EFFECTS OF SALINITY AND ADULT EXTRACT ON SETTLEMENT OF THE OLIGOHALINE BARNACLE BALANUS-SUBALBIDUS

Balanus subalbidus (Henry) has the most oligohaline distribution of th ree congeneric barnacles in Chesapeake Bay and tolerates prolonged exp osure to fresh water. We studied larval settlement (i.e., permanent at tachment 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 degrees C in the presence and absence of settlement factor consisting of adult B. subalbidus extract ; (2) in the presence of conspecific or congeneric settlement factors; and (3) cyprids which were, and were not, induced to delay metamorpho sis were compared in their capacities to settle in a range of saliniti es. Discrepancies between salinity profiles of larval settlement in th e laboratory and adult oligohaline distribution in the estuary were st riking, and there was a significant interaction between salinity and s ettlement factor. Averaging results of four different batches of larva e, although peak settlement (87+/-9%) of B. subalbidus occurred at 2 p pt 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 fact or was relatively high (>50%) and peaked at mid-salinity ranges (e.g. 56+/-10% at 15 ppt). Variation observed in settlement among larval bat ches reflected detailed differences in settlement between adjacent tes t salinities. No difference in settlement occurred between replicate a liquots of cyprids within a batch. Cyprids of B. subalbidus settled mo st abundantly in the presence of settlement factor extracted from cons pecifics, followed in decreasing order by settlement factor extracted from B. improvisus and B. eburneus. Delay of metamorphosis produced by keeping B. subalbidus cyprids for 8 d at 5 degrees C resulted in a de creased level of settlement, but settlement frequency patterns of dela yed and non-delayed cyprids were indistinguishable relative to salinit y. These results indicate that the oligohaline distribution of adult B . subalbidus is probably not determined by larval behavior at settleme nt. We suggest that pre-settlement behavior, resulting in larval reten tion in low saline waters, could be an important factor in determining distribution of this species.