Pomacentridae is one of the most representative families of herbivorous fishes inhabiting both tropical and temperate reefs, yet the vast majority of studies examining feeding within this family have been undertaken in tropical rather than temperate regions. Despite the high abundances of the pomacentrid Parma mccullochi in temperate waters of Western Australia, and their likely importance in removing algae from reefs in the region, there is a lack of information on their diet and their impact on the reef algal community. This study aimed to determine the role of Parma mccullochi as an ecosystem engineer on temperate algal-dominated reefs in the metropolitan waters of Perth, Western Australia. To achieve this, the diet of P. mccullochi and any ontogenetic differences, and its impact on the reef in terms of algal composition and algal recruitment were determined. P. mccullochi in the temperate reefs of Western Australia was found to be a strict herbivore, with its diet comprising almost entirely red foliose and filamentous algae such as Hypnea spp., Ceramium sp. and Brongniatrella sp., and showing no ontogenetic shift. Based on electivity indices, P. mccullochi showed a positive selection for specific algal taxa such as Brongniartella sp., Dasyclonium sp., Hypnea spp. and Dictyopteris spp. The species composition of macroalgae differed significantly between inside and outside P. mccullochi territories (P = 0.010), and a caging experiment in P. mccullochi territories indicated a moderate effect on the composition of recruiting algae (P = 0.067). Algal assemblages inside the territories were characterised by Hypnea spp.and Dasyclonium spp., while those outside the territories were characterised by the brown algae Ecklonia radiata and Sargassum spp., the foliose red alga Rhodimenia sonderi and the coralline red alga Amphiroa anceps. Total algal biomass was significantly lower (P = 0.0126) while species richness was higher (P = 0.0114) inside compared to outside territories. P. mccullochi has the capacity to structure the benthic composition of reefs and maintain high biodiversity patches within kelp canopies. This effect is amplified by the high abundances of the species observed in Perth metropolitan waters, highlighting its importance in ecosystem processes of temperate reefs in the region.
Edith Cowan University
Department of Parks and wildlife
February 2011 – March 2013
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