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Lizard Island - a Hub for Research on Larval FishesBy Jeff Leis, Australian Museum
Almost all coral reef fishes reproduce by spawning eggs and sperm into the water where the eggs are fertilised. Tiny larvae develop and these live in open water for weeks or months, well away from the reefs occupied by their parents. Late-stage larvae settle onto reefs and metamorphose into adult fish. Because fish larvae are small and ocean currents are powerful and ubiquitous, it has been assumed that larvae behave as passive particles in the sea. Other ideas about reef fish communities flow on from this assumption and these have important consequences for practical things like fisheries management. For example, if fish larvae are passive particles in a current that flows the same way during the larval lifetime, then it is unlikely that a larva will settle on the same reef inhabited by its parents. Reef fish larvae are difficult to study in the field because of their small size, so it is only in the last few decades that research has challenged various assumptions about them. Lizard Island Research Station has played a major role in the advance of knowledge on larvae of coral-reef fishes: no other location on earth has had so much larval reef-fish work based near-by. The extensive collections of reef fish larvae taken in the vicinity of Lizard Island have provided the raw material for much taxonomic work by Australian and overseas researchers. To appreciate the contribution of the Research Station, one need only see the large number of illustrations in standard works on tropical fish larvae that are based on specimens collected from the Lizard Island area. Work on the distributional ecology of fish larvae in the Lizard Island area by Jeff Leis of the Australian Museum featured prominently during the 1980s. This work was based on plankton net collections and both vertical and horizontal distributions were studied. This helped establish that different species had different distributions, and showed where the larvae actually spent their pelagic period. These findings helped lay the foundation for questioning the classical notion that larvae were passively distributed by currents - if the larvae originated from the same reef and were passively drifting, how could they have different distributions? This was combined with dedicated studies of currents in the Lizard Island area to help work out the interaction between currents, larval input and distributions. Evidence emerged that some species probably achieved life-cycle closure in Lizard Island Lagoon or in the waters immediately adjacent to the island, thus leading to an initial questioning of the "open population paradigm". Because of the types of sampling gear in use, this early phase of the work concentrated on smaller, younger larvae. It was during this period that the first rigorous comparison of various methods of capturing reef fish larvae was conducted: methods included the newly-trendy light trap, plankton purse seines, and more conventional sampling gear. This study included scientists from three of the major institutions involved in research on the reef - the Australian Institute of Marine Science (AIMS), the Australian Museum (AM), and James Cook University (JCU). The initial work was done from the Station's small (less than 7 m) boats, but in 1983 the Station's purpose-built research vessel RV Sunbird became available. Sunbird greatly expanded the types of work that could be done, and for the next eight years it was used extensively for larval fish work, including forays into the Coral Sea to study larval fish ecology at isolated atoll-like reefs. The larval purse-seine featured prominently in studies by Howard Choat and Mark McCormick of JCU, and this helped lead the way toward studies on the larger, older pelagic stages of reef-fishes. In the late 1980s, the Lizard Island Research Station served as the base for the first sustained use of the larval light trap designed by Peter Doherty of AIMS, when Maria Milicich of JCU did her PhD work there. This provided unique, long-term data sets that have had a major influence on views of the way recruitment works. Starting in the 1990s, the light trap began a new life as a means of capturing late-stage larvae for both laboratory and field studies of larval biology. Several workers, including Geoff Jones and co-workers from JCU used light-trap larvae to 'semi-naturally' increase recruitment in controlled experiments. Others, including Mark McCormick and Brigid Kerrigan of JCU used the larvae for physiological and nutritional studies in the laboratory and in work on metamorphosis. Behavioural studies on reef-fish larvae began at Lizard Island in the 1980s, when Hugh Sweatman of JCU used natural recruitment to look at settlement. In the 1990s, Ilona Stobutzki of JCU used larvae caught in light traps to establish the amazing swimming endurance of late-stage larvae in the Station's aquarium. In the field, Ilona was also able to demonstrate that larvae in open water know where the reef is in relation to themselves. Jeff Leis and co-workers from the AM used light-trap larvae to study larval behaviour in situ, both in open "blue water" near Lizard Island, and near to the Lizard Island reefs. All this behavioural work has shown that reef-fish larvae:
In short, reef-fish larvae are anything but the passive "biological drift cards" of tradition, and this has major implications for the "open population paradigm" and importantly, for how reefs and marine protected areas are managed. Much larval fish work is underway today at the Lizard Island Research Station and we can expect that contributions from Lizard Island researchers will continue to open up new areas and push back the frontiers in larval fish biology. Relevant links
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