Effects of salinity and adult extract on settlement of the oligohaline barnacle <Emphasis Type="Italic">Balanus subalbidus</Emphasis>

Abst rac t Balanus subalbidus (Henry) has the most oligohaline distribution of three congeneric barnacles in Chesapeake Bay and tolerates prolonged exposure to fresh water. We studied larval settlement (i.e., permanent attachment and metamorphosis) of B. subalbidus in the laboratory, over a 3 yr period, May 1989 to March 1992, under the following conditions: (1) across an array of salinities at 25~ in the presence and absence of settlement factor consisting of adult B. subaIbidus extract; (2) in the presence of conspecific or congeneric settlement factors; and (3) cyprids which were, and were not, induced to delay metamorphosis were compared in their capacities to settle in a range of salinities. Discrepancies between salinity profiles of larval settlement in the laboratory and adult oligohaline distribution in the estuary were striking, and there was a significant interaction between salinity and settlement factor. Averaging results of four different batches of larvae, although peak settlement (87_+9%) ofB. subalbidus occurred at 2 ppt salinity in the presence of adult cue, substantial settlement also occurred at higher salinities: >70% at 5, 10 and 15 ppt; and 47% at 20 and 25 ppt. In addition, settlement in the absence of settlement factor was relatively high (>50%) and peaked at mid-salinity ranges (e.g. 56+10% at 15 ppt). Variation observed in settlement among larval batches reflected detailed differences in settlement between adjacent test salinities. No difference in settlement occurred between replicate aliquots of cyprids within a batch. Cyprids of B. subalbidus settled most abundantly in the presence o f settlement factor extracted from conspecifics, followed in decreasing order by settlement factor extracted from B. improvisus and B. eburneus. Delay of metamorphosis produced by keeping B. subalbidus