Big Bank Shoals of the Timor Sea
An environmental resource atlas

FILTER-FEEDING ECOSYSTEMS

Biology and ecology of sponges

Reproduction

Sponges have a variety of sexual and asexual reproductive modes, but are renowned for truly remarkable regenerative powers. This is well-illustrated by the classic experiment of forcing a piece of sponge through silk, which dissociates the cells. Within a short period of time the dissociated cells re-aggregate into the proper relationship, although this cannot be achieved with all species.

The ability to regenerate is closely correlated with asexual reproduction. A bud or small fragment broken from the parent sponge can generate a new sponge. Some sponges produce special, asexual reproductive bodies called gemmules. These consist of an aggregate of essential cells; food-filled archeocytes and amoebocytes, which are capable of giving rise to any other type of cell. They are all protected by a sheath of protective spongocytes. Gemmules remain viable for extended periods of time. Some types are even resistant to freezing and desiccation. When suitable conditions are found a gemmule can grow to form a new sponge, genetically identical to the parent. Gemmules provide a means of dispersal and are a way of maintaining local distribution and abundance. They allow the genotype of an individual sponge to persist through extreme environmental conditions.

The majority of sponges are hermaphroditic, and therefore capable of producing both sperm and eggs, though generally at different times. Because sponges do not have cells organised into tissues or organs, sperm and eggs are produced by the amoebocytes and choanocytes. Mature sperm are shed into the water column, where they are carried into the water canals of neighbouring sponges and where they fertilise their eggs. Fertilised eggs are then either carried into the water column where they undergo further development in the sea or, as is the case with most sponges, they are brooded and develop within the body of the parent sponge. Embryonic development leads to free-swimming larvae, a stage that is important for species dispersion in sessile animals. After a brief free-swimming existence, the larvae settle to the bottom and develop into adult sponges.

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Last updated - 1 September 98

Copyright ©1996-1998 Australian Institute of Marine Science

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