Lack of Planktonic Dispersal of Rocky Intertidal Fish Larvae

Although planktonic drift is presumed for larvae of most marine fish species, the extent of larva dispersal by intertidal species is largely unknown. Oblique tows with a net of 500-μm mesh were made at distances of 0, 4, 20, and 500 m from steep rocky shores, divers guiding the 0-m tows. Ichthyoplankton of the extreme nearshore area was more dense than that of offshore waters. Species composition shifted radically from inshore to offshore; intertidal species (cottids, stichaeids, pholids, gobiesocids) were dominant inshore. Larvae of rocky intertidal fishes occurred more frequently along rocky shores than on an adjacent sandy beach. The evidence suggests that larvae of rocky intertidal fishes resist offshore and possibly longshore dispersal. In contrast to information for sandy beaches, data for the rocky nearshore area reveal that all stages of larvae remain inshore, not just those within a narrow size range. Populations of rocky intertidal fishes may thus be relatively isolated genetically.