Fishy 'fingerprints' to identify coral killers
'It is not currently known if, or to what extent, many small fishes rely on corals for food'
ARC Centre of Excellence Coral Reef Studies © Click Here to view large photo
Scientists are poised to solve a major underwater crime mystery and pinpoint the guilty suspects in the case of 'who killed the coral reef'.
2007 Churchill Fellow, Dr Morgan Pratchett from the ARC Centre of Excellence for Coral Reef Studies, is applying a new technique to solve the issue of the role of coral reef fishes in finishing off coral reefs which have been weakened by bleaching and other impacts.
For some time researchers have suspected that starving fish, deprived of food by coral bleaching, may play an unfortunate but critical role in killing the few surviving corals.
Dr Pratchett recently returned from the UK armed with stable isotope techniques that may help identify which fishes feed on, and potentially wipe out, reef corals. The technology has previously been used to study the food chain in large marine food fisheries, but never before to analyse fish behavior and impacts on coral reefs.
Dr Pratchett was awarded the inaugural Quicksilver Connections Churchill Fellowship and has spent the last two months at the University of Newcastle, UK, exploring the use of stable isotopes to study feeding interactions between corals and fishes. 
Stable isotopes are chemical markers such as Carbon 13 or Nitrogen 15 which have a unique ratio in different types of marine foods. As fish feed on particular corals or algae, the unique signature of the each food type is retained in the fishes' bodies, providing evidence of otherwise unseen feeding activities.
'The feeding activities of most coral reef fishes are very difficult to observe', Dr Pratchett said. 'If we can apply them to corals and other reef food species, these techniques may help identify the full range of fishes that feed on corals.'
Identifying which fishes rely on coral for food is important to establish those species that might be most susceptible to climate-induced coral depletion. It is also probable that fishes that feed on corals are guilty of contributing to the death of corals, which already face stress from changing environmental conditions and human activities. 
While based at the University of Newcastle, Dr Pratchett worked closely with Professor Nicholas Polunin and Dr Chris Sweeting, who are leading international experts in stable isotope ecology.
Dr Pratchett hopes to answer questions such as whether certain coral reef fish can survive on food gleaned from the open sea at times when bleaching leads to the complete death of their reef - or whether they simply die out when their favorite food disappears.
'I'll be collecting samples of both corals and reef fish to get an idea of what is dining on what - and how feeding patterns change when the corals on a reef come under stress or start to die,' he explains.
The information will also help in identifying which reefs and which fish species are most at risk during episodes of coral bleaching - information which may help in designing management strategies designed to reduce the impact of climate change and other assaults on the reef resulting from human activity.
'It will enable us to say with greater certainty where the extinction risk is highest, for both fish and corals, and thus to understand the vulnerability of various reef communities to major impacts,' he says. 
www.coralcoe.org.au/
by ARC Centre of Excellence for Coral Reef Studies 
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Devonport, TAS
