Finding a correlation between zooplankton abundance and the aggregation of Abudefduf saxatilis (sergeant major damselfish) beneath boats

Abudefduf saxatilis, or sergeant major damselfish, are a common reef fish in the Caribbean and western Atlantic that form large feeding aggregations. Abudefduf saxatilis are primarily planktivorous, with zooplankton making up over 50% of their diet. Zooplankton are known to have diel movements to avoid predation, which have been shown to be triggered by the presence of ultra violet radiation. Beneath boats along the coast of Bonaire, aggregations of A. saxatilis have been observed, but why they prefer these areas over the open water column had not previously been examined. The abundance of zooplankton was estimated beneath boats as well as in the open water, up-current from the boats. Both the abundance and bite rates of A. saxatilis were also estimated beneath the boats that corresponded to the estimates of zooplankton abundance. In addition, the bite rates of A. saxatilis were estimated in the open water. It was found that the zooplankton abundance (p<0.001) and the bite rate of A. saxatilis (p<0.001) were both significantly greater beneath boats than in the open water. Also, a significant correlation was found between increasing abundances of zooplankton and A. saxatilis (p<0.01). These results demonstrate that one of the main drivers for the aggregation of A. saxatilis beneath boats is likely to feed on the zooplankton, which are in high abundance. In turn, this could alter community structure on the reef due to a decrease in the amount of algae grazing by A. saxatilis

This student research was retrieved from Physis: Journal of Marine Science XVII (Spring 2015)19: 51-57 from CIEE Bonaire.