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Sponge reefs in the Queen Charlotte Basin, Canada: controls on distribution, growth and development Kim W. Conway1, Manfred Krautter2, J. Vaughn Barrie1, Frank Whitney3, Richard E. Thomson3, Henry Reiswig4, Helmut Lehnert5, George Mungov3, Miriam Bertram6 1

Geological Survey of Canada, Pacific Geoscience Centre, 9860 W Saanich Rd, Box 6000, Sidney, BC, V8L 4B2, Canada ([email protected]) 2 Institute of Geology and Palaeontology, Herdweg 51, D-70174 Stuttgart, Germany 3 Institute of Ocean Sciences, Sidney, BC, Canada 4 Royal British Columbia Museum, 675 Belleville Street, Victoria BC, V8W 3N5, Canada 5 Eichenstr. 14, D-86507 Oberottmarshausen, Germany 6 Pacific Marine Environmental Laboratory, Seattle, WA, USA Abstract. Sponge reefs in the Queen Charlotte Basin exist at 165-240 m depth within tidally influenced shelf troughs subject to near bottom current velocities of 25-50 cm s-1 where nutrient supply from coastal runoff is augmented by windinduced upwelling of nutrient rich water from the adjacent continental slope. Large reef mounds to 21 m in elevation affect tidally driven bottom currents by deflecting water flows through extensive reef complexes that are up to 300 km2 in area. Three hexactinellid species construct reefs by building a siliceous skeletal framework through several framebuilding processes. These sponge reefs exist in waters with 90 to 150 μM dissolved oxygen, a temperature range of 5.9 to 7.3°C and salinity of 33.2 to 33.9 ‰. Relatively high nutrient levels occur at the reef sites, including silica, which in bottom waters are typically >40 μM and may be up to 80 μM. A high dissolved silica level is potentially an important control on occurrence of these and other dense siliceous sponge populations. The sponge reefs are mainly confined to seafloor areas where exposed iceberg plough marks are common. Sediment accumulation rates are negligible on the relict, glacial surface where the reefs grow, and trapping of flocculated suspended particulate matter by hexactinosidan or framework skeleton hexactinellid sponges accounts for a large proportion of the reef matrix. Suspended sediment concentration is reduced within the nepheloid layer over reef sites suggesting efficient particle trapping by the sponges. The reef matrix sediments are enriched in organic carbon, nitrogen and Freiwald A, Roberts JM (eds), 2005, Cold-water Corals and Ecosystems. Springer-Verlag Berlin Heidelberg, pp

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carbonate, relative to surrounding and underlying sediments. The sponges baffle and trap suspended sediments from water masses, which in one trough have a residence time of approximately 6 days, ensuring a close association of the sponges with the bottom waters. The location of the reef complexes at the heads of canyons provide a means of regionally funnelling particulate material that sponges can trap to enrich their environment with organic carbon and biogenic Si. Like deep-sea coral reefs, the sponge reefs are a remote and poorly known ecosystem that can present logistical challenges and survey costs. Also like deep-sea coral reefs, many of the hexactinosidan sponge reefs have been damaged or destroyed by the groundfish trawl fishery. Keywords. Porifera, sponge reefs, Hexactinellida, British Columbia, oceanography, marine geology

Introduction Hexactinellid sponge reefs, formed by framework skeleton sponges of the Order Hexactinosida, have developed in three glacial troughs that cross the continental shelf of northwestern Canada (Conway et al. 1991; Krautter et al. 2001). These reefs form extensive complexes, with bioherms up to 21 m in height and flat lying, biostromal areas that can cover many square kilometres of seabed (Fig. 1), and they have existed at some sites for up to 9000 years (Conway et al. 2001). The four main reef complexes are found in 165-240 m water depth, separated by up to 80 kilometres, but all share a common late Quaternary geologic history (Barrie and Conway 2002). The reefs are constructed through several processes of framebuilding by three hexactinosidan species (Fig. 2) and baffling and trapping of suspended sediments by these sponges (Krautter et al. 2001). The reefs are thought to provide habitat for many species of fishes, including rockfish, and a wide variety of invertebrates (Jamieson and Chew 2002). On the Alaskan and Washington State continental shelves this habitat association is also indicated by a large sponge bycatch coupled with the rockfish catches in the trawl fishery (Malecha et al. in press; Lowry written communication). Geological and palaeontological scientific interest in the reefs is stimulated by their similarity to widespread Mesozoic Era reefs that formed a discontinuous belt 7,000 km long during the Late Jurassic along the northern margin of the Tethys Ocean. This was the largest reef belt ever to exist on earth (Krautter et al. 2001).

