Hawaiian Reef Fauna — The Invertebrates continued

Hawaiian sea stars are equally diverse and variable in form. A number of important species occur here, some of which have a significant impact on the reefs. First and foremost is the Crown-of-Thorns Sea Star (Acanthaster planci). Due to its penchant for coral polyps, the Crown-of Thorns Sea Star can devastate a coral reef, leaving only bleached skeletons in its wake. This species can grow up to 18 inches across and is covered with sharp, poisonous spines. This bane of the coral reef is preyed upon by the magnificent Triton's Trumpet snail, just about the only creature able to tackle this sea star.

Other interesting Hawaiian forms include the aptly-named Toenail Star (Asterodiscides tuberculosus) and the enormous Magnificent Star (Luidia magnifica) which can grow to a diameter of 2 feet or more! The gorgeous Red Velvet Star (Leiaster glaber) is found in Hawaiian waters as are a number of other beautiful sea stars including the most common species, the Spotted Linckia (Linckia multiflora). Some star fish in Hawaii have extremely reduced arms or no arms at all! One example of this bizarre form of sea star is the Cushion Sea Star (Culcita novaeguineae). This odd-looking species impacts the reef in much the same way that the Crown-of-Thorns Sea Star does - it feeds on coral polyps. Brittle stars are extremely common in Hawaiian waters, and of these, the Toothed Brittle Star (Ophiocoma dentata) is probably the most abundant. The largest species is the Spiny Brittle Star (Ophiocoma erinaceus), with flexible arms up to 5½ inches in length.

Sea urchins are also well-represented in the coral reef systems of the Hawaiian Islands. Their most recognizable feature, their spines, are quite variable and may be either long or short, thin or stubby, or sometimes even club-like in shape. One family of sea urchins is notorious for its exceptionally long spines which are exceedingly sharp and occasionally venomous.

Another family of short-spined urchins known as the "flower urchins" is widely feared for its ability to inflict a dangerous and sometimes fatal sting. About 75 species of sea urchins occur in Hawaiian waters. Their variability and diversity rivals that of the other echinoderms and indeed, sea urchins can be found at all depths and in every type of marine community. Like the sea stars, some sea urchin species can impact the reef itself. Two species of rock-boring urchins are found in Hawaii, the Math Sea Urchin (Echinometra mathaei) and the Oblong Sea Urchin (Echinometra oblonga).

Like the rock-boring clam Penitella penita, these infaunal sea urchins actually burrow into rocks and coral reefs. The sea urchin population of Hawaii also includes some very colorful and distinctive forms, among them the common Ten-Lined Urchin (Eucidaris metularia), the resplendent Blue-Spotted Urchin (Astropyga radiata), the most common long-spined species of urchin in Hawaii, the Banded Urchin (Echinothrix calamaris), the unusual Helmet Urchin (Colobocentrotus atratus) with its flattened, shingle-like spines, and the strikingly beautiful Red Pencil Urchin (Heterocentrotus ammillatus).