Publications

Seagrasses are hugely valuable to human life, but the global extent of seagrass meadows remains unclear. As evidence of their value, a United Nations program exists (http://data.unep-wcmc.org/datasets/7) to try and assess their distribution and there has been a call from 122 scientists across 28 countries for more work to manage, protect and monitor seagrass meadows (http://www.bbc.com/news/science-environment-37606827). Emerging from the 12th International Seagrass Biology Workshop, held in October 2016 has been the view that grazing marine megafauna may play a useful role in helping to identify previously unknown seagrass habitats. Here we describe this concept, showing how detailed information on the distribution of both dugongs (Dugong dugon) and green sea turtles (Chelonia mydas) obtained, for example, by aerial surveys and satellite tracking, can reveal new information on the location of seagrass meadows. We show examples of how marine megaherbivores have been effective habitat indicators, revealing major, new, deep-water seagrass meadows and offering the potential for more informed estimates of seagrass extent in tropical and sub-tropical regions where current information is often lacking.

Abstract. The circulation patterns and the impact of the lateral export of nutrients and organic matter off NW Africa are examined by applying an inverse model to two hydrographic datasets gathered in fall 2002 and spring 2003. These estimates show significant changes in the circulation patterns at central levels from fall to spring, particularly in the southern boundary of the domain related to zonal shifts of the Cape Verde Frontal Zone. Southward transports at the surface and central levels at 26∘ N are 5.6±1.9 Sv in fall and increase to 6.7±1.6 Sv in spring; westward transports at 26∘ W are 6.0±1.8 Sv in fall and weaken to 4.0±1.8 Sv in spring. At 21∘ N a remarkable temporal variability is obtained, with a northward mass transport of 4.4±1.5 Sv in fall and a southward transport of 5.2±1.6 Sv in spring. At intermediate levels important spatiotemporal differences are also observed, and it must be highlighted that a northward net mass transport of 2.0±1.9 Sv is obtained in fall at both the south and north transects. The variability in the circulation patterns is also reflected in lateral transports of inorganic nutrients (SiO2, NO3, PO4) and dissolved organic carbon (DOC). Hence, in fall the area acts as a sink of inorganic nutrients and a source of DOC, while in spring it reverses to a source of inorganic nutrients and a sink of DOC. A comparison between nutrient fluxes from both in situ observations and numerical modeling output is finally addressed.

Seagrasses have experienced major losses globally mostly attributed to human impacts. Recently they are also associated with marine heat waves. The paucity of information on seagrass mortality thermal thresholds prevents the assessment of the risk of seagrass loss under marine heat waves. We conducted a synthesis of reported empirically- or experimentally-determined seagrass upper thermal limits (T limit ) and tested the hypothesis that they increase with increasing local annual temperature. We found that T limit increases 0.42± 0.07°C per°C increase in in situ annual temperature (R 2 = 0.52). By combining modelled seagrass T limit across global coastal areas with current and projected thermal regimes derived from an ocean reanalysis and global climate models (GCMs), we assessed the proximity of extant seagrass meadows to their T limit and the time required for T limit to be met under high (RCP8.5) and moderate (RCP4.5) emission scenarios of greenhouse gases. Seagrass meadows worldwide showed a modal difference of 5°C between present T max and seagrass T limit . This difference was lower than 3°C at the southern Red Sea, the Arabian Gulf, the Gulf of Mexico, revealing these are the areas most in risk of warming-derived seagrass die-off, and up to 24°C at high latitude regions. Seagrasses could meet their T limit regularly in summer within 50-60 years or 100 years under, respectively, RCP8.5 or RCP4.5 scenarios for the areas most at risk, to more than 200 years for the Arctic under both scenarios. This study shows that implementation of the goals under the Paris Agreement would safeguard much of global seagrass from heat-derived mass mortality and identifies regions where actions to remove local anthropogenic stresses would be particularly relevant to meet the Target 10 of the Aichi Targets of the Convention of the Biological Diversity.

A correction to this article has been published and is linked from the HTML and PDF versions of this paper. The error has not been fixed in the paper.

Abstract Ring sea anemones (Cnidaria, Actiniaria) engage in symbiotic associations with octocorals by attaching to their branches and surrounding them with tissue junctions, causing a significant reduction of the host’s coenenchyme. They have previously been reported from the North Atlantic, Western Indian, and Pacific Oceans, from 30 m to aphotic depths, colonising species of sea fans and sea pens in potentially parasitic relationships. Here, we report the first record of ring sea anemones from the Saudi Arabian Red Sea mesophotic waters, living on an octocoral host of the family Ellisellidae at 97 m depth. Through morphological and phylogenetic analyses based on the sequencing of the 12S small subunit rRNA region, we confirmed the identification of these ring sea anemones as Peronanthus sp. (Actiniaria, Amphianthidae). While expanding our knowledge on the geographic range of this genus, this finding emphasises the importance of explorations of coral-associated fauna at mesophotic depths, to better understand their diversity, their relationships with their hosts, and their potential ecological roles within these ecosystems.

Abstract The El Niño‐Southern Oscillation (ENSO), a key driver of interannual climate variability, significantly influences marine phytoplankton dynamics. Rising sea surface temperatures (SST) have further stimulated the occurrence of phytoplankton blooms, potentially increasing the role of seaweed farming in regulating phytoplankton communities. However, the impact of seaweed farming on the resilience of phytoplankton to ENSO events is still poorly understood. Here, using integrated in situ monitoring data from a high‐yield seaweed farm in China, combined with satellite chlorophyll (Chl) data and time‐frequency analysis, we find that seaweed farming regulates phytoplankton blooms and their periodic fluctuations, attenuating SST‐driven growth patterns. We find that seaweed harvesting induces short‐term phytoplankton growth. Seaweed farming enhances the teleconnection between phytoplankton and ENSO, but its regulation of phytoplankton mitigates the stimulation of phytoplankton blooms by increased SST, allowing them to exhibit a more regular and stable SST‐driven pattern. These findings suggest that moderately expanded seaweed farming can be a scalable, nature‐based solution for enhancing coastal ecosystem resilience to ENSO.

Although millions of tons of plastics end up in oceans each year, floating plastics account for only about 1% of all plastic inputs in the ocean. Particularly, microplastics below 1 mm in length, are missing in surface waters due to removal processes like ingestion by marine animals, biofouling and sinking. Here, we studied how a species of mushroom corals (Danafungia scruposa), common in the Maldives, contributed to the removal of microplastics from the water suspension through active (ingestion) and passive (adhesion to the surface) mechanisms. We evaluated if removal rates were affected by the presence of the coral natural prey (i.e. Artemia salina) and by biofouling on the surface of the microplastic. We found that the coral quickly interacts both actively and passively with microplastics and that the probability for the coral to ingest and retain microplastics was higher when the surface of the microplastic was biofouled. We also found that passive adhesion of microplastics was the primary mechanism through which corals sequester microplastics from the water column.