Sarah E Cook
email: sarah_cook@shaw.ca

Kim W Conway

Brenda Burd

Status of the glass sponge reefs in the Georgia Basin

Keywords: Georgia Basin, Continental shelf, Glass sponge reefs, Hexactinellida, Multibeam, Sidescan sonar, Effects -bottom trawling, Megafauna, Relative abundance, Reef status, Rockfish

The purpose of this paper is to describe the status and general faunal composition of sponge reefs in the Georgia Basin (GB), British Columbia, Canada. Fourteen distinct deep water glass sponge (Hexactinellid) reefs have been mapped using multibeam bathymetry and sidescan sonar in the GB. Seven of these have been surveyed visually using video from Remotely Operated Vehicles (ROVs). Analysis of video data indicated that three reefs were undamaged, two were damaged and the other two were damaged but potentially recovering. The nature of the damaged reefs, with large areas of scattered dead sponge skeleton fragments and few live reef-building sponges (Aphrocallistes vastus and Heterochone calyx), as well as video evidence of tracks suggest they were damaged mechanically by mobile fishing gear.

Introduction

Glass sponge reefs built by sponges of Class Hexactinellida, Order Hexactinosida, are found along the continental shelf of the Pacific Northwest. Sponges of this order have a skeleton of fused silica spicules that remains remarkably intact after the death of the sponge [START_REF] Krautter | Recent Hexactinosidan sponge reefs (silicate mounds) off British Columbia, Canada: frame-building processes[END_REF] and that can be used by sponge larvae for settlement. These large, suspension-feeding animals act as baffles that slow currents at the seabed, causing entrained sediment to drop out of suspension [START_REF] Krautter | Recent Hexactinosidan sponge reefs (silicate mounds) off British Columbia, Canada: frame-building processes[END_REF]. This process results in the development of three-dimensional mound structures composed of massive, clay-rich sediments and siliceous sponge skeletons, with live reef-building sponges attached to exposed sponge skeletons on the reef surface (Conway et al., 2005a;[START_REF] Krautter | Recent Hexactinosidan sponge reefs (silicate mounds) off British Columbia, Canada: frame-building processes[END_REF]. Individual reef mounds grow with time, and aggregations of these mounds form large reef complexes, which have been identified off British Columbia, Canada, discontinuously covering over 700 km 2 of the continental shelf in the Queen Charlotte Basin (QCB) [START_REF] Conway | Holocene sponge bioherms on the western Canadian continental shelf[END_REF][START_REF] Krautter | Discovery of a "living dinosaur": globally unique modern Hexactinellid sponge reefs off British Columbia, Canada[END_REF]. A number of smaller complexes have also been described in the Georgia Basin (GB) [START_REF] Conway | Modern siliceous sponge reefs in a turbid siliciclastic setting: Fraser River delta, British Columbia, Canada[END_REF]Conway et al., 2005a;[START_REF] Conway | Mapping sensitive benthic habitats in the Strait of Georgia, coastal British Columbia: deep-water sponge and coral reefs[END_REF],and these are the focus of this paper.

The Strait of Georgia, which forms a large part of the Georgia Basin, is an enclosed body of water with moderately strong tidal currents and large fresh water input from the Fraser River. The Fraser River strongly influences sedimentation rates and organic flux in the GB (Burd et al., this issue; Hill et al., this issue). Multibeam mapping, geophysical surveys and textural data from grab samples indicate a complex pattern of sediment accumulation, transport and erosion in the southern strait [START_REF] Barrie | Georgia Basin: Seabed features and marine geohazards[END_REF]. The oceanographic and geologic settings of the reef complex on the Fraser Ridge (reef 1) and the McCall Bank complexes (reefs 2 -4) (see Fig. 1 for locations) in the GB are described by [START_REF] Conway | Modern siliceous sponge reefs in a turbid siliciclastic setting: Fraser River delta, British Columbia, Canada[END_REF] and Conway et al. (2005a), respectively. The geologic setting of the reef complexes near the entrance to Active Pass in the GB is described by [START_REF] Conway | Mapping sensitive benthic habitats in the Strait of Georgia, coastal British Columbia: deep-water sponge and coral reefs[END_REF].

