Habitats & ecology
 
  Included in this section is the topic of glass-sponge reefs, while GROWTH FORMS, and CHIMNEYS are considered elsewhere.
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  Glass-sponge reefs
 
Research study 1
 

map of the west coast of British Columbia showing the different inlets studied for sponge reefs in the submersible Pisces IV
Southwest corner of British Columbia up to southern Alaska. Inlets sampled are shown in bold typeface

Glass sponges (Hexactinellida) are difficult to study because most species grow only in deep water (500-3000m). British Columbia fjords are unusual in having hexactinellids growing abundantly from 16-650m in depth. The only other areas in the world where glass sponges grow shallower than 50m are in Antarctica, southern New Zealand, and a few caves in the Mediterranean. Deep surveys of British-Columbia fjords by the manned submersible ‘Pisces IV’ indicate that highest abundances coincide with seawater containing high levels of dissolved silicate, low light levels, reasonably high oxygen levels, temperatures between 9-10oC, and low amounts of suspended sediments.

photograph of interior of submersible Pisces IV

 

 

 

Inside view of Pisces IV
showing external
video feed

 

The graph shows the depth distributions for two major groups of glass sponges in Jervis Inlet, the ‘dyctyonine' sponges (sponges with fused spicules, such as Aphrocallistes vastus and Heterochone calyx) and the ‘lyssacine’ sponges (sponges with a skeleton loosely held together by tissue strands, such as Rhabdocalyptus dawsoni, Staurocalyptus dowlingi, and Acanthascus sp.). The authors note an oxygen minimum layer at 150-300m depth in Jervis Inlet that is stable for most of the year and may explain the abrupt disjunction in abundance at this depth.  Leys et al. 2004 Mar Ecol Prog Ser 283: 133.

NOTE  a paper contemporaneous with this one written by a consortium of international scientists provides a detailed list of oceanographic conditions associated with glass-sponge habitats in Hecate Strait, British Columbia.  Whitney et al. 2005 Continental Shelf Res 25: 211.

histograms showing depth distributions of different types of sponges in Jervis Inlet, British Columbia
 
photograph of hexactinellid sponge Aphrocallistes vastus courtesy  Sally Leys and the Department of  Fisheries & Oceans, Canada
DYCTYONINE: Aphrocallistes vastus
(above Left, 0.05X), Heterochone calyx
(above Right, 0.05X).
Photos courtesy
Sally Leys and the Department of
Fisheries & Oceans, Canada
photograph of deep-water sponge Heterochone calyx courtesy  Sally Leys and the Department of  Fisheries & Oceans, Canada photograph of hexactinellid sponge Rhabdocalyptus dawsoni courtesy  Sally Leys and the Department of  Fisheries & Oceans, Canadaphotograph of a deep-water sponge Staurocalyptus dawlingi courtesy  Sally Leys and the Department of  Fisheries & Oceans, Canadaphotograph of a deep-water sponge Acanthascus sp courtesy  Sally Leys and the Department of  Fisheries & Oceans, Canada
LYSSACINE: Rhabdocalyptus dawsoni (above Left, 0.1X), Staurocalyptus dawlingi ( above Middle), Acanthascus sp. (above Right)
   
 

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Research study 2

 

maps of the Haida Gwai and Georgia Strait regions of British Columbia showing the location of glass-sponge reefs

 

sonargram of a sponge-reef ridge at depth

Multibeam imagery and ROV photography/collection surveys show that the area along the British Columbia continental shelf is host to 5 large sponge-reef complexes, 2 of which in Haida Gwaii (Queen Charlotte Islands) are hundreds of km2 in size.
In the Strait of Georgia basin northwest of Vancouver there are 3 large reef complexes.
These consist of ridges up to 7km long and 21m in height. 
 
photograph of several hexactinellid sponges Heterochone calyx courtesy Kim Conway, Geological Survey of Canada, Canadian Hydrographic Service, and Environment CanadaTwo predominant sponge components of the Georgia basin reefs are the hexactinellids Heterochone calyx and Aphrocallistes vastus, some specimens of which grow to over 1m in height (both photos 0.1X) photograph of several hexactinellid sponges Aphrocallistes vastus courtesy Kim Conway, Geological Survey of Canada, Canadian Hydrographic Service, and Environment Canada
 
   
  Such reef complexes are unique, having been identified only in these Canadian west-coast areas. The authors note their similarity to extinct Mesozoic sponge reