Linking the presence of visual indicators of aquaculture deposition to changes in epibenthic richness at finfish sites installed over hard bottom substrates.

Effects of finfish aquaculture on benthic communities at hard bottom sites can be assessed using visual indicators of organic enrichment, namely bacterial mats, opportunistic polychaetes, and/or barren substrates (i.e., with no visible epifauna). Under some regulatory frameworks, the presence of visual indicators beyond a certain threshold proportion (e.g., > 70%) of mandatory sampling stations at a site signals an unacceptable degree of benthic organic loading. However, relationships between visual indicator presence and other biological characters such as epibenthic taxon richness are unclear, and should be examined to advise on the validity of existing legislative frameworks. Here, we used video data collected for regulatory purposes before and after aquaculture production to document (1) change in epibenthic taxon richness (TR) and its discriminatory power in determining aquaculture impact and (2) the association between TR change and the presence of visual indicators. Despite low richness values overall, our results show a significant post-production decrease in TR in the near-cage area, which was predicted to be affected by aquaculture. Decreases in TR were associated with visual indicator presence, validating the use of a suite of visual indicators to detect organic deposition. Importantly, visual indicators should be considered together in the context of regulation, given that relationships between TR and indicators were not linear when the latter are considered individually.

Temporal Bacterial Surveillance of Salmon Aquaculture Sites Indicates a Long Lasting Benthic Impact With Minimal Recovery.

Coastal aquaculture has experienced substantial growth in the last few decades and associated impacts on natural environments are of increasing importance. Understanding both the effects of aquaculture on marine ecosystems and the processes of recovery during fallowing periods is crucial for the development of a more environmentally sustainable industry. Because bacteria are sensitive to environmental change, surveying fluctuations in bacterial communities is a promising tool for monitoring the status of benthic environments. Here, we used 16S rRNA gene high-throughput sequencing to characterize bacterial communities in flocculent matter samples collected over a period of 3 years and at various distances from cages (0-200 meters) at production and fallow (3-35 months) salmon aquaculture sites in southern Newfoundland to evaluate the environmental impact of aquaculture on predominantly hard-bottom substrates. Bacterial composition analysis revealed four clusters, three of which (defined as "recently disturbed," "intermediate impact," and "high impact") differed markedly from a fourth "low impact" cluster that contained far-field samples collected >500 m from cages. Samples within the high impact group were most often collected directly under cages, whereas those in the intermediate impact group were mainly sampled from 20 to 40 m from cages. Large scale phylum shifts (increases of Bacteroidetes, Firmicutes, Spirochaetes, and decreases in Proteobacteria and Epsilonbacteraeota) and a decline in bacterial diversity were observed in the high impact cluster, indicating significant ecological change. Samples from sites of different fallow duration were found in the high impact cluster, indicating a lack of recovery, even after 35 months of fallowing. Finally, we identified 28 genera as bacterial biomarkers, specific to one or more clusters, including genera associated with organically enriched environments and previously reported in the context of aquaculture impacts. Tracking the relative abundance of biomarkers in relation to different lengths of fallowing in the three more impacted clusters showed that these markers remained significantly above low impact cluster levels at all times, further pointing toward incomplete recovery. Our results suggest that coastal aquaculture on hard-bottom substrates is prone to long lasting impacts on bacterial communities, especially below cages, and that effects can be accurately tracked using bacterial community profiles or specific biomarkers.

The usage of visual indicators in regulatory monitoring at hard-bottom finfish aquaculture sites in Newfoundland (Canada).

Finfish aquaculture can be installed over hard and patchy substrates where grab sampling is challenging and use of video can be an appropriate tool to document benthic changes. Video monitoring can show visual indicators of enrichment, namely flocculent matter, Beggiatoa-like mats, and opportunistic polychaete complexes (OPC). We examined factors influencing presence of indicators using 52 video monitoring reports collected in Newfoundland, Canada. The main driving factor was distance to cage, with indicators showing a higher probability of occurrence within 10m from cages due to low current velocities. Indicators were less prevalent on sites dominated by hard substrates while OPC in particular were restricted to depths >35m. Beggiatoa-like bacteria covered a larger surface than the two other indicators; however, our results suggest the necessity of amalgamating information related to all the indicators (including bare stations that could indicate anoxia) to establish a more accurate evaluation of aquaculture impact.

