Effects of aquaculture effluents on the slender sea pen Virgularia mirabilis.

This study aims to assess in situ the impact of effluents originating from an Atlantic salmon (Salmo salar) farm on a nearby slender sea pen (Virgularia mirabilis) field. We evidenced (1) the presence and persistence of emamectin residues (i.e. a common chemotherapeutants used for treating ectoparasites in salmons) in V. mirabilis tissue 56 days after treatment and (2) lethal and sublethal responses of V. mirabilis to effluents discharged by the salmon farm. Particularly, sea pens near the fish farm exhibited significant overproduction of mucus, contraction of polyps' tentacles, and disappearance of associated fauna. Furthermore, sea pens located directly underneath the farm showed substantial tissue necrosis and, in the most severe case, complete tissue loss and mortality. Our results suggest that lethal damages on sea pens occur directly below the farm, and that sublethal effects are visible up to 500 m from the farm. However, the presence of V. mirabilis below the studied farm, which has been active for more than twenty years, suggests that V. mirabilis population possesses the capacity to recover from the impacts of the farm, thereby preventing the complete disappearance from the area. In this context, it would be particularly interesting to run a temporal survey following the health state of V. mirabilis during an entire production cycle to have a more precise overview of fish farm impacts on this species, including during and after the post-production fallowing period.

Effects of the sea lice chemotherapeutant, emamectin benzoate, on metabolism and behaviour of the sea-pen Pennatula phosphorea.

Chemotherapeutants used to control infestations by sea lice can be released into the marine environment surrounding aquaculture farms. Among these therapeutic agents, emamectin benzoate is extensively utilized even though its impact on non-target taxa has not been thoroughly examined. In this context, we explored the effects of emamectin benzoate on a common Norwegian habitat-forming species: the phosphorescent sea-pen Pennatula phosphorea. Specifically, we examined P. phosphorea metabolic and responses before, during and after exposure to emamectin benzoate. Results indicate that an 8-day emamectin benzoate exposure (0.8 mg/L) did not induce P. phosphorea mortality or significant behavioural or metabolic modifications. However, we highlighted the presence and persistence of emamectin benzoate in exposed P. phosphorea tissue. These results indicate that emamectin benzoate is unlikely to adversely impact P. phosphorea populations in the environment. However, persistence of emamectin benzoate in tissue constitutes a potential for bioaccumulation with repeated treatments and should be examined in further studies.

Effect of sea lice chemotherapeutant hydrogen peroxide on the photosynthetic characteristics and bleaching of the coralline alga Lithothamnion soriferum.

The proliferation of sea lice (Lepeophtheirus salmonis) represents a major challenge for the salmonid aquaculture industry in Norway. Hydrogen peroxide (H2O2) is a chemotherapeutant frequently used on Norwegian farms, however, its toxicity to non-target benthic species and habitats remains poorly understood. Maerl beds are constructed by the accumulation of non-geniculate coralline algae and provide important ecological functions. Due to the rapid expansion of aquaculture in Norway and the continued use of H2O2 as an anti-sea lice treatment, it is crucial to understand the impact of H2O2 on the physiology of maerl-forming species. The effects of a 1 h exposure to H2O2 on the photophysiology and bleaching of the coralline alga Lithothamnion soriferum were examined here through a controlled time-course experiment. PAM fluorimetry measurements showed that H2O2 concentrations ≥ 200 mg l-1 negatively affected photosystem II (PSII) in thalli immediately after exposure, which was observed through a significant decline in maximum photochemical efficiency (Fv/Fm) and relative electron transport rate (rETR). The negative effects on PSII induced by oxidative stress, however, appear to be reversible, and full recovery of photosynthetic characteristics was observed 48 h to 28 days after exposure to 200 mg H2O2 l-1 and 2000 mg H2O2 l-1, respectively. At 28 days after exposure, there was evidence of two- to four-times more bleaching in thalli treated with concentrations ≥ 200 mg H2O2 l-1 compared to those in the control. This indicates that despite the recovery of PSII, persistent damages can occur on the structural integrity of thalli, which may considerably increase the vulnerability of coralline algae to further exposure to H2O2 and other chemical effluents from salmonid farms.

Impact of ocean acidification and warming on the productivity of a rock pool community.

This study examined experimentally the combined effect of ocean acidification and warming on the productivity of rock pool multi-specific assemblages, composed of coralline algae, fleshy algae, and grazers. Natural rock pool communities experience high environmental fluctuations. This may confer physiological advantage to rock pool communities when facing predicted acidification and warming. The effect of ocean acidification and warming have been assessed at both individual and assemblage level to examine the importance of species interactions in the response of assemblages. We hypothesized that rock pool assemblages have physiological advantage when facing predicted ocean acidification and warming. Species exhibited species-specific responses to increased temperature and pCO2. Increased temperature and pCO2 have no effect on assemblage photosynthesis, which was mostly influenced by fleshy algal primary production. The response of coralline algae to ocean acidification and warming depended on the season, which evidenced the importance of physiological adaptations to their environment in their response to climate change. We suggest that rock pool assemblages are relatively robust to changes in temperature and pCO2, in terms of primary production.

Does encapsulation protect embryos from the effects of ocean acidification? The example of Crepidula fornicata.

Early life history stages of marine organisms are generally thought to be more sensitive to environmental stress than adults. Although most marine invertebrates are broadcast spawners, some species are brooders and/or protect their embryos in egg or capsules. Brooding and encapsulation strategies are typically assumed to confer greater safety and protection to embryos, although little is known about the physico-chemical conditions within egg capsules. In the context of ocean acidification, the protective role of encapsulation remains to be investigated. To address this issue, we conducted experiments on the gastropod Crepidula fornicata. This species broods its embryos within capsules located under the female and veliger larvae are released directly into the water column. C. fornicata adults were reared at the current level of CO2 partial pressure (pCO2) (390 µatm) and at elevated levels (750 and 1400 µatm) before and after fertilization and until larval release, such that larval development occurred entirely at a given pCO2. The pCO2 effects on shell morphology, the frequency of abnormalities and mineralization level were investigated on released larvae. Shell length decreased by 6% and shell surface area by 11% at elevated pCO2 (1400 µatm). The percentage of abnormalities was 1.5- to 4-fold higher at 750 µatm and 1400 µatm pCO2, respectively, than at 390 µatm. The intensity of birefringence, used as a proxy for the mineralization level of the larval shell, also decreased with increasing pCO2. These negative results are likely explained by increased intracapsular acidosis due to elevated pCO2 in extracapsular seawater. The encapsulation of C. fornicata embryos did not protect them against the deleterious effects of a predicted pCO2 increase. Nevertheless, C. fornicata larvae seemed less affected than other mollusk species. Further studies are needed to identify the critical points of the life cycle in this species in light of future ocean acidification.