excursions to deep areas (> 50 m), where they aggregated to spawn. This study advances our understanding about the functioning of an established MPA and provides important insights into the biology and management of a small sedentary species, suggesting the relevance of rare but important fish behaviours.

Cold-Water Corals and Anthropogenic Impacts in La Fonera Submarine Canyon Head, Northwestern Mediterranean Sea

We assess the occurrence and extent of cold-water coral (CWC) species Madrepora oculata and Dendrophyllia cornigera, as well as gorgonian red coral Corallium rubrum, in La Fonera canyon head (Northwestern Mediterranean Sea), as well as human impacts taking place in their habitats. Occurrence is assessed based on Remotely Operated Vehicle (ROV) video imaging. Terrain classification techniques are applied to high-resolution swath bathymetric data to obtain semi-automatic interpretative maps to identify the relationship between coral distribution patterns and canyon environments. A total of 21 ROV immersions were carried out in different canyon environments at depths ranging between 79 and 401 m. Large, healthy colonies of M. oculata occur on abrupt, protected, often overhanging, rocky sections of the canyon walls, especially in Illa Negra branch. D. cornigera is sparser and evenly distributed at depth, on relatively low sloping areas, in rocky but also partially sedimented areas. C. rubrum is most frequent between 100 and 160 m on highly sloping rocky areas. The probable extent of CWC habitats is quantified by applying a maximum entropy model to predict habitat suitability: 0.36 km² yield M. oculata occurrence probabilities over 70%. Similar predictive models have been produced for D. cornigera and C. rubrum. All ROV transects document either the presence of litter on the seafloor or pervasive trawling marks. Nets and longlines are imaged entangled on coral colonies. Coral rubble is observed at the foot of impacted colonies. Some colonies are partially covered by sediment that could be the result of the resuspension generated by bottom trawling on neighbouring fishing grounds, which has been demonstrated to be responsible of daily increases in sediment fluxes within the canyon. The characteristics of the CWC community in La Fonera canyon are indicative that it withstands high environmental stress of both natural and human origin.

The behaviors of microplastics in the marine environment

Despite the pollution of microplastics being internationally recognized, the understanding of their behaviors in marine environment is still developing. Microplastics are ubiquitous in the marine environment, with the potential to cause harm to marine ecosystem. Here, we would classify the behaviors of microplastics as physical behaviors (i.e. migration, sedimentation and accumulation), chemical behaviors (i.e. degradation and adsorption) and biobehaviors (i.e. ingestion, translocation and biodegradation), and a further discussion on their behavioral mechanisms were presented to better understand their impacts for the marine environment.

Delivery of unprecedented amounts of perfluoroalkyl substances towards the deep-sea

The finding of perfluoroalkyl substances (PFASs) in particles sinking to the deep northwestern Mediterranean Sea confirms the role of the latter as ballast for the transfer of pollutants to the deep sea. The transfer of particulate matter down to the deep is enhanced during atmosphere-driven, high-energy physical oceanographic processes like dense shelf water cascading (DSWC), which is caused by winter surface heat losses and evaporation. Here we present data from samples collected during winter 2012, when dense shelf water formation and subsequent cascading triggered the flushing of large amounts of PFASs through a submarine canyon to depths in excess of 1000 m. The finding of quantifiable concentrations of long-chain PFOA, PFOS and PFNA substances and significantly high concentrations of the short-chain substances PFHxA and PFBA indicates that these compounds, sorbed onto particulate matter, are quickly and directly transferred to the ocean's interior, thus highlighting the role of DSWC in removing those pollutants from the coastal ocean. Eventually, uncertainties about our results arising from the limited number of samples available are counterbalanced by their intrinsic value as intense DSWC events, like the one in 2012, occur only every 5-7 years in the study area, which seriously restricts sampling opportunities. Our results add PFASs to the list of persistent organic pollutants like polychlorinated biphenyls, chlorobenzenes or polycyclic aromatic hydrocarbons known to be conveyed to the deep marine environment.

