Mutualism between the antipatharian Antipathes fiordensis and the ophiuroid Astrobrachion constrictum in New Zealand fjords

Abstract

A large and accessible population of the antipatharian Antipathes fiordensis occurs in the fjords of southern New Zealand. Many colonies support specimens of the perching asteroschematid ophiuroid, Astrobrachion constrictum, some of which have been observed in situ for over 5 y. Adults A. constrictum are restricted to A. fiordensis, and have never been found on any other organism. In situ experiments have shown that A. constrictum feeds at night, primarily on mucus produced by A. fiordensis polyps, but also on planktonic prey captured by the antipatharian’s nematocysts. Feeding movements of the ophiuroid arms clear the antipatharian colony of suspended material that might smother the polyps. Observations following natural catastrophic events and transplant experiments have shown that survival of A. fiordensis is probably increased if A. constrictum is present.