The rose sponge is one of the most common sponge’s in Australia’s cool southern waters, easily recognised by its bright pink colouration and spikey appearance. It can occur free-standing from rocks or the sea floor, or encrust both the reef and other sessile animals. The skeleton of the rose sponge consists of repeatedly branched spongin fibres, rather than the sharp siliceous spicules present in many species of sponge.
They lack true tissue and organs and therefore the cells are relatively unspecialised. Sponges are filter feeders. The surface of the sponge has many pores (ostia) through which water is drawn into the body. The water is drawn into a series of canals and chambers where food particles (plankton) are trapped. The water then passes out of the body through larger pores (oscules). A sponge can pump hundreds of litres through its body each day.
Generally, sponges have few predators. Most carnivorous animals avoid sponges due to their poor nutritional value, their splinter-like spicules, or toxic chemicals produced by their cells. Some specialised carnivores, however, feed exclusively on sponges. The rose sponge provides habitat for the amazing rose sponge nudibranch, which mimics the form and texture of the rose sponge almost perfectly. The rose sponge grows slowly, and is not outcompeted for space, nor does it dominate neighbouring species.
Occurrence at the Busselton Jetty:
Small patches of this beautiful sponge are visible on the jetty piles from the underwater observatory, though they are always surrounded by masses of other colourful invertebrate life. Spotting the cryptic rose sponge nudibranch is an almost impossible task, as it is rarely observed from the underwater observatory.
Image by: R. Austin