PYCNOIB: biodiversity and biogeography of Iberian pycnogonids

Biodiversity and biogeographic studies comparing the distribution patterns of benthic marine organisms across the Iberian Atlantic and Mediterranean waters are scarce. The Pycnogonida (sea spiders) are a clear example of both endemicity and diversity, and are considered a key taxon to study and monitor biogeographic and biodiversity patterns. This is the first review that compiles data about abundance and diversity of Iberian pycnogonids and examines their biogeographic patterns and bathymetric constraints using GIS tools. A total of 17762 pycnogonid records from 343 localities were analyzed and were found to contain 65 species, 21 genera and 12 families. Achelia echinata and Ammothella longipes (family Acheliidae) were the most abundant comprising ~80% of the total records. The Acheliidae is also the most speciose in Iberian waters with 15 species. In contrast, the family Nymphonidae has 7 species but is significantly less abundant (<1% of the total records) than Acheliidae. Species accumulation curves indicate that further sampling would increase the number of Iberian species records. Current sampling effort suggests that the pycnogonid fauna of the Mediterranean region may be richer than that of the Atlantic. The Strait of Gibraltar and the Alboran Sea are recognized as species-rich areas that act as buffer zones between the Atlantic and Mediterranean boundaries. The deep waters surrounding the Iberian Peninsula are poorly surveyed, with only 15% of the sampling sites located below 1000 m. Further deep-water sampling is needed mainly on the Iberian Mediterranean side.

The deep sea is a major sink for microplastic debris

Marine debris, mostly consisting of plastic, is a global problem, negatively impacting wildlife, tourism and shipping. However, despite the durability of plastic, and the exponential increase in its production, monitoring data show limited evidence of concomitant increasing concentrations in marine habitats. There appears to be a considerable proportion of the manufactured plastic that is unaccounted for in surveys tracking the fate of environmental plastics. Even the discovery of widespread accumulation of microscopic fragments (microplastics) in oceanic gyres and shallow water sediments is unable to explain the missing fraction. Here, we show that deep-sea sediments are a likely sink for microplastics. Microplastic, in the form of fibres, was up to four orders of magnitude more abundant (per unit volume) in deep-sea sediments from the Atlantic Ocean, Mediterranean Sea and Indian Ocean than in contaminated sea-surface waters. Our results show evidence for a large and hitherto unknown repository of microplastics. The dominance of microfibres points to a previously underreported and unsampled plastic fraction. Given the vastness of the deep sea and the prevalence of microplastics at all sites we investigated, the deep-sea floor appears to provide an answer to the question-where is all the plastic?

Contemporary sediment-transport processes in submarine canyons

Submarine canyons are morphological incisions into continental margins that act as major conduits of sediment from shallow- to deep-sea regions. However, the exact mechanisms involved in sediment transfer within submarine canyons are still a subject of investigation. Several studies have provided direct information about contemporary sedimentary processes in submarine canyons that suggests different modes of transport and various triggering mechanisms. Storm-induced turbidity currents and enhanced off-shelf advection, hyperpycnal flows and failures of recently deposited fluvial sediments, dense shelf-water cascading, canyon-flank failures, and trawling-induced resuspension largely dominate present-day sediment transfer through canyons. Additionally, internal waves periodically resuspend ephemeral deposits within canyons and contribute to dispersing particles or retaining and accumulating them in specific regions. These transport processes commonly deposit sediments in the upper- and middle-canyon reaches for decades or centuries before being completely or partially flushed farther down-canyon by large sediment failures.

Trophic dynamics of deep-sea megabenthos are mediated by surface productivity

Most deep-sea benthic ecosystems are food limited and, in the majority of cases, are driven by the organic matter falling from the surface or advected downslope. Species may adapt to this scarceness by applying a wide variety of responses, such as feeding specialisation, niche width variation, and reduction in metabolic rates. The Mediterranean Sea hosts a gradient of food availability at the deep seafloor over its wide longitudinal transect. In the Mediterranean, broad regional studies on trophic habits are almost absent, and the response of deep-sea benthos to different trophic conditions is still speculative. Here, we show that both primary and secondary production processes taking place at surface layers are key drivers of deep-sea food web structuring. By employing an innovative statistical tool, we interpreted bulk-tissue δ(13)C and δ(15)N isotope ratios in benthic megafauna, and associated surface and mesopelagic components from the 3 basins of the Mediterranean Sea at 3 different depths (1200, 2000, and 3000 m). The trophic niche width and the amplitude of primary carbon sources were positively correlated with both primary and secondary surface production indicators. Moreover, mesopelagic organic matter utilization processes showed an intermediate position between surface and deep benthic components. These results shed light on the understanding of deep-sea ecosystems functioning and, at the same time, they demand further investigation.

