Distribution of lipid droplets in the gut epithelium of <i>Ophryotrocha cyclops</i> from aquaculture sites and whale bones

Ophryotrocha cyclops Salvo et al. 2014 is a dorvilleid known from aquaculture sites in Newfoundland (Canada) and experimentally deployed whale bones in Greenland. At aquaculture sites, O. cyclops feed on microbes and lipid-rich fish pellets, and lipid droplets were observed in their midgut epithelium. These droplets might represent energy stores, and their abundance could vary according to habitat and food availability and along the length of the gut. To explore this, we quantified the relative surface area covered by lipid droplets in transverse sections of the gut epithelium of 15 O. cyclops from aquaculture sites and whale bones, comparing percent coverage in anterior, middle and posterior regions. We also explored the effects of starvation on lipid droplet coverage. In annelids from aquaculture sites, the percent coverage of lipids was higher in anterior and middle compared to posterior regions, and an apparent percent coverage decline in all body regions was observed with increasing length of starvation. In contrast, O. cyclops from whale bones contained few lipid droplets in their gut epithelium. Our limited samples suggest that O. cyclops consumes lipids at aquaculture sites. Additional work should examine whether lipid accumulation and storage might affect survival and reproductive output in these dorvilleids.