Mobile epibenthic fauna consume organic waste from coastal fin-fish aquaculture.

Organic waste released from fin-fish aquaculture is being dispersed further as industry growth has led to the expansion of open net cages in dynamic coastal locations. Here we investigate the response of three mobile epibenthic invertebrates (brittle stars, urchins and brown crabs), whose natural habitats overlap with large scale coastal salmon farming. Using fatty acids and stable isotopes, we found these organisms displayed decreases in δ13C and δ15N and elevated levels of C18 fatty acids reflective of terrestrial components of fin-fish feeds. Furthermore, we found these three species consume aquaculture organic waste not only directly adjacent to the farm vicinity (0-20 m from cage edge) but up to 1 km away in the case of brittle stars and brown crabs. As aquaculture feeds shift to contain more terrestrial ingredients, the biochemistry of fauna feeding on organic waste is also being shifted, the result of these changes is currently unclear.

The response of a boreal deep-sea sponge holobiont to acute thermal stress.

Effects of elevated seawater temperatures on deep-water benthos has been poorly studied, despite reports of increased seawater temperature (up to 4 °C over 24 hrs) coinciding with mass mortality events of the sponge Geodia barretti at Tisler Reef, Norway. While the mechanisms driving these mortality events are unclear, manipulative laboratory experiments were conducted to quantify the effects of elevated temperature (up to 5 °C, above ambient levels) on the ecophysiology (respiration rate, nutrient uptake, cellular integrity and sponge microbiome) of G. barretti. No visible signs of stress (tissue necrosis or discolouration) were evident across experimental treatments; however, significant interactive effects of time and treatment on respiration, nutrient production and cellular stress were detected. Respiration rates and nitrogen effluxes doubled in responses to elevated temperatures (11 °C & 12 °C) compared to control temperatures (7 °C). Cellular stress, as measured through lysosomal destabilisation, was 2-5 times higher at elevated temperatures than for control temperatures. However, the microbiome of G. barretti remained stable throughout the experiment, irrespective of temperature treatment. Mortality was not evident and respiration rates returned to pre-experimental levels during recovery. These results suggest other environmental processes, either alone or in combination with elevated temperature, contributed to the mortality of G. barretti at Tisler reef.