Victoria’s subtidal reefs occur either as extensions of intertidal rocky shores or as isolated offshore reefs. They can take the form of banks of stones or cobbles, large underwater boulders, cascading shelves of rock, or as canyons, caves and arches carved out of the seafloor. They are scattered throughout Victorian waters from the low-water mark to a depth of 100 metres.

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; 70% are endemic to the area. The fauna is derived from ancient Gondwanan species and more recent Indo-Pacific species that have invaded Australia as it has drifted slowly northwards.

Typically the shallow reefs (0–20 m) are dominated by kelps or other kinds of large brown seaweeds. Bubble Kelp (Phyllospora sp.) and Leather Kelp (Ecklonia sp.) combine to cover many of the exposed reefs. Sargassum and Cystophora dominate in more sheltered areas. The Southern Giant Kelp (Macrocystis sp.) forms small ‘forests’ up to 10 metres tall at several moderately sheltered localities throughout the centre and west of the state. An understorey of smaller plants and animals occurs beneath these kelp canopies. Abalone, seastars, rock lobsters, sea urchins and feather stars are common. Sea urchins can form large ‘barren’ areas in the far east of the state.

Deep-water reefs (beyond 20 m depth) are too dark to support much plant life. Instead they are covered in numerous plant-like invertebrates such as sponges, corals, bryozoans, sea-whips and ascidians, which in turn shelter a multitude of smaller invertebrates. Subtidal reefs support a diverse fish fauna, ranging from wrasse, Sweep, Old Wives and leatherjackets to Port Jackson Sharks.

The easy access to most of these reefs from shore or small boat makes them extremely popular with recreational divers. Reefs to 18 m depth are accessible to all certified divers and many are accessible to snorkellers. 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.

The main challenge in managing Victoria’s subtidal reefs is to ensure 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. The abundance of abalone, lobster, and wrasse within Victoria have declined over the last 100 years.

Along the open coast, the Bunurong Sanctuary Zone protects the full range of reef species in the area.