The distribution of herbivorous fishes on the Great Barrier Reef

Abstract

The composition and functionality of ecologically important herbivorous Wsh assemblages were examined throughout much of Australia's Great Barrier Reef (GBR). Diversity and abundance of surgeonWshes (Acanthuridae), parrotWshes (Labridae) and rabbitWshes (Siganidae) were strongly associated with position on the continental shelf, whilst eVects of latitude were weaker and inconsistent. Species distributions varied considerably amongst taxonomic groups; parrotWshes were mostly widespread whilst distributions of surgeonWshes were often restricted. Most inshore environments supported depauperate herbivore assemblages dominated by diVerent taxa and functional groups compared with assemblages in oVshore environments. There were also strong cross-shelf transitions in the main taxa performing each functional role. Overall, this study show that the functional contributions of herbivorous Wsh assemblages to important ecosystem processes and the contributing taxa vary considerably amongst diVerent GBR environments. Additionally, the two most numerically dominant herbivores actively select detritus, not algae, supporting increasing evidence for the importance of detritus in coral reef ecology.

Regional-scale variation in the distribution and abundance of farming damselfishes on Australia’s Great Barrier Reef

“…The spatial patterns we found concur with the broad-scale distributions of other groups of fishes on the GBR, including large roving herbivores (Williams 1982;Russ 1984a, b;Hoey and Bellwood 2008;Cheal et al 2012;Wismer et al 2009) and butterflyfishes . The crossshelf variation we found suggests broad-scale underlying processes that are linked to broad environmental gradients between the coastal and oceanic waters.…”

“…The subregional differences in community structure of farming damselfishes identified in this study, and butterflyfishes and large roving herbivores in other similar studies Cheal et al 2012), question the generality of conclusions from small-scale manipulative experiments: results obtained on patch reefs at one location on the GBR may not necessarily apply in locations in other subregions. Furthermore, the lack of consistent relationship between farmer abundance and measured benthic variables across all subregions highlights the potential difficulties in extrapolating the findings of small-scale studies to broader spatial scales.…”

“…Grazers fall into two broad functional groups: large, roving grazers and small, territorial grazers (Ceccarelli et al 2001). The distribution, abundance and biology of large, roving grazers, primarily rabbitfishes (Siganidae), parrotfishes (Labridae) and surgeonfishes (Acanthuridae), have received considerable attention, as have the roles of these fishes in maintaining ecosystem function and reef resilience (Choat and Bellwood 1985;Horn 1989;Bellwood and Choat 1990;Hoey and Bellwood 2008;Cheal et al 2010Cheal et al , 2012. Whilst the reproduction, recruitment and behaviour of territorial grazers, predominantly damselfishes (Pomacentridae), have also been studied extensively (e.g.…”

Spatial variation in the functional characteristics of herbivorous fish communities and the resilience of coral reefs

“…In support of this, no phase shifts were recorded in these subregions, and three reefs in the Cooktown/ Lizard Island outer shelf subregion, which had particularly high measures of herbivore function, recovered relatively rapidly from major coral mortality without phase shifts ). The Pompey mid-shelf subregion was unusual among offshore (mid-and outer shelf ) environments in having relatively low measures of herbivore function, mainly due to a lack of surgeonfishes (Cheal et al 2012), but there is no clear explanation for this anomaly. A distinguishing environmental feature of the Pompey subregion is the extreme tidal ranges that are among the highest recorded on the GBR and often cause very strong currents (.2.6 m/s [5 knots]) on survey sites, though there is no obvious reason why such currents should particularly affect surgeonfishes.…”

“…Strategies that allow fishing but regulate fishing pressure so as to maintain critical herbivore functions are beginning to appear (McClanahan et al 2011), but remain difficult to implement. This is partly because of considerable spatial variation in the structure of herbivorous fish communities within and between reefs (Russ 1984, Cheal et al 2012, with associated spatial variation in their functional characteristics. Strong spatial patterns in herbivorous reef fish communities can result from differing habitat preferences and competitive interactions but may also be influenced by regional evolutionary histories.…”