LARVAL SETTLEMENT OF THE POLYHALINE BARNACLE BALANUS-EBURNEUS (GOULD)- CUE INTERACTIONS AND COMPARISONS WITH 2 ESTUARINE CONGENERS

The effect of salinity on larval settlement of the polyhaline estuarin e barnacle Balanus eburneus (Gould) was investigated by challenging la boratory reared cyprids to settle (permanently attach and metamorphose ) under a number of permutations of salinity and adult extract (settle ment factor). When cyprids were exposed to an array of salinities rang ing from 2 to 35 ppt in the presence of conspecific extract adsorbed t o slate panels, maximum settlement occurred at salinities of 15 and 20 ppt. In the absence of adult extract, few larvae settled at any salin ity. No differences in settlement frequencies across the array of test salinities were observed between replicate aliquots within a cyprid b atch, but significant differences in settlement were observed between batches of cyprids. When settlement of newly molted cyprids was contra sted with that of cyprids forced to postpone metamorphosis, settlement peaked at 20 and 15 ppt salinity, respectively, and overall settlemen t levels of the ''delayed'' cohort increased. B. eburneus cyprids sett led significantly more frequently on substrata adsorbed with conspecif ic extract than on substrata adsorbed with extract from B. improvisus (Darwin) or B. subalbidus (Henry), but settlement on these latter two treatments did not differ. Although post-settlement processes cannot b e overlooked, our results indicate that larval behavior at settlement could play a substantial role in determining adult distribution of B. eburneus along the estuarine salinity gradient. Contrasting settlement patterns of B. eburneus with those obtained previously for mesohaline B. improvisus and oligohaline B. subalbidus indicates that settlement behavior of the former two species could be influential in structurin g their distribution, whereas pre-settlement behavior could be a deter mining factor in B. subalbidus distribution.