The QCB reef complexes support diverse communities that are distinct from surrounding shelf communities and play a role as nursery habitats for rockfish (Sebastes spp.) [START_REF] Cook | Ecology of the Hexactinellid sponge reefs on the Western Canadian continental shelf[END_REF]. Rockfish are commercially important and have been subject to conservation efforts in recent years [START_REF] Dfo | Rockfish conservation areas: protecting British Columbia's rockfish[END_REF]. Juvenile rockfish have been found at abundances five times higher on live reefs than on adjacent dead reef and off-reef areas in the QCB [START_REF] Cook | Ecology of the Hexactinellid sponge reefs on the Western Canadian continental shelf[END_REF]. Dead portions of the reefs, which are less structurally complex and mainly consist of sponge skeleton rubble, were also found to have significantly lower taxonomic richness and abundance of invertebrate fauna than live reef areas [START_REF] Cook | Ecology of the Hexactinellid sponge reefs on the Western Canadian continental shelf[END_REF]. There

have not yet been any studies characterizing the community associated with the reef complexes in the GB.

The reef-building sponge species in the GB are Aphrocallistes vastus and Heterochone calyx. The reef-building species are found on gravel and rock substrates, such as glacial till ridges [START_REF] Krautter | Recent Hexactinosidan sponge reefs (silicate mounds) off British Columbia, Canada: frame-building processes[END_REF], which can be found in very close proximity to the Fraser River on the Fraser Ridge (see Fig. 1) [START_REF] Conway | Modern siliceous sponge reefs in a turbid siliciclastic setting: Fraser River delta, British Columbia, Canada[END_REF]. The GB reef complexes are found in water depths of 90-300 m where bottom currents prevent sediment from accumulating (Conway et al., 2005a). The GB reefs grow in linear patterns along ridges, sometimes forming distinctive 'chevron' [START_REF] Conway | Mapping sensitive benthic habitats in the Strait of Georgia, coastal British Columbia: deep-water sponge and coral reefs[END_REF] or wave-form shapes (Conway et al., 2005a). The reef mounds in the GB have been recorded to heights of 14 m above the sea-floor [START_REF] Conway | Modern siliceous sponge reefs in a turbid siliciclastic setting: Fraser River delta, British Columbia, Canada[END_REF]Conway et al., 2005a).

Sidescan sonar and video surveys in the QCB undertaken between 1991 and 2002 revealed that damage had been done to some of the reef complexes in areas heavily fished by bottom trawlers [START_REF] Krautter | Discovery of a "living dinosaur": globally unique modern Hexactinellid sponge reefs off British Columbia, Canada[END_REF][START_REF] Conway | Hexactinellid sponge reefs on the Canadian continental shelf: a unique 'living fossil[END_REF]. Fisheries and Oceans Canada closed the QCB reefs to bottom trawling in July 2002 in recognition of their susceptibility to the effects of fishing gear and is considering designating them as Marine Protected Areas [START_REF] Jamieson | Hexactinellid sponge reefs: areas of interest as marine protected areas in the North and Central Coast areas[END_REF]. [START_REF] Conway | Mapping sensitive benthic habitats in the Strait of Georgia, coastal British Columbia: deep-water sponge and coral reefs[END_REF] qualitatively described the health of the sponge reef complexes (healthy or unhealthy) in the GB; however, this was not a systematic description from the video and the terms 'healthy' and 'unhealthy' were not defined. This study builds upon that work with the goals of using a systematic analysis of the ROV video surveys to make a preliminary assessment of the status, or condition, of the surveyed sponge reef complexes in the Georgia Basin, and of characterizing the megafaunal communities associated with each. Possible reasons for status and differences in associated fauna among reef complexes will be discussed.

Materials and methods

Reef status

Sponge reefs in the GB were originally mapped using multibeam bathymetry and sidescan sonar collected and analyzed to determine possible locations and extents of sponge reef complexes in the GB (Conway et al., 2005a). In this paper, the status of the reefs and their associated megafaunal organisms were assessed using video transects collected by the Pacific Geoscience Centre between 2002 and 2006 (see Table 1).

