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

Abstract

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.

Keywords: Brittle stars Ophiocomina nigra; Brown crabs Cancer pagurus; Fatty acids; Stable isotopes; Urchins Echinus esculentus.