Care of marine invertebrates
The Australian Museum displays marine invertebrates that live in the cool temperate water of Sydney Harbour.
The Marine Aquarium
Marine Invertebrates require special environmental conditions (temperature, water quality, pH etc), however the Reaper Cuttlefish, Sepia mestus, are the most sensitive species currently being held in our marine aquarium. The Australian Museum has kept and displayed two species of Cuttlefish (or 'Cuttles' for short); the Mourning Cuttlefish, S. plangon and the Reaper Cuttlefish S. mestus. Both of these species are amazing animals, however it was soon discovered that the Reaper Cuttles are much better at camoflauging and blending in with the rocks compared to the Mourning Cuttles. This attribute makes this species harder to locate in the display, however it also reduces the stress the animals are subjected to, which increases the lifespan of the animals. The Reaper Cuttles may be harder to spot, however with a bit of dedication, a visitor won't be disappointed once they have been found. The aquarium is also home to a range of other marine invertebrates such as crabs, sea stars, sea urchins and sea snails.
Water in the aquarium is filtered and circulated to maintain a high quality through a system of filtration media, tubes and pumps. The seawater is kept well aerated and is chilled to a low temperature of between 16-20oC through the use of a chiller. The pH is kept at neutral and regular water tests are carried out to monitor nitrates, nitrites and ammonia. The filtration system currently employed by the Australian Museum (see filtration diagram) is a semi-closed system requiring new saltwater to be added on a regular basis. Salinity should be maintained at 30 parts per million. Water is changed over every five weeks to maintain good water quality.
Marine invertebrates such as cuttlefish require target feeding almost every day. Target feeding requires the keeper to access the top of the aquarium and hold a piece of food (prawn or whitebait) at the end of long forceps which is directed to a ‘targeted’ individual. Feeding the cuttles is a difficult task as a keeper has to be very careful not to intimidate the cuttles by making sudden movements inside or outside of the tank as Cuttles tend to watch the keeper as much as they do the food item. At the same time if the food is simply tossed into the water the cuttles will not eat it and the food will pollute the aquarium.
Many invertebrates such as sea stars feed on decaying matter at the bottom of the aquarium. Sea snails graze on algae from rocks and glass and anemones pluck food in the current. The diversity of animals in the aquarium allows waste products from some animals to be consumed by other aquarium inhabitants. Various species of crabs (from tiny hermit crabs to large shore crabs) are efficient scavengers and will clean up any food items dropped by fussier animals such as cuttlefish.
A behavioural enrichment program has been developed for the cuttlefish whereby pieces of food are placed into old film canisters which have four holes drilled into the top, bottom and sides. The cuttles then exercise their dextrous arms and intelligence in order to obtain the piece of food.
The water flows through a filtration system consisting of a series of filtration media from fine ‘wool’ to coarse gravel. The system helps to both filter large particles and provide an environment for beneficial bacterial cultures to keep the water clean. The gravel is siphoned clean to remove waste that has settled at the bottom. Excess algae are scrubbed off the glass using magnetic scrubbers.
Although cephalopods such as cuttlefish are predators for small fish and crustaceans they are no-where near the top of the food chain and can fall prey to larger predators. Cuttlefish are therefore nervous by nature and are always on the lookout for threats. Like other cephalopods, cuttles will discharge a cloud of thick membranous ink into the water and quickly jet to the side to avoid the pursuer. Cuttlefish will also shoot ink when they are startled or feel stressed in captivity, as well as shooting ink which can heavily pollute the aquariums filtration system, a stressed cuttlefish will jet backwards rapidly to escape danger.
- Eager, E. and Peterson, K. (eds) 1988. Great Barrier Reef Aquarium. Australian Science Mag. No. 3 p18-56.
- Taylor, L. 1993. Aquariums: Windows into nature. Prentice Hall. New York.
- Watson-Russell, C. 1980. Cuttlefish of Sydney Harbour. Australian Natural History Vol 20(2) p159-164.
- The Sydney Aquarium. 1992. Sydney Aquarium Guide Book. Schulz Hollis. Wollahra.
Chris Hosking , Interpretive Officer