What is a predator?

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Good question. Not an easy one, either. Most of the fishes on typical coral reefs are carnivores — only about 20% of the species on many reefs are herbivores. Among the carnivorous fishes may be those that feed on zooplankton (e.g., chromis), cleanerfishes (such as gobies in the Caribbean and wrasses in the Pacific) that feed on crustacean parasites, and both nocturnal and diurnal fishes that feed on invertebrates hidden in the substrate or in crevices (such as wrasses, trunkfishes, goatfishes, and butterflyfishes. Piscivores (predators that eat fishes) include specialists such as nocturnal crevice predators (morays), diurnal crevice predators (like the banded sea snake), ambush predators (stonefish, lizardfishes, flounders, and diurnal water column stalkers (great barracuda, needlefishes, trumpetfishes). Other predation may occur on eggs (wrasses are particularly known for this) and larvae of fishes, but the predators of this type do not specialize but will opportunistically seize eggs if possible (unlike the cichlids of tropical fresh waters that have evolved extreme feeding specialties). Even those fishes not normally categorized as predaceous often take advantage of opportunities to feed on smaller fishes, crustaceans, or eggs when they arise. Damselfishes, predominantly herbivorous, are one example. This makes the question of who is a predator on the reef a rather more complicated one than it may at first seem, and this 'diffuse predation' is one factor that confounds studies that attempt to determine the absolute effects of predators on coral reef fish communities.

Like many successful predators, the great barracuda is an opportunist. Basically, great bararcuda tend to feed on whatever they can, wherever they can, probably living quite heavily by the Law of Least Effort whenever possible. We tend to classify animals by their predatory modes and even by the time of day at which they feed, but great barracuda (and many other predatory fishes) naturally defy such rigid categorization.