Role of food source and predator avoidance in habitat specialization by an octocoral-associated amphipod

Abstract

Small marine invertebrates often use sessile organisms as microhabitats, which can provide food sources and/or serve as refuges from predators. Because of the availability of external food items such as epibionts and detritus in the marine environment, these invertebrates may not depend on the sessile organisms as sole food sources. In this study, I hypothesized that habitat specialization by a marine invertebrate is determined by factors other than food. Results of Weld surveys oV the coast of the Izu Peninsula, on the eastern coast of Japan, showed that, with few exceptions, the distribution of the amphipod Incisocalliope symbioticus was restricted to the octocoral Melithaea Xabellifera. When presented with several habitat options, I. symbioticus selected M. Xabellifera most frequently, although some individuals chose the octocoral Acabaria japonica. The selection was proximately determined by water-borne cues from M. Xabellifera that appear to be unrelated to the octocoral as a food source, since the amphipod preferred detritus to the octocoral. As a chemical refuge, M. Xabellifera had an allelopathic eVect that deterred Wsh predation on the exposed epifauna. With regard to octocoral habitat in the study area, I. symbioticus may be restricted to M. Xabellifera because this was the only abundant octocoral consistently occurring in shallow water (·10 m), where predation is intensive. The relationship between I. symbioticus and M. Xabellifera was commensal and was ultimately driven by the value of M. Xabellifera as a chemical refuge from predation, rather than its food value. This study supports the idea that protection from predators, rather than food utilization, can promote ecological specialization.

Effects of habitat structure on the epifaunal community in Mussismilia corals: does coral morphology influence the richness and abundance of associated crustacean fauna?

“…Marine sessile organisms are used by small invertebrates as microhabitats (Kumagai 2008); different sessile species may provide different types of habitat complexity and heterogeneity. Several studies have identified such organisms hosting other organisms, e.g., sponges (Ribeiro et al 2003), hydroids (Genzano 2001), gorgonians (Kumagai 2008) and zoanthids (Pérez et al 2005); however, few studies have evaluated the importance of the habitat structure provided by such organisms (Vytopil and Willis 2001).…”

“…Several studies have identified such organisms hosting other organisms, e.g., sponges (Ribeiro et al 2003), hydroids (Genzano 2001), gorgonians (Kumagai 2008) and zoanthids (Pérez et al 2005); however, few studies have evaluated the importance of the habitat structure provided by such organisms (Vytopil and Willis 2001).…”

Extreme habitat specialisation and population structure of two gorgonian-associated pygmy seahorses

“…An association with gorgonians can be beneficial to other organisms due to the gorgonians' temporal stability as hosts, their unpalatability, thus acting as a chemical refuge, and their provision of access to rich food resources via their position in high water flow (Goh et al 1999, Puglisi et al 2000, Kumagai 2008. Two of the 7 described species of pygmy seahorses are obligate associates of gorgonian corals and form small groups of individuals that appear to spend their entire post-pelagic life on a single host (Smith 2011).…”

Dynamics of Stony Coral and Octocoral Juvenile Assemblages Following Disturbance on Patch Reefs of the Florida Reef Tract

“…Octocorals found in the Florida Keys span a range of functional groups. Some grow as fans and plumes, creating canopies that provide habitat and protection for reef organisms [26], while encrusting species protect reef framework from bioeroding grazers such as parrot fish [27].…”