The long-lived deep-sea bivalve Acesta excavata is sensitive to the dual stressors of sediment and warming.

Human influence in the deep-sea is increasing as mining and drilling operations expand, and waters warm because of climate change. Here, we investigate how the long-lived deep-sea bivalve, Acesta excavata responds to sediment pollution and/or acute elevated temperatures. A. excavata were exposed to suspended sediment, acute warming, and a combination of the two treatments for 40 days. We measured O2 consumption, NH4+ release, Total Organic Carbon (TOC), and lysosomal membrane stability (LMS). We found suspended sediment and warming interacted to decrease O:N ratios, while sediment as a single stressor increased the release of TOC and warming increased NH4+ release in A. excavata. Warming also increased levels of LMS. We found A. excavata used protein catabolism to meet elevated energetic demands indicating a low tolerance to stress. A. excavata has limited capacity for physiological responses to the stressors of warming and sediment which may lead to decreased fitness of A. excavata.

Recycling pathways in cold-water coral reefs: Use of dissolved organic matter and bacteria by key suspension feeding taxa.

Cold-water coral (CWC) reefs are one of the most diverse and productive ecosystems in the deep sea. Especially in periods of seasonally-reduced phytodetritus food supply, their high productivity may depend on the recycling of resources produced on the reef, such as dissolved organic matter (DOM) and bacteria. Here, we demonstrate that abundant suspension feeders Geodia barretti (high-microbial-abundance sponge), Mycale lingua (low-microbial-abundance sponge) and Acesta excavata (bivalve) are able to utilize 13C-enriched (diatom-derived) DOM and bacteria for tissue growth and respiration. While DOM was an important potential resource for all taxa, utilization of bacteria was higher for the sponges as compared to the bivalve, indicating a particle-size differentiation among the investigated suspension feeders. Interestingly, all taxa released 13C-enriched particulate organic carbon, which in turn may feed the detritus pathway on the reef. Especially A. excavata produced abundant (pseudo-)fecal droppings. A second stable-isotope tracer experiment revealed that detritivorous ophiuroids utilized these droppings. The high resource flexibility of dominant reef suspension feeders, and the efficient recycling of their waste products by the detritivore community, may provide important pathways to maintain the high productivity on cold-water coral reefs, especially in periods of low external food supply.

Impact of particulate sediment, bentonite and barite (oil-drilling waste) on net fluxes of oxygen and nitrogen in Arctic-boreal sponges.

To meet the increasing global energy demand, expanding exploration for oil and gas reserves as well as associated drilling activities are expected in the Arctic-boreal region where sponge aggregations contribute to up to 90% of benthic biomass. These deep-water sponges along with their microbial endobionts play key roles in the nitrogen cycling in Arctic-boreal ecosystems. This study aimed to investigate the effects of drilling discharges and associated sediment resuspension events on net fluxes of oxygen, ammonium, nitrate and nitrite in three common deep-water sponge species in the form of explants. Sponges were exposed to suspended bentonite and barite, the primary particulate compounds in drilling waste, as well as suspended natural sediment particles for a period of 33 days (on average 10 mg L-1 for 12 h day-1). The exposure period was followed by a pollution abatement period for a further 33 days. No sponge mortality was observed during the experiment. However, exposure to these particles, especially to barite, led to reduced oxygen consumption by up to 33% that was linearly correlated with reduced nitrite/nitrate release by the sponges. The changes in net fluxes were accompanied by decreased tissue oxygenation by up to 54% within the sponges. These findings reveal the effects of fine particles on sponge metabolic processes by reducing aerobic respiration and microbial nitrification, and possibly by favouring anaerobic processes such as microbial denitrification. Most of the sponge responses recovered to their control levels upon the pollution abatement period, but the effects caused by barite may not be reversible. Our findings provide the first insight into the ecological consequences of oil and gas drilling activities on sponge-mediated nitrogen cycling in the Arctic-boreal region.

Microbiome analysis of a disease affecting the deep-sea sponge Geodia barretti.

Reports of sponge disease are becoming increasingly frequent, although almost all instances involve shallow-water, tropical species. Here, we describe the first disease affecting the deep-water sponge, Geodia barretti. The disease is characterised by brown/black discolouration of the sponge tissue, extensive levels of tissue disintegration and increased levels of fouling. Disease prevalence was quantified using video survey transects conducted between 100 and 220 m in Korsfjorden, Norway, and the microbial communities of healthy and diseased sponges were compared using 16S rRNA gene sequencing. Highly divergent community profiles were evident between the different health states, with distinct community shifts involving higher relative abundances of Bacteroidetes, Firmicutes and Deltaproteobacteria in diseased individuals. In addition, three operational taxonomic units were exclusively present in diseased individuals and were shared between the disease lesions and the apparently healthy tissue of diseased individuals, suggesting a non-localised infection or dysbiosis. Genomic analysis of the G. barretti microbiome combined with experimental work to assess the mechanisms of infection will further elucidate the role of microorganisms in the disease.

Consumption of aquaculture waste affects the fatty acid metabolism of a benthic invertebrate.

