Pisaster ochraceus

Pisaster ochraceus, generally known as the purple sea star, ochre sea star, or ochre starfish, is a common starfish found among the waters of the Pacific Ocean. Identified as a keystone species, Pisaster is considered an important indicator for the health of the intertidal zone.

Description

This sea star has five stout rays that range in length from 10 to 25 centimeters (4 to 10 in). The rays are arranged around an ill-defined central disk. While most individuals are purple, they can be orange, orange-ochre, yellow, reddish, or brown. The aboral surface contains many small spines (ossicles) that are arranged in a netlike or pentagonal pattern on the central disk. The ossicles are no higher than 2 mm. In Pisaster the tube feet have suckers on their distal ends which allow them to attach to the rocky substrate and live in heavily wave-swept areas.

Two species that can be mistaken for Pisaster ochraceus are Pisaster giganteus, which has blue rings around white or purple spines, and Pisaster brevispinus, which is pink with small white spines. These two species have different aboral spines and coloration which allows one to distinguish between the species. Evasterias troscheli may be confused with Pisaster ochraceus at times as well. It can be distinguished by its smaller disk size and longer, tapering rays which are often thickest a short distance out from their base rather than at the base as in Pisaster ochraceus.

Starfish

Starfish or sea stars are star-shaped echinoderms belonging to the class Asteroidea. Common usage frequently finds these names being also applied to ophiuroids, which are correctly referred to as brittle stars or "basket stars". About 1,500 species of starfish occur on the seabed in all the world's oceans, from the tropics to frigid polar waters. They are found from the intertidal zone down to abyssal depths, 6,000 m (20,000 ft) below the surface.

Starfish are marine invertebrates. They typically have a central disc and five arms, though some species have a larger number of arms. The aboral or upper surface may be smooth, granular or spiny, and is covered with overlapping plates. Many species are brightly coloured in various shades of red or orange, while others are blue, grey or brown. Starfish have tube feet operated by a hydraulic system and a mouth at the centre of the oral or lower surface. They are opportunistic feeders and are mostly predators on benthic invertebrates. Several species have specialized feeding behaviours including eversion of their stomachs and suspension feeding. They have complex life cycles and can reproduce both sexually and asexually. Most can regenerate damaged parts or lost arms and they can shed arms as a means of defence. The Asteroidea occupy several significant ecological roles. Starfish, such as the ochre sea star (Pisaster ochraceus) and the reef sea star (Stichaster australis), have become widely known as examples of the keystone species concept in ecology. The tropical crown-of-thorns starfish (Acanthaster planci) is a voracious predator of coral throughout the Indo-Pacific region, and the northern Pacific sea star is considered to be one of the world's 100 worst invasive species.

MV Sea Star

Sea Star was a supertanker that spilled some 115,000 tons of crude oil into the Gulf of Oman on December 19, 1972, after colliding with the Brazilian tanker Horta Barbosa. After the collision both vessels caught fire and were abandoned by their crews. 12 of the crew members died in the fire, which burned for five days. Recovery of Sea Star was attempted before the fires on board were extinguished, but following several explosions the vessel sank into the Persian Gulf on December 24. The first ship on the scene was the USS Charles R Ware DD-865. The crew of the Ware fought the fires on the Horta Barbosa and picked up about 26 crewmen from the Sea Star, most of whom were taken to Bahrain for medical assistance and repariation.

References

Coordinates: 25°18′N 57°34′E / 25.300°N 57.567°E / 25.300; 57.567