Database – geological, oceanographic and biological datasets Multiparameter scientific surveys to examine the sponge reefs in detail were mounted in 1999 (PGC99001) with Canadian Coast Guard Ship (CCGS) John P. Tully, 2001 (PGC01004) with CCGS Vector, and in 2002 (PGC02002) with CCGS John P. Tully. In addition CCGS Vector collected multibeam swath bathymetric data in summer 2003 in two of the four reef complexes. These extensive data sets

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include grab and water samples, piston and gravity cores, high-resolution seismic and sidescan sonar underway geophysical surveys (Krautter et al. 2001) as well as oceanographic moorings deployed as part of the 2002 program which included current meters and sediment traps. In addition, in February 2000 and September 2002, detailed oceanographic surveys were completed in the vicinity of the northern sponge reef collecting nutrient, transmissivity and conductivity, temperature and

Fig. 1 Distribution of sponge reefs in the Queen Charlotte Basin. The basin includes the seafloor of Dixon Entrance, Hecate Strait, Queen Charlotte Sound and much of the subaerial Queen Charlotte Islands

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depth (CTD) data. Other samplings of opportunity collected small data sets in the vicinity of the reefs. Extensive diving operations by the manned submersible Delta (1999) and an HD2+2 DeepOcean Engineering Remote Operated Vehicle (2002) provided a library of seabed video and still imagery (http://www.pgc.nrcan.gc.ca/marine/ sponge/index_e.htm and http://www.porifera.org; see Krautter 2000 and Geological Survey of Canada 2002. In addition archived geophysical and sample data housed at the Pacific Geoscience Centre of the Geological Survey of Canada provided data compiled from many previous regional geophysical surveys (Conway et al. 1991; Barrie and Conway 2002).

Fig. 2 A Surface of sponge reef in Hecate Strait. Scale bar is 60 cm. B-C Farrea occa. Note Puget Sound King crab to left of sponge in B and juvenile rockfish at lower left in C; D-E Aphrocallistes vastus. Note squat lobster (Munida sp.) at lower left and juvenile rockfish partially hidden at centre in D. F-G Heterochone calyx. Scale bar is 20 cm in B-G


