INTEGRATED MULTI-TROPHIC AQUACULTURE (IMTA) WITH THE CALIFORNIA SEA CUCUMBER Parastichopus californicus: UTILIZING ANIMAL BEHAVIOUR AND CAGE DESIGN TO OPTIMIZE IMTA SYSTEM EFFICIENCY

In order to optimize the environmental sustainability of Integrated Multi-Trophic Aquaculture (IMTA), it is important to optimize nutrient transfer between trophic levels. Previous research has shown that the majority of organic particulate waste from aquaculture farms (e.g. salmon, oysters) accumulates directly below or adjacent to the farm. The major implication of this finding is that benthic deposit-feeding species may be the most important component for ensuring overall IMTA system efficiency, with respect to the recycling of organic nutrients.   

The California sea cucumber, Parastichopus californicus, is a promising benthic species for IMTA due to its deposit-feeding behaviour, ability to efficiently extract nutrients from aquaculture wastes, and valuable market price. We are investigating sea cucumber containment with the goal of effectively containing juvenile sea cucumbers within an IMTA system in such a way that optimizes nutrient extraction. Because of the sea cucumber's morphology and behaviour, containment can be difficult without reducing nutrient transfer and overall IMTA efficiency (i.e. mesh sizes and lids of cages/trays needed to effectively contain small sea cucumbers may restrict flow of farm particulates to them). We are making use of animal behaviour and habitat preference to optimize retention of the sea cucumbers within trays without hindering nutrient transfer to this benthic component.

Juvenile sea cucumbers exhibit cryptic behaviour and a preference for hard substrates with wild juvenile P. californicus found in high abundances on and below oyster farm gear. These behaviours were carefully considered when developing suspended cage designs. Eight modified high-flow oyster tray designs were initially tested in the laboratory, with six designs subsequently chosen for field trials at a Pacific oyster (Crassostrea gigas) farm. Modifications included (alone or in combination): the addition of nylon mesh (< 1 mm) on the walls/lid, 2 kg of oyster shell in the bottom of the tray, and a novel mesh fringe (instead of a lid) encircling the upper rim of the tray. During the four-month field trial, the six tray designs were stocked with 14 juvenile P. californicus each and suspended beneath oyster rafts and at a reference site 320 m away. Containment and growth of the juvenile sea cucumbers were monitored. Oyster faeces/pseudo-faeces deposition, particle retention efficiency of each tray/cage design, and the change in total carbon and total nitrogen in sediments due to sea cucumber presence were also examined. Results will be discussed.