What would eat a spiny urchin?!

From a post on Climate Shift by Dr. John Bruno who has done research in Akumal Bay:

The black spiny Caribbean urchin Diadema antillarum is a formitable looking creature. It is basically a pin cushion with black hypodermic needles for spines. It seems reasonable to conclude that its spines are an adaptation to deter predators, and moreover, that they would be fairly effective. In fact, many Caribbean reef scientists assume few predators can eat Diadema. For example, Harbone et al (2009) recently stated;

“Urchins are particularly susceptible to unregulated ‘plagues’ because only a few specialist predators can overcome their defensive spines“

But surprising as it might seem, a wide range of fishes and invertebrates consume Diadema and could control it’s behavior and population densities. (I love these natural history surprises that defy logic and human biases.)

Predators of Diadema include: snapper, jacks, porcupinefishes, trunkfishes, grunts including black margate, porgies, triggerfishes, pufferfish, large wrasses, parrotfish, octopuses, lobsters, large gastropods and even small crabs (which eat juvenile Diadema).

The classic paper on predators of Diadema on Caribbean reefs is Randall et al. (1964). This paper, published before I was born, is a masterpiece of natural history and an invaluable documentation of the ecology of Diadema before it was wiped out by a disease in the early 1980s. Randall et al. reported;

"Predators of D. antillarum include 15 fishes of the families Balistidae, Carangidae, Diodontidae, Labridae, ostraciidae, Sparidae, and Tetraodontidae, two gastropod of the genus Cassis, and the spiny lobster (Panulirus argus)."