Starfish
Facts

Facts about starfish

Environment

The starfish is common all along the  coasts. It is found on rocky and stony bottoms as well as on soft bottoms, notably on mussel and oyster banks. Mobility is attained by a unique hydro-vascular system of tube-feet that enable the starfish to move at speeds of between 3-5 miles an hour.

What it eats

The starfish is commonly known for its ability to open large mussels. To open a mussel the starfish places itself over the mussel, rather like an umbrella and places a great number of tube-feet on the two shell halves. An adult starfish using this technique can exert a large traction force. It was thought that the starfish secreted a substance that paralyzed the mussel, but it appears that traction is enough to open the mussel. It is enough that the shell is opened 1 mm for the starfish to get its stomach into the mussel shell and come into contact with the mussels softer parts, and accordingly break it down.

Because the starfish averts its stomach and encompasses its prey when it eats, it is able to digest rather large prey. It is able to prey on organisms that have a diameter equal to the length of its arm.  The starfish has the ability to smell its prey over long distances. A young starfish (radius 3.5 mm) that had recently fallen to the bottom, ate during its first 6 days, 56 small mussels (1.5-3.5 mm long) per day, which equals about 25-30 % of its own weight. As the starfish gets older, its consumption decreases, adults eat about 3-4 % of their body weight daily. It is the young that are most gluttonous and appear in large numbers. During the winter, consumption decreases markedly, and ceases totally at 2-3 °C.

The Young Starfish

The starfish usually becomes sexually mature at about 12-14 months, but it is commonly size that dictates maturity. Mating mainly takes place between May and June (water temp. about 8 °C) when the whole population are at the same depth and like an epidemic, release their eggs and sperms into the water. Individuals stand up on their arms, even climbing up on rocks and algae to be as high as possible. A large female can yield as many as 2.5 million eggs during a 2 hour period. During June and July large numbers of starfish larvae can be found in the water. When the larvae reach a length of about 2 mm, a young starfish develops at the end of the larvae.

When starfish fall to the bottom they are about 1 mm long. In the beginning they mainly consume small barnacles and mussels that have also just landed on the bottom. Under favorable circumstances they reach a radius of 5 mm during the first month, and reach 3-4 cm during the first year. Growth is dependant on food and temperature, which makes it difficult to determine their age by size.

At the tip of each arm is a pigmented marking that functions as a primitive eye, and thus able to distinguish between light and dark.

Within the fishing industry, the starfish is considered to be vermin, because it competes with plaice and flounder for food, and it also attacks fish caught in nets.  Starfish are one of the main food groups for gulls.