The influence of small-scale flow and chemical cues on the settlement of two congeneric barnacle species

Abstract

We report the results of 2 types of field experiment done to examine the influence of the interaction between small-scale flow disruptions and chemical cues associated with conspecific individuals on the settlement of larvae of 2 congeneric barnacle species, Elminius modestus and E. covertus. One series of experiments (ridge experiments) examined the effects of the chemical component of barnacle presence and flow disruptions at the scale of settlement plates (<10 cm). Cyprids could contact surfaces containing chemical cues from conspecific adults on either ridged or flat plates. Settlement was greatest on plates with cues but was not affected by flow disruptions. The other experiment (mimic experiment) used settlement plates with either live barnacles or casts of adult barnacles attached, as well as flat control plates, to test the influence of conspecific presence and flow disruption at the scale of individual barnacles (< 1 cm) on the settlement of cyprids. Settlement was affected by both live barnacles and barnacle mimics, indicating that a combination of flow and conspecific-derived cues influence settlement. Hence, the importance of flow disruption to the settlement of cyprids is dependent on the scale of the disruption. The survival of barnacles for up to 2 mo after settlement was also followed in the ridge experiments. The settlement patterns larvae showed early in these experiments were not evident after periods of heavy recruitment; we discuss possible causes.