These transects were collected using a digital video camera mounted on either a Phantom HD2 Remotely Operated Vehicle (ROV) or the Remotely Operated Platform for Ocean Science (ROPOS). Both vehicles had laser pointers mounted 10 cm apart that were visible in the video. The remotely operated vehicle transects ranged from 420 to 5718 m in length, and the compiled video segments provide a transect for each complex.

The categories of reef status are: undamaged, damaged, damaged and possibly recovering, and unknown. Observations of the condition of the reef-building sponges were made along the on-reef portions of each transect, by recording estimates of percent alive or dead as well as the condition of the dead sponge (standing or fragmented and broken). Status was assigned based on the condition of the majority (>50%) of the transect. An undamaged reef consists mainly of areas of live reef-building sponges (Fig. 2a) (Aphrocallistes vastus and Heterchone calyx) and areas of standing dead sponge (Fig. 2b) growing on mounds of dead sponge skeletons and skeletal fragments in a sediment matrix. A damaged reef consists mainly of areas of broken and fragmented dead sponge, possibly with small areas of standing dead sponge (Fig. 2c), and few isolated live reef-building sponges. A damaged and possibly recovering reef consists of mostly broken and fragmented dead sponge, but with widespread areas where young reef-building sponges are colonizing the fragmented, dead sponge skeletons (Fig. 2d).

Unknown status indicates that the reef complex has been identified but not yet surveyed using video techniques.

Associated Fauna

The whole of each transect was viewed, and all visible megafauna were identified to the lowest taxonomic level possible aided by digital photos taken by ROPOS (see Table 2).

Reef 4 was not included in this analysis, because the video became corrupted after the reef status was determined. Each transect was divided into sections based on whether the video was on-reef or off-reef. The abundance of organisms was recorded for the onreef sections in a semi-quantitative way, either by counting the number of individuals, or, if the number of individuals was difficult to establish due to visibility, complex terrain or very high abundance, by estimation. Counts and estimates were converted into a measure of relative abundance (Few<Some<Many) for each reef complex, in recognition of the fact that accurately quantifying some organisms was not feasible (criteria for the conversion to relative abundance are described below; Table 2). The relative abundance of different taxa is useful for comparing differences in faunal composition among reefs.

Results

Reef distribution and status

Fig. 1 shows the locations of reef complexes in the Georgia Basin as identified from analysis of multibeam swath bathymetry data [START_REF] Conway | Mapping sensitive benthic habitats in the Strait of Georgia, coastal British Columbia: deep-water sponge and coral reefs[END_REF]. Table 1 lists the reef complexes by number, with geographic location, dive number, date surveyed and current status as determined from video analysis. The reefs are numbered in order of their discovery (after [START_REF] Conway | Mapping sensitive benthic habitats in the Strait of Georgia, coastal British Columbia: deep-water sponge and coral reefs[END_REF]. Seven of the 14 identified reef complexes in the GB have been surveyed visually.

Four of the seven surveyed reefs (3, 6, 9 and 13) were classified either as damaged (3 and 9), or as damaged and possibly recovering (6 and 13), based on video surveys. The remaining three (1, 4 and 7) were classified as undamaged.

Associated fauna

Table 2 presents the reef complexes on which each taxon was present. Only four taxa were found on all six classified reef complexes for which there was usable video: spot prawns (Pandalus platyceros), squat lobsters (Munida quadrispina), blood stars (Henricia sp.) and ratfish (Hydrolagus colliei), which are all common species in British Columbia's subtidal coastal waters (Cook, unpublished data from video surveys of B.C. coast). The reef complex with the highest number of observed taxa (24) was undamaged reef 7. Six of the taxa at this reef complex were species of rockfish (Sebastes spp.). The lowest number of taxa (8) was observed at reef complex 1 (undamaged). The damaged reef in the southern part of the GB (reef 9) had 12 taxa, and the damaged reefs in the northern GB (3, 6 and 13) had between 15 and 20 taxa each.

Table 3 includes relative abundance data for each of the taxonomic groups identified in Table 2 for each reef complex. The northern group of reefs (3 (damaged), 6 and 13 (damaged and possibly recovering)) had the highest relative abundance of lyssacine sponges and demosponges, and was the only set of reefs where shortspine thornyheads (Sebastolobus alascanus) were present. Brittle stars and sea urchins were only observed at high relative abundance at reef 9 (damaged). Reef complex 7 (undamaged) had the highest relative abundance of rockfish (Sebastes spp.). All other reefs had relatively few rockfish. For example, 176 juvenile and adult rockfish were observed on reef 7 (undamaged), and only 4 rockfish were observed on reef 9 (damaged). Corals, mostly large Gorgonians, were observed on reefs 1 and 7 (both undamaged) in the southern GB, although the highest abundance of corals was on reef 13 (damaged and possibly recovering) in the northern GB.

