adult copepods. This poor capture ability is most likely due to the lack of effective nematocysts, resulting in the selection of less motile prey (Fabricius et al., 1995b). In fact, Fabricius (unpubl. data) found that an inability to feed on zooplankton was widespread amongst zooxanthellate soft coral genera on the Great Barrier Reef (i.e. Sarcopbyton 3 spp., Sinularia 2 spp., Cladiella sp., Nephthea sp. and Paralemnalia sp.). The role that zooplankton play in the nutrition of photosynthetic octocorals is as yet unclear but new information is showing that they contribute only a small portion to the nutritional budget of many octocorals (Fabricius et al., 1995a and b).
For azooxanthellate genera the capture of prey is vitally important in order to acquire nutrients. Several studies have shown that soft corals, gorgonians and sea pens can feed on a variety of zooplankton such as copepod nauplii and eggs, other invertebrate eggs, and other small items of poor mobility (Coma et al., 1994). However, there have been indications that azooxanthellate soft corals, gorgonians and sea pens may feed on other items. For many years it was assumed that octocorals fed mainly on zooplankton. However, octocorals contain few, small nematocysts and have poor ciliary and flagellar structures. When coupled with the fact that their tentacles and pinnules appear to be better adapted for feeding on small particles and/or the direct uptake of organic materials by offering a large surface area, it appears less likely that prey the size of zooplankton are a major food source (Fabricius et al., 1995b). The question remains then, if not zooplankton, what are their main prey items?
Phytoplankton is an order of magnitude more common on coral reefs than zooplankton. Studies have shown that phytoplankton is somehow depleted over corals reefs, though where it goes no one knows (in Fabricius et al., 1995b). in 1961, Roushcly and Hansen showed that the asymbiotic soft coral Alcyonium digitatum feeds on 14C labeled phytoplankton. In 1969 it was shown that the temperate water sea pen Ptilosarcus gurneyi feeds primarily on phytoplankton (Birkelancl, 1969); its bright orange colour is the result of carotenoids derived from a diet of dinoflagellates (in Best, 1988). Elyakova et al. (1981), in a general survey of carbohydrases in marine invertebrates, found the presence of laminarinase and amylase in three species of the zooxanthellate soft coral genus Alcyonium. These chemicals are enzymes involved in the digestion of plant material. It was not until 1995 that Fabricius et al. (1995a and b) published papers that demonstrated quite clearly that the Red Sea azooxanthellate soft coral
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