Trophic subsidies can drive widespread ecological change, thus knowledge of how keystone species respond to subsidies is important. Aquaculture of large carnivorous fish generates substantial waste as faeces and lost feed, providing a food source to mobile benthic invertebrates. We used a controlled feeding study combined with a field survey to better understand the interaction between salmon aquaculture and the sea urchin, Echinus acutus, a dominant mobile invertebrate in Norwegian fjords. We tested if diets affected urchin fatty acid composition by feeding them one of three diet treatments ("aquafeed", "composite" and "natural") for 10weeks. To test if proximity to fish farms altered E. acutus fatty acid composition, populations were sampled at 10 locations in Hardangerfjord and Masfjord (Western Norway) from directly adjacent and up to 12km from farms. Fatty acids were measured in gonads and eggs in the diet experiment and in gonads and gut contents from wild animals. Urchins directly assimilated aquaculture waste at farm sites, as evidenced by elevated linoleic acid (LA), oleic acid (OA) and ∑LA, OA in their tissues. The diet experiment highlighted the biosynthetic and selective dietary sparing capacity of E. acutus in both gonads and eggs, with evidence for the elongation and desaturation of eicosapentaenoic acid (EPA) and arachidonic acid (ARA) from C18 fatty acid precursors. Elevated biosynthesis of non-methylene interrupted (NMI) fatty acids, in particular 20:3Δ7,11,14 and 20:2 Δ5,11, were also linked to a high C18 fatty acid, low ≥C20 long-chain polyunsaturated fatty acid (LC-PUFA) diet. Fatty acid composition of gonads of wild urchins indicated a highly variable diet. The study indicates that the generalist feeding ecology of E. acutus, coupled with extensive biosynthetic capacity, enables it to exploit aquaculture waste as an energy-rich trophic subsidy.

Sub-lethal effects of water-based drilling muds on the deep-water sponge Geodia barretti.

Offshore oil and gas activities can result in the discharge of large amounts of drilling muds. While these materials have generally been regarded as non-toxic to marine organisms, recent studies have demonstrated negative impacts to suspension feeding organisms. We exposed the arctic-boreal sponge Geodia barretti to the primary particulate components of two water-based drilling muds; barite and bentonite. Sponges were exposed to barite, bentonite and a natural reference sediment at a range of total suspended solid concentrations (TSS = 0, 10, 50 or 100 mg/L) for 12 h after which we measured a suite of biomarker responses (lysosomal membrane stability, lipid peroxidation and glutathione). In addition, we compared biomarker responses, organic energy content and metal accumulation in sponges, which had been continuously or intermittently exposed to suspended barite and natural sediment for 14 d at relevant concentrations (10 and 30 mg TSS/L). Lysosomal membrane stability was reduced in the sponges exposed to barite at 50 and 100 mg TSS/L after just 12 h and at 30 mg TSS/L for both continuous and intermittent exposures over 14 d. Evidence of compromised cellular viability was accompanied by barite analysis revealing concentrations of Cu and Pb well above reference sediments and Norwegian sediment quality guidelines. Metal bioaccumulation in sponge tissues was low and the total organic energy content (determined by the elemental composition of organic tissue) was not affected. Intermittent exposures to barite resulted in less toxicity than continuous exposure to barite. Short term exposures to bentonite did not alter any biomarker responses. This is the first time that these biomarkers have been used to indicate contaminant exposure in an arctic-boreal sponge. Our results illustrate the potential toxicity of barite and the importance of assessments that reflect the ways in which these contaminants are delivered under environmentally realistic conditions.

Impact of deep-water fish farms on benthic macrofauna communities under different hydrodynamic conditions.

In this study the environmental impacts of two fish farms located over deep water (180-190 m) were compared. MC-Farm was located at a site with slightly higher water currents (mean current speed 3-5 cms(-1)) than LC-farm (<2 cms(-1)). Macrofauna composition, bioirrigation and benthic fluxes (CO2 and NH4(+)) were quantified at different stages of the production cycle, revealing very different impact of the two farms. Macrofauna abundance and bioirrigation were stimulated compared to a non-impacted reference site at MC-farm, while macrofauna diversity was only moderately reduced. In contrast, macrofauna communities and related parameters were severely impoverished at LC-Farm. This study suggests that deep-water fish farms should not be sited in low current areas (<2 cms(-1)), since this will hamper waste dispersal and aggravate environmental impacts. On the other hand, fish farming at slightly more dynamic sites can lead to stimulated benthic macrofauna communities and only moderate environmental impacts.

Biogeochemical malfunctioning in sediments beneath a deep-water fish farm.

We investigated the environmental impact of a deep water fish farm (190 m). Despite deep water and low water currents, sediments underneath the farm were heavily enriched with organic matter, resulting in stimulated biogeochemical cycling. During the first 7 months of the production cycle benthic fluxes were stimulated >29 times for CO(2) and O(2) and >2000 times for NH(4)(+), when compared to the reference site. During the final 11 months, however, benthic fluxes decreased despite increasing sedimentation. Investigations of microbial mineralization revealed that the sediment metabolic capacity was exceeded, which resulted in inhibited microbial mineralization due to negative feed-backs from accumulation of various solutes in pore water. Conclusions are that (1) deep water sediments at 8 °C can metabolize fish farm waste corresponding to 407 and 29 mmol m(-2) d(-1) POC and TN, respectively, and (2) siting fish farms at deep water sites is not a universal solution for reducing benthic impacts.