Deep-sea sponge aggregations

Description of Deep-sea sponge aggregations


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Deep sea sponge aggregations are principally composed of sponges from two classes: Hexactinellida and Desmospongia. They are known to occur between water depths of 250 m to 1300 m (Bett & Rice, 1992), where the water temperature ranges from 4-10°C and there is moderate current velocity (0.5 knots). Deep sea sponge aggregations may be found on soft substrata or hard substrata, such as boulders and cobbles which may lie on sediment. Iceberg plough-mark zones provide an ideal habitat for sponges because stable boulders and cobbles, exposed on the seabed, provide numerous attachment/settlement points (B. Bett, pers comm.). However, with 3.5 kg of pure siliceous spicule material per m2 reported from some sites (Gubbay, 2002), the occurrence of sponge fields can alter the characteristics of surrounding muddy sediments. Densities of occurrence are hard to quantify, but sponges in the class Hexactinellida have been reported at densities of 4-5 per m2, whilst ‘massive’ growth forms of sponges from the class Desmospongia have been reported at densities of 0.5 to 1 per m2 (B. Bett, pers comm.). Deep sea sponges have similar habitat preferences to cold-water corals, and hence are often found at the same location. Research has shown that the dense mats of spicules present around sponge fields may inhibit colonisation by infaunal animals, resulting in a dominance of epifaunal elements (Gubbay, 2002). Sponge fields also support ophiuroids, which use the sponges as elevated perches.