The Mediterranean benthic herbivores show diverse responses to extreme storm disturbances

Catastrophic storms have been observed to be one of the major elements in shaping the standing structure of marine benthic ecosystems. Yet, little is known about the effect of catastrophic storms on ecosystem processes. Specifically, herbivory is the main control mechanism of macrophyte communities in the Mediterranean, with two main key herbivores: the sea urchin Paracentrotus lividus and the fish Sarpa salpa. Consequently, the effects of extreme storm events on these two herbivores (at the population level and on their behaviour) may be critical for the functioning of the ecosystem. With the aim of filling this gap, we took advantage of two parallel studies that were conducted before, during and after an unexpected catastrophic storm event. Specifically, fish and sea urchin abundance were assessed before and after the storm in monitored fixed areas (one site for sea urchin assessment and 3 sites for fish visual transects). Additionally, we investigated the behavioural response to the disturbance of S. salpa fishes that had been tagged with acoustic transmitters. Given their low mobility, sea urchins were severely affected by the storm (ca. 50% losses) with higher losses in those patches with a higher density of sea urchins. This may be due to a limited availability of refuges within each patch. In contrast, fish abundance was not affected, as fish were able to move to protected areas (i.e. deeper) as a result of the high mobility of this species. Our results highlight that catastrophic storms differentially affect the two dominant macroherbivores of rocky macroalgal and seagrass systems due to differences in mobility and escaping strategies. This study emphasises that under catastrophic disturbances, the presence of different responses among the key herbivores of the system may be critical for the maintenance of the herbivory function.

Rapid northward spread of a zooxanthellate coral enhanced by artificial structures and sea warming in the western Mediterranean

The hermatypic coral Oculina patagonica can drive a compositional shift in shallow water benthic marine communities in the northwestern Mediterranean. Here, we analyze a long-term, large-scale observational dataset to characterize the dynamics of the species' recent northward range shift along the coast of Catalonia and examine the main factors that could have influenced this spread. The variation in the distributional range of Oculina patagonica was examined by monitoring 223 locations including natural and artificial habitats along >400 km of coastline over the last 19 years (1992–2010). Abundance of the species increased from being present in one location in 1992 to occur on 19% of the locations in 2010, and exhibited an acceleration of its spreading over time driven by the join action of neighborhood and long-distance dispersal. However, the pattern of spread diverged between artificial and natural habitats. A short lag phase and a high slope on the exponential phase characterized the temporal pattern of spread on artificial habitats in contrast to that observed on natural ones. Northward expansion has occurred at the fastest rate (22 km year⁻¹) reported for a coral species thus far, which is sufficiently fast to cope with certain climate warming predictions. The pattern of spread suggests that this process is mediated by the interplay of (i) the availability of open space provided by artificial habitats, (ii) the seawater temperature increase with the subsequent extension of the growth period, and (iii) the particular biological features of O. patagonica (current high growth rates, early reproduction, and survival to low temperature and in polluted areas). These results are indicative of an ongoing fundamental modification of temperate shallow water assemblages, which is consistent with the predictions indicating that the Mediterranean Sea is one of the most sensitive regions to global change.

Impacts on coralligenous outcrop biodiversity of a dramatic coastal storm

Extreme events are rare, stochastic perturbations that can cause abrupt and dramatic ecological change within a short period of time relative to the lifespan of organisms. Studies over time provide exceptional opportunities to detect the effects of extreme climatic events and to measure their impacts by quantifying rates of change at population and community levels. In this study, we show how an extreme storm event affected the dynamics of benthic coralligenous outcrops in the NW Mediterranean Sea using data acquired before (2006-2008) and after the impact (2009-2010) at four different sites. Storms of comparable severity have been documented to occur occasionally within periods of 50 years in the Mediterranean Sea. We assessed the effects derived from the storm comparing changes in benthic community composition at sites exposed to and sheltered from this extreme event. The sites analyzed showed different damage from severe to negligible. The most exposed and impacted site experienced a major shift immediately after the storm, represented by changes in the species richness and beta diversity of benthic species. This site also showed higher compositional variability immediately after the storm and over the following year. The loss of cover of benthic species resulted between 22% and 58%. The damage across these species (e.g. calcareous algae, sponges, anthozoans, bryozoans, tunicates) was uneven, and those with fragile forms were the most impacted, showing cover losses up to 50 to 100%. Interestingly, small patches survived after the storm and began to grow slightly during the following year. In contrast, sheltered sites showed no significant changes in all the studied parameters, indicating no variations due to the storm. This study provides new insights into the responses to large and rare extreme events of Mediterranean communities with low dynamics and long-lived species, which are among the most threatened by the effects of global change.