June 29, 2011

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Cloud Sponge off Canada

On the last day of the IMCC2 meeting, an afternoon session was dedicated to discussion of conservation of Deep-Sea Sponge Communities.  This topic has gained attention from the realization they were often habitat for juveniles of commercial fish species, and at considerable risk from human activities, particularly deep-sea trawling.  The discovery of beds of an unusual kind of reef building glass sponge off the west coast of Canada in 1987-1988 brought this issue to broader attention (c.f. Conway, et al., 1991).  These sponges were of a type known only from fossils and believed long extinct.  Much media attention followed the discovery of these “Jurassic reefs” which in places rise to heights as great as 21 meters (Krautter, et al., 2001).  Protection from trawling was sought on an emergency basis.  As more information was collected in subsequent years, the protected areas were expanded and revised.  The existence of the Canadian sponge reefs stimulated research on sponge communities throughout the world, including the waters off the coast of Alaska and New Zealand.  The talks in this session at IMCC were aimed at updating research results and clarifying the status of deep-sea sponge conservation.

Pregnant female Rockfish species in a glass sponge

A talk by Robert Stone of NOAA focused on documentation of glass sponge communities off the Aleutians.  Stone is co-author, with Helmut Lehnert and Henry Reiswig, of a book which has documented the richness of some of Alaska’s sponge fauna, “A Field Guide to Deep-water Sponges of the Aleutian Island Archipelago” (Stone, et al., 2011).  It has illustrations and data on 112 sponge species found in Alaskan waters, with distribution maps showing that many species are distributed across the North Pacific and arctic.  Glass sponges, such as the one the left, are those which have a skeleton comprised principally of interwoven silica spicules [small spines].  Glass sponges are different than the more common demosponges used in the bath which may or may not have silica spicules, but have their body mainly constructed of a protein matrix called spongin. While demosponges can be found in shallow waters worldwide, glass sponges occur in the deep-sea in most parts of the world, but in the colder waters of the arctic and sub-arctic they can be found in much more shallow waters.  Although the Alaskan glass sponge reef areas are small in comparison with those of Canada, they are still of interest as possible juvenile fish habitat.  In Alaska these sponge reef habitats are at risk.

Stone pointed out that in Alaska bycatch of sponges is four times the bycatch of fish (by weight), totaling an estimated 352 metric tons of sponges/year.  This is the equivalent of removing a square kilometer of sponge habitat every year.  NOAA studies estimate trawls also damage 14-67% of sponges they leave behind: in the Aleutians an average of 21% of remaining sponges are damaged by trawls.  Even fisheries using long lines appear to damage sponges, with 33% of the large demosponges and 16% of glass sponges being damaged.  Roberts noted that while Canada has set aside areas for protection of sponges, there are currently no equivalent conservation measures in place in Alaska: some Aleutian areas have restrictions on certain gear types, but do not offer complete protection.

Another NOAA scientist, Liz Clarke, discussed ongoing mapping of Alaska sponge habitats using autonomous underwater vehicles which hover a specific distance above the seafloor while taking video transect data as they move along.  Densities of sponges and associated biota can be very high.  Seafloor video transect data can be used to evaluate whether certain areas should be considered “Critical Fish Habitat,” which is assessed by NOAA every five years to determine what areas warrant protection.  She also noted that one of the other aspects of collecting such data is the fact that fish use of sponge habitats may differ between night and day, and further work will be required to clarify what time of day data should be collected to document periods of maximal sponge habitat use.  To make a distinction between sponges on soft bottom, and sponge reefs, which by definition are on hard bottom, sub-bottom acoustic profiling systems which can reveal whether the bottom is rocky or not, may also be required in future.

Image of deepwater coral hotspot

The broader perspective on where high biodiversity deepwater habitats occur, and which areas should be a focus of protection efforts, has been addressed using existing deepwater coral data to model abundance and diversity hotspots in the world’s oceans.  A recent paper highlights deepwater coral global hotspots, particularly off New Zealand and the UK  (Davies and Guinotte, 2011). Similar work will be needed to highlight priority areas for deepwater sponge conservation.  However, it is clear from work in Alaska and Canada that trawling puts sponge communities at risk, and Sponge Bob and his buddies, including commercial fish that use these as habitat, would benefit from further conservation efforts.

More pictures and information on the Pacific Northwest sponges reefs may be found at:
http://www.mareco.org/khoyatan/spongegardens/home/index.asp

Written by Dr. Philip McGillivary 

References:

Conway. K.W., J.V. Barrie, W.C. Austin, and J.L. Luternauer. 1991. Holocene sponge bioherms on the British Columbia continental shelf. Coastal Shelf Research. 11(8):771-790.

Davies, A.J and J.M. Guinotte. 2011. Global habitat suitability for framework-forming cold-water corals. PLoS ONE 6(4): e18483. doi:10.1371/journal.pone.0018483

Krautter, M., K.W. Conway, J.V. Barrie and M. Neuweiler. 2001.  Discovery of a ‘living dinosaur’: globally unique modern hexactinellid sponge reefs off British Columbia, Canada. Facies 44:265-282.

Marliave, J., K.W. Conway, D.M. Gibbs, A. Lamb and C. Gibbs. 2009. Biodiversity and rockfish recruitment in sponge gardens and bioherms of southern British Columbia, Canada.  Mar. Biol. 156:2247-2254. DOI 10:1007/s00227-009-1252-8.

Stone, R.P., H. Lehnert, and H. Reiswig. 2011. A guide to the deep-water sponges of the Aleutian Island Archipelago. NOAA Professional Paper 12:1-216.

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