Settlement of Pomatoceros lamarkii (Serpulidae) larvae on biofilmed surfaces and the effect of aerial drying

The settlement responses of Pomatoceros lamarkii (Polychaeta: Serpulidae) l arvae to biofilms of varying age on slate surfaces and to dried biofilms on slate surfaces were investigated in the laboratory. Settlement experiments were performed as multi-treatment, still water assays. Larvae did not sett le on clean, non-biofilmed slates but settled on biofilms up to 28 days old . Settlement intensity was closely related to the bacterial density of a bi ofilm. Drying a biofilmed surface for 1-2 h at 20 degreesC to simulate a si ngle tidal emersion completely negated the former inductive effect of the b iofilm. Drying also negated the larval settlement-inducing effect that norm ally results from the presence of conspecific adults, The settlement inhibi tion lasted for approximately 5 days following a single drying event. Larva e settled readily on biofilms exposed to formalin and antibiotics. Treating biofilms with formalin or antibiotics before or after drying had no effect upon larval avoidance of dried biofilms. Freeze-drying a biofilm had the s ame effect as aerial drying. The biofilm drying effect could not be mimicke d by exposing biofilms to hyper-saline seawater. The finding that P, lamark ii larvae do not settle on dried biofilms could have significance in explai ning the natural distribution of this species in the intertidal. (C) 2001 E lsevier Science B.V. All rights reserved.