Abstract
The decline in herbivorous fishes is an important contributing factor to the degradation of coral reefs, because their reduction contributes to macro algae overgrowth, which can have harmful effects on corals. Herbivorous fish often form mixed-species groups to locate foraging sites and for defense. The movements and compositions of these groups are dependent on the relative numbers of different species present. Some species, such as the striped parrotfish (Scarus iserti) and ocean surgeonfish (Acanthurus bahianus), serve as core species that lead mixed-species groups. Others, such as the redband (Sparisoma aurofrenatum) and stoplight parrotfishes (Sparisoma viride), follow core species as their associates. Despite the potential importance and abundance of mixed-species groups on reefs, little attention has been given to their composition and movements. Our intent was to determine whether the social dynamics of mixed-species groups in Jamaica were similar to those of Grand Cayman. The overall sizes of mixed-species groups were smaller in Grand Cayman. Focal striped parrotfish in Grand Cayman formed smaller groups, changed composition less, and moved less frequently than in Jamaica. Although probably more abundant than striped parrotfish, the ocean surgeonfish in Grand Cayman did not function as a core species but rather attached themselves as associates to the smaller striped parrotfish groups. Redband parrotfish moved less often in Grand Cayman, and appeared to be more dependent on striped parrotfish groups than stoplight parrotfish. While previous studies on herbivorous reef fish have shown that changes in foraging patterns can change with location, perhaps related to structural heterogeneity and resource distribution, this study illustrates that social interactions between common members of mixed-species groups also change. We suggest that the intra and interspecific social interactions in Grand Cayman are less attuned to finding erratically located high quality resources than those in Jamaica. Other plausible explanations are also considered.
Highlights
Coral reefs are widely viewed as in decline [1] [2] [3] [4] [5], and the overfishing of algae-grazing fishes is often considered an important contributing factor [5] [6] [7] [8] but see [9]
The core species fluctuated between two species, the striped parrotfish (Scarus iserti) and the ocean surgeonfish (Acanthurus bahianus), with both feeding in open areas on the uniformly abundant turf-filamentous algae
Regardless of focal species or island location, there was a main effect of non-focal fish composition which indicated that the four species of interest were not represented in replicate groups
Summary
Coral reefs are widely viewed as in decline [1] [2] [3] [4] [5], and the overfishing of algae-grazing fishes is often considered an important contributing factor [5] [6] [7] [8] but see [9]. Itzkowitz [25] [26] followed the foraging movements of mixed-species groups in Jamaica as they meandered around the reefs in order to quantify how the movements of one species influenced the others He determined that the most abundant species led the group (termed “core” species), with all other species following (termed “associate” species). Most associate species used the core species group as a way to move safely through open areas on their way to the macro-algae on large rubble and coral
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