Ecological and genetic evidence of the vulnerability of shallow‐water populations of the stylasterid hydrocoral Errina novaezelandiae in New Zealand's fiords

Abstract

Abstract Some of the key life history characteristics that make modular marine invertebrates such as corals vulnerable to disturbance and stress are susceptibility to damage, slow growth, longevity, and philopatry. This may be particularly so for marginal populations at the limits of their range and, for instance, that are attractive to scuba divers. In this study we examined the population structure and incidence of damage, quantified growth rates and estimated gene flow to assess the effects of divers on the deep‐water emergent populations of the fragile red coral Errina novaezelandiae in the Te Awaatu Marine Reserve in Fiordland, New Zealand. We found that population structure in red corals is skewed, with small colonies the most abundant. Damage was up to eight times higher in dived than in non‐dived populations of red coral, and large colonies were more likely to be damaged. Growth in red corals can be high (up to 7 cm −1), although net growth is much lower (0.7 cm yr−1) due to the effects of partial mortality. On the basis of the slow growth rate, we estimate that large corals (>20 cm diameter) will be in excess of 30 yr old. We also found high genetic subdivision among red coral populations and evidence of inbreeding, indicative of limited larval dispersal among neighbouring populations. Overall, our results indicate the shallow‐water populations of red coral in Fiordland will be susceptible to impacts from scuba diving, and the development of a management strategy to ensure ecologically sustainable tourism and to minimize the effects of divers will be essential for their conservation. Copyright © 2003 John Wiley & Sons, Ltd.