Tuesday, October 6, 2009

Stars of the Sea

Green Linckia
Copyright 2009 by Barry Fackler

No reef or beach scene is complete without the prerequisite sea star, or starfish as it is more commonly called. Although abundant elsewhere, Hawai'i does not have a large variety of sea stars. Sea stars are simple, but fascinating. Like other echinoderms (which include sea urchins and sea cucumbers), they have a five-part body plan consisting of a central disc and radiating rays. Usually a sea star has five rays but some species can have up to fifty. If a ray is lost, it can be regenerated. They have a "water vascular system" which pumps water through a series of canals to numerous tube feet on the underside. The vascular system regulates water pressure, thus controlling the tube feet which are used for locomotion.  Water enters the vascular system through a filter on the upper side of the sea star. The central disc has a mouth on the bottom and an anus on the dorsal surface.

Spotted Linckia
Copyright 2009 by Barry Fackler

Cushion stars have extremely short rays and resemble puffy pillows on the sea floor. They come in a variety of vivid colors including red, yellow and even purple.

Cushion Stars
Copyright 2009 by Barry Fackler

The knobby sea star, below, was unknown to us until just recently. We found this one in deep water, around 100', in Honaunau Bay.

Knobby Sea Star
Copyright 2009 by Barry Fackler

By far the most common sea star on the Kona coast is the infamous Crown-of-Thorns. It preys upon coral polyps leaving behind white patches of denuded coral. Unlike a typical sea star, it has 12 to 19 rays and is covered with venomous spines which can cause considerable pain in humans.  They can get quite large, spanning up to 18 inches.

Crown-of Thorns
Copyright 2009 by Barry Fackler

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