Potential use of the Caribbean spider crab Maguimithrax spinosissimus for biofouling removal on marine aquaculture cages

Abstract

Biofouling is a significant issue on marine aquaculture pens and is conservatively estimated to contribute to 15% of production costs. With a global increase in the demand for sustainable aquaculture products a search for sustainable non-toxic alternatives to chemical treatment and manual removal of biofouling organisms, such as biological control, are becoming more sought after. In the laboratory experiments Caribbean spider crabs (Maguimithrax spinosissimus) exhibited nocturnal patterns of activity. They consumed between 3.3 and 4.16% bodyweight (BW) of algae in 22–24 °C water, and between 5.61 and 8.55% BW in 26–28 °C water. Although this species is primarily herbivorous they also readily consumed whole fish (Lutjanus apodus). The spider crabs were placed on a heavily fouled, unoccupied SeaStation 3000 cage offshore of Eleuthera, The Bahamas, to determine their ability to remove fouling organisms. Large crabs (382 g – 1344 g) confined in mesh cages on the outside of the pen effectively removed between 40% (after two weeks), and 90% (after four weeks) of fouling organisms. Crabs were more effective at removing growth than manual scrubbing by a diver. Grazing by the crabs was non-discriminatory, with no significant change in the proportional makeup of epibionts at the end of the trial. The survival rates of crabs inside the cage varied between 50% and 55% when not including escapees, and between 66% and 94% when including escapees during 3 to 6 month trials, with no significant decline in health status (blood protein levels). The Caribbean spider crab is a good candidate both economically and environmentally for controlling biofouling on aquaculture cages, could be used in multi-trophic aquaculture systems, and marketed as an environmentally friendly seafood.