Sébastien Jaquemet’s research while affiliated with University of Rhode Island and other places

Invertebrates have a central role in food webs and ecosystem functioning. By boosting productivity, allochthonous nutrient inputs influence the food webs of recipient communities. Understanding how allochthonous nutrient subsidies affect invertebrates is crucial, particularly in highly productive coastal areas. Here, we examine how mangrove macroinvertebrates are impacted by nutrient‐rich guano delivered by nesting seabird populations at Aldabra Atoll in the Indian Ocean. We compare nitrogen and carbon stable isotope ratios and nitrogen composition of basal resources and macroinvertebrate consumers in mangroves with and without nesting seabirds. Seabird‐derived nutrient enrichment increased the nitrogen content of basal food sources and herbivorous littorinid gastropods and sesarmid crabs. In mangroves with breeding seabirds, mean carapace widths of sesarmid and omnivorous portunid crabs were 6% and 11% larger, respectively. Isotopic niches of littorinid gastropods and sesarmid crabs were larger and had higher overlap at seabird compared to non‐seabird sites. Epiphytic macroalgae and guano comprised >50% of resource contributions to littorinid gastropods and sesarmid crabs at seabird sites. This differed markedly from non‐seabird sites where the main resource contributions were 77% mangrove leaves for littorinid gastropods, 36% sediment organic matter, and 41% mangrove leaves for sesarmid crabs. The increased sizes of mangrove crabs suggest that seabird nutrient enrichment can promote mangrove crab fisheries productivity and benefit the provisioning of mangrove ecosystem services. By shifting resource use of functionally important macroinvertebrates, we discuss how seabirds modify trophic interactions, with potential consequences for mangrove ecosystem processes and resilience.

Marine plastic pollution is well described by bioindicator species in temperate and polar regions but remains understudied in tropical oceans. We addressed this gap by evaluating the seabird Barau’s petrel as bioindicator of plastic pollution in the South-West Indian Ocean. We conducted a multifaceted approach including necropsies of birds to quantify plastic ingestion; GPS tracking of breeding adults to identify their foraging areas; manta trawling of plastic debris to measure plastic pollution at sea and modelling of plastic dispersal. We developed a spatial risk index of seabird exposure to plastic ingestion. Seventy-one percent of the analysed birds had ingested plastic. GPS tracking coupled with manta trawling and dispersal modelling show that adults consistently foraged at places with high level of plastic concentration. The highest ingestion risk occurred in the northwest of Reunion Island and at latitude 30°S. Our findings confirm that Barau’s petrel is a reliable bioindicator of plastic pollution in the region.

Marine plastic pollution is increasing. The Indian Ocean is understudied compared to the Pacific and Atlantic Oceans. This study investigates plastic pollution in the Southwest Indian Ocean using a multi-faceted approach that includes both floating (visual survey and manta trawls) and beach-collected plastics, assessing their concentration, composition, and origin. Through 19 oceanographic campaigns and 153 uninhabited beach surveys, a total of 101,055 pieces of marine litter were identified, with 95% being plastics. Floating macroplastics were predominantly found near remote island waters, particularly at Glorieuses (10 ³ items.km ⁻² ). Meanwhile, an increasing gradient of floating microplastic concentrations was observed from 40°E (10 ³ items.km ⁻² ) to 65°E (10 ⁵ items.km ⁻² ) along 30°/33°S. High concentration of beached macroplastics where observed on the east coast of Madagascar and Tromelin. Mesoplastics were more abundant than macroplastics, on remote islands. Floating and beached plastic debris were mainly hard fragments, mostly made of polyethylene (floating, beached: 72%, 57%) or polypropylene (26%, 34%). The majority of macroplastics identified in the brand audit, was mainly mineral water food packaging (81%) from Southeast Asian manufacturers. Our results will inform national management and provide evidence to support international plastic treaty negotiations on legacy plastics.

Marine nutrients underpin productivity and functioning of oceanic island ecosystems. On islands where they nest, seabirds represent a primary source of marine nutrients. In tropical regions, some of the largest seabird populations nest on atolls, yet there is limited information available on seabird contributions to atoll ecosystem nutrient dynamics. To investigate the spatial and seasonal dynamics of seabird contributions, we assessed seabird colonies of different taxa, including red‐footed boobies and terns, nesting on separate islands of Farquhar Atoll, Seychelles. We assessed nutrient concentrations of guano, soil, coastal plants, and nearby seagrass in seabird colonies and at a control island with no seabirds, during the wet and dry seasons. Sooty terns contributed the highest quantities of nutrients, estimated at 71.2 N tonne/year and 52.2 P tonne/year. Seabird‐derived nutrient transfer occurred year‐round from seabird colonies to soil, coastal plants and seagrass. Soil macro‐ and inorganic nutrients were higher in the high‐density tern colony and during the dry season, coinciding with the breeding period of sooty terns. Both red‐footed booby and tern colonies maintained high nitrogen levels in coastal plants year‐round, while phosphorus levels did not differ between islands or seasons. Seabird‐derived nitrogen reversed nitrogen limitation of seagrass during the dry season. We provide the first insights into seabird nutrient contributions to atoll ecosystems in Seychelles, with recommendations for seabird conservation to boost and support atoll and island ecosystem resilience. Our results from a relatively undisturbed atoll serve as a baseline with which more impacted atolls and future changes can be assessed.

