University of Melbourne, NORTH MELBOURNE, AUSTRALIA
Density-dependent mortality and growth are important in the early life history stages of many benthic marine invertebrates and are significant in shaping the adult populations. They are particularly interesting in commercially valuable species such as abalone where a mechanistic understanding of these processes is crucial to viable mariculture and fisheries management. The behaviour of post-larval Haliotis rubra was examined to identify possible intraspecific competitive mechanisms. The effects of density and food levels on post-larval growth and survival were then tested and interpreted in light of these observations. Post-larval grazing leaves distinct patches that have been cleared of their algal food source. At high densities, growth and survival is reduced, though this appears to be largely independent of the food availability. Exploitative competition for food may be occuring whereby at high densities individuals often encounter patches that have already been depleted. This explanation fits the evidence for post-larval growth, but density-dependent mortality seems to relate to another, currently unknown factor. This significant finding suggests an important direction for future research.