DNA evidence of whale sharks (Rhincodon typus) feeding on red crab (Gecarcoidea natalis) larvae at Christmas Island, Australia
M. G. Meekan A E , S. N. Jarman B , C. McLean C and M. B. Schultz DA Australian Institute of Marine Science, the University of Western Australia (MO96) Botany Building, 35 Stirling Highway, Crawley, WA 6009, Australia.
B Australian Antarctic Division, Channel Highway, Kingston, Tas. 7050, Australia.
C Australian Institute of Marine Science, PMB 3, Townsville MC, Qld 4810, Australia.
D Charles Darwin University, PO Box 41775, Casuarina, NT 0811, Australia.
E Corresponding author. Email: m.meekan@aims.gov.au
Marine and Freshwater Research 60(6) 607-609 https://doi.org/10.1071/MF08254
Submitted: 3 September 2008 Accepted: 2 February 2009 Published: 19 June 2009
Abstract
Whale sharks (Rhincodon typus) are thought to aggregate in nearshore waters around Christmas Island (105°37′E, 10o29′S) to consume the marine larvae of the endemic red land crab (Gecarcoidea natalis). However, there have been no direct observations of sharks feeding on crab larvae. Whale shark faeces were analysed using genetic testing to confirm the presence of crab larvae in their diet. Primers were designed for amplifying two Gecarcoidea natalis mitochondrial small-subunit (mtSSU) rDNA regions. Gel electrophoresis of polymerase chain reaction (PCR) products amplified from whale shark faecal DNA produced bands of the expected size for G. natalis templates. Specificity of both primer sets for G. natalis mtSSU rDNA was expected to be high from comparisons with mtSSU rDNA regions from closely related crabs and we confirmed their specificity empirically. The amplification of fragments from faecal DNA of the same size as those produced from G. natalis DNA indicates that the whale shark had been feeding on G. natalis and that enough of the crab DNA survived digestion to be detected by these PCRs. Our study provides further evidence that aggregations of whale sharks in coastal waters occur in response to ephemeral but predictable increases in planktonic prey.
Additional keywords: diet, faeces.
Acknowledgements
We thank the staff at Christmas Island National Park and Christmas Island Divers for support of this research project. Emma Ross, Peter Talbot and Claire Davies provided assistance in the field. We also thank two anonymous reviewers for useful comments on draft versions of the manuscript. BigWave Ltd, Sea World Research and Rescue Foundation, Australian Institute of Marine Science, the Australian Antarctic Division and the Australian Government Department of Environment, Water, Heritage and the Arts (DEWHA) provided funding for this project. All research was conducted under research permits provided by DEWHA and in accordance with guidelines approved by the animal ethics committee of Charles Darwin University.
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