Proximate causes of mortality determining the distribution and abundance of the barnacle Balanus improvisus Darwin in Chesapeake Bay

The effects of predation and competition on survival of the barnacle,Balanus improvisus Darwin, in the upper Chesapeake Bay varied from location to location in 1972 and probably vary from year to year. The flatworm,Stylochus ellipticus Girard, was the predominant predator on barnacles and the bryozoan,Victorella pavida Kent, was the major spatial competitor. Those intertidal barnacles not killed by the flatworms or bryozoans died from exposure to a combination of high winds (25 knots) and low air temperature (−9° C) in the winter. Subtidal barnacle populations were not eliminated by biotic or physical factors and may be the source of those larvae recolonizing the intertidal zone every spring.