Changes in a seagrass-associated decapod assemblage after 25 years of eutrophication and degradation of a Caribbean reef lagoon

Coastal eutrophication and habitat degradation can have long-term impacts on coastal ecosystems and communities. In the Mexican Caribbean, the Puerto Morelos reef lagoon was highly oligotrophic in 1995, but by 2020 it had changed to mesotrophic-eutrophic because of a gradual increase in nutrient and organic matter inputs related with an explosive growth in population and coastal development since the late 1990s, and massive inundations of holopelagic Sargassum since 2014. Here, we aimed to compare the seagrass-associated decapod assemblage in the reef lagoon after 25 years of environmental change. In summer and winter of both periods (1995 and 2020), day and night samples were taken in the same way on five lagoon sites. Of 159 decapod taxa, 108 were obtained in 2020 and 106 in 1995. The number of decapods collected in 2020 (138,046) was 2.5 times the number collected in 1995 (53,211). Three canopy-dwelling carideans ( Latreutes fucorum , Palaemonella americana , and Thor spp.) accounted for ~ 50% of individuals in 1995, whereas bottom-dwelling hermit crabs Clibanarius tricolor and Pagurus spp. constituted 56% of individuals in 2020. Richness and abundance were higher in 2020 and night samples, but did not vary with season. The assemblage composition also varied more with period and time of day than with season. These findings, and the change in dominance from omnivore/herbivore shrimps in 1995 to omnivore/detritivore hermit crabs in 2020, suggest increases in benthic eutrophication over time. Our study provides insights into how ecological changes are affecting seagrass-associated invertebrates.