Abstract
A new opportunistic annelid (Ophryotrocha cyclops) discovered on benthic substrates underneath finfish aquaculture sites in Newfoundland (NL) may be involved in the remediation of organic wastes. At those aquaculture sites, bacterial mats and O. cyclops often coexist and are used as indicators of organic enrichment. Little is known on the trophic strategies used by these annelids, including whether they might consume bacteria or other aquaculture-derived wastes. We studied the lipid and fatty acid composition of the annelids and their potential food sources (degraded flocculent organic matter, fresh fish pellets and bacterial mats) to investigate feeding relationships in these habitats and compared the lipid and fatty acid composition of annelids before and after starvation. Fish pellets were rich in lipids, mainly terrestrially derived C18 fatty acids (18:1ω9, 18:2ω6, 18:3ω3), while bacterial samples were mainly composed of ω7 fatty acids, and flocculent matter appeared to be a mixture of fresh and degrading fish pellets, feces and bacteria. Ophryotrocha cyclops did not appear to store excessive amounts of lipids (13%) but showed a high concentration of ω3 and ω6 fatty acids, as well as a high proportion of the main fatty acids contained in fresh fish pellets and bacterial mats. The dorvilleids and all potential food sources differed significantly in their lipid and fatty acid composition. Interestingly, while all food sources contained low proportions of 20:5ω3 and 20:2ω6, the annelids showed high concentrations of these two fatty acids, along with 20:4ω6. A starvation period of 13 days did not result in a major decrease in total lipid content; however, microscopic observations revealed that very few visible lipid droplets remained in the gut epithelium after three months of starvation. Ophryotrocha cyclops appears well adapted to extreme environments and may rely on lipid-rich organic matter for survival and dispersal in cold environments.
Highlights
Where finfish aquaculture is conducted, organic matter is released in the environment and may accumulate on the seafloor, thereby influencing benthic communities and sediment biogeochemistry
In NL, Beggiatoa-like mats and Ophryotrocha cyclops are present at aquaculture sites, where they are usually associated with flocculent matter and surround the cage area with a high spatial and temporal variation according to site characteristics, distance from cage area, production cycle or season [49]
Within a single aquaculture site, we identified three main potential food sources available to O. cyclops, all of which harbored distinct lipid and fatty acid (FA) signatures as revealed by the multivariate analysis
Summary
Where finfish aquaculture is conducted, organic matter (e.g., uneaten feed and feces) is released in the environment and may accumulate on the seafloor, thereby influencing benthic communities and sediment biogeochemistry. In NL, off the east coast of Canada, drop camera surveys have identified two indicator taxa that are abundant beneath salmonid aquaculture cages: mat-forming filamentous bacteria (considered to belong to the genus Beggiatoa) and dorvilleid annelids forming Opportunistic Polychaete Complexes (OPC), which may consist of one or more species [13,14,15]. Beggiatoa are sulfur-oxidising bacteria that form conspicuous white mats at redox interfaces [16,17], while OPC (a term used in aquaculture regulation) are aggregates of opportunistic polychaetes that colonize organically enriched substrates. Dorvilleids often co-occur with Beggiatoa-like mats in environments with high levels of (often transient) organic matter such as hydrothermal vents [19,20,21], whale bones [22,23], or aquaculture sites [24,25,26]
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