Mesocosm trials to determine survival of Ophryotrocha cyclops (Salvo, 2014) to different oxygen conditions

Presence of opportunistic species can be used as a proxy to determine benthic impact of organic enrichment due to aquaculture operations. Among these indicator species, the newly described dorvilleid species Ophryotrocha cyclops forms polychaete complexes under aquaculture cages and on whale bones. This species has been documented to exhibit temperature restrictions whereas its tolerance to different oxygen conditions is unknown. O. cyclops co-occurs with sulfato-reductant bacterial mats (another visual indicator of organic enrichment) suggesting an adaptation to low oxygen levels. In this study, three substrate types (water, sand, and flocculent matter) and three oxygen conditions (normoxic: 80-100%, moderate oxygen: 40-60% and low oxygen: 5-25%) were tested in a mesocosm study to determine O. cyclops oxygen depletion tolerance. Results showed lower survival rates of O. cyclops when O2 < 25%. When flocculent matter was used as a substrate polychaete survival was decreased even in normoxic conditions. This is probably due to oxygen exhaustion subsequent to organic matter degradation processes creating an inadequate microenvironment in the containers. In conditions of organic deposition where temperatures are higher than 8 °C (as described in the literature) and oxygen conditions lower than 25% the usage of O. cyclops as an indicator of aquaculture enrichment might not be informative.