What are sponges?

Sponges are invertebrate, aquatic animals belonging to the Phylum Porifera. They are filter feeding organisms, meaning that their bodies are specialised to separate suspended food particles out of the water. They spend their adult lives attached to the seabed (i.e., they are sessile benthic organisms). As the name Porifera (‘pore bearers’) suggests, sponges possess pores through which water enters and leaves, and their bodies consist of mesh-like tissues arranged into elaborate and varied growth forms, often with elegant internal ‘skeletons’. Water is pumped through the body in a system of flagellated canals where food and other metabolites are extracted by the sponge.

Sponges are thought to be the oldest living animal group: they are known to have existed for over 600 million years. There are over 8500 species described and it is predicted that more than 25000 species exist. The vast majority of sponges are marine (though there are approximately 150 species found in freshwater environments) and they inhabit depths from the intertidal zone of shallow, shelf seas to the lower continental slope / abyssal plain transition (depth approx. 3000m) of the deep sea.

In many deep-sea areas, sponges may be the dominant organism, forming structurally complex and often highly diverse ecosystems known as sponge grounds, gardens, aggregations, and reefs. These are found globally on continental shelves, slopes, seamounts, and mid-ocean ridges, and in submarine canyons and fjords. Such deep-sea sponge-dominated communities represent vulnerable marine ecosystems, and their locations coincide with fishing and other human activities. In contrast to other deep-sea ecosystems, such as cold-water coral reefs and vent/seep systems, they have until now received relatively little scientific or conservation attention.