Concentrations and uptake of neutral monosaccharides along 140 degrees W in the equatorial Pacific: Contribution of glucose to heterotrophic bacterial activity and the DOM flux
Population dynamics of coral reef fishes and spiny lobster appear to be determined by variable recruitment interacting with post-settlement processes, particularly predation. The risk of predation may be modified by the scaling between prey and shelter size, which enhances the protective capacity of a reef. We experimentally tested these predictions by manipulating densities of predatory Nassau grouper Epinephelus striatus on 8 artificial 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 which we randomly selected equivalent numbers of small and large reefs to serve as permanent grouper removal versus 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 size of shelters from predation jointly explained the observed distribution and abundance patterns of spiny lobster and reef fish prey inhabiting artificial 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 fish prey (1 to 10 cm TL), we were unable to detect any significant effects on prey abundance or species diversity due to low statistical power. However, the total abundance and species richness of medium size reef fish (4 to 10 cm TL) was significantly higher in small shelters from which grouper were removed. In comparing species' relative abundances on reefs with low versus high numbers and Nassau grouper, the results indicated that grouper reduce prey abundances in a generalized, non-selective pattern, with no difference in the number of rare versus common prey species that were extirpated. Thus, juvenile Nassau grouper inhabiting certain patch reefs produce a general predatory impact, whereby predation reduces prey abundance and diversity in proportion to the initial relative abundance of prey. Our results support the prediction that at certain scales of space and time, post-settlement predation is a critical determinant of population abundance and species diversity of reef-fish and spiny lobster prey, and that the effect of predation is mediated by the protective capacity of a reef.