Effects of habitat versus fisheries management on spatio-temperal variation in fish assemblages on the Great Barrier Reef

Emslie, Michael J. (2016) Effects of habitat versus fisheries management on spatio-temperal variation in fish assemblages on the Great Barrier Reef. PhD thesis, James Cook University.

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Reef fishes are an important component of coral reef ecosystems, providing pathways of energy transfer from primary producers through to higher trophic levels. Reef fishes also exert substantial influence on the structure and functioning of reef ecosystems, and are in turn influenced by the biotic and physical structure of reef habitats. While there has been extensive research into habitat associations of coral reef fishes, much of the knowledge of their distribution and abundance has been accumulated from numerous small-scale studies. Broad-scale assessments of taxonomic differences in the distribution of reef fishes across large reef systems have been largely prevented by logistical constraints. On Australia's Great Barrier Reef (GBR), for example, cross shelf variation in the structure of reef fish assemblages has been studied in just two distinct latitudinal bands, while large scale patterns in the abundance and distribution of reef fishes have rarely been considered. Similarly, there is a paucity of information regarding temporal dynamics in the structure of reef fish assemblages, particularly in response to large-scale disturbances.

Coral reefs are inherently dynamic systems and disturbances (e.g., coral bleaching, outbreaks of the corallivorous starfish (Acanthaster planci) coral disease and storms) have frequently impacted reefs on the GBR over the last few decades. While many studies have reported impacts to reef fish assemblages by natural disturbances, they are generally opportunistic and restricted to one type of disturbance at one location. Thus, there is a lack of knowledge about how different disturbances impact reef fish assemblages and whether impacts vary across large spatial scales. There is increasing recognition that cumulative impacts have degraded coral reefs in many parts of the world and many advocate the use of no-take marine reserves to protect reef biodiversity and increase resilience. However, whether no-take marine reserves can indeed impart resilience to coral reefs and buffer the effects of disturbances remains the subject of much debate. This thesis aims to fill a number of substantial knowledge gaps by documenting the distribution and abundance of reef fishes across much of the GBR, how they respond to multiple types of disturbances and whether no-take marine reserves can offer any insurance against the increasing frequency and severity of disturbances.

Comprehensive and extensive surveys of coral reef fishes undertaken at 47 reefs across the GBR revealed marked spatial differences in species composition across several distinct groups of fishes, including butterflyfishes, damselfishes, and parrotfishes. Variation in the structure of fish assemblages was most apparent when comparing along cross-shelf gradients from inshore to offshore reefs. Cross-shelf variation in fish assemblages was conspicuous across all taxa, latitudes and years, suggesting the existence of pervasive underlying drivers of reef fish assemblage structure across the continental shelf, most likely related to environmental gradients in water quality and exposure and their differential effects on settlement preferences and survival of larval fish. While there was substantial temporal variation, reef fish assemblages of the GBR are defined by their subregional setting. This is a novel finding. Despite some level of temporal variation in reef fish assemblages usually brought about by disturbance impacts, it was never strong enough to disrupt the spatial structure such that a given community in a sub-region changed to resemble another. This thesis also highlighted that the impacts of disturbances to reef fishes were variable depending on the type of disturbance and the closeness of association of fishes to live coral and habitat complexity. Importantly, the combined effects of loss of both live coral cover and habitat complexity affected a greater variety of fishes than impacts to live coral alone. Indeed, the impact of disturbances on reef fishes and their subsequent recovery was largely determined by the level of habitat complexity, afforded by both the underlying rugosity of the substrate and the fine scale complexity offered by the skeletons of scleractinian corals. An exciting result to emerge from this thesis was that not only do no-take marine reserves boost populations of exploited fishes inside their boundaries, but they can also retain benefits for exploited fish stocks in the face of strong tropical cyclones that are predicted to occur with greater frequency in the coming decades.

This body of work has greatly improved our knowledge of the distribution and abundance of coral reef fishes across much of the GBR. It demonstrates that there is strong spatial structure to reef fish assemblages, and despite a long disturbance history, reef fish assemblages appear largely resilient to the effects of disturbances. The level of impact is closely linked to the closeness of association with live coral cover, but importantly is strongly determined by the level of alteration in habitat complexity. While reef fishes are impacted by disturbances, exemplified by changes to their abundance, diversity and assemblage structure, they have shown the ability to recover to pre-disturbance levels. Somewhat surprisingly, no-take marine reserves also contributed to reef fish resilience, ensuring the maintenance of important ecological functions essential to recovery following disturbances.

