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Shallow tropical waters are remarkable places. Many of the creatures, like these Sea Stars, are extremely rich with color.
Photo: Genevieve Johnson

July 13, 2001
Sea Stars
  Real Audio
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Log Transcript

Today while visiting Krangket Island, we happened upon a narrow estuary that meandered out through the mangrove forests and into the sea. The locals told us that they never swim here because of the saltwater crocodiles, although none of them had actually seen one. As we walked beneath the shadows of the forest, we reached the head of the stream. We couldn't believe what we saw, the late afternoon sunlight was filtering through the leaves, illuminating the most spectacular ensemble of sea stars only inches beneath the surface. We moved closer, to obtain a better view of these beautiful electric blue creatures. As we donned our snorkelling masks, we looked at each other a little nervously, remembering why the locals never swam there!

The relative abundance of these creatures in the shallow waters of the tropics, made them no less spectacular, in fact it was their sheer numbers that made them so impressive.

Sea stars generally have five arms (although some species have many more), with light sensitive eyes at each tip. These arms radiate out from a central disk containing the mouth and stomach and are entirely flexible allowing the animal to bend its body to fit the contours of the reef and to arch their arms around their prey. Most sea stars are veracious predators, moving through a bed of shellfish, such as clams or mussels, pulling open their shells and devouring them. Once the sea star has forced open the shell, it thrusts its stomach through its mouth, its stomach membrane in direct contact with the tissue of its victim. Secreting digestive juices, the sea star effectively digests its mollusc meal inside its own shell.

As a result, many species of sea star are seen as a threat to the multi-million dollar shellfish industry. In fact, fishers used to attempt to control their numbers by cutting them up. However, this only increased their population due to their remarkable powers of regeneration. Sea stars can replace missing arms and if cut in two, will most likely create an entire animal from each piece.

The fossil records of echinoderms, which includes the sea, brittle, feather and basket stars, sea urchins, sand dollars and sea cucumbers, dates back over 500 million years. The current number of living species is close to six thousand. However, these sedentary animals are facing an increasing threat from destructive and wasteful fishing practices such as trawling, where their percentage losses as bycatch is very high, others are over harvested and sold on Asian markets where they are highly prized.

This is Genevieve Johnson speaking to you from Madang in Papua New Guinea.

Log by Genevieve Johnson

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