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Geological and physiographic controls on reef development The physiography of the north-western continental shelf has been shaped by successive glaciations, resulting in the formation of glacial troughs to 450 m deep, with intervening banks rising to 40 m water depth (Luternauer and Murray 1983). The most recent Late Quaternary glaciation, when ice advanced to the shelf edge in all the major shelf troughs (Josenhans et al. 1995), combined with post-glacial sealevel changes, established the surficial sediment distribution of seafloor substrates on much of the continental shelf (Barrie and Bornhold 1989; Luternauer et al. 1989a, b; Barrie and Conway 2002). The surficial geological units are similar in all three major toughs (Fig. 1) where the sponge reefs are found; with a relatively thick (up to 50 m) late Quaternary diamicton overlying the Neogene aged Skonun Formation that forms much of the sedimentary infill of the Queen Charlotte Basin (Barrie et al. 1991; Woodsworth 1991). Glaciomarine sediments of variable thickness rest conformably on this diamicton, with a total thickness of Quaternary sediments of up to 100 m in some areas (Barrie and Conway 1999). Sea-levels in the Queen Charlotte Basin were as low as 150 m below present on the continental shelf (Josenhans et al. 1995; Barrie and Conway 2002) and this led to a widespread distribution of coastal deposits and thick sublittoral sediments in some areas and erosion and intensive sediment transport across much of the shelf. Where sublittoral sands and silts were deposited during the lowstand, the antecedent coarse glacial substrates were buried and sealed off from access by epibenthic organisms requiring hard substrate. Holocene terrestrial sediments are largely trapped in the deep fiords and channels that border the continental shelf on the British Columbia mainland (Luternauer and Murray 1983). On the inner to mid shelf, the seabed remained relict, and iceberg furrowed glaciomarine sediments were preserved at the seabed (Fig. 3; Luternauer and Murray 1983; Barrie and Bornhold 1989) as sea-level rose. Iceberg furrows form suitable attachment sites for benthic epifauna as the berms of the furrows tend to be more coarse as boulders are cast up by the ploughing action of the iceberg (Woodward-Lynas et al. 1991). Fines are winnowed from the berms of the furrow by bottom currents further concentrating coarse debris (Conway et al. 1991). Sponge bioherms are preferentially initiated on the coarse debris on the shoulders of the furrows (Fig. 3). After establishment of the bioherm, subsequent lateral and vertical growth is dependent on the capture of suspended sediments by trapping and baffling, and the biological processes of reef growth that include several related ways of frame building by the sponges (Krautter et al. 2002). This relationship is similar to that described for the Lophelia pertusa reefs found on the Sula Ridge, on the Norwegian continental shelf, where coral reefs are clustered along relict iceberg ploughmarks (Freiwald et al. 1999, 2002). Ultimately the small sponge bioherms grow vertically as well as laterally over less favourable seafloor substrates and coalesce to form very large continuous structures covering kilometres of seafloor (Fig. 4). The mechanisms of reef growth are further described below. Modern tractive transport of fine sands occurs along bank margins in water

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Fig. 3 Sidescan sonogram and high-resolution seismic record of sponge reef in southern Queen Charlotte Sound. Note the small bioherms concentrated along the trace of the relict iceberg furrow. Bioherms are up to 10 m in height at this site

depths to 140 m (Barrie et al. 1988) and oscillation (wave) ripples can develop in depths to at least 110 m (Yorath et al. 1979). Hexactinosidan sponges, with their glass frame skeletons, are fragile and require quiescent conditions and so are precluded from colonizing such energetic areas. The glacially and sea-level derived sediment distribution pattern coupled with present day shelf bathymetry thus control distribution of potential reef sites. The sponge reefs are found in dense clusters of various shapes at four locations in the troughs (Fig. 1). These clusters consist of steep sided bioherms or reef mounds, and also as elongate irregularly shaped and variably sloping ridges, where bioherms have coaleseced and grown together over time. In addition, flat lying sponge meadows, or biostromal reefs are found at these sites. We refer to each of these four geographically separate groupings of diverse reef forms, as reef complexes (Conway et al. 2001).

Oceanographic controls on development The oceanography of the northern British Columbia continental shelf is a mixed semi-diurnal, meso to macrotidal regime where circulation is affected by winds, runoff, and shore configuration (Thomson 1981). Bathymetric constraints are prevalent in focussing of currents within and along the axes of the shelf troughs. Shelf waters within British Columbia are noted to have a high ambient relative silica concentration and this has been suggested to be an important control on shallow populations of hexactinellid sponges (Austin 1998). Seasonal wind


