No abstract

No abstract

Cold-water corals (CWCs) have come under increasing pressure from human activities over the last decades. Of particular concern in Norway is the potential impact of open net pen aquaculture on CWC reefs formed by Lophelia pertusa, a threatened and declining habitat. We conducted a 1 yr in situ transplantation experiment and corresponding field measurements of 2 reefs located close to fish farms to elucidate the impacts of particulate organic waste released from the farms on coral colonies. Our study provided new evidence of negative impacts of organic effluents on L. pertusa ecophysiology. After 1 yr, both naturally occurring and transplanted corals, at distances ranging from 250 m to 1 km downstream of what would be regarded as an average-sized Norwegian fish farm, exhibited depressed metabolic rates compared to corals outside the main depositional footprint of the farms. The metabolic depression impeded energy acquisition, reducing growth and energy reserves by up to 70 and 50%, respectively. No clear threshold for significant biological impact could be detected along a distance gradient. Instead, a gradual decrease in metabolic rates, growth and lipid reserves occurred with increasing modelled sedimentation rate of organic waste from the farm. The strong statistical correlation between oxygen consumption, growth, energy stores and sedimentation rates implies that predictions of the short-term impact of aquaculture effluents on L. pertusa ecophysiology and CWC reef development may be achievable in the future. This would significantly improve the ability of management to make informed decisions on the licensing of new farms near CWC reefs.

The influence of substrate type and particle age on the remobilization of settled Atlantic salmon Salmo salar faecal material was studied through a set of controlled experiments in horizontal flow flumes, simulating different bottom conditions present in fish-farming locations along the coast of Norway. There was no significant effect of pellet age on remobilization for up to 1 week old faecal material, but critical shear stresses (τc) and velocities required for resuspending faecal pellets were strongly dependent on substrate type. Smooth substrates such as mud and rock slate required lower stresses for the onset of faeces resuspension (τc %%CONV_ERR%% 0.06 Pa) than rougher surfaces such as sand (τc %%CONV_ERR%% 0.12 Pa) or fragmented rock (τc %%CONV_ERR%% 0.32 Pa), where bedforms and large fractures shield the particles from the direct influence of the drag forces. These newly determined substrate-dependent τc resuspension thresholds will contribute to the construction of more accurate numerical models that include bottom type as a parameter regulating the extent of particle spreading, in contrast to the constant-value approach that has been used to date.

No abstract

Large-scale finfish farms are increasingly located in dispersive hard-bottom environments where Laminaria hyperborea forests dominate; however, the interactions between farm effluents and kelp forests are poorly understood. Effects of 2 levels of salmonid fish-farming effluents (high and low) on L. hyperborea epiphytic communities were studied by sampling canopy plants from 12 sites in 2 high-energy dispersive environments. Specifically, we assessed if farm effluents stimulated fast-growing epiphytic algae and faunal species on L. hyperborea stipes—as this can impact the kelp forest community composition—and/or an increased lamina epiphytic growth, which could negatively impact the kelp itself. We found that bryozoan biomass on the stipes was significantly higher at high-effluent farm sites compared to low-effluent farm and reference sites, resulting in a significantly different epiphytic community. Macroalgal biomass also increased with increasing effluent levels, including opportunistic Ectocarpus spp., resulting in a less heterogeneous macroalgae community at high-effluent farm sites. This habitat heterogeneity was further reduced by the high bryozoan biomass at the high-effluent sites. Such changes in the epiphyte community could have implications for the faunal community that relies on the epiphytes for food and refuge. On the kelp lamina, no clear response to farm effluents was found.

No abstract