Victoria’s subtidal reefs are either extensions of intertidal rocky reefs, or isolated offshore reefs. Taking the form of banks of stones or cobbles, large underwater boulders, cascading shelves of rock, or canyons, caves and arches carved out of the seafloor, they are scattered throughout Victorian waters from low-water mark to a depth of 100 metres.  Granite reefs occur in Wilsons Promontory Marine National Park, and sandstone reefs in Point Addis Marine National Park

The rocky reefs of southern Australia support a highly endemic marine flora and fauna.  Over 1400 species of algae have been recorded from southern Australia, and 70% are endemic (found nowhere else in the world). The species we find on our reefs evolved from ancient Gondwanan species and more recent Indo-Pacific species that have invaded Australia as it has drifted slowly northwards. Australian Fur Seals (Arctocephalus pusillus doriferus) and Southern Rock Lobsters (Jasus edwardsii) are found on rocky reefs, which also support sponges, sea anemones, lace corals, tube worms and sea squirts, and are a home for abalone, crayfish, sea urchins, wrasse, perch and leatherjackets.

Caption: A Horseshoe Leatherjacket on a subtidal reef 📷 Karen Barwise

Shallow/nearshore reefs (2-15 m depths) are dominated by kelp and other seaweeds, and are among the most productive habitats in the world. Algae cover varies considerably, depending on the depth, exposure to swell and waves, currents, water clarity, nutrient regime and presence of sand. Bull Kelp (Durvillea potatorum) are found on the shallowest, most exposed reefs, while Golden Kelp (Ecklonia radiata) and Crayweed (Phyllospora comosa) are abundant on less exposed reefs. Under their canopy, foliose macroalgae and sessile (non-moving) invertebrates such as sponges, bryozoans, hydoirds and ascidians form an understory. Crustose coralline algae also grows here. Gastropods, crustaceans, echinoderms and fish are all present on shallow subtidal reefs.

Intermediate reefs (15-30 m depths) may look a lot like shallow subtidal reefs, but the assemblage changes as the amount of light and exposure to swell decreases. Kelps begin to be replaced by thallose (plant-like) red algae as the dominant algal cover and there are more sessile invertebrates such as sponges, bryozoans and ascidians. There tend to be fewer gastropods at greater depths, but you’ll still see plenty of molluscs, echinoderms, crustaceans, and reef fish like morwong and snapper.

Deep subtidal reefs (30+ m depths) can be found between Point Lonsdale and Point Nepean at Port Philliip Heads, Point Addis near Anglesea, and Wilson’s Prom. The assemblages found on deep reefs can vary but can include sponges, hydroids, bryozoans and soft corals such as sea whips and gorgonians.

Caption: Lobster and other valuable species found on subtidal reefs are at risk of over-harvesting 📷 Karen Barwise

Most of these reefs are easily accessible from shore or small boat, and this makes them popular with recreational divers. Reefs to 18 m depth are accessible to all certified divers, and many to snorkelers. Caves and deeper reefs are accessible only to those with advanced training and experience.  Dive schools emphasise the importance of conserving the animals and plants and discourage interference with natural communities.

Victoria’s reefs are of great conservation value because of their high species diversity and the large number of endemic species. The main challenge in managing reefs is ensuring that any harvesting of resources is ecologically sustainable. Over-harvesting of reef fish, octopus, lobster, abalone, and urchins have removed these animals from many reefs in other parts of the world, and abalone, lobster, and wrasse have declined in Victoria over the last 100 years.