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Fig. 4 Coincident sidescan sonar and high-resolution seismic record of sponge reefs in Hecate Strait showing relationship to underlying geological units. Dark grey tones indicate areas of higher reflectivity. Sponge reefs are clay rich so much less reflective than the underlying sandy and gravelly glacial sediments. The reefs coalesce to form larger continuous structures

induced upwelling is an important process whereby nutrient rich slope waters are brought to the surface through the shelf troughs (Crawford 2001). This area is at the northern extreme of coastal upwelling, according to upwelling indices provided by the National Atmospheric and Oceanic Administration (NOAA). Upwelling is wind driven and restricted to the summer months when the appropriate northwest wind and water density conditions exist. Because higher salinity waters are brought onto shelf regions during summer (Dodimead et al. 1963; Herman et al. 1989), salinity and nutrient concentrations are considerably higher in summer, compared with winter. Measured near bottom nitrate increased from 27 to 35 μM as salinity increased from 33.2 to 33.7 ‰. Likewise, silicate increased from 49 to 70 μM and oxygen decreases from 152 to 101 μM from winter to summer. Measurements of

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conductivity, temperature and depth show the effects of winter downwelling and summer upwelling clearly. Summer bottom waters are thus cooler, more saline, nutrient rich and oxygen poor (Whitney et al. in press). Using results from the World Ocean Circulation Experiment (WOCE), concentrations of silicate and oxygen are shown for the 200 m depth strata (Fig. 5) along a section that starts in the North Atlantic, extends into the Southern Ocean (WOCE section A16), then runs northward through the Pacific Ocean to the Aleutian Islands (WOCE section P15). The x-axis on this plot is an along-track measure of the distance from the first station, located at 63°20'N, 20°0'W. The final station is in the North Pacific, near the coast of Alaska (53°55'N, 164°59'W). A section at 200 m matches the depth of the sponge reefs and also is representative of the source of upwelled nutrients in the Northeast Pacific (Freeland and Denman 1982; Wheeler et al. 2003). The two regions with highest silicate levels are in the Southern Ocean, south of the Polar Front, and in the North Pacific, north of the Subarctic Front. Silicate concentrations range from 300 μmol/kg in the Southern Ocean and ~270 μmol/kg in the North Altantic and Pacific, to as little as 56 μmol/kg in the subarctic Pacific and 16 μmol/kg in the Equatorial Pacific. The trough head location of the sponge reefs provides a means of funnelling these enriched bottom waters to the reefs. Detrital material, derived from both onshore coastal sources and the resuspension of offshore particles, is suspended in a bottom nepheloid layer and effectively trapped by dense populations of sponges (Whitney et al. in press). Trapping of these materials results in the observed enrichment of organic carbon, nitrogen and opal as measured in core, relative to surrounding and

Fig. 5 Silicate (green curve) and oxygen concentrations at 200 m along a section starting at 63°N in the North Atlantic, extending to the Southern Ocean in the Atlantic and Pacific, then heading northward through the Pacific to 54°N


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underlying sediments (Conway et al. 2001). Near bottom currents are constrained and focused by bathymetry at all sponge reef complexes (Fig. 6). The sponges thus

Fig. 6 Near bottom current directions at sponge reef complexes (stippled areas) are strongly constrained by bathymetry. Current roses show distribution of all measured current directions. Current velocities are discussed in text. The value below the current rose refers to height of current meter above seabed. Data courtesy of Department of Fisheries and Oceans (DFO), Canada

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exist in relatively enriched zones where several oceanographic processes ensure an optimal delivery of dissolved nutrients and potential food particles. Furthermore, the reefs are situated within a current regime where seabed currents reach a maximum of 50 cm/sec. This both provides access to required nutrients and keeps fine sediments in suspension, preventing smothering by sediment deposition. Tidal currents repeatedly cycle bottom waters across the reefs. In Hecate Strait, where the northernmost sponge reef is located, such bottom water has a residence time over the reef within the trough of approximately six days, calculated from the net transport by currents measured at mooring sites. This water residence time ensures a close association of the reefs with the bottom water. The sponges are exposed to suspended sediment in a nepheloid layer that is up to 30 m thick above the seabed. In transmissivity profiles obtained at reef sites, particle concentrations are reduced in the nepheloid layer relative to profiles obtained nearby; suggesting particle trapping by sponges is efficient (Fig. 7). Construction of large mounds

Fig. 7 Light transmission (%) vs. depth at stations at North Hecate Strait reef complex (MT 7, 8 and 9) and 28 km south (MT6) and 30 km north (MT10) of reef. Particle density is reduced in the vicinity of the reefs


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is probably favoured by a positive feedback by increased access to nutrients by sponges living on high points of the reef (Conway et al. 1991). The large obstructing mounds on the seabed appear to deflect the tidal currents, creating flow conditions that are more locally complex than outside of the reef areas.

