Habitat characteristics as determinants of the local diversity and structure of coral reef fish communities

Komyakova, Valeriya (2009) Habitat characteristics as determinants of the local diversity and structure of coral reef fish communities. Masters (Research) thesis, James Cook University.

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Abstract

Habitat structure has a major influence on the composition of all animal communities. In complex coral reef environments, a range of habitat features appear to influence the structure of reef fish assemblages, with the effects of live coral cover and topographic complexity receiving most attention. The role of coral diversity in determining the structure of local fish communities and the consequences of species specific fish-coral interactions in these ecosystems have not been fully explored. The aim of this thesis was to investigate the relationships between coral reef fish assemblages and habitat structure by sampling species-specific fish and coral associations in the lagoon at Lizard Island on the Great Barrier Reef. Specifically, I examined (a) the relative importance of coral cover, habitat topographic complexity and coral diversity in explaining the structure of the local fish community, (b) the role of different coral species in supporting diverse and abundant fish communities and, the structural characteristics of coral species likely to be responsible for the observed relationships, (c) the effects of sampling scale on the strength of the measured associations between fish and corals, (d) patterns of habitat specialisation and habitat overlap among the 14 co-existing damselfish species, and among ontogenetic stages. The relationships between a range of habitat features and local fish diversity, abundance and community structure were investigated by sampling over sixty 2m² quadrats at three sites in the Lizard Island lagoon. Fish species richness, total abundance and community structure were examined in relation to location within the lagoon and a wide range of habitat variables, including topographic complexity, habitat diversity, coral diversity, coral species richness, hard coral cover, branching coral cover and the cover of corymbose corals. Fish species richness and total abundance were strongly related to coral species richness and cover, but only weakly related to topographic complexity. Regression tree analysis indicated that coral species richness accounted for over 63% of the variation in fish species richness, while hard coral cover explained more variation in total fish abundance (17.4%), than any other variable. The results suggest that the diversity of scleractinian corals is critical in maintaining local coral reef fish diversity, and loss of coral species will in turn lead to declining fish diversity.

Further surveys were carried out to assess the relative importance of different coral species in structuring fish communities, to identify the characteristics of corals that support higher fish diversity, and to evaluate whether sampling scale has any effect on the perceived strength of fish-habitat relationships. The communities of fishes present on colonies of eight common coral species (Porites cylindrica, Echinopora horrida, Hydnophora rigida, Stylophora pistillata, Seriatopora hystrix, Acropora formosa, A. tenuis and A. millepora) were examined at three spatial scales of sampling (2x2 m, 1x1 m, 0.5x0.5 m) at multiple sites in the Lizard Island lagoon. Coral species was the only variable that explained significant amount of variation in fish species richness among the samples. It also explained a significant amount of variation in total fish abundance. Coral species explained more of the variability in fish species richness (36-54%), than in fish abundance (10-15%). Colonies of E. horrida and H. rigida, which exhibited an intermediate level of branching structure, supported more fish species and individuals than similar sized colonies of all other coral species. Species of coral with either very fine branching structure (A. millepora, A. tenuis, S. hystrix) or very open branching structure (A. formosa), supported the lowest number of species and individuals. The relationships between coral species and fish species richness or abundance became stronger as the spatial scale of sampling increased. These results indicate that the types of coral present on reefs can significantly influence the structure of reef fish communities, and that coral species with an intermediate level of branching structure support the most diverse and abundant fish communities. Furthermore, the spatial scale of sampling can influence the perceived relationship between fish communities and their habitats.

The decline in fish diversity with coral diversity may be explained by habitat specialisation and partitioning among reef fishes and/or common preferences for particular corals that are susceptible to disturbance. These preferences may develop at different life history stages. To test this, I examined species-specific habitat preferences and ontogenetic habitat shifts among 14 co-occurring damselfish species in the Lizard Island lagoon. The percent cover of 17 substratum types was estimated at four sites within the lagoon: Palfrey Island, Lagoon centre, Lizard Head and Bird Island. The habitat use of each damselfish species was then estimated by focal animal sampling across the lagoon. Although live coral cover contributed only 26% of the substratum, 28% of adults and 57% of new settlers were mostly found on live coral substratum, indicating a strong preference for live coral habitat by these species. Some species exhibited a high degree of habitat specialisation and low overlap in habitat use with other species, which could help explain the importance of coral diversity on fish community structure. In general, however, there was a substantial overlap within coral associated and non-coral associated groups, with different species using similar resources. Some species exhibited ontogenetic habitat shifts. In particular, new settlers were commonly associated with finely branched corymbose corals, whereas adults were more commonly linked to more open branching morphologies or non-coral substratum.

The results from this study indicate a closer association between fish and coral diversity than previously demonstrated. It suggests that human impacts on the composition and diversity of coral communities are likely to have profound and negative effects on reef fish biodiversity, more so than would be predicted on the basis of declining coral cover or topographic complexity alone.

Item ID: 7998
Item Type: Thesis (Masters (Research))
Keywords: coral reef fishes, fish abundance, coral reef habitats, Great Barrier Reef, coral cover, species richness, damselfishes, fish diversity, coral diversity
Date Deposited: 14 Jan 2010 00:33
FoR Codes: 06 BIOLOGICAL SCIENCES > 0602 Ecology > 060205 Marine and Estuarine Ecology (incl Marine Ichthyology) @ 50%
06 BIOLOGICAL SCIENCES > 0602 Ecology > 060207 Population Ecology @ 50%
SEO Codes: 96 ENVIRONMENT > 9608 Flora, Fauna and Biodiversity > 960808 Marine Flora, Fauna and Biodiversity @ 50%
97 EXPANDING KNOWLEDGE > 970106 Expanding Knowledge in the Biological Sciences @ 50%
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