Diversity and host specificity of shrimp-like crustaceans (Decapoda: Caridea) associated with mesophotic and deep-sea coral communities in the western Atlantic

Background. Mesophotic and deep-sea coral ecosystems support diverse crustacean assemblages, yet the diversity and host associations of their shrimp fauna remain poorly understood. This study investigates the diversity, species boundaries, and host associations of shrimp-like decapods, primarily caridean shrimps, associated with coral communities in the western Atlantic. Results. Through an integrative approach combining morphological analyses, genome skimming, molecular species delimitation, and ecological analyses, we identified 61 species from samples collected between 29 and over 1,800 m depth. Molecular analyses revealed multiple putative cryptic or pseudocryptic lineages. Of the 61 species, 22 were classified as obligate associates, 11 as potential facultative associates, and 28 had no documented symbiotic associations. Octocorals were the most frequently recorded hosts, followed by sponges and black corals. Host use varied among shrimp taxa, ranging from associations with a single host group to broader host ranges. Remotely operated vehicles and autonomous reef monitoring structures sampled complementary assemblages, highlighting the value of combining sampling methods. Rarefaction analyses indicated that species richness remains incompletely documented, particularly below 300 m depth. Conclusions. These findings reveal substantial hidden species and ecological diversity among shrimp-like decapods associated with western Atlantic mesophotic and deep-sea coral communities. Integrating morphological, molecular, and ecological evidence improves biodiversity assessments and highlights the need for further sampling and integrative taxonomic studies. This work provides a baseline for future research on host associations and for biodiversity monitoring and conservation of these vulnerable and unknown ecosystems.