Wedgefishes (Rhinidae) are threatened by unsustainable fishing globally, and especially in the Southwest Indian Ocean (SWIO), due to their high-value fins in the shark trade. The whitespotted wedgefish Rhynchobatus djiddensis and the bottlenose wedgefish R. australiae are both classified as Critically Endangered on the IUCN Red List of Threatened Species, yet a lack of species-specific knowledge and taxonomic uncertainty still exists within this genus. Genetic approaches aid in taxonomic classification and identifying distinct populations for targeted conservation. Morphological specimen identification of samples (n = 189) collected across the SWIO was confirmed based on the cytochrome oxidase c subunit I ( COI ) and/or nicotinamide adenine dehydrogenase subunit 2 ( ND2 ) gene regions. The genetic diversity and population structure within and between species and sampling locations were investigated using a dual marker approach: (1) 2 concatenated mitochondrial gene regions, namely COI and the control region (n = 117), and (2) 9 nuclear microsatellite markers (n = 146). The overall genetic diversity was moderate, with an indication that different evolutionary forces are at play on a mitochondrial versus nuclear level. The 2 species were delineated based on both marker types, and for R. djiddensis , the sampling locations of South Africa and Mozambique were genetically homogeneous. For R. australiae , significant differentiation was found between sampling locations, with Madagascar and Tanzania being genetically the most similar. This information provides critical insights into the distribution range and population structure of the whitespotted wedgefish species complex that can support the sustainable management of wedgefishes.

The distribution of marine predators is influenced by a variety of natural and, in some cases, anthropogenic environmental factors. In particular, the optimal foraging theory predicts that microhabitat selection should be the result of a trade-off between prey availability, energy expenditure, and predation risk. In addition, the risk-disturbance hypothesis suggests that anthropogenic disturbance may be perceived by animals in the same way as predation risk. Habitat selection may also be locally influenced by individual behavior and physiological state (defining functional habitats): variation in their needs should affect their optimal trade-off. We tested these hypotheses in a population of bottlenose dolphins living in a tropical lagoon using a habitat modeling approach. Bottlenose dolphins were predominantly distributed within the lagoon, with a preference for the vicinity of fringing and inner reefs (with lower predation risk than the outer reef), and were located in areas of high fish productivity, consistent with optimal habitat selection. We also observed an interaction between habitat and dolphin behavior, suggesting the existence of functional habitats: foraging was more common in nearshore habitats with probable higher prey density while resting and socializing were more common further from shore. Similarly, females with calves were preferentially found in shallower waters compared to other social groups. We did not observe any effects of anthropogenic disturbance variables and therefore cannot conclude on the risk-disturbance hypothesis for this population.

Eutrophication by human-derived nutrient enrichment is a major threat to mangroves, impacting productivity, ecological functions, resilience, and ecosystem services. Natural mangrove nutrient enrichment processes, however, remain largely uninvestigated. Mobile consumers such as seabirds are important vectors of cross-ecosystem nutrient subsidies to islands but how they influence mangrove ecosystems is poorly known. We assessed the contribution, uptake, cycling, and transfer of nutrients from seabird colonies in remote mangrove systems free of human stressors. We found that nutrients from seabird guano enrich mangrove plants, reduce nutrient limitations, enhance mangrove invertebrate food webs, and are exported to nearby coastal habitats through tidal flow. We show that seabird nutrient subsidies in mangroves can be substantial, improving the nutrient status and health of mangroves and adjacent coastal habitats. Conserving mobile consumers, such as seabirds, is therefore vital to preserve and enhance their role in mangrove productivity, resilience, and provision of diverse functions and services.

Marine litter is ubiquitous and associated with both ecological and socio-economic consequences. Beaches are major sinks of marine litter and as such its assessment and monitoring are needed. An opportunistic marine litter survey was performed for 12 consecutive days on the island of Juan de Nova in the central Mozambique Channel in February 2007. Plastic dominated the marine beach litter with daily accumulation of plastic positively related to the tide height (R2 = 0.768, p<0.01). Annual deposits could reach an average of 1 t.km-1, suggesting that regular cleaning of the coastline should be conducted to limit the impact on the local wildlife of this protected area.

Recent studies have uncovered mosaic patterns of allometric and isometric growth underlying ontogenetic shifts in the body form of elasmobranch species (shark and rays). It is thought that shifts in trophic and spatial ecology through ontogeny drive these morphological changes; however, additional hypotheses relating to developmental constraints have also been posed. The bull shark (Carcharhinus leucas) is a large-bodied coastal shark that exhibits strong ontogenetic shifts in trophic and spatial ecology. In this study, we utilise a large data set covering a large number of morphological structures to reveal ontogenetic shifts in the body form of C. leucas, stratifying analyses by sex and size classes to provide fine-scale, more ecomorpho-logically relevant results. Our results indicate shifts in functional demands across the body through ontogeny, driven by selective pressures relating to trophic and spatial ecology driving the evolution of allometry. We also find significant differences in scaling trends between life stages, and between the sexes, highlighting the importance of utilising large, diverse datasets that can be stratified in this way to improve our understanding of elasmobranch morphological evolution. Ultimately, we discuss the implications of these results for existing ecomorphological hypotheses regarding the evolution of specific morphological structures, and pose novel hypotheses where relevant.