Marine reserves demonstrate trophic interactions across habitats

Abstract

Several infaunal bivalve taxa show patterns of decreased biomass in areas with higher densities of adjacent reef-associated predators (the snapper, Pagrus auratus and rock lobster, Jasus edwardsii). A caging experiment was used to test the hypothesis that patterns observed were caused by predation, using plots seeded with a known initial density of the bivalve Dosinia subrosea to estimate survivorship. The caging experiment was replicated at several sites inside and outside two highly protected marine reserves: predators are significantly more abundant inside these reserves. Survivorship in fully caged, partially caged and open plots were then compared at sites having either low (non reserve) or high (reserve) predator density. The highest rates of survivorship of the bivalve were found in caged plots inside reserves and in all treatments outside reserves. However, inside reserves, open and partially caged treatments exhibited low survivorship. It was possible to specifically attribute much of this mortality to predation by large rock lobsters, due to distinctive marks on the valves of dead D. subrosea. This suggests that predation by large rock lobster could indeed account for the distributional patterns previously documented for certain bivalve populations. Our results illustrate that protection afforded by marine reserves is necessary to investigate how depletion through fishing pressure can change the role of upper-level predators and trophic processes between habitats.

Habitat complexity and predation risk determine juvenile snapper (Pagrus auratus) and goatfish (Upeneichthys lineatus) behaviour and distribution

“…Alternatively, indirect effects of fishing, such as changes in the composition of benthic communities (e.g. Shears and Babcock 2003;Langlois et al 2006b), may result in differential recruitment or habitat selection after settlement. Coralline turf, which goatfish were positively associated with, was more abundant at our non-reserve sites.…”

Proximity to reef influences density of small predatory fishes, while type of seagrass influences intensity of their predation on crabs

“…Experiments have sometimes shown that prey densities near reefs increase when predators are excluded (e.g. Posey & Ambrose 1994, Langlois et al 2006), but not always, indicating that other influences might often be more important (e.g. Jones et al 1992, Barros 2005.…”

Effects of fish predation on Posidonia oceanica amphipod assemblages

“…However, caging experiments remain a valuable tool in predation studies of seagrass meadows (Edgar 1990;Hindell et al 2001;Moksnes et al 2008) and other marine ecosystems (Connell 1997;Sala 1997;Langlois et al 2006). It is difficult to eliminate the possibility that any effects that were detected were due to caging artefacts.…”