In the mid 1700s scientists suggested that sponges were animals rather than plants. At this time, organisms were considered 'animal' if they were capable of muscular response or movement. The phylum was eventually named Porifera (pore-bearing), after the perforated surfaces of the sponge's tissue.
Sponges possess an apparently simplistic body structure that lacks organs and true tissues. The body of the sponge is organised around the system of pores, ostia, canals and chambers that guide the water current from the inhalent canal to the exhalent oscules. Despite being classified as the most primitive and simple multi-cellular animals, sponges have demonstrated sophisticated cellular systems, complex developmental and reproductive processes, versatility in feeding behaviour, production of unique natural chemicals, cellular communication networks and intimate symbiotic relationships with other organisms.
The taxonomic classification of sponges is still unresolved especially at the lower taxonomic levels. About 5000–6000 species have been described worldwide although it is believed that the number of extant species may be three times this number. The number of sponge species within Antarctica is presently unknown.
The presence of soft sponge elements and fossil sponge embryos have been reported from Chinese Guizhou deposits dated at almost 580 million years old.
Sponges are sessile (non-mobile) filter feeders that regularly process large volumes of water (up to 200 litres of seawater per hour) and may be capable of reducing soluble and particulate-associated pollution in the environment. They have no mechanical means for avoiding pollution and must consequently rely on physiological mechanisms for tolerating toxic chemicals. For these reasons, sponges may be useful in bioremediation and bio-monitoring of polluted sites.
Sponges are the source of more natural chemicals than any other marine invertebrate and many of these compounds have potent bioactive properties (anti-tumour, anti-inflammatory, anti-viral and anti-microbial). Sponges can produce metabolites for chemical defense against predation and fouling, to repel parasites and microbes, to assist in chemical interactions with fast growing species and for chemical communication with other symbiotic organisms.
Symbiosis is broadly defined as a permanent association between two individuals of different species. Sponges are often host to a diverse array of microorganisms, many of which form intimate symbiotic relationships with their host. Some of the benefits sponges may receive by maintaining these symbiotic relationships include nutrition, transportation of chemicals throughout the sponge tissue, assistance in chemical defence and removal of waste products from the sponge. Microbial biomass can actually contribute to sponge structural rigidity.
The microbial community associated with Antarctic sponges is well adapted to extreme and pristine, environmental conditions. This makes them potentially susceptible to small-scale fluctuations in water quality and levels of environmental contamination.
Pioneering work by marine scientists over many years has shown that Antarctic benthic marine communities are stable in space and time. Sponge characterised communities were found to be important in terms of their dominance sub-tidally and also in terms of the diversity/biomass they supported.
Antarctic sponges were found to be long lived and were sensitive to disturbance. As such, they represent sensitive indicator species reflecting environmental health.
Written by: Nicole Webster, Australian Institute of Marine Science and University of Canterbury.