Biological controls on development The sponges that form the framework of the reefs are all members of the Hexactinosida, and possess a mainframe skeleton composed of fused spicules of hydrated amorphous silica. The three sponges that build the reef framework (Farrea occa (Figs. 2B, C), Heterochone calyx (Figs. 2D, E) and Aphrocallistes vastus (Figs. 2F, G)) all require firm substrate for attachment of larvae (Conway et al. 1991). The sponges variably cover the surface of the reef mounds, and may completely cover the seafloor (Fig. 2A). The framework is created through three related processes that include 1) stabilizing, accessory outgrowths (Figs. 8A-C, E), 2) skeletal welding, where a living sponge overgrows or incorporates the skeleton of a neighbouring sponge, and 3) larval attachment (Fig. 8D) (Neuweiler 2001; Krautter et al. 2002). These processes all require the availability of a bare hexactinosidan skeleton (Neuweiler 2001). The surface of the bioherm is only successfully colonised by larvae where unburied skeletons project from the seabed. The development of a bioherm is also dependent on the natural selection for larvae that preferentially attach to the reef surface rather than available adjacent hard substrates (gravel). Hexactinosidan sponges are, in general, less common in the Atlantic than in the Pacific Ocean, and the genus Heterochone, which has the most robust and durable skeleton of the three reef framework builders, is entirely Pacific in distribution (Reiswig 2002). Sponge morphology includes broad forms including dish, basket and shield shapes (Fig. 8A), (Krautter et al. 2001; Conway et al. 2004) In such cases the site of growth of one of these broad forms may initially be a small clast or, in later stages of development, a fragment of projecting skeleton on the bioherm surface. The surface area eventually covered by such a sponge may be several square metres (Fig. 2A) resulting in a greatly expanded surface area for attachment of subsequent sponge generations when this sponge dies and becomes partially buried. In this way sponge morphology may contribute to the lateral expansion of the bioherm over adjacent seafloor. The sediment trapping and baffling capacity of the sponges is an important control on reef growth in that sponges control the sedimentation at reef sites through these processes (Conway et al. 2004). The biological controls on development are perhaps the least known factors, as this group of sponges have not been extensively studied. Aspects that are very poorly known include such subjects as sponge larval production and motility as well as life span and growth rates. In addition mechanisms of sediment capture and particle removal and surface cleaning by the sponge are not understood. Seasonal aspects of sponge growth and reproduction are probably important, given the seasonal oceanographic changes in nutrient and sediment flux. Other sponges are evident on the reef surface though they are not

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involved in forming the reef framework. These include the rossellid hexactinellid species Rhabdocalyptus dawsoni, Staurocalyptus dowlingi, Acanthascus platei, Acanthascus cactus. Demosponges are present in abundance, both on the reefs as individuals such as Poecillastra tenuilaminaris and Geodia mesotriaena, and also as cryptic commensal, epizootic or possibly parasitic sponges that grow on and within hexactinosan skeletons including Halichondria disparilis, Desmacella sp., Poecilastra rickettsi, Asbestopluma lycopodium, and Antho (Plocamia) illgi. It is most likely that hexactinosidan sponges have no natural predators. Reef accompanying benthic organisms are echinoderms, crustaceans, bryozoans, foraminifera, brachiopods and bivalves to a minor degree. Frequently immature rockfish are seen in the complex surface of the reef, suggesting a refugium function for the reef. Reef destroying organisms are absent. Due to the dysaerobic conditions in the sediment infaunal organisms are rare except terebellid worms. Organic carbon content of the sediments is typically greater than 3 %, which leads to this hypoxic subsurface condition (Conway et al. 2001).

