Predator and shelter-size effects on coral reef fish and spiny lobster prey

Abstract

Population dynamics of coral reef fishes and spiny lobster appear to be determined by variable recruitment interacting wlth post-settlement processes, part~cularly p reda t~on The nsk of predation may be modified by the scaling between prey and shelter slze, whlch enhances the protective capaclty of a reef LVc experimentally tested these pred~ctlons by manlpula t~ng densities of predatory Nassau grouper Epinephelus striatus on 8 a r t ~ f ~ c ~ a l patch reefs of 2 sizes (small, large) In a large seagrass bed near Lee Stocking Island, Bahamas. We initially censused patch reefs for 7 mo, after w h ~ c h we randomly selected equivalent numbers of small and large reefs to serve as permanent grouper removal vrrsus control (non-removal) reefs. We continued to census patch reefs for 12 mo after predators were removed from certain reefs The abundance of predatory Nassau grouper and the slze of shelters from predatlon jointly explained the observed d~strlbution and abundance patterns of splny lobster and reef flsh prey inhabiting artiflclal patch reef habitats For example, the abundance of small lobsters was highest In small reefs where Nassau grouper were experimentally removed. When we assessed the effects of predator abundance on all reef flsh prey (1 to 10 cm TL), we were unable to detect any sign~ficant effects on prey abundance or species d ~ v e r s ~ t y due to low statistical power. However, the total abundance and specles richness of medium size reef fish (4 to 10 cm TL) was s~gnificantly higher in small shelters from w h ~ c h grouper were removed In comparing species' relative abundances on reefs with low versus hlgh numbers and Nassau grouper, the results indicated that grouper reduce prey abundances In a generalized, non-selective pattern, with no difference in the nuinber of rare versus common prey species that were extirpated. Thus. l uven~ le Nassau grouper Inhabiting certaln patch reefs produce a general predatory Impact, whereby predatlon reduces prey abundance and diversity in proportion to the lnitial relatlve abundance of prey Our results support the prediction that a t certain scales of space and time, post-settlement predatlon is a crl t~cal determinant of population abundance and species d~versity of reef-flsh and spiny lobstelprey, and that the effect of predation is m e d ~ a t e d by the protective capacity of a reef