Larval settlement of the polyhaline barnacle Balanus eburneus (Gould): cue interactions and comparisons with two estuarine congeners

The effect of salinity on larval settlement of the polyhaline estuarine barnacle Balanus eburneus (Gould) was investigated by challenging laboratory reared cyprids to settle (permanently attach and metamorphose) under a number of permutations of salinity and adult extract (settlement factor). When cyprids were exposed to an array of salinities ranging from 2 to 35 ppt in the presence of conspecific extract adsorbed to slate panels, maximum settlement occurred at salinities of 15 and 20 ppt. In the absence of adult extract, few larvae settled at any salinity. No differences in settlement frequencies across the array of test salinities were observed between replicate aliquots within a cyprid batch, but significant differences in settlement were observed between batches of cyprids. When settlement of newly molted cyprids was contrasted with that of cyprids forced to postpone metamorphosis, settlement peaked at 20 and 15 ppt salinity, respectively, and overall settlement levels of the “delayed” cohort increased. B. eburneus cyprids settled significantly more frequently on substrata adsorbed with conspecific extract than on substrata adsorbed with extract from B. improvisas (Darwin) or B. subalbidus (Henry), but settlement on these latter two treatments did not differ. Although post-settlement processes cannot be 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 structuring their distribution, whereas pre-settlement behavior could be a determining factor in B. subalbidus distribution.