Energetic costs of chronic fish predation on reef-building corals

Cole, Andrew (2011) Energetic costs of chronic fish predation on reef-building corals. PhD thesis, James Cook University.

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Abstract

Interactions between predators and prey organisms are of fundamental importance to ecological communities. While the ecological impacts that grazing predators can have in terrestrial and temperate marine systems are well established, the importance of coral grazers on tropical reefs has often been overlooked. Fishes that feed from live corals (corallivores) are a conspicuous component of healthy coral reef environments. Published records document that at least 128 corallivorous fish species from 11 different families feed at least in part upon scleractinian corals, with 69 of these belonging to the family Chaetodontidae. One third of all coral-feeding fishes feed almost entirely upon corals, with more than 80% of their diet based on live coral tissue. This thesis aims to assess the energetic cost and relative importance that predation from polyp-feeding fishes has on reef-building corals by: 1) determining how the frequency and intensity of predation is dispersed both among and within common species of reef-building corals, 2) quantifying the amount of coral tissue consumed by corallivorous butterflyfishes and determining the proportion of available coral tissue biomass and potential productivity of tabular acroporid corals this consumption represents, and 3) assessing the energetic cost that chronic tissue consumption by juvenile and adult corallivores has on the growth and condition of reef-building corals.

To assess how corallivore predation is dispersed both among and within coral species I used an observational study to quantify grazing rates on four common reef corals (Acropora hyacinthus, Acropora millepora, Pocillopora damicornis, and massive Porites). I also assessed the variation in predation intensity within A. hyacinthus and A. millepora by standardising grazing rates by colony surface area. Rates of grazing on individual colonies were highest (16.75 (± 0.30 SE) bites.20 minutes⁻¹) for A. hyacinthus. Within coral species, grazing rates showed a linear increase with increasing size of the colony, however the intensity of predation showed a negative relationship with increasing colony size. Predation intensity was highest for small to medium sized colonies with a peak intensity of 1.13 (± 0.17) bites 100cm⁻².20minutes- 1.colony⁻¹ for A. hyacinthus colonies and 0.56 (± 0.09) bites 100cm⁻².20 minutes⁻¹.colony⁻¹ for A. millepora colonies (200-600cm²). In contrast, predation intensity was lowest for both very small and very large colonies, with very small colonies (<200cm²) rarely consumed by corallivorous fishes.

To assess the magnitude of coral tissue that is removed from the reef by corallivorous fishes I undertook aquarium based feeding trials to quantify the bite size of four prominent species of coral-feeding butterflyfishes. Sub-adult butterflyfishes (60-70mm TL, 6-11g wet weight) remove between 0.6 and 0.9g of live coral tissue per day, while larger adults (>110mm TL, 40-50g wet weight) remove between 1.5 and 3g of coral tissue each day. These individual consumption rates were extrpolated based on population sizes of corallivores at three exposed reef crest habitats at Lizard Island, Great Barrier Reef; these fishes consume between 14.6g (± 2.0) and 27.4g (± 1.5) 200m⁻².day⁻¹ of coral tissue. When standardised to the biomass of butterflyfishes present, a combined reef wide removal rate of 4.2g (± 1.2) of coral tissue is consumed per 200m⁻².kg⁻¹ of coral-feeding butterflyfishes. Feeding observations identified that between 61-68% of this consumption is directed towards tabular acroporid corals on exposed reef crest habitats at Lizard Island. This selective feeding resulted in an annual consumption of between 8.9-13.5% of the total available tissue biomass and between 52-79% of the annual productivity of these tabular acroporid corals. The effects of this predation, however, were mixed.

Juvenile butterflyfishes were found to settle directly into live coral and feed entirely upon a single colony for at least the first 6-8 weeks post settlement. This highly concentrated predation had negative effects on coral condition. In a field experiment coral tissue biomass declined by 26.7%, 44.5% and 53.4% in low, medium and high predation intensity treatments. Total lipid content of host corals declined by 29-38% across all treatments including controls and was not related to predation intensity; rather, this decline coincided with the mass spawning of corals and the loss of lipidrich eggs. In contrast, the reef wide effect of predation by adult corallivores was less clear. Whole colony growth rates, tissue mass per unit area, total lipid content and fecundity were all higher for corals on experimental reefs with reduced predation, however these differences were small and only significant for the total lipid content of Acropora hyacinthus, which was 9.3% higher (52.6% ± 0.8 vs 48.1% ± 0.7) on reefs with reduced predation relative to controls. This result indicates that on healthy reef systems, where photosynthesis and energy acquisition is not impaired, corals have a high tolerance to the chronic damage caused by polyp-feeding fishes and the energy used to regenerate lost tissue does not result in an energy trade-off with other life history functions. However, on reefs already stressed by other factors where energy acquisition is impaired (e.g. during a coral bleaching event), chronic predation is more significant and can affect the survivorship of highly preferred prey corals.

