ASSESSING HETEROTROPHIC FEEDING IN ECOLOGICALLY DOMINANT CARIBBEAN SPONGE SPECIES
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Parry, Alexander Idwal
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The success of sponges in the Caribbean has long been linked to their ability to efficiently exploit particulate organic matter via heterotrophic feeding. Recent work, however, has highlighted diverse sources of organic matter (living particulate organic matter [LPOC], detritus, and dissolved organic matter [DOC]) in this ocean basin and shown that individual sponges vary in their exploitation of these resource pools. Sponges also host microbial symbiont communities that provide their hosts with access to novel nutrients on coral reefs. The abundance of these microbial communities varies broadly across host species (leading to the delineation of sponges into high or low microbial abundance groups [HMA or LMA, respectively]), and there is also substantial interspecific variation in the diversity and community composition of these microbiomes. Thus, it is likely that Caribbean sponges vary in their reliance on heterotrophic feeding, but to date, no studies have assessed the heterotrophic efficiency of dominant sponge species in the Caribbean. To address this gap, we fed ~1 μm heterotrophic bacteria to sponges and assessed feeding capacity by measuring bacterial cell removal over time via flow cytometry. There was no significant difference in clearance rate or bacterial removal rates between HMA and LMA species. There was, however, evidence of substantial interspecific variation in feeding efficiency, with <i>Niphates erecta </i>(LMA) and <i>Verongula rigida</i> (HMA) having the highest average clearance rates, while <i>Mycale laevis</i> (LMA) and <i>Aiolochroia crassa</i> (HMA) had the lowest clearance rates. This is the first study to demonstrate host-driven niche partitioning in dominant Caribbean sponge species.