Micropredation by gnathiid isopods on settlement-stage reef fish in the eastern Caribbean Sea

The transition from a planktonic larval to a benthic or demersal juvenile stage is a crucial event the life history of coral reef fishes, and recruitment success a strong influence on reef-fish population size. Post-settlement is thought to limit recruitment success. studies on post-settlement predation have focused on reef fishes. However, recent studies in the tropical Ocean suggest that blood-feeding ectoparasites may be an important source of predation. Here we provide evidence that a gnathiid ectoparasite is capable of “micropredation” on settlement-stage fish in the eastern Sea. On 12 occasions in May–August, 2014 and 2015, during plankton light-trap recovery, we observed postsettlement from the families Apogonidae, Bothidae, , Labrisomidae, and Tripterygiidae with attached juvenile gnathiid isopods. In one laboratory in which 10 settlement-stage French grunt, flavolineatum (Desmarest, 1823), were fed upon an average of one gnathiid per fish, all fish died compared none in the control group. In a subsequent experiment in individual settlement-stage French grunt were exposed 0–3 gnathiids each, all 50 fish that were fed upon by at least gnathiid died, compared with only one of 78 that were fed on by any gnathiids. Combined with observations on from the Pacific Ocean, these findings suggest gnathiids are capable of micropredation on larval fish at of reef settlement and that micropredation should be evaluated as a factor affecting success of settlement thus recruitment success of coral reef fishes.