The spatial ecology of coral reef fishes

Welsh, Justin Quentin (2014) The spatial ecology of coral reef fishes. PhD thesis, James Cook University.

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Abstract

Movement is a fundamental component of a species' ecology and the study of space use in organisms has a long-standing history as a conservation tool. Within an ecosystem, numerous functional processes are conferred by taxa, and are essential to maintain stable ecosystem processes. The application of functional roles is, however, bound by the home ranges of the taxa responsible, and thus, the spatial ecology of organisms is of great significance to ecosystem health. Coral reefs are among the most vulnerable ecosystems to degradation and yet, the spatial ecology of key species which support coral reef resilience remain largely unknown. In this thesis I therefore endeavoured to quantify the spatial ecology of functionally important coral reef herbivores to further our understanding of ecological processes.

Passive acoustic receivers are commonly used to remotely monitor animal movements in the marine environment. The detection range and diel performance of acoustic receivers was assessed using two parallel lines of 5 VR2W receivers spanning 125 m, deployed on the reef base and reef crest. The working detection range (distance within which > 50% of detections are recorded) for receivers was found to be approximately 90 m on the reef base and 60 m on the reef crest. No diel patterns in receiver performance or detection capacities were detected. These results are in contrast to those in non-reef environments, with coral reefs presenting a unique and challenging environment for the use of acoustic telemetry.

Using a dense array of passive acoustic receivers, the maximum potential areas occupied by the schooling herbivorous fish, Scarus rivulatus, was quantified over 7 months. Despite schooling, all S. rivulatus were site attached. On average, the maximum potential home range of individuals was 24,440 m² and ranges overlapped extensively in individuals captured from the same school. The area shared by all members of the same school was smaller than that of individual's average home range, measuring 21,652 m². This suggests that school fidelity in this species may be low and while favourable, schooling represents a facultative behavioural association. However, schooling was found to have a beneficial influence on ecosystem processes, with feeding rates in schooling S. rivulatus being double those of non-schooling individuals.

Despite adult parrotfish being largely site attached, the ontogeny of these fishes' home range expansion is not yet known. This study therefore assessed the home range size of three different parrotfish species at every stage of development following settlement onto the reef. With masses spanning five orders of magnitude, from the early post-settlement stage through to adulthood, no evidence of a response to predation risk, dietary shifts or sex change on home range expansion rates was found. Instead, a distinct ontogenetic shift in home range expansion with sexual maturity was documented. Juvenile parrotfishes displayed rapid home range growth until reaching approximately 100 - 150 mm long. Thereafter, the relationship between home range and mass broke down. This shift reflected changes in colour patterns, social status and reproductive behaviour associated with the transition to adult stages.

The majority of herbivorous reef fishes are regarded as 'roving herbivores', despite new evidence recording these taxa as being highly site attached. The extents to which site-attached behaviour is prevalent in herbivorous reef fishes was assessed by quantifying the movements of a largely overlooked family of functionally important coral reef browsers, the Kyphosidae, and comparing their movements to other coral reef herbivores. Kyphosus vaigiensis exhibited regular, large-scale (> 2 km). Each day individual K. vaigiensis cover, on average, 2.5 km of reef (11 km maximum). A metaanalysis of home range data from other herbivores found a consistent relationship between home range size and body length. Only K. vaigiensis departs significantly from the expected home-range body size relationship, with home range sizes more comparable to large pelagic predators rather than other reef herbivores. These largescale movements of K. vaigiensis suggest that this species is a mobile link, providing functional connectivity, and helping to support functional processes across habitats and spatial scales.

Habitat degradation in the form of macroalgal outbreaks is becoming increasingly common on coral reefs. However, the response of herbivores to algal outbreaks has never been evaluated in a spatial context. Therefore, the spatial response of herbivorous reef fishes was assessed with a combination of acoustic and video monitoring, to quantify changes in the movements and abundances, respectively, of coral reef herbivores following a simulated outbreak. An unprecedented accumulation of functionally important herbivorous taxa was found in response to the algae. Herbivore abundances increased by 267%, but only where algae were present. This pattern was driven entirely by the browsing species, Naso unicornis and K. vaigiensis, which were over 10x more abundant at the sites of simulated degradation. Resident individuals at the site of the degradation exhibited no change in their movements. Instead, analysis of the size classes of the responding individuals indicates that the increase in the abundance of functionally important individuals occurred as large non-resident individuals changed their movement patterns to feed on the algae.

Overall, the site attached nature of coral reef fish spatial ecology highlights a spatial limitation to the scale of functional processes, and the vulnerability of reefs to localized impacts. Indeed, the movements of the most mobile known herbivore, K. vaigiensis, while extensive, were restricted to a single island, despite distances of only 250 m between islands. This suggests that functional connectivity provided by mobile adults may be limited, and that processes occurring within-reefs are highly important. Even resident taxa may be unwilling to shift their spatial patterns to consume algal outbreaks, leaving reefs vulnerable to a patchwork of algal establishment. Such fixed spatial patterns in coral reef fish emphasize the importance of large mobile taxa. However, these larger individuals are often the most highly targeted by extractive activities and can easily move beyond the boundaries of marine protected areas (MPAs). Therefore, to protected highly important individuals, management initiatives are required beyond small-scale reserves. Species specific management may be required.

Item ID: 40758
Item Type: Thesis (PhD)
Keywords: acoustic telemetry; coral reef fishes; coral reef; coral reefs; cross-scale interactions; detection efficiency; detection range; ecosystem function; functional connectivity; habitat; herbivorous fishes; herbivory; home range; Kyphosidae; Kyphosus vaigiensis; marine conservation; microalgae; ontogeny; parrotfish; passive monitoring; Scarus; spatial ecology; spatial resilience
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Additional Information:

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

Chapter 2: Welsh, J.Q., Fox, R.J,, Webber, D.M., and Bellwood, D.R. (2012) Performance of remote acoustic receivers within a coral reef habitat: implications for array design. Coral Reefs, 31 (3). pp. 693-702.

Chapter 3: Welsh, J.Q., and Bellwood, D.R. (2012) How far do schools of roving herbivores rove? A case study using Scarus rivulatus. Coral Reefs, 31 (4). pp. 991-1003.

Chapter 4: Welsh, J.Q., Goatley, C.H.R., and Bellwood, D.R. (2013) The ontogeny of home ranges: evidence from coral reef fishes. Proceedings of the Royal Society of London Series B, Biological Sciences, 280 (1773). pp. 1-7.

Other publications:

Welsh, J.Q., and Bellwood, D.R. (2014) Herbivorous fishes, ecosystem function and mobile links on coral reefs. Coral Reefs, 33 (2). pp. 303-311.

Date Deposited: 14 Oct 2015 02:25
FoR Codes: 05 ENVIRONMENTAL SCIENCES > 0501 Ecological Applications > 050102 Ecosystem Function @ 33%
05 ENVIRONMENTAL SCIENCES > 0501 Ecological Applications > 050199 Ecological Applications not elsewhere classified @ 33%
05 ENVIRONMENTAL SCIENCES > 0502 Environmental Science and Management > 050205 Environmental Management @ 34%
SEO Codes: 96 ENVIRONMENT > 9613 Remnant Vegetation and Protected Conservation Areas > 961303 Protected Conservation Areas in Marine Environments @ 34%
96 ENVIRONMENT > 9606 Environmental and Natural Resource Evaluation > 960602 Eco-Verification (excl. Environmental Lifecycle Assessment) @ 33%
96 ENVIRONMENT > 9605 Ecosystem Assessment and Management > 960599 Ecosystem Assessment and Management not elsewhere classified @ 33%
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