Discussion

Reef distribution and status

Glass sponge reefs are distributed across a diverse range of oceanographic conditions and depths in the Georgia Basin; however, more than half of the surveyed reef complexes in the GB have been damaged. Reef-building glass sponges are brittle and prone to fragmentation with physical contact. The nature of damaged reefs surveyed in this study, with highly fragmented dead sponge skeleton and little or no standing dead sponge, suggests that the reef complexes were damaged mechanically. It is well documented that certain forms of fishing, such as bottom trawling, can cause this type of damage to large sessile benthic fauna, including glass sponges on sponge reefs [START_REF] Krautter | Discovery of a "living dinosaur": globally unique modern Hexactinellid sponge reefs off British Columbia, Canada[END_REF], other megafaunal sponges [START_REF] Freese | Effects of trawling on seafloor habitat and associated invertebrate taxa in the Gulf of Alaska[END_REF] and deep-water corals [START_REF] Hall-Spencer | Trawling damage to Northeast Atlantic ancient coral reefs[END_REF][START_REF] Fosså | The deep-water coral Lophelia pertusa in Norwegian waters: distribution and fishery impacts[END_REF][START_REF] Reed | Mapping, habitat characterization, and fish surveys of the deep-water Oculina coral reef Marine Protected Area: a review of historical and current research[END_REF]. Sidescan sonar data from damaged reef complex 3 shows relatively continuous and frequently parallel tracks or marks on the seabed (Fig. 3), which were likely left by mobile fishing gear, such as heavy net doors on otter trawls. These marks have been described on reef complexes in QCB in areas where the trawl fisheries are or have been active (Conway et al., 2001;[START_REF] Krautter | Discovery of a "living dinosaur": globally unique modern Hexactinellid sponge reefs off British Columbia, Canada[END_REF].

The presence of young reef-building sponges on damaged reefs 6 and 13 is evidence that re-colonization can occur. Individual reef-building sponges were often observed growing on bedrock or glacial till substrate adjacent to the damaged reefs (Fig. 4) [START_REF] Conway | Mapping sensitive benthic habitats in the Strait of Georgia, coastal British Columbia: deep-water sponge and coral reefs[END_REF], and these off-reef areas could provide a source of larvae for recolonization. Possible recovery time for a reef complex can only be suggested based on growth rates and size of the reef complexes. The reef-building sponge Aphrocallistes vastus has a calculated mean growth rate of 1 cm per year and a maximum rate of 7 cm per year [START_REF] Krautter | Discovery of a "living dinosaur": globally unique modern Hexactinellid sponge reefs off British Columbia, Canada[END_REF], calculated from data in [START_REF] Levings | A unique collection of baseline biological data: benthic invertebrates from an underwater cable across the Strait of Georgia[END_REF]. The size of the reefs makes it likely that recovery would occur on a time scale of hundreds of years (Conway et al., 2005b). Lyssacine glass sponges, such as Acanthascus (Rhabdocalyptus) dawsoni, and encrusting and erect forms of demosponges, such as Vulcanella sp. or Desmacella sp., also colonize dead sponge skeleton [START_REF] Cook | Ecology of the Hexactinellid sponge reefs on the Western Canadian continental shelf[END_REF][START_REF] Lehnert | Desmacella austini sp. nov. from sponge reefs off the Pacific coast of Canada[END_REF]. These taxa were observed on most of the damaged reefs, suggesting that these sites are still capable of sustaining a large suspension feeding community. It appears that lyssacine sponges can be primary colonizers of dead reefs, which is not surprising since Acanthascus (Rhabdocalyptus) dawsoni has twice the mean growth rate of Aphrocallistes vastus [START_REF] Leys | Hexactinellid sponge ecology: growth rates and seasonality in deep water sponges[END_REF]. However, there is currently no literature available on the progression of colonization on dead sponge fragments.

