Based particularly on the stable isotope data from Aumack (2010), we investigated the relationship between P. fissicauda and P. cartilagineum as well as other chemically defended red macroalgae with similar stable carbon isotope signatures. Paradexamine fissicauda does indeed readily consume P. cartilagineum as well as the chemically defended red alga Picconiella plumosa (Kylin) De Toni, but does not routinely consume several other chemically defended red and brown macroalgae

that this website were included in the assays (Amsler et al. 2013). Although it is probably able to consume epiphytes on its hosts, its stable isotope signature indicates that these are not important parts of its diet (Aumack 2010).

Consequently, P. fissicauda appears to be a “cheater” in this community of mutualists. It is of particular note that P. fissicauda not only tolerates the defenses of P. cartilagineum, whose crude extracts were among the very most deterrent in a study of most macroalgae in the community (Amsler et al. 2005), but it also appears to sequester them for its own defense against fish predation. Paradexamine fissicauda maintained on a diet of P. cartilagineum for 2 months were observed to have halogenated defenses from P. cartilagineum in their tissues, while individuals maintained on Palbociclib price a diet of the undefended alga P. decipiens did not have detectible levels of these metabolites (Amsler et al. 2013). The amphipods that had fed on the chemically

defended algae were significantly more likely to be rejected in feeding assays with the fish N. coriiceps compared to amphipods fed on the non-defended alga (Amsler et al. 2013). This is the first evidence of the sequestration of dietary-derived chemical defenses by an aquatic arthropod for use as a defense against its own predators and, to our knowledge, the first such example in any marine Fossariinae organism outside of opisthobranch molluscs. There are many similarities between macroalgal–amphipod interactions on the WAP and those from lower latitude systems, and with the exception of an amphipod sequestering macroalgal defenses for its own use, no individual component of the interactions along the WAP that has not been reported or at least suggested elsewhere. However, taken as a whole, there are a number of features that make WAP macroalgal–amphipod interactions unique compared to the reports from lower latitudes (as discussed above and summarized by Taylor and Steinberg 2005). Many of these are probably the result, at least in part, of notable differences in the communities as a whole. The total standing macroalgal biomass on the WAP is much higher than in the communities studied by Hay, Duffy, and others in North Carolina and in the tropics and also probably much higher than in the Australasian communities studied by Taylor and Steinberg.