Maria Island Marine Reserve

• Introduction
• Access
• Activities
• Highlights
• Maps

The Underwater Landscape

The variation in the geological formations found on Maria Island is reflected in the underwater landscape. Large submarine caverns and tunnels extend up to 40m into the limestone cliffs of Fossil Bay. On the protected western shore, dolerite formations break down to cobbled beaches which are interspersed with white sand beaches. In some places sandstone reefs still withstand the weathering forces of nature. These contrast with the giant granite cliffs of the east coast which form reefs that drop steeply to depths of 40m and more. Water temperatures range from 11-20°C. In the cool, clear, winter waters visibility is usually 20-30m. Storms can stir up sediments in Mercury Passage at any time of the year and spring plankton blooms can reduce visibilty to less than 10m.

Flora - the Seaweeds and Sea-grasses

There are a wide variety of seaweeds to be found in the different habitats of the reserve. On the sheltered sandstone areas of the west coast of the island, look out for Neptune's necklace, sea-lettuce and many other seaweeds in the rock-pools and on the flats between high and low tide. Expansive beds of sea-grass cover the soft sandy sea-floor that extends into Mercury Passage.

On the wave-battered north-eastern shore, the bull kelp withstands the force of the pounding seas at the water's edge. Offshore, the fronds of string kelp float along the water surface, attached by long stems to holdfasts on the rocks 6-20m below.

Cray-weed, strap weed and sea-lettuce can be seen close to shore in both exposed and sheltered areas. The kelp Ecklonia is the dominant seaweed in deeper water, except where string kelp shades out the light on the sea-floor, like a rainforest canopy. Among the holdfasts of the string kelp, coralline and other red algae use the last of the available light.

Many seaweeds and invertebrates can be seen on the jetty pylons and in the rock pools around the shore. Crabs, barnacles, sea-stars and anemones are abundant in the shallow waters. Large schools of jack mackerel are often seen from the jetty, as well as colourful wrasse and leatherjackets. In deeper water, medusa-like yellow zoanthids and colourful jewel anemones smother the vertical and overhanging rock faces where seaweeds can't grow.

Sponges, anemones and feather-like hydroids filter the passing currents for morsels of food. Sea-stars and sea-urchins prowl in search of prey or graze the algae growing on the rocky reef. Ornate, slug-like nudibranchs feed on the sponges that are unpalatable to other animals. Their bright colours are a warning to predators that they are toxic. On the sandstone reefs, feather worms tentatively fan the currents for food, withdrawing hastily into their rigid tubes at the first hint of danger.

 

Jackass and banded morwong, barber perch, bastard trumpeter, cod and rosy wrasse are abundant in exposed areas. In more sheltered waters little rock whiting and brown striped leather-jackets are more common. Blue throated and purple wrasse, boarfish, senator fish, toothbrush leather-jackets, hula fish and bullseyes are widespread throughout the reserve. Other fish from the Australian mainland coastal areas follow the warm ocean currents of summer to the northern end of Maria Island. These include herring cale, rock blackfish, mado and other warm water species which are often sighted in waters surrounding Ile du Nord and Fossil Bay.