Ocean management and trawl impacts Sponge reefs have sustained extensive and well-documented damage by groundfish trawling (Conway et al. 2001; Jamieson and Chew 2002) at all four reef complexes. The reefs were presumably subject to large-scale damage during the years of unrestricted fishing by foreign trawling fleets fishing Pacific Ocean Perch and other rockfish in Queen Charlotte Sound 1956-1971 (DFO 1999). Between 1971 and 1977 foreign fleets continued to operate, but at a somewhat reduced level. This fishery was largely located within the troughs that form the known sponge reef habitat (Conway et al. 2001). Reefs in central Hecate Strait, which were outside of the areas targeted by the foreign fishery (DFO 1999), remain the most pristine and undamaged. Closure of the sponge reef areas to groundfish trawling was instituted in July 2002 as a control measure to reduce trawl fishery impacts on the reefs. Recovery from trawl impacts may be very slow as the sponges grow to a large size relatively slowly. A 1 m tall hexactinellid sponge may be up to 220 years old, based on work by Leys and Lauzon (1998) focused on the volumetric relationship of sponge lengths to measured growth rates and recovery of a destroyed reef surface may thus take 100-200 years (Conway 1999). Uncertainty of recovery from trawl impacts also stems from the almost complete lack of knowledge of the reproductive strategies of hexactinosidan sponges. Recovery from the widespread trawl fishery impacts may depend on the longevity, motility and transport of the, as yet undiscovered, larval Fig. 8 A Heterochone calyx at centre with A. vastus at lower right; B H. calyx is at left above scale bar; C Cluster of H. calyx displays elongate accessory stabilizing supports or holdfasts that attach to the bioherm surface. Scale bar is 20 cm. D Scanning electron microscope micrograph of a young hexactinosidan sponge of uncertain species, 1 mm in diameter, growing on the surface of the skeleton of A. vastus. Scale bar is 1 mm (after Neuweiler 2001). E Close up view of attachment points of secondary holdfasts of H. calyx. Note moss or spider web-like covering of bioherm surface. Scale bar is 10 cm

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stages of the reef forming hexactinosidan sponges. Analysis of the groundfish trawl fishery bycatch indicates that close to 95 % of the sponge bycatch in the Queen Charlotte Sound/Hecate Strait area was caught close to the reef complexes between 1996 and 2002 (Fig. 9). Fish and crab trap, and longline fisheries continue to operate in, and presumably have some impact on sponge reefs in all areas.

Fig. 9 Distribution of groundfish trawl sets where 95 % of the total sponge bycatch was reported in the fishery between 1996 and 2002. Most sponge bycatch, regionally, is captured in or near the reef complexes (red tone). Data provided courtesy of Alan Sinclair (Pacific Biological Station, DFO, Canada)


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Summary and conclusions Physical environmental conditions favourable to the formation of large siliceous sponge reefs include a relict, environmentally stable shelf, in quiescent water that is below wave base, which in much of the Queen Charlotte Basin is below 140 m. A seafloor of low slope angle with the availability of coarse (gravel) substrate is required. Oceanographic conditions include the delivery of suspended sediments and appropriate nutrient levels including a relatively high concentration of dissolved silicate (>40 μM). Moderate currents, directed and focussed by tidal processes within the shelf troughs, enriched by a combination of seasonal upwelling and coastal runoff and surface water productivity are also critical conditions for development. These oceanographic and geological conditions provide an enriched, yet nondepositional, benthic environment that is very favourable to dense hexactinellid sponge populations. Development of hexactinosidan sponge reefs also requires the appropriate frame building sponge fauna be present. The framebuilding capability of the three species of hexactinosidan sponges includes three related mechanisms for framework formation that include skeletal “welding”, or intergrowth, secondary holdfast development seen especially in Heterochone calyx, and attachment of larvae to the reef framework. The Atlantic Ocean is less well endowed with such a Hexactinosidan sponge fauna than is the Pacific Ocean, with the important reefforming genus, Heterochone, restricted entirely to the Pacific. Although the sponge reefs found on the western Canadian continental shelf appear to be unique to this region, many continental margin areas of the Pacific remain to be surveyed, so that their occurrence elsewhere cannot be precluded. However, in view of the critical oceanographic, geological and biological processes that in combination control reef development on the western Canadian continental shelf, it is apparent that conditions favourable to the formation of extensive hexactinellid sponge reefs are not commonly found in the present world ocean.

