Berumen, Michael Lee (2006) Influence of resource availability on lifehistory traits in coral-feeding butterflyfishes (Pisces: Chaetodontidae). PhD thesis, James Cook University.

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Abstract

Given the highly stochastic nature of larval supply, coral reef fishes often settle in sub-optimal habitats with limited access to prey or other resources. Variation in the availability and quality of resources among different reef habitats is likely to have significant effects on the physiological condition and subsequent fitness of resident fishes, if not their absolute abundance. The first component of this study compared the abundance, feeding, and condition of two species of coral-feeding butterflyfishes (Chaetodon baronessa and C. lunulatus) across contrasting habitats with markedly different prey availability. Despite differences in prey availability, densities of C. baronessa and C. lunulatus were very similar between locations. However, there was significant spatial variation in their feeding and physiological condition. In front-reef locations, where coral prey was highly abundant, C. baronessa fed preferentially and almost exclusively on the coral Acropora hyacinthus. In contrast, in back-reef locations where coral prey was scarce and A. hyacinthus lacking, C. baronessa was much less selective and consumed a wider range of different coral prey. C. lunulatus was less selective than C. baronessa, but the diet of C. lunulatus also differed significantly between habitats. C. lunulatus consumed mostly A. hyacinthus in front-reef locations, but not in greater proportions than it was available. In back-reef locations, C. lunulatus preferentially consumed A. intermedia and Porites spp.. The physiological condition of both C. baronessa and C. lunulatus was much lower in back-reef locations compared to front-reef locations, which may reflect differences in the quantity and/or quality of prey available in different habitats. This work suggests that small scale (within-reef) differences in prey availability can have significant effects on the physiological condition and subsequent fitness of coral reef fishes. Having established that resource availability may have a significant influence on physiological condition of fishes, I wanted to explore variation in growth and longevity of butterflyfishes associated with variation in resource availability. However, little basic life-history information on chaetodontids exists, so it was first necessary to establish the best model to describe the growth of these fish. von Bertalanffy growth functions were fitted to size-at-age data for four species of chaetodontids from Lizard Island. Special emphasis on juveniles provided detailed information of the early growth period. All four species demonstrated rapid initial growth achieving an average of 92% of maximum theoretical size in the first 2 years of their life. Within the von Bertalanffy growth function, I used various constraints of the theoretical age at length zero (t0) in an analysis of both complete data sets and data sets using only adult fish. An unconstrained value of t0 resulted in the best-fit (maximum r2) curve when juveniles were included. When excluding juveniles, it was necessary to constrain t0 to an approximate settlement size to most closely represent the growth of the species.

Several species of corallivorous butterflyfishes are known to have specific feeding preferences. Foraging theory predicts that organisms should specialise on a given resource only if there are tangible fitness benefits, such as increased growth. To assess the influence of different prey types on juvenile growth for two species of highly selective coral-feeding butterflyfish, C. plebeius and C. trifascialis, individuals were held in tanks for one month on an exclusive diet of only one coral species. The feeding habits of both these species have been well documented in the field, and this study utilised existing data to quantify specific feeding preferences. Selection functions revealed that C. plebeius selectively consumes both Pocillopora damicornis and A. hyacinthus, while C. trifascialis selectively consumes A. hyacinthus. To test the fitness consequences of prey preferences, controlled feeding experiments were conducted in which individual butterflyfish were fed exclusively one of three different branching corals (A. hyacinthus, P. damicornis and Porites cylindrica) to compare growth on highly preferred coral species (e.g., A. hyacinthus and P. damicornis), versus coral prey that was never eaten in the field (P. cylindrica). Chaetodon trifascialis grew .053mm per day when feeding on A. hyacinthus, but actually decreased in total length when feeding on both P. damicornis and P. cylindrica. Chaetodon plebeius, meanwhile, grew at .051mm per day on P. damicornis, versus .038mm per day on A. hyacinthus and decreased in total length on P. cylindrica. This study shows that both C. trifascialis and C. plebeius selectively consume the coral prey that maximises juvenile growth and probably increases overall fitness. Variation in the early growth of these fish due to resource availability may explain patterns or anomalies in their large-scale population demographics.

