Meeting Abstract
Rocky intertidal shores are characterized by vertical zonation, the distribution of species into distinct vertical band along the shore. Physiological stress has long been implicated as a cause of zonation, as higher shore sites have greater duration of low tide exposure and increased temperature and desiccation stress. Yet, high shore animals also have reduced opportunities for feeding and it is possible the energy limitation, rather than physiological stress, sets upper vertical limits. To test this hypothesis, we conducted a field manipulation of food supply on the barnacle Balanus glandula. We collected adult B. and attached them to ceramic tiles placed at one of 4 shore heights, hanging from an unused wharf in the Port of Los Angeles, CA USA. Tiles were grouped into three feeding treatments (fed, manipulated control, unmanipulated control). To feed barnacles, we removed tiles at high tide and placed them in coolers of seawater and brine shrimp. We followed growth and survival of the barnacles for 39 days, with supplemental food provided on 18 days. Survival was significantly greater at lower shore heights, but there was no effect of feeding on survival. Growth differed significantly among shore heights and feeding treatments. Food supplementation increased final mass by up to 36% over controls. The feeding effect declined with shore height. Our results suggest that barnacle growth is food-limited across its vertical range.
