INTERACTIVE EFFECTS OF SALINITY AND ADULT EXTRACT UPON SETTLEMENT OF THE ESTUARINE BARNACLE BALANUS-IMPROVISUS (DARWIN, 1854)

Balanus improvisus (Darwin, 1854) is distributed in mesohaline regions of esturaries worldwide. In Chesapeake Bay, USA, it occurs intermediately along a horizontal salinity gradient between two congeners, oligohaline B. subalbidus (Henry, 1973) and the more polyhaline B. eburneus (Gould, 1841). Laboratory reared cyprids of B. improvisus were exposed to slate substrata treated or untreated with conspecific settlement factor as salinity was varied. Peak settlement occurred at salinities of 10 and 15 parts per thousand on treated substrata, reflecting an interactive effect of these two parameters. Settlement on untreated substrata was low and showed no salinity pattern. Cyprids of B. improvisus settled in significantly greater numbers on intra-than on interspecific settlement factor adsorbed to slate, and they settled in lowest numbers on settlement factor from B. eburneus compared to B. subalbidus. In addition, surface effects upon settlement were less obvious as age of cyprids increased.