Rapid assessment of anemone and anemonefish populations at the Keppel Islands [electronic resource]: a report to the Great Barrier Reef Marine Park Authority

Frisch, Ashley J., and Hobbs, Jean-Paul A. (2009) Rapid assessment of anemone and anemonefish populations at the Keppel Islands [electronic resource]: a report to the Great Barrier Reef Marine Park Authority. Report. Great Barrier Reef Marine Park Authority, Australia.

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Abstract

This project was commissioned by the Great Barrier Reef Marine Park Authority to address concerns that the abundance of anemonefishes and their host anemones at the Keppel Islands has declined significantly in recent years. Potential causes of this decline include collection by fishers and (or) bleaching events, the effects of which may be depth-dependent. The objectives of this study were therefore to (1) assess the species richness, abundance and size structure of anemones and anemonefishes on reefs in the Keppel Islands, and (2) compare the size and abundance of anemones and anemonefishes among sites that differ with respect to fishing status (‘open’ or ‘closed’), prior bleaching status (‘high’ or ‘low’) and depth (3, 7 or 15 m).

Underwater visual surveys (timed-swims) were conducted at 46 sites across the Keppel Islands, resulting in a total search area of 139225 m2 (i.e. 1.5% of the known reef area at the Keppel Islands). These surveys found two species of host anemones (Entacmaea quadricolor and Heteractis crispa) and three species of anemonefishes (Amphiprion melanopus, A. akindynos and A. clarkii). Total counts of anemones and anemonefishes (all species combined) were 1100 and 112, respectively. Of these, approximately 40% were found at a single site (Egg Rock) and 100% were found at just 12 sites. It was concluded that both groups of organisms are currently rare at the Keppel Islands, especially when compared with other locations.

Because of the paucity of anemones and anemonefishes at the Keppel Islands, many of the attempted spatial comparisons [see (2), above] were compromised by low statistical power. Despite this problem, the mean size of host anemones was found to be significantly different between open and closed sites, between sites with high and low bleaching status, and among depths. In particular, closed sites generally had larger anemones than did open sites; low-bleached sites generally had larger anemones than did high-bleached sites; and sites that were surveyed at either 3 or 15 m generally had larger anemones than did sites that were surveyed at 7 m. Whilst it is possible that these differences were caused by collecting and (or) bleaching, it was not possible to reach an unequivocal conclusion with respect to causality.

No statistically significant spatial differences were observed in anemone and anemonefish density, or anemonefish size. Similarly, habitat type and percentage coral cover were observed to have little or no influence on the abundance of either organism. Thus, habitat type and percentage coral cover are probably unsuitable surrogates on which to base any future spatial management scheme. Given the rarity of anemones and anemonefishes at the Keppel Islands, the few sites where significant numbers of these organisms were found may warrant close attention by management agencies.

Because of the unusual biological characteristics of anemones and anemonefishes (e.g. mutual dependence, low reproductive rates, limited dispersal capability, susceptibility to bleaching), they are vulnerable to environmental disturbance and over-exploitation. These factors should be considered in any management plan aimed at ensuring the long-term survival of these organisms at the Keppel Islands.

Item ID: 4803
Item Type: Report (Report)
Keywords: anemonefish, anemone, Amphiprion, bleaching, overfishing, Keppel Islands, Great Barrier Reef
ISBN: 978-1-876945-85-5
Date Deposited: 21 Jul 2009 07:16
FoR Codes: 06 BIOLOGICAL SCIENCES > 0602 Ecology > 060205 Marine and Estuarine Ecology (incl Marine Ichthyology) @ 65%
05 ENVIRONMENTAL SCIENCES > 0502 Environmental Science and Management > 050202 Conservation and Biodiversity @ 35%
SEO Codes: 96 ENVIRONMENT > 9605 Ecosystem Assessment and Management > 960507 Ecosystem Assessment and Management of Marine Environments @ 60%
96 ENVIRONMENT > 9603 Climate and Climate Change > 960307 Effects of Climate Change and Variability on Australia (excl. Social Impacts) @ 20%
83 ANIMAL PRODUCTION AND ANIMAL PRIMARY PRODUCTS > 8302 Fisheries - Wild Caught > 830204 Wild Caught Fin Fish (excl. Tuna) @ 20%
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