Finally, to directly assess the influence of resource availability on life history traits, I quantified large-scale variation in some life history traits of chaetodontids across reefs with marked differences in the abundance of certain coral species. Samples of four species of chaetodontids (C. citrinellus, C. lunulatus, C. melannotus, and C. trifascialis) were collected at a northern Great Barrier Reef location (Lizard Island) and at a southern Great Barrier Reef location (One Tree Island). Population characteristics were assessed using a re-parameterised von Bertanlanffy growth function, allowing for better comparisons between populations. Although chaetodontids often had measurable variation between populations in growth rates, longevities, and mean maximum sizes, the variations were not consistent among species. These variations could not be consistently explained by preferred resource availability, temperature/latitude, or conspecific abundance. For, it was expected that growth rates would be higher where preferred resources are more abundant, but this was not found. It is likely that a combination of resources, latitude (seasonal temperature variation), and conspecific abundance (including behavioural interactions) ultimately determine the large-scale differences in the demographics of butterflyfish populations.

Overall, this study shows that resources play an important role in determining life history characteristics of butterflyfishes. In particular, access to specific resources during the juvenile stage may have significant implications for life-long fitness and will likely effect survivorship and reproductive output. Ultimately, variation in the availability of resources is also likely to directly impact local abundance of butterflyfishes, especially for highly specialised species. While this was not apparent in this study, it is likely that several confounding factors such as competition, predation, and local environmental conditions may obscure the importance of resources in determining population demographics in complex environments, such as coral reefs. Future studies must therefore attempt to isolate the effects of different factors using further experimentation and well-designed sampling programs.

Item ID:	1258
Item Type:	Thesis (PhD)
Keywords:	Coral-feeding butterflyfishes, Abundance, Feeding, Condition, Chaetodon baronessa, Chaetodon lunulatus, Habitats with markedly different prey availability, Front-reef locations, Acropora hyacinthus, Back-reef locations, Acropora intermedia, Porites, Physiological condition, Von Bertalanffy growth functions, Feeding preferences, Chaetodon plebeius, Chaetodon trifascialis, Pocillopora damicornis, Controlled feeding experiments, Porites cylindrica, Chaetodon citrinellus, Chaetodon melannotus, Variation in life history traits across reefs
Related URLs:	http://eprints.jcu.edu.au/10246/ http://eprints.jcu.edu.au/4870/ http://eprints.jcu.edu.au/1790/
Additional Information:	Publications arising from this thesis are available from the Related URLs field. The publications are: Pratchett, M.S., Wilson, S.K., Berumen, M.L., and McCormick, M.I. (2004) Sublethal effects of coral bleaching on an obligate coral feeding butterflyfish. Coral Reefs, 23 (3). pp. 352-356. Berumen, Michael L., and Pratchett, Morgan S. (2006) Effects of resource availability on the competitive behaviour of butterflyfishes (Chaetodontidae). Proceedings of the International Coral Reef Symposium. 10th International Coral Reef Symposium , 28 June - 2 July 2004, Okinawa Convention Cente, Okinawa, Japan , pp. 644-650. Berumen, Michael L., and Pratchett, Morgan S. (2006) Recovery without resilience: persistent disturbance and long-term shifts in the structure of fish and coral communities at Tiahura Reef, Moorea. Coral Reefs, 25 (4). pp. 647-653.
Date Deposited:	20 Nov 2006
FoR Codes:	06 BIOLOGICAL SCIENCES > 0602 Ecology > 060205 Marine and Estuarine Ecology (incl Marine Ichthyology) @ 50% 06 BIOLOGICAL SCIENCES > 0603 Evolutionary Biology > 060308 Life Histories @ 50%
SEO Codes:	96 ENVIRONMENT > 9608 Flora, Fauna and Biodiversity > 960808 Marine Flora, Fauna and Biodiversity @ 100%
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