Scale-dependant control of motile epifaunal community structure along a coral reef fishing gradient

Type Journal Article - Journal of Experimental Marine Biology and Ecology
Title Scale-dependant control of motile epifaunal community structure along a coral reef fishing gradient
Volume 278
Issue 1
Publication (Day/Month/Year) 2002
Page numbers 1-29
Large-scale fishing is mostly conducted using towed gears that reduce the biomass and diversity
of benthic invertebrates. However, it is impossible to differentiate between the physical disturbance
effect of towed gears from the effect of fish predator removal upon benthic invertebrate communities.
Here we explore the impact of fish removal alone on the community structure of small motile coral
reef invertebrates (epifauna) along a subsistence fishing intensity gradient in the Lau group, Fiji. We
deployed settlement plates at three areas in each of six fishing grounds and examined the density and
class richness of the motile epifaunal communities and the associated algal communities in relation
to the structure of fish and benthic communities. Motile epifaunal density was unrelated to fishing
intensity. However, at smaller inter-area scale (0.5 – 10 km) motile epifaunal density was negatively
related to plate algal biomass, whereas at the larger inter-fishing-ground scale (4 – 180 km) motile
epifaunal density was positively related to the rugosity (substrate complexity) of the surrounding
benthos. The class richness and diversity (Margalef’s d) of motile epifaunal communities were
negatively related to fishing intensity, but unrelated to grazing intensity, rugosity or algal biomass at
either scale. Benthic community structure varied significantly with fishing intensity; hard-coral cover
was lower and turf-algal cover was higher at high fishing pressure. The variation in benthic
community structure was associated with variation in fish community structure, which in turn varied
with fishing intensity. Motile epifaunal community structure upon plates was linked to the structure
of the surrounding benthic community, but was not directly linked to the plate algal community. We
suggest the decline in richness of the motile epifauna community along the fishing gradient is
attributable to either to exploiter-mediated coexistence or the reduction in ‘habitat quality’ of thesurrounding benthos. At the large spatial scale substrate complexity is the key determinant of motile
epifaunal density, suggesting predation by fishes plays an important structuring role at this scale.
Assuming that rugosity is inversely related to predation risk then this study represents the first
evidence for spatial-dependence on the top-down (predation) vs. bottom-up (algal biomass) control
of community structure. We argue fisheries exploitation, in the absence of a physical disturbance can
negatively influence motile epifaunal community structure at large spatial scales.

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