SETTLEMENT OF OYSTER (CRASSOSTREA-VIRGINICA) LARVAE - EFFECTS OF WATER-FLOW AND A WATER-SOLUBLE CHEMICAL CUE

Although previous evidence indicates that larvae of benthic marine invertebrates can respond to waterborne cues in still water, the importance of waterborne cues in mediating natural settlement out of flowing water has been questioned. Here, we summarize the results of flume experiments demonstrating enhanced settlement of oyster larvae in small target wells (circles of 7-cm diam) with the release of a waterborne settlement cue compared to identical substrates without the cue. In concurrent still-water experiments, more oyster larvae settled in solutions of waterborne cue than in seawater controls. Velocity and electrochemical measurements of a conservative tracer verified that at low flow velocities (2 and 6 cm s(-1)) with U* values <0.25 cm s(-1), the waterborne cue was present above the targeted substrate to a height of less than or equal to 4 mm. Rapid vertical swimming or sinking in response to the waterborne cue can concentrate larvae in near-bottom waters and enhance larval settlement. Our investigation provides the first experimental evidence to demonstrate that dissolved chemical cues can mediate settlement by larvae under hydrodynamic conditions approaching those of natural benthic habitats.