Algae chemically defended

Temporal and spatial shifts in the abundance of chemically undefended algae and cyanobacteria may leave grazers with few dietary options except to consume low-quality, chemically defended food items. While some herbivores may be able to either tolerate or inactivate these toxins (Samelle and Wilson 2005), species that lack tolerance may be faced with the dilemma of either remaining on a low-quality patch or migrating to a different patch, thus increasing their risk of predation by visual predators (Krivan and Vrkoc 2000). In systems that experience seasonal... 

An increasing number of specialized interactions between small mobile invertebrates and chemically defended algae or sessile invertebrates have been reported in the marine environment,6167183 and such interactions are also well known between terrestrial plants and insects.200 However, there is some debate as to the ultimate factors driving this ecological specialization. Several authors have suggested that a plant s value as a refuge from predators (i.e., enemy-free space 84201) may be more important than the value of the plant as a food resource,202 but this... 

The relationship described above might lead one to suspect that the reason that the hyperiid amphipod Plyperiella dilatata abducts and carries a chemically defended sea butterfly (Clione antarctica) is that it lacks the ability to synthesize or produce its own chemical defenses. Indeed, Hay et al.39 have also shown that amphipods may associate with chemically defended algae to provide defense against fish predators, rather than produce defensive compounds themselves. 

A number of mesoherbivores are trophic specialists that consume one or a few algal species,9167169-177 often chemically defended ones.9 167 175 176 Other, more generalized feeders may also have strong preferences for, and form close associations with, chemically defended algae.135 166 178-180 However, in comparison with terrestrial environments,181,182 feeding specialization among marine herbivores is rare.9,104,167... 

In contrast to generalist consumers, specialists that recruit to and feed only from certain hosts may be stimulated by unique metabolites produced only by that host. This is true for the crab Caphyra rotundifrons which feeds only on the chemically defended tropical seaweed Chlorodesmis fastigiata. The cytotoxic diterpenoid chlorodesmin (Fig. 3.2a), the major secondary metabolite of Chlorodesmis, deters fishes from consuming this alga, but stimulates feeding by the specialist crab when it is applied to a red alga (Fig. 3.3) that the crab will not normally consume (Hay et al. 1989). There are numerous similar cases where specialist crabs, amphipods, or... 

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