Short Spined Crown Of Thorns Starfish, Acanthaster brevispinus

The short-spined crown-of-thorns starfish (Acanthaster brevispinus) is a species of starfish that is classified within the Acanthasteridae family. This species has a large range that includes the Great Barrier Reef, the Philippines, and the Seychelles in the Indian Ocean. Because these areas are so far away from one another, the full range of this starfish cannot be known, but it can be said that it resides in a tropical or subtropical environment. It was first discovered by W.K. Fisher, who classified it as the subspecies A. brevispinus brevispinus, although it was in fact new and distinct species.

The short-spined crown-of-thorns starfish holds many similar features to other starfish, but it is also distinct from other species in many ways. The disk, or body, of this species is large compared to its many arms, and holds a larger number of spines than other species. The stomach of this species comprises a larger portion of its underbelly and its two rows of tube feet make it more flexible than other starfish. It shares its range with A. planci and can be distinguished from it by its thick spines, purple-brown color, and short spines along its arms, among many other features.

The diet of the short-spined crown-of-thorns starfish is not yet known, but scientists have discovered that scallops may comprise are large portion of its meals. In laboratory studies, where factors were controlled, members of this species were found to be able to occasionally catch and consume active scallops. Despite the small amount of scallops caught, when the starfish were fed commercial scallop meat, they lifted their bodies in the same manner as when hunting, suggesting that scallops may comprise a large portion of their diet. Laboratory studies using A. planci did not show this behavior.

The similarities of the short-spined crown-of-thorns starfish and A. planci sparked a hybridization study in 1973, conducted by Lucas and Jones. In December of that same year, A. brevispinus individuals were gathered along with A. planci individuals, which were ready to breed. Eggs and sperm were taken from the A. planci individuals while gonad tissues were taken from A. brevispinus individuals. After the eggs were artificially inseminated, four groups of eggs were raised. This created two groups of hybrids known as A. brevispinus hybrids, which were made from that species’ eggs, sperm, and the sperm of A. planci, and A. planci hybrids, which were made with the eggs and sperm of that species and the sperm of A. brevispinus.

It was found that the sperm and eggs between these two species held a high rate of fertilizations, suggesting that the two species could breed in the wild without complications. All of the eggs developed in the way that A. plenci develops, although many larvae did not develop after six weeks. At this period, there were five thirty A. planci hybrids, six A. brevispinus hybrids, sixty A. planci individuals and no A. brevispinus individuals. During the first few months of development, the young hybrid starfish were not distinguishable from young A. planci starfish, but after the hybrids reached 7.8 inches in diameter, differences began to emerge. Both sets of hybrids displayed similar and different characteristics from both parent species, including reaching sexual maturity at two years of age. Both sets of hybrids raised their bodies slightly as they fed on scallops, although not as much as A. brevispinus individuals.

Image Caption: Specimen collected by trawling on soft substrate inshore of the Great Barrier Reef. Credit: JSLUCAS75/Wikipedia (CC BY-SA 3.0)