Reef complex 1 (undamaged) is unique in that it is beneath the buoyant particulate plume of the Fraser River. Although the ridge at reef complex 1 is a remnant glacial feature rising above the sedimented basin, it is in an area with an unusually high sedimentation rate (see Table 1 and Burd et al., this issue). [START_REF] Leys | Patterns of glass sponge (Porifera, Hexactinellida) distribution in coastal waters of British Columbia, Canada[END_REF] and [START_REF] Farrow | Suspended particulate loading on the macrobenthos in a highly turbid fjord: Knight Inlet, British Columbia[END_REF] suggest that high sedimentation rates are associated with lower abundance of glass sponges, since a sediment veneer can negatively affect the ability of glass sponges to become established. In the case of reef complex 1, tidal currents are sufficiently strong to keep sediment in suspension and the ridge surface non-depositional [START_REF] Conway | Modern siliceous sponge reefs in a turbid siliciclastic setting: Fraser River delta, British Columbia, Canada[END_REF], allowing glass sponges to colonize the gravel substrate. The reef mounds on the ridge enlarge as growing sponges baffle the tidal currents and trap suspended sediment [START_REF] Krautter | Recent Hexactinosidan sponge reefs (silicate mounds) off British Columbia, Canada: frame-building processes[END_REF]. The reef-building sponges on reef 1 were observed to be more tube-shaped, with narrower oscula compared to the reef complexes in the QCB [START_REF] Conway | Modern siliceous sponge reefs in a turbid siliciclastic setting: Fraser River delta, British Columbia, Canada[END_REF] and to the other reefs in the GB. According to evidence from the fossil record, a narrower osculum can compensate for increased sedimentation rates and reduce the amount of sediment trapped in the sponge cavity. This adaptation helps to prevent sediment from overwhelming cleaning mechanisms, which can cause the death of the sponge [START_REF] Conway | Modern siliceous sponge reefs in a turbid siliciclastic setting: Fraser River delta, British Columbia, Canada[END_REF]. The presence of a healthy sponge reef beneath the Fraser River plume shows that these organisms can adapt to unusual sedimentation conditions, if current regime, seabed sediment transport rates, temperature, and dissolved oxygen and silica levels are suitable [START_REF] Leys | Patterns of glass sponge (Porifera, Hexactinellida) distribution in coastal waters of British Columbia, Canada[END_REF][START_REF] Whitney | Oceanographic habitat of sponge reefs on the Western Canadian Continental Shelf[END_REF].

The most recently discovered reef complex (14 in Howe Sound, see Fig. 1 for location) was identified by Natural Resources Canada personnel (unpublished data, 2008), subsequent to the publication of the discovery of the other sponge reefs by [START_REF] Conway | Mapping sensitive benthic habitats in the Strait of Georgia, coastal British Columbia: deep-water sponge and coral reefs[END_REF]. Reef complex 14 appears to be undamaged; however, ROV survey videos of that reef have not yet been analyzed and further work will be required to assess the status of this reef complex and its associated faunal community.