Lipid Classes and Fatty Acids in Ophryotrocha cyclops, a Dorvilleid from Newfoundland Aquaculture Sites.

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.

A new annelid species from whalebones in Greenland and aquaculture sites in Newfoundland: Ophryotrocha cyclops, sp. nov. (Eunicida: Dorvilleidae).

A new species of Ophryotrocha was discovered on whalebones in Greenland (120 m depth) and at finfish aquaculture sites in Newfoundland (30-70 m depth), where it is considered to be a bioindicator of aquaculture-related organic enrichment. Phylogenetic analyses based on three genes (COI, 16S mitochondrial and H3 nuclear genes) show close affinities with O. lobifera and O. craigsmithi, two species also found on both whalebones and at aquaculture sites (North Sea), and with O. shieldsi from aquaculture sites in Tasmania. The new species is named Ophryotrocha cyclops sp. nov. due to the juxtaposed, quasi-fused central eyes that give the impression of a single eye in live specimens.

Divergent chemosymbiosis-related characters in Thyasira cf. gouldi (Bivalvia: Thyasiridae).

Within the marine bivalve family Thyasiridae, some species have bacterial chemosymbionts associated with gill epithelial cells while other species are asymbiotic. Although the abundance of symbionts in a particular thyasirid species may vary, the structure of their gills (i.e., their frontal-abfrontal thickening) does not. We examined gill structure in a species tentatively identified as Thyasira gouldi from a Northwest Atlantic fjord (Bonne Bay, Newfoundland) and found remarkable differences among specimens. Some individuals had thickened gill filaments with abundant symbionts, while others had thin filaments and lacked symbionts. We could differentiate symbiotic and asymbiotic specimens based on the size and outline of their shell as well as 18S rRNA, 28S rRNA and CO1 sequences. The wide morphological, genetic and symbiosis-related disparity described herein suggests that chemosymbiosis may influence host divergence, and that Thyasira gouldi forms a cryptic species complex.

Correlation between perkinsosis and growth in clams Ruditapes spp.

Perkinsosis is one of the most widespread diseases affecting commercially important species of molluscs globally. We examined the impact of Perkinsus spp. on shell growth at the individual scale in 2 clam species: Ruditapes decussatus from Mundaka Estuary (Spain) and R. philippinarum from Arcachon Bay (France). At Arcachon, 2 contrasting sites in terms of environment and Perkinsus olseni presence were chosen: Arguin (disease-free) and Ile aux Oiseaux (infected site). We monitored the dynamics of perkinsosis over the course of the experiment at Mundaka and Ile aux Oiseaux. Prevalences were high (>70%), and intensities were around 105 cells g-1 wet gills at Ile aux Oiseaux, and 106 cells g-1 at Mundaka. No significant differences in prevalence or intensity were observed over time. A 2 yr field growth experiment of tagged-recaptured clams was performed to determine individual clam growth rate, condition index (CI), and Perkinsus spp. infection intensity. Clams were collected at Ile aux Oiseaux and transplanted to Arguin. The growth rate was always significantly and negatively correlated with Perkinsus spp. infection, and positively correlated with CI. CI and Perkinsus spp. infection explained 19% and 7% of the variability of the growth rate at Mundaka and Ile aux Oiseaux, respectively. In experimental clams at Arguin, P. olseni infection explained 26% of the variability of the growth rate at the lower tidal level. Our results suggest that at a concentration of between 105 and 106 cells g-1, perkinsosis affects the physiological functions of the clams, highlighted by its impact on the growth rate.