Indirect effects of protection from exploitation: Patterns from populations of Evechinus chloroticus (Echinoidea) in northeastern New Zealand

Abstract

The influence of predators on populations of the sea urchin Evechinus chloroticus in northeastern New Zealand was investigated by comparing densities, population size structure, and crevice occupancy in marine reserve ('protected') and exploited locality pairs. There was no overall difference in sea urchin density between protected and exploited localities, but population size structures were generally more bimodal in the protected localities, Size-related patterns of crevice occupancy did not vary consistently between protected and exploited locality pairs. The effects of protection were most pronounced in the Cape Rodney - Okakari Point (CROP) Marine Reserve, where relative to the adjacent fished area (1) sea urchin densities were ~3 times lower, (2) size structures were more bimodal, and (3) sea urchins remained crevice-bound to larger sizes (~40 mm test diameter). Sea Urchin transplant experiments showed higher losses of 30 to 40 mm test diameter E. choroticus at a protected locality than a fished locality. Tests of adult sea urchins were heavier at sites in the reserve relative to the fished reference area. We suggest that predatory fishes, which were larger and more numerous in the reserve, were the cause of the differences. A strong bimodal size structure persisted and density declined over 10 yr at one site in CROP Marine Reserve. We suggest that generalising from reserve studies to exploited areas may lead to erroneous conclusions.