Acknowledgements Officers and crews of the CCG Ships John P. Tully and Vector and many colleagues at Institute of Ocean Sciences, and Pacific Geoscience Centre (Sidney, BC) are thanked for invaluable assistance at sea and in the lab. Bill Austin (Marine Ecology Station – Sidney) provided valuable discussions and assistance with early phases of this work. Richard Höfling and Henko de Stigter are thanked for thoughtful reviews that helped improve the paper. The authors wish to recognize André Freiwald for his encouragement of a broad perspective in the study of deep-water ecosystems. Support from the German Research Foundation (DFG KR 1902/2-2) is gratefully acknowledged.

References Austin WC (1998) The relationship of silicate levels to the shallow water distribution of Hexactinellids in British Columbia. Mem Queensland Mus 44: 44

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Barrie JV, Bornhold BD (1989) Surficial geology of Hecate Strait, British Columbia continental shelf. Can J Earth Sci 26: 1241-1254 Barrie JV, Conway KW (1999) Late Quaternary glaciation and postglacial stratigraphy of the northern Pacific margin of Canada. Quatern Res 51: 113-123 Barrie JV, Conway KW (2002) Contrasting glacial sedimentation processes and sea-level changes in two adjacent basins on the pacific margin of Canada. Geol Soc London Spec Publ 203: 181-194 Barrie JV, Emory-Moore M, Luternauer JL, Bornhold BD (1988) Origin of modern heavy mineral deposits, northern British Columbia continental shelf. Mar Geol 84: 43-51 Barrie JV, Bornhold BD, Conway KW, Luternauer JL (1991) Surficial geology of the northwestern Canadian continental shelf. Cont Shelf Res 11: 701-715 Conway KW (1999) Hexactinellid sponge reefs on the British Columbia continental shelf: geological and biological structure with a perspective on their role in the shelf ecosystem. Canad Stock Assess Secr Res Doc 99/192, 21 pp Conway KW, Barrie JV, Austin WC, Luternauer JL (1991) Holocene sponge bioherms on the western Canadian continental shelf. Cont Shelf Res 11: 771-790 Conway KW, Krautter M, Barrie JV, Neuweiler M (2001) Hexactinellid sponge reefs on the Canadian continental shelf: a unique “living fossil”. Geosci Canada 28: 71-78 Conway KW, Barrie JV, Krautter M (2004) Modern siliceous sponge reefs in a turbid, siliciclastic setting: Fraser River delta, British Columbia, Canada. N Jb Geol Paläont Mh 6: 335-350 Crawford WR (2001) Oceans of the Queen Charlotte Islands. Can Tech Rep Fish Aqua Sci 2383 Department of Fisheries and Oceans Canada (DFO) (1999) Pacific Ocean Perch, British Columbia Coast. DFO Stock Status Report A6-11 Dodimead AJ, Favorite F, Hirano T (1963) Salmon of the North Pacific Ocean, Part II. Review of Oceanography of the Subarctic Pacific region. Int North Pacific Fish Comm Bull 13, 195 pp Freeland HJ, Denman KL (1982) A topographically controlled upwelling center off southern Vancouver Island. J Mar Res 40: 1069-1093 Freiwald A, Wilson JB, Henrich R (1999) Grounding Pleistocene icebergs shape recent deepwater coral reefs. Sediment Geol 125, 1-8 Freiwald A, Hühnerbach V, Lindberg B, Wilson JB, Campbell J (2002) The Sula reef complex, Norwegian shelf. Facies 47: 179-200 Geological Survey of Canada (2002) Marine/sponge reef project website. http://www.pgc. nrcan.gc.ca/marine/sponge/index_e.htm Hermann AJ, Hickey BM, Landry MR, Winter DF (1989) Coastal upwelling dynamics. In: Landry MR, Hickey BM (eds) Coastal Oceanography of Washington and Oregon. Elsevier, Amsterdam, pp 211-253 Jamieson GS, Chew L (2002) Hexactinellid sponge reefs: areas of interest as marine protected areas in the north and central coast areas. Canad Sci Adv Secr, Res Doc 2002/12 Josenhans HW, Fedje DW, Conway KW, Barrie JV (1995) Post glacial sea levels on the western Canadian continental shelf: evidence for rapid change, extensive subaerial exposure and early human habitation. Mar Geol 125: 73-94 Krautter M (2000) Sponge reef website.http://www.porifera.org Krautter M, Conway KW, Barrie JV, Neuweiler M (2001) Discovery of a “living Dinosaur”: globally unique modern hexactinellid sponge reefs off British Columbia, Canada. Facies 44: 265-282 Krautter M, Conway KW, Barrie JV, Neuweiler M (2002) Hexactinosan sponges: larval


