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MEPS prepress abstract   -  DOI:

Depth dependent trophic strategies of Caribbean sponges on mesophotic coral reefs

Keir J. Macartney*, M. Sabrina Pankey, Amelia Clayshulte Abraham, Marc Slattery, Michael P. Lesser

*Corresponding author:

ABSTRACT: Mesophotic coral reef ecosystems are characterized by gradients in irradiance, temperature and trophic resources. On Caribbean mesophotic reefs as depth increases particulate organic matter increases, while dissolved organic matter decreases, and the increase in particulate organic matter is directly related to the increase in sponge abundances and growth rates on MCEs. To further understand the trophic ecology of sponges, changes in microbiome composition and function, stable isotopic composition, and proximate biochemical composition of 4 Caribbean reef sponges (Amphimedon compressa, Agelas tubulata, Plakortis angulospiculatus and Xestospongia muta) were quantified along a shallow to mesophotic depth gradient on Grand Cayman Island. Increases in the δ15N for all sponges as depth increased were observed, indicating an increasing reliance on heterotrophic food resources. Species-specific changes in the symbiotic microbial community composition were also observed as depth increased, and the predicted functional genes associated with nitrogen and carbon cycling showed species-specific changes between depths. Regardless of species-specific changes in microbiome community structure or function, or whether sponges were classified as high microbial or low microbial abundance, sponges increased their consumption of particulate organic matter with increasing depth into the lower mesophotic zone.