DAILY SETTLEMENT VARIABILITY OF THE BARNACLE SEMIBALANUS-CARIOSUS - IMPORTANCE OF PHYSICAL FACTORS AND DENSITY-DEPENDENT PROCESSES

Settlement abundances of barnacles are determined by larval supply and the ratio of settlement to larval supply (K). This ratio can be divid ed into 2 functions: the ratio of settlement on bare space to larval s upply (k(1)), and the loss of cyprids due to the preempting of rock sp ace by sessile organisms (k(2)). To examine the 3 functions of settlem ent (i.e. larval supply, k(1) and k(2)) of the barnacle Semibalanus ca riosus, we monitored the daily water column larval supply and the dail y settlement density in plots where all benthos were removed and in na tural-community plots, which were left undisturbed, during one settlin g season. In both low- and mid-tidal sites, k(1) explained > 75 % of d ay-to-day variability in K, k(1) and k(2) were density dependent, whil e daily settlement densities were Linearly related to larval supply, k (1) varied with tidal height and daily larval supply, but not with oth er physical variables. k(2) varied with daily settlement densities in community-removal plots and was not related to any physical or biologi cal variable. Such density dependence in k(1) and k(2) may have been c aused by 3 processes: (1) inhibition of larval settlement by planktoni c larvae, (2) enhancement of settlement by conspecifics (and their che mical attractants) on days with relatively low larval density, and/or (3) preemption of suitable settlement substrata by settlers that attac hed on days with relatively high larval density.