Item ID: 52673
Item Type: Thesis (PhD)
Keywords: abundance; benthic communities; butterflyfish; community structure; coral reef fishes; damselfish; distribution; fish assemblages; fisheries management; Great Barrier Reef (GBR); habitat; spatial patterns
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This is a thesis by publication. Published articles included as chapters 2, 3, 4, 5 and 8 have been redacted from the thesis due to copyright restrictions. The full thesis may either be requested via document delivery at your local library or viewed in the Eddie Koiki Mabo Library at JCU, Townsville.

Publications arising from this thesis are available from the Related URLs field. The publications are:

Chapter 2: Emslie, M.J., Pratchett, M.S., Cheal, A.J., and Osborne, K. (2010) Great Barrier Reef butterflyfish community structure: the role of shelf position and benthic community type. Coral Reefs, 29 (3). pp. 705-715.

Chapter 3: Emslie, M.J., Logan, M., Ceccarelli, D.M., Cheal, A.J., Hoey, A.S., Miller, I., and Sweatman, H.P.A. (2012) Regional-scale variation in the distribution and abundance of farming damselfishes on Australia's Great Barrier Reef. Marine Biology, 159 (6). pp. 1293-1304.

Chapter 4: Cheal, Alistair, Emslie, Michael, Miller, Ian and Sweatman, Hugh (2012) The distribution of herbivorous fishes on the Great Barrier Reef. Marine Biology, 159 (5). pp. 1143-1154.

Chapter 5: Emslie, M.J., Pratchett, M.S., and Cheal, A.J. (2011) Effects of different disturbance types on butterflyfish communities of Australia's Great Barrier Reef. Coral Reefs, 30 (2). pp. 461-471.

Chapter 6: Emslie M.J., Cheal A.J., Johns K.A. (2014) Retention of habitat complexity minimizes disassembly of reef fish communities following disturbance: a large-scale natural experiment. PLoS ONE 9 (8). pp. 93-101. https://doi.org/10.1371/journal.pone.0105384

Chapter 7: Emslie M.J., Cheal A.J., Sweatman H.P.A. and Delean S. (2008) Recovery from disturbance of coral and reef fish communities on the Great Barrier Reef, Australia. Marine Ecology Progress Series. 371. pp. 177-190. https://doi.org/10.3354/meps07657

Chapter 8: Emslie, Michael J., Logan, Murray, Williamson, David H., Ayling, Anthony M., MacNeil, M. Aaron, Ceccarelli, Daniela, Cheal, Alistair J., Evans, Richard D., Johns, Kerryn A, Jonker, Michelle J., Miller, Ian R., Osborne, Kate, Russ, Garry R., and Sweatman, Hugh P.A. (2015) Expectations and outcomes of reserve network performance following re-zoning of the Great Barrier Reef Marine Park. Current Biology, 25 (8). pp. 983-992.

Date Deposited: 26 Feb 2018 02:02
FoR Codes: 06 BIOLOGICAL SCIENCES > 0602 Ecology > 060205 Marine and Estuarine Ecology (incl Marine Ichthyology) @ 60%
05 ENVIRONMENTAL SCIENCES > 0502 Environmental Science and Management > 050206 Environmental Monitoring @ 20%
05 ENVIRONMENTAL SCIENCES > 0502 Environmental Science and Management > 050209 Natural Resource Management @ 20%
SEO Codes: 83 ANIMAL PRODUCTION AND ANIMAL PRIMARY PRODUCTS > 8302 Fisheries - Wild Caught > 830204 Wild Caught Fin Fish (excl. Tuna) @ 20%
96 ENVIRONMENT > 9605 Ecosystem Assessment and Management > 960507 Ecosystem Assessment and Management of Marine Environments @ 50%
97 EXPANDING KNOWLEDGE > 970105 Expanding Knowledge in the Environmental Sciences @ 30%
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