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CSIRO Marine and Atmospheric Research
Past Seminars

Seminar Abstract

Benthic community structure and variation in indirect effects of fishing in Australasian kelp forests

Studies from north-eastern New Zealand provide some of the best evidence, so far available, that kelp forest habitat can be converted to coralline algal dominated barrens as an indirect effect of fishing for rock lobsters and fish. A reversion from urchin barrens to kelp forests has been shown in areas of north-east NZ where lobster densities were 1.6–4.0 times higher than in fished areas. While such barrens are present in many parts of Australasia and around the world, their distribution is far from uniform. For example, at Rottnest Island in Western Australia, habitats are relatively uniform across fished and unfished areas, despite a 6.5-fold difference in lobster density. Such inconsistencies present real difficulties for predicting marine ecosystem responses to fishing and consequently for the implementation of ecosystem based fisheries management. Differences between the two systems are likely to be the result of different ecosystem dynamics rather than differences in levels of fishing pressure.

A general theory attempting to explain this variation in temperate reef structure is proposed in which the strength of top-down (fishing) effects are modified by the availability of nutrients and recruits, and by the strength of interactions between key elements of kelp forest ecosystems, such as predators and urchins, or urchins and kelp. Broadly speaking the distribution of urchin barrens in Australia and New Zealand is consistent with this theory. Obtaining the data to test the theory presents significant logistical challenges but is probably attainable through a collaborative approach to obtaining comparable data sets at appropriate scales, and utilising nascent MPA networks.

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CSIRO = Marine Laboratories Auditorium, Castray Esplanade, Hobart

For further information, or to schedule a seminar, contact:
Peter Oke, (Oceanographic seminars) CSIRO Marine Research (03) 6232 5387
Piers Dunstan, (Biological seminars) CSIRO Marine Research (03) 6232 5382
Katrina Nitschke, Antarctic Climate and Ecosystems CRC (03) 6226 2265 & IASOS, University of Tasmania (03) 6226 2509