Enhanced feeding by pelagic juvenile myctophid fishes within a region of island-induced flow disturbance in the Coral Sea

Abstract

The feeding success of post larvae and juveniles of 2 myctophid fishes (Diaphus kapalae and Myctophum sp.) was compared between the free stream and a flow-disturbed region in the lee of Cato Reef in the south Coral Sea using particle-size analysis. Both taxa fed more successfully in the disturbed region than in the free stream, where uplifting resulted in up to 50 % greater concentrations of small (250 to 1000 μm equivalent spherical diameter) prey items at depths between 30 and 70 m around the thermocline. Gut fullness in both taxa was significantly related to the concentrations of small-sized zooplankton (D. kapalae: r = 0.63, p < 0.05; Myctophum sp.: r = 0.55, p < 0.05). There were, however, differences in the sizes of food items consumed in the free stream and the disturbed region and between the 2 taxa of fishes studied. Non parametric multi-dimensional scaling analysis indicated that similarsized individuals of D. kapalae and Myctophum sp. within a region consumed a different particle-size community, probably enabling them to co-exist. The taxonomic composition of the diets of the 2 taxa reflected the available prey items around the island. In an oligotrophic environment such as the south Coral Sea, island-induced disturbance appeared to be an important contributor to the pelagic food web.