The absorption efficiency of the suspension-feeding sea cucumber, Cucumaria frondosa, and its potential as an extractive integrated multi-trophic aquaculture (IMTA) species

Abstract

Finfish aquaculture commonly releases waste material in the form of excess feed and faeces, which can impact the surrounding environment, often through increased oxygen demand in the benthos as a result of a buildup of organic matter. Integrated multi-trophic aquaculture (IMTA) in the Bay of Fundy co-cultures extractive species such as mussels (Mytilus edulis) and kelps (Saccharina latissima) alongside of the fed finfish to partially mitigate the impacts associated with excess inorganic and organic nutrients. The orange-footed sea cucumber (Cucumaria frondosa) is being examined as a potential extractive species to remove additional particulate organic waste in some of the larger particle size categories. Sea cucumbers were exposed to natural (IMTA sites and natural seston) particles and enhanced laboratory diets where the organic content (OC) of the food and faeces were determined to estimate absorption efficiency (AE). AE ranged between 68 and 85% for all the experimental trials but averaged 70±3% when evaluating their response to only the natural diets. Sea cucumbers were capable of consuming aquaculture waste material when exposed to it in the laboratory and when deployed at an IMTA site, feeding directly upon the particulates released. There was a strong positive relationship (R2=0.82) between food and faeces OC, making it possible to predict the faecal OC from the food supply OC. AE was not as readily predictable from the food supply OC although there was a significant positive relationship between food OC and AE. Sea cucumbers are efficient in absorbing organic material (70±3%) within the range (>30 and <50% OC) they are typically exposed to in their natural environment. When challenged with particulate material of higher organic content (>60% OC), such as cultured microalgae or salmon food and faeces they exhibit equal or enhanced (>80%) AE's. Our results show that C. frondosa has a great deal of potential to become an effective organic extractive IMTA species and aid in the reduction of organic loading occurring at aquaculture sites.