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Scavengers you dare not touch!

Last week we introduced you to a group of fascinating creatures living in the sea - starfish. This week we aim to have a closer look at their varieties, eating habits, and their predators, as well as some other important facts about starfish. So, let's move ahead with our latest details about the starfish.

There are many fascinating varieties of starfish. Some may amaze you, because they are totally different from the picture you have in mind.

Starfish eat anything that's too slow to escape. Most starfish are scavengers, feeding on lots of different plants and animals. As the majority of the starfish are carnivorous, they feed on sponges, bryozoans, ascidian and mollusc.

Other starfish are detritus (organically enriched film that covers rocks) feeders, or scavengers. There are some starfish that are specialised feeders, for example, the Crown-of-thorns (starfish variety) that feeds on live coral polyps. Some groups, like the Brisingids, are adapted for suspension feeding (trapping and eating plankton suspended in the water).

A variety of starfish known as Asterias eat mussels. Starfish that eat bivalves can use their tube feet to hang on to the shell, while pulling the two halves of the shell apart. As soon as the gap opens, even a small one, they extend their stomach into the shell and digest the mussel inside!

Starfish eat and digest food outside their bodies. They have a complete digestive system with a mouth at the centre of their underside (the oral side), and an anus on their upper surface (the aboral side). Food can be brought into the stomach through the mouth, or, in many species, the cardiac stomach can be extended out through the mouth to digest food outside the body. Suspension-feeding starfish use their tube feet to pass food to their mouth. A few species, such as the Spiny star of the North Atlantic, eat other starfish!

That's enough about the amazing digestive system of a starfish. Now we'll move to another area that is not as beautiful as their appearance.

What do you think about the spiny skin of the starfish? (Last week we featured a picture of the skin). If you find a starfish, will you want to touch it?, Maybe not. Here's a good reason not to touch a starfish.

Their skin is poisonous! Not really harmful, but if you jab one of your fingers onto one of the spines, the toxin will leave you with a sharp, burning sensation which would gradually fade away after a few hours. Symptoms including nausea, vomiting and swelling are fairly common reactions to the poison, if you get a sufficient dose of it. It is unlikely to kill you, but you will remember the event your whole life. So it's not really safe to step on to the reefs barefooted. You have to make sure that you are safe when you are having fun on a beach trip.

With all these protective measures that starfish have, they still have predators. But, just a few, because they are relatively strong and tough against their enemies. Their spiny skin is not very tasty to other sea creatures.

The giant triton (a fish species) is one of the well-known predators which is most adept at feeding on both large and small Crown-of-thorns starfish. The triton uses its rather primitive foot-like fin to restrain the starfish, and then inserts its proboscis (trunk-like feeding organ) inside the animal to feed on its soft tissues. Often the starfish will escape from the triton by leaving behind the part of its body which is being held (tentacles). Small starfish are normally ingested whole by the triton.

After the starfish has been eaten, the spines and other skeletal material are normally regurgitated (swallowed food brought back to mouth).Another predator is the shrimp. It attacks the less protected tissues underneath by turning the starfish over.

As this animal is only about ten centimetres in length, it has difficulty in doing this to large starfish. Most of the fish predators have horny plate-like scales and very strong, sharp teeth which enable them to attack starfish with apparent immunity.

Sounds scary, isn't it? Poor little creatures. But to remain in this world, all creatures should be controlled in someway. If not there will be a day that the sea is covered with too many starfish. Then you might not feel they are nice, because they will be a menace.

Some starfish varieties...

Cushion starfish are a variety with a thickish body and short legs. They are brown, orange, red or yellow in colour. They have hard shells with raised knobbly spines, and a diameter around ten inches. They can be found on sandy bottoms in the Atlantic Ocean. The Sunflower starfish are the largest members of the starfish family.

These giant members have 24 arms, and are 24 inches or two feet in diameter. Their colour varies from purple to red, pink, brown, orange or yellow. They are really common along the Pacific Ocean. Then, there is a variety called Pacific starfish which are also common.

Their colour too varies from red to orange, yellow and purple. Their diameter is around eight inches. They feed on small sponges and algae. Shark spine starfish are a cold water species. They are mostly found in the Northern waters. They come in orange, red, purple, yellow and white. Their dark red varieties are known as Blood stars.

They scavenge along the rocky sea bottom. Another common species, the Orange starfish are covered with colourful markings and are docile in nature. Their diameter is around four inches. They are common around the Indian Ocean, near Indonesia. They also feed on small sponges and algea. The Reticulate Brittle stars have five long, thin tentacles which are around three inches. They are coloured with white and brown rings. These creatures are common around the coast of Florida. They can be found in sandy areas and under rocks on the reefs.

Basket Stars have an alien look and are common around the Caribbean regions. Their tentacles are 20 inches long! These creatures are used to filter plankton and other organisms from the water. They are nocturnal animals; they feed at night and are wrapped into tight balls during the day. The Feather starfish are an unusual species. They are more like plants, with colours ranging from brown to orange, yellow and black, they also filter feeders like Basket stars and are nocturnal. There are many more varieties of starfish, but most of these sea creatures are threatened today.

Recently, scientists warned that the build-up of carbon dioxide in the air - as a result of the burning of the fossil fuels, could wipe out coral and vast species of sea creatures.

They claim that the situation is not only spurring climate change, but also making the oceans more acidic, endangering the marine life that helps to remove carbon dioxide from the atmosphere. We can't predict the exact scales and time periods, but the grim threat alone is enough reason to protect, treasure and enjoy the world's array of starfish and other marine life, while it's not too late to do so.

Preserve a starfish...

We've got some interesting information for you, if you want to preserve a dead starfish, you may find someday. Then, you can show it to your friends and keep it as a token from your childhood. Here's what you should do to preserve a dead starfish.

Soak the starfish in 70 per cent isopropyl alcohol overnight. After that, let it dry overnight on a paper towel, out in the sun if possible. It's better to weigh down the legs, so that they wont curl up when they dry, and will remain the same as you found it.

- Janani Amarasekara

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