Association of the mysid Idiomysis inermis with the sea anemone Stichodactyla haddoni in Moreton Bay, Australia

Abstract

Some mysids (Crustacea: Mysida) live symbiotically with a variety of marine invertebrates, including cnidarians. One of these, the carpet anemone Stichodactyla haddoni (Cnidaria: Actiniaria), is known to host the mysid Idiomysis inermis, but quantitative survey data on this association are lacking. Therefore, we surveyed the spatial distribution pattern of I. inermis in relation to the sea anemone S. haddoni in Moreton Bay, Queensland, Australia. Of the 20 anemones examined, nine (45 %) were colonized by altogether 114 individuals of mysids, which were found swarming above the host’s oral disc and tentacles. The number of mysids ranged 6–24 per anemone, with a mean of 12.7 individuals per host. The same actiniarians colonized by I. inermis were also host to the anemone shrimp Ancylomenes holthuisi. Our findings suggest that I. inermis was not limited by space, as several hosts were not colonized. No positive correlation was observed between anemone size and number of mysids, suggesting that host size did not seem to play a major role in determining the density of this mysid species. The association between I. inermis and S. haddoni is shown to be a facultative commensalism.