Marine Animals Living in Kelp Forests

Points covered:

• Where are kelp forests?
• What animals do kelp forests support?

Words to know:

• KELP - the largest seaweeds (brown algae).
• ENCRUSTING ALGAE - algae that covers rocks.
• DETRITIVORES - animals that feed on detritus.
• DETRITUS - disintegrated organic matter or debris.
• BRYOZOANS - a group of animals, some of which are known as lace coral.
• NUDIBRANCH - a group of sea slugs which are usually brightly coloured and have 'gills' on their mantle.
• FILTER-FEEDING ANIMALS - animals which feed by filtering organic matter from the water.

Kelp forests are large underwater colonies of kelp that dominate shallow rocky reefs in temperate waters around Australia. Kelp forests are home to many animals including fishes, snails, lace corals, worms, crustaceans, sea urchins and sponges. Kelp provides a canopy and shelter for these animals.

Some sea urchins, such as Centrostephanus rodgersi and Heliocidaris erythrogramma live on the sea floor under kelp forests. They keep the rocks relatively bare by grazing on the microalgae and spores that settle there.

Another sea urchin, Holopneustes purpurescens, lives in 'nests' which it makes by pulling the fronds of the kelp plants around itself. This urchin has very small spines so living in a kelp nest may help protect it. These nests are also a protective home to a herbivorous snail, Phasianotrochus eximius, which would be an easy target for hungry fish if it crawled around openly on the kelp.

Abalone (Haliotis sp.) live in rocky crevices in kelp forests. Small abalone feed on encrusting algae while large abalone feed on drift algae.

The bryozoan Membranipora membranacea is usually found growing on kelp plants. Its lacy white skeleton often covers large areas of the plant. One family of nudibranch sea slugs called Corambidae have made Membranipora both their home and their food. To hide from predators, the nudibranchs have evolved a white network pattern on their bodies to exactly match the pattern of the bryozoan skeleton. In addition, kelp is also an essential source of nutrients for many animals. For example, limpets ingest broken pieces of kelp from offshore beds and detritivores ingest microscopic pieces of kelp after it has broken down in the surf. Filter-feeding animals, such as sponges, are found on the rock surface beneath the kelp canopy and feed on detritus.

Many commercially important fish also find shelter and food beneath the kelp canopy. Fishes such as bream (Acanthopagurus australis), blackfish (Girella tricuspidata) and snapper (Pagrus auratus), feed on the algae and small crustaceans on the reef beneath the kelp.

See also:
The Sea Slug Forum

Bill Rudman
Malacology
Australian Museum

Penny Berents
Marine Invertebrates
Australian Museum