Effects of conspecific density on settlement, growth and post-settlement survival of a temperate reef fish

Settlement, growth and post-settlement mortality of the cunner ( Tautogolabrus adspersus Walbaum) was investigated on isolated boulder reefs in St. Margaret's Bay, Nova Scotia. Populations of cunner on these reefs were subjected to experimental manipulations of adult and recruit population density. Settlement of cunner was unaffected by the density of prior resident adults. Elevation of adult densities to approximately twice natural levels resulted in complete mortality of newly settled fish, while removal of adults resulted in enhanced growth and recruitment success over natural populations. This clearly demonstrates that natural populations of cunner in St. Margaret's Bay are sufficiently high to result in density-dependent growth and post-settlement mortality. Growth and mortality of newly settled fish were also suppressed by high recruit densities and enhanced by low densities of conspecific recruits. On all study reefs, newly settled cunner formed social dominance hierarchies, and both growth rate and post-settlement survival were positively correlated with fish size. Recruitment success of species such as cunner, for which post-settlement mortality is size-dependent, may be strongly influenced by processes affecting growth rate.