A critical evaluation of the symbiotic association between tropical tube-dwelling Polychaetes and their Hermatypic coral hosts, with a focus on Spirobranchus giganteus (Pallas, 1766)

Abstract

Coral reefs are high in species diversity with a low effective population size for most species and a high incidence of specific co-evolved relationships. Hermatypic corals are associated with, and attract a variety of, symbionts and commensals which helps to maintain coral reef biodiversity. However, little is known about such associations. Tropical tube-dwelling polychaetes provide an interesting surrogate in the enhancement of current understanding of such associations posing the question: what is the nature of the symbiotic association between tropical tube-dwelling polychaetes and their hermatypic coral hosts? This question is addressed by reviewing the life history and ecology of the conspicuous serpulid Spirobranchus giganteus (Pallas, 1766), an obligate associate of living hermatypic corals showing host species specificity. The distribution, life history and behavioural patterns of this taxon are suggestive of more than the currently perceived commensal association between its coral hosts. Most notably, recent studies have suggested the up regulation of Spirobranchus giganteus symbiotic association from commensalism to mutualism, with Spirobranchus giganteus protecting the coral host from predation, and increased water circulation to adjacent polyps facilitating coral recovery in algal dominated coral colonies. Such recent evidence illustrates the importance of associate organisms on coral reefs.