Associated fauna

Reef-building sponges appear to be foundation species, as defined by [START_REF] Dayton | Experimental evaluation of ecological dominance in a rocky intertidal algal community[END_REF], since they are organisms that create habitat for other organisms, and thereby exert a disproportionately large influence on community structure. Therefore, fauna associated with the reefs could be affected by changes to the status of the reef. To determine the effect of reef status on the associated community, a comparison was made between reefs 7 (undamaged) and 9 (damaged) in the southern basin, which are located close together (~8 km apart) and were surveyed only days apart. The higher number of taxa and greater abundance of both adult and juvenile rockfish at reef 7 (undamaged) is consistent with published results that link increased habitat complexity, or structural heterogeneity, to increased taxonomic richness and abundance of individuals [START_REF] Crowder | Habitat structural complexity and the interaction between bluegills and their prey[END_REF][START_REF] Diehl | Fish predation and benthic community structure: the role of omnivory and habitat complexity[END_REF][START_REF] Garcia-Charton | Correlation between habitat structure and a rocky reef fish assemblage in the Southwest Mediterranean[END_REF][START_REF] Wyda | The Response of fishes to submerged aquatic vegetation complexity in two ecoregions of the Mid-Atlantic Bight: Buzzards Bay and Chesapeake Bay[END_REF][START_REF] Garcia-Charton | Multi-scale spatial heterogeneity, habitat structure, and the effect of marine reserves on Western Mediterranean rocky reef fish assemblages[END_REF]. It is therefore likely that undamaged sponge reefs in the GB can provide refugia for adult rockfish and a nursery habitat for juveniles, as found in the QCB [START_REF] Cook | Ecology of the Hexactinellid sponge reefs on the Western Canadian continental shelf[END_REF]. However, it should be noted that the other undamaged reef where fauna were assessed (reef 1), had the lowest number of taxa of all the surveyed reefs. This result seems inconsistent with the supposition that sponge reefs in the GB are refugia supporting enhanced bio-diversity. However, as mentioned in section 4.1, this reef complex is in a unique oceanographic setting, with a high concentration of suspended sediment and a high sedimentation rate, which may be less than ideal for the settlement of other sessile species typically associated with the reefs. Regional variations in physical and biological factors have been shown to affect the distribution and abundance of fish assemblages [START_REF] Garcia-Charton | Multi-scale spatial heterogeneity, habitat structure, and the effect of marine reserves on Western Mediterranean rocky reef fish assemblages[END_REF]; the same may be true for invertebrate fauna. A statistically rigorous comparison of reef fauna between damaged and undamaged reefs was not possible using this dataset; however these results provide a preliminary basis for more in-depth assessment of the reefs in the future.

Reef 6 (damaged, possibly recovering) had the highest number of taxa of the northern GB complexes. Unfortunately, there were no undamaged reefs in the northern GB on which the fauna could be assessed for this study, so it cannot be determined whether the taxonomic richness observed on reef 6 was typical of the area. Reef 13 (damaged, possibly recovering), also in the northern GB, had a higher relative abundance of sessile filter feeders than did the other reef complexes. Hydrodynamic conditions or biological factors, such as abundance of suspended food particles, may encourage settlement of these sessile filter feeders at damaged reef sites.

One of the consequences of trawling damage is to decrease habitat complexity [START_REF] Watling | Disturbance of the seabed by mobile fishing gear: a comparison to forest clearcutting[END_REF][START_REF] Kaiser | Fishing-gear restrictions and conservation of benthic habitat complexity[END_REF]. This could be especially detrimental for the juvenile fish that use these complex structural habitats. For example, it was observed that the shortspine thornyheads (Sebastolobus alascanus) on the damaged reefs in the northern GB, which were almost all in the juvenile to intermediate colour phase [START_REF] Love | The rockfishes of the Northeast Pacific[END_REF], were frequently observed within or near the scattered areas of higher relief, such as patches of standing dead sponge. Juvenile rockfish (Sebastes spp.) also have an affinity for structurally complex habitats (O' Connell and Carlile, 1994;[START_REF] Cote | Microhabitat use of juvenile Atlantic cod in a coastal area of Newfoundland determined by 2D telemetry[END_REF][START_REF] Diaz | The importance of physical and biogenic structure to juvenile fishes on the shallow inner continental shelf[END_REF]. Rockfish are a dwindling fisheries resource throughout the Pacific Northwest and have been the focus of conservation initiatives in recent years [START_REF] Ralston | The status of federally managed rockfish on the U.S West Coast[END_REF][START_REF] Musick | Marine, estuarine, and diadromous fish stocks at risk of extinction in North America (exclusive of Pacific salmonids)[END_REF][START_REF] Yamanaka | Inshore rockfish: Pacific Region DFO Science Stock Status Report[END_REF][START_REF] Dfo | Rockfish conservation areas: protecting British Columbia's rockfish[END_REF]. Protection of refugia and nursery habitat, such as sponge reefs, would be consistent with this conservation strategy [START_REF] Yoklavich | Applications of sidescan sonar and in situ submersible survey techniques to marine fisheries habitat research[END_REF].

Conclusions

The sponge reefs in the GB exist in a range of bathymetric settings and oceanographic conditions, and are distributed throughout the GB. Over half of the reefs that have been visually surveyed show significant damage, likely by fishing activities, such as bottom trawling. The damaged reefs appear to be capable of recovery, although the time required for sponge and reef re-growth is unknown. Undamaged reefs appear to have the potential to act as refugia and nursery habitat for commercially valuable fish species.

