Deep Reefs

Article | Updated 2 months ago

Deep reefs are largely made up of rock structures and may be deep outcrops or areas of flat pavement rock. Pavement areas mainly occur in locations where currents or tides are very strong. The waters around deep reefs may be turbid, causing sand and other matter to be suspended in the water.

As the name suggests, these habitats more commonly occur in relatively deep water. At these depths, light penetration is reduced and is insufficient to allow the extensive growth of corals and algae seen on shallower coral reefs.

Plants and Animals of Deep Reef Habitats

Deep reef habitats that occur on flat pavement areas have been referred to as "sponge gardens". Although few plants grow at such depths due to the reduced penetration of light, many of the animals that are abundant in these areas are plant-like in their appearance. These animals occur in a range of spectacular shapes, colours and sizes that rival the flowering plants that occur on land in their visual appeal.

Strong ocean currents and tidal movements mean plants and animals that are found on or around deep reefs must be either firmly attached to the reef, cling to other attached animals or be strong swimmers. Corals that occur on deep reefs generally form flat encrusting and heavy solid structures that can withstand strong water movement. Many of the other animals found in these habitats are flexible, e.g. fan-shaped or branching sponges, allowing them to bend with the currents. These animals tend to be the most common inhabitants of deep reef habitats.

Ocean currents may carry a rich supply of food to deep reefs, making them an ideal habitat for animals such as crustaceans (e.g. crabs, prawns), molluscs (e.g snails), echinoderms (e.g. sea stars, sea urchins) and fishes.

Methods for Sampling Deep Reef Habitats

SCUBA diving is used to sample the organisms that inhabit deep reefs. For safety reasons, these dives are carried out when tidal movement is low, a period known as slack tide.

During marine surveys of the Dampier Archipelago, divers counted the individuals of each species as they swam along transects - marked by measuring tapes laid out in a straight line over the reefs. This allowed researchers to count the number of organisms in a set area. Specimens observed along this transect were either identified while underwater or collected for later identification.

This method is not as useful for faster moving animals, such as fishes. For these animals, visual identification and estimates of their abundance were performed whilst underwater.