Foragers versus farmers: contrasting effects of two behavioural groups of herbivores on coral reefs |
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Authors: | Email author" target="_blank">Daniela?M?CeccarelliEmail author Geoffrey?P?Jones Laurence?J?McCook |
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Institution: | (1) School of Marine Biology and Aquaculture, James Cook University, Townsville, 4811, QLD, Australia;(2) Centre for Coral Reef Biodiversity, School of Marine Biology and Aquaculture, James Cook University, Townsville, 4811, QLD, Australia;(3) Australian Institute of Marine Science, PMB3, Townsville MC, 4810, QLD, Australia;(4) Present address: Great Barrier Reef Marine Park Authority, Townsville, 4810, QLD, Australia |
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Abstract: | Herbivorous fishes have been attributed a central role in structuring benthic communities on coral reefs. However, the relative
importance of different behavioural groups of herbivores may differ and their interactions may be complex. This study focuses
on an experiment that discriminates between two groups of herbivorous fish: (1) “Foragers” (relatively mobile, schooling grazers,
including parrotfishes and surgeonfishes) and (2) “Farmers” (highly site-attached, territorial species, primarily damselfishes).
Preliminary observations at Kimbe Bay (Papua New Guinea) showed that both groups were common, and that farmers defended areas
from foragers and maintained algal communities that were distinct from the surrounding undefended substratum. An orthogonal
combination of a farmer removal treatment and a forager exclusion treatment was applied to isolate their separate effects
on algae and corals, and to determine whether farmer territory composition results from forager exclusion or algal cultivation.
The experiment showed that foragers had quantitatively greater and qualitatively different effects on sessile benthic community
structure than farmers. Where foragers were excluded, there were substantial increases in the cover and biomass of macro-algae
and a decline in some corals, regardless of the presence of farmers. Where farmers were removed there was a moderate decline
in the cover of some food algal species, regardless of whether foragers had access. No effect of the exclusion of foragers
by farmers could be detected. Our results support prevailing views that foragers have a major impact on coral reefs and farmers
cultivate selected algae, but challenge the hypothesis that damselfish influence habitat structure by moderating forager disturbance. |
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Keywords: | Territorial damselfish Benthic algae Herbivorous fish Cage experiment |
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