HADFIELD, M.G.*; KOEHL, M.A.R.; ZARDUS, J.D.; University of Hawaii, Kewalo Marine Lab; University of California, Berkeley; University of Hawaii, Kewalo Marine Lab: The affect of chemical cues on the adhesion strength of settling invertebrate larvae.

Locating and adhering to a suitable substratum at the end of the pelagic larval period is a crucial step in the life cycle of many marine invertebrates, especially sessile ones. Many invertebrates rely on dissolved chemical cues released by host or prey organisms or adsorbed cues on surfaces to guide their settlement. Though mechanisms of attachment range widely across taxa, chemical signaling frequently induces a cascade of behaviors, including secretion of an attachment adhesive and culminating in metamorphosis. Attachment may be temporary or permanent with the strength of adhesion varying over time and in some cases involving primary and secondary stages. Chemical cues help initiate settlement, but can they also affect adhesion strength? This question was addressed by measuring the wall shear stress required to dislodge larvae of several marine invertebrates that may attach temporarily, then permanently, and employ a variety of attachment mechanisms. Species tested included: the nudibranch Phestilla sibogae, which settles in response to dissolved cue from its host coral and attaches temporarily; the tubeworm Hydroides elegans, which attaches first by a sticky filament and then cements a secondary permanent tube; the bryozoan Bugula neritina, which glues its body to the substratum; and the barnacle Balanus amphitrite, which initially glues its antennules to the substratum, then metamorphoses and permanently cements its juvenile shell. Nudibranch larvae were exposed to different levels of dissolved cue and allowed to attach to a surface; the other taxa were allowed to settle onto clean and biofilmed surfaces and placed in a precision flow channel for testing. Results indicate a trend of increased adhesion strength in the presence of the chemical cues.