Item ID: 37611
Item Type: Thesis (PhD)
Keywords: consumption; coral decline; coral mortality; coral predation; coral reefs; corallivorous fish; corallivorous fishes; corallivory; corals; ecology; feeding; grazing; impacts; polyp-feeders; predators; reef degredation; reef-building
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Publications arising from this thesis are available from the Related URLs field. The publications are:

Chapter 2: Cole, Andrew J., Pratchett, Morgan S., and Jones, Geoffrey P. (2008) Diversity and functional importance of coral-feeding fishes on tropical coral reefs. Fish and Fisheries, 9. pp. 286-307.

Chapter 3: Cole, A.J., and Pratchett, M.S. (2011) Inter-specific variation in susceptibility to grazing among common reef corals. Marine Ecology Progress Series, 422. pp. 155-164.

Chapter 4: Cole, A.J., Lawton, R.J., Pratchett, M.S., and Wilson, S.K. (2011) Chronic coral consumption by butterflyfishes. Coral Reefs, 30 (1). pp. 85-93.

Chapter 5: Cole, A.J., and Pratchett, M.S. (2011) Effects of juvenile coral-feeding butterflyfishes on host corals. Coral Reefs, 30 (3). pp. 623-630 .

Chapter 6: Cole, Andrew J., Lawton, Rebecca J., Wilson, Shaun K., and Pratchett, Morgan S. (2012) Consumption of tabular acroporid corals by reef fishes: a comparison with plant–herbivore interactions. Functional Ecology, 26 (2). pp. 307-316.

Lawton, Rebecca J., Cole, Andrew J., Berumen, Michael L., and Pratchett, Morgan S. (2012) Geographic variation in resource use by specialist versus generalist butterflyfishes. Ecography, 35 (6). pp. 566-576.

Chong-Seng, K.M., Cole, A.J., Pratchett, M.S., and Willis, B.L. (2011) Selective feeding by coral reef fishes on coral lesions associated with brown band and black band disease. Coral Reefs, 30 (2). pp. 473-481.

Cole, A.J. (2010) Cleaning to corallivory: ontogenetic changes in feeding behaviour of tubelip wrasse. Coral Reefs, 29 (1). pp. 125-129.

Cole, A.J, Pratchett, M.S., and Jones, G.P. (2010) Corallivory in tubelip wrasses: diet, feeding and trophic importance. Journal of Fish Biology, 76 (4). pp. 818-835.

Cole, A.J., Pratchett, M.S., and Jones, G.P. (2009) Coral-feeding wrasse scars massive Porites colonies. Coral Reefs, 28 (1). p. 207.

Cole, A.J., Pratchett, M.S., and Jones, G.P. (2009) Effects of coral bleaching on the feeding response of two species of coral-feeding fish. Journal of Experimental Marine Biology and Ecology, 373. pp. 11-15.

Cole, Andrew J, Chong-Seng, Karen, Pratchett, Morgan S., and Jones, Geoffrey P. (2009) Coral-feeding fishes slow progression of black-band disease. Coral Reefs, 28 (4). p. 965.

Date Deposited: 05 Aug 2015 05:43
FoR Codes: 05 ENVIRONMENTAL SCIENCES > 0501 Ecological Applications > 050102 Ecosystem Function @ 50%
06 BIOLOGICAL SCIENCES > 0602 Ecology > 060202 Community Ecology (excl Invasive Species Ecology) @ 50%
SEO Codes: 97 EXPANDING KNOWLEDGE > 970106 Expanding Knowledge in the Biological Sciences @ 50%
96 ENVIRONMENT > 9603 Climate and Climate Change > 960305 Ecosystem Adaptation to Climate Change @ 50%
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