Trawl closures have been implemented as a fisheries management measure at the large sponge reef complexes in the Queen Charlotte Basin in recognition of their fragile nature and importance to fisheries resources; similar protection may be warranted for the sponge reefs in the Strait of Georgia.

Figure Titles

Fig. 1. Location of known glass sponge reef complexes in the Georgia Basin. They are numbered in order of discovery by multibeam swath bathymetry surveys conducted by the Geological Survey of Canada (after [START_REF] Conway | Mapping sensitive benthic habitats in the Strait of Georgia, coastal British Columbia: deep-water sponge and coral reefs[END_REF]. Only six complexes (1,3,6,7,9,13) have been surveyed using visual techniques. Fig. 2. A) Dense live reef-building sponges (undamaged reef 7), B) Standing dead sponge skeleton (damaged and possibly recovering reef 13). Crimson anemones (Cribrinopsis fernaldi), boot sponges (Rosselid sponges) and a small reef building sponge are attached, C) Fragmented dead sponge skeleton spread over the seabed (damaged reef 9), D) Small reef-building sponges attached to fragmented dead sponge skeleton (damaged but possibly recovering reef 6). Several tube-dwelling anemones (Pachycerianthus fimbriatus) are also present.

ACCEPTED MANUSCRIPT

Figure3

Table 3 Relative abundance of invertebrate groups between surveyed reef complexes (F=Few<S=Some<M=Many). A line indicates none were observed. Measure indicates whether individuals were counted (C) or estimated (E). Criteria for converting estimates and counts into a relative abundance is given below the table.

19 † For all taxa where total number of individuals was estimated F=<10, S=10-50 and M=>50.

*For taxa where individuals were counted (except Sea Stars) F=<10, S=10-20 and M=>20.

**For Sea Stars F=<15, S=15-50 and M=>50; this criteria is different from the other taxa that were counted due to the higher general abundance of this taxon.

Reef

S F  F F  M F F F  F   M 3 F   S S F M F S   F S F S 6   S S S  S M M   S S M M 7 F F  F F F S M F F  M  F S 9 F    F  F S M M M F  F M 13 M M M M M  M S S    M F S Measure E † C* E E E C E C C** C E C C C E

Fig. 3 .

 3 Figure TitlesFig.1. Location of known glass sponge reef complexes in the Georgia Basin. They are numbered in order of discovery by multibeam swath bathymetry surveys conducted by the Geological Survey of Canada (after[START_REF] Conway | Mapping sensitive benthic habitats in the Strait of Georgia, coastal British Columbia: deep-water sponge and coral reefs[END_REF]. Only six complexes(1,3,6,7,9,13) have been surveyed using visual techniques. Fig.2. A) Dense live reef-building sponges (undamaged reef 7), B) Standing dead sponge skeleton (damaged and possibly recovering reef 13). Crimson anemones (Cribrinopsis fernaldi), boot sponges (Rosselid sponges) and a small reef building sponge are attached, C) Fragmented dead sponge skeleton spread over the seabed (damaged reef 9), D) Small reef-building sponges attached to fragmented dead sponge skeleton (damaged but possibly recovering reef 6). Several tube-dwelling anemones (Pachycerianthus fimbriatus) are also present. Fig. 3. Sidescan sonar and interpretation from reef complex 3 (McCall Bank) showing parallel lines in the reef surface that are interpreted as the marks left from the heavy doors of bottom trawl gear. Fig. 4. Reef-building sponges growing on glacial till adjacent to the reef complexes in the McCall Bank area.D

Acknowledgments

Funding for this study was provided through the Ambient Monitoring Program for the southern Strait of Georgia, which arises from a collaborative agreement between the Department of Fisheries and Oceans, Metro Vancouver (formerly the Greater Vancouver Regional District) and Natural Resources Canada.

Table 1 Current status of the glass sponge reefs in the Georgia Basin. The reef complexes are numbered in order of their discovery, after [START_REF] Conway | Mapping sensitive benthic habitats in the Strait of Georgia, coastal British Columbia: deep-water sponge and coral reefs[END_REF].