Sponge reef

Sponge reefs serve an important ecological function as habitat, breeding and nursery areas for fish and invertebrates. The reefs are currently threatened by the fishery, offshore oil and gas industries. Attempts are being made to protect these unique ecosystems through fishery closures and potentially the establishment of Marine Protected Areas (MAPs) around the sponge reefs.

Hexactinellid sponge reefs were common in the Late Jurassic period, and were believed to have gone extinct during or shortly after the Cretaceous period. Living sponge reefs were discovered in the Queen Charlotte Basin (QCB) in 1987–1988, and were reported in the Georgia Basin (GB) in 2005. These sponge reefs are considered to be "living fossils".

Hexactinellids, or "glassy" sponges are characterized by a rigid framework of spicules made of silica. Unlike other poriferans, hexactinellids do not possess the ability to contract. Another unique feature of glassy sponges is that their tissues are made up almost entirely of syncytia. In a syncytium there are many nuclei in a continuous cytoplasm; nuclei are not packaged in discrete cells.

As a result, the sponge has a distinctive electrical conduction system across its body. This allows the sponge to rapidly respond to disturbances such as a physical impact or excessive sediment in the water. The sponge’s response is to stop feeding. It will try to resume feeding after 20–30 minutes, but will stop again if the irritation is still present.

Hexactinellids are exclusively marine and are found throughout the world in deep (>1000 m) oceans. Individual sponges grow at a rate of 0–7 cm/year, and can live to be at least 220 years old. Little is known about hexactinellid sponge reproduction. Like all poriferans, the hexactinellids are filter feeders. They obtain nutrition from direct absorption of dissolved substances, and to a lesser extent from particulate materials. There are no known predators of healthy reef sponges. This is likely because the sponges possess very little organic tissue; the siliceous skeleton accounts for 90% of the sponge body weight.

Hexasterophoran sponges have spicules called hexactines that have six rays set at right angles. Orders within hexasterophora are classified by how tightly the spicules interlock with Lyssanctinosan spicules less tightly interlocked than those of Hexactinosan sponges.

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