INTERRELATIONS BETWEEN SEA-URCHINS AND SPINY LOBSTERS IN NORTHEASTERN NEW-ZEALAND

The interrelation between the sea urchin Evechinus chloroticus and the spiny lobster Jasus edwardsii was investigated in the shallow subtidal zone of rocky reefs in northern New Zealand. Both species were found in large numbers in the Shallow Broken Rock habitat. During the day spiny lobsters and sea urchins were spatially segregated on a small scale. Movement patterns of spiny lobsters indicate that sea urchins are accessible to nocturnally foraging lobsters. Laboratory experiments demonstrated that large lobsters ate all sizes of sea urchins. All sizes of lobster ate small sea urchins (< 50 mm TD) in preference to larger sea urchins. The provision of herbivorous gastropods (also eaten by lobsters) and shelter for sea urchins did not mean that more larger sea urchins were eaten. The removal of large brown algae or sea urchins and gastropods from areas of reef did not cause significant reductions in the daytime density of J. edwardsii. We argue that differing micro-habitat requirements of the 2 species mean that large abundances of E. chloroticus are unlikely to depress J. edwardsii densities. The necessary experiments to test this hypothesis are discussed.