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attachment mechanism and related reef framebuilding processes. Boll Mus Inst Biol Genova: 66-67 Leys SP, Lauzon NRJ (1998) Hexactinellid sponge ecology: growth rates and seasonality in deep water sponges. J Exp Mar Biol 230: 111-129 Luternauer JL, Murray JW (1983) Late Quaternary morphologic development and sedimentation, central British Columbia continental shelf. Geol Surv Canad Pap 83-21, 38 pp Luternauer JL, Clague JJ, Conway KW, Barrie JV, Blaise B, Mathewes RW (1989a) Late Pleistocene terrestrial deposits on the continental shelf of western Canada: evidence for rapid sea-level change at the end of the last glaciation. Geology 17: 357-360 Luternauer JL, Conway KW, Clague JJ, Blaise B (1989b) Late Quaternary geology and geochronology of the central continental shelf of western Canada. Mar Geol 89: 57-68 Malecha PW, Stone RP, Heifetz J (in press) Living substrate in Alaska: distribution, abundance and species associations. In: Barnes P, Thomas J (eds) Benthic habitats and the effects of fishing. Amer Fish Soc Proc, Bethesda, MD Neuweiler M (2001) Untersuchungen an Kieselnadeln rezenter hexactinellider Schwämme. Unpubl MSc thesis, Univ Stuttgart, 166 pp Reiswig HM (2002) Family Aphrocallistidae. In: Hooper JNA, Van Soest RWM (eds) Systema Porifera: A Guide to the Classification of Sponges. 2, Kluwer/Plenum, New York, pp 1282-1286 Thomson RE (1981) Oceanography of the British Columbia Coast. Canad Spec Publ Fish Aqua Sci 56: 291 pp Wheeler PA, Huyer A, Fleischbein J (2003) Cold halocline, increased nutrients and higher chlorophyll off Oregon in 2002. Geophys Res Lett 30: 8021 Whitney F, Conway KW, Thomson RE, Barrie JV, Krautter M, Mungov G (in press) Oceanographic habitat of sponge reefs on the western Canadian Continental Shelf. Cont Shelf Res Woodsworth GJ (1991) Evolution and hydrocarbon potential of the Queen Charlotte Basin, British Columbia. GSC Pap 90-10, 569 pp Woodworth-Lynas CMT, Josenhans HW, Barrie JV, Lewis CFM, Parrot DR (1991) The physical process of seabed disturbance during iceberg grounding and scouring. Cont Shelf Res 11: 939-961 Yorath CJ, Bornhold BD, Thomson RE (1979) Oscillation ripples on the northeast Pacific continental shelf. Mar Geol 31: 45-58