Role of sea stars

Educational value

• Sea stars belong to the phylum Echinodermata, an exclusively marine group that also includes sea urchins, sea cucumbers, brittle stars and feather stars. Commonly known as starfish, sea stars are invertebrates and should not be confused with true fish, which are vertebrates. Adult sea stars do not swim, but feed on the sea floor.
• Many species of sea stars have five arms but some have more. The upper (dorsal) surface is covered with spines and on the lower (ventral) surface are hundreds of small tube feet, which are used for movement and feeding. The sea star's mouth is at the centre of the ventral surface, and most species are able to push the lower stomach out through the mouth to digest prey larger than they can swallow.
• Sea stars are important predators, feeding on clams, oysters, snails and many other animals that have few other predators. They make up only a small proportion of a marine community, but an event that reduces the sea star population may result in an explosion of their prey populations, causing the ecosystem to be out of balance. For this reason, sea stars are well known as keystone species in marine environments.
• The research described in this clip is aimed at understanding the feeding behaviour of sea stars and their importance as keystone species. The research is being carried out in the coastal waters of New Zealand, particularly Fiordland.

Year level

5; 6; 7; 8; 9

Topics Food chains Predation Marine habitats Sea stars Ecological niches