Inhabiting the Intertidal

The intertidal zone, also known as the littoral zone, is that area between high tide and low tide. It is home to many species of animals and plant-like organisms (algae). Many of the animals are invertebrates (animals without backbones). It is a harsh environment for organisms to live in. Organisms in this zone thus have a variety of adaptations to allow them to survive.

Barnacles attach themselves to hard substrates with a glue-like substance on their head. They filter feed plankton from the water with feathery appendages.

Periwinkles can survive for long periods out of the water due to their horny, tight-fitting trap door (operculum) which retains moisture within their shell.

Chitons have eight separate shell plates that act like armour. They lack eyes and use a modified mouth part called a radula to scrape algae off rocks.

Limpets have a cone-shaped shell and muscular foot. They graze on algae at high tide and generally return to the exact place that they left.

Sea lettuce (Ulva sp.), a type of green algae, is named for its appearance and the fact that it is edible.

Caulerpa racemosa grows to depths of 4 metres and in areas of good wave action. It is easily identified by its bubble-like branches (called ramuli).

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Gastropods or marine snails form the largest class of molluscs. Most species have a spirally coiled shell, and are grazers, although some species are scavengers while some are predators, including the infamous cone shell.

Turban snails can pull their body inside their shell and completely close the aperture with a shelly trap door called an operculum (inset picture).

Abalone have a hard, rough, ear-shaped shell that is smooth and shiny on the inside to protect the animals soft body from damage. Abalone do not have a blood-clotting agent and therefore may bleed to death if damaged or injured when removed from the reef.

Anemones are related to corals and also sea jellies. They have a central mouth surrounded by one or more rows of tentacles.

Mussels are a bivalve mollusc, meaning they have a shell with two halves (valves). They attach to the substrate by tough, yet flexible threads (byssal threads).

Red algae are the most numerous of the three seaweed groups. They can tolerate lower light levels than other algae, and are thus most abundant in deeper water. The texture of red algae varies from fine and delicate to hard and crusty.

Funnel weed is a brown algae with fan shaped fronds that give it its name. It is the only brown alga in Australia that accumulates a thin chalky coating on one surface, known as calcification.

Sargassum can generally be identified by the small bubble-like floats. Sargassum is a Spanish term for ‘floating seaweed’

Kelp can form large beds that become home to numerous invertebrates and is an important food source for sea urchins, buffalo bream and other animals.

Kelp and other brown algae contain a gelatinous substance called algin that is widely used as a thickening or stabilising agent in many of our foods.

Sponges are often mistaken for plants but are in fact very simple animals. Their bodies are full of tiny holes which help them to eat and breathe by filtering seawater.

Sea urchins are grazers, feeding on encrusting organisms such as sponges and algae. Their mouth is in the centre on the underside and contains a set of jaws and horny teeth, named Aristotle’s lantern.

© Department of Fisheries, Michael Burgess

© Department of Fisheries, Michael Burgess

Sea stars are a type of echinoderm, consisting of five or more arms radiating out from a central disc. The mouth and tube feet are located on the underside of the body. Many echinoderms are able to regrow lost or damaged parts of their bodies.

Sea cucumbers are echinoderms, related to sea stars and sea urchins. They move using their tube feet, or by squeezing up and then stretching out their bodies.

Sea hares are a type of mollusc, closely related to nudibranchs (or sea slugs). They graze on algae and have a very short life span of only a year, dying after laying their long, tangled strings of eggs.

Crabs are a type of crustacean. They have a hard exoskeleton that serves as a suit of armour. In order to grow, crabs periodically shed their exoskeleton, a process known as moulting.

Small fish, such as blowies – a scavenger species, may also inhabit the lower intertidal zone at high tide.