Trophic analyses of opportunistic polychaetes (Ophryotrocha cyclops) at salmonid aquaculture sites

Abstract

A new species of dorvilleid polychaete,Ophryotrocha cyclops, has been observed on the rocky seafloor underneath deep salmonid aquaculture sites on the south coast of Newfoundland, Canada. The distribution of these opportunistic worms is likely related to organic matter accumulation on the seafloor, and this species may have a role in remediation processes. To better understand the functional role ofO. cyclopsat aquaculture sites, it is important to know what they feed upon. Here, stable isotope analyses (δ13C, δ15N and δ34S) and trace element analyses were performed on dorvilleids and their potential food sources at three aquaculture sites. Stable isotope analyses revealed spatial and temporal variation in the isotopic carbon signature ofO. cyclops, highlighting possible differences in the food sources of individual dorvilleids within and between sites. The isotopic composition of dorvilleids was closest to that of fish pellets; the presence of abundant lipid droplets in gut epithelial cells ofO. cyclopssuggests the assimilation of fish pellet-derived lipids. Trace element analysis indicated thatO. cyclopsdoes not concentrate the aquaculture tracers Zn or Cu to a large extent. However, concentrations of sulphur were high inO. cyclopscompared with other sources. Taken together, results show thatO. cyclopsmost likely consume both fish pellets and flocculent matter-associated bacteria. As such, they are involved in sulphur cycling and fish pellet degradation at aquaculture sites.