The contribution of seagrass carbon to coastal marine ecosystems around the island of Mauritius, Western Indian Ocean.

Understanding the role of marine vegetation in shaping coastal carbon dynamics and supporting productivity is essential for robust ecological and socio-economic assessments and effective policy development. Our study employed stable isotope analysis (δ13C and δ15N) to investigate the importance of seagrass carbon as a source of nutrition to important invertebrates spanning different trophic levels (i.e., planktonic, filter-feeding and grazing) around the island of Mauritius. Isotope mixing models confirmed high levels of assimilation of seagrass carbon across three trophic levels (dietary proportions ranging from: 35% to 95% for zooplankton, 34% to 59% for the urchin Echinometra mathaei and 14% to 34% for the bivalve Pinna muricata). The degree to which consumers relied on seagrass was strongly influenced by site-specific trends in the relative cover and health of seagrass meadows (i.e., dietary importance declined at sites of observed seagrass loss). Thus, seagrass health is directly implicated in the diet of marine invertebrates, many of which are central to artisanal fisheries and the local blue economy. By integrating novel isotopic data and ecological modelling, we show that seagrass meadows in Mauritius exhibit tight trophic coupling with marine prey species underscoring their importance as engines of nearshore productivity and highlight the urgent need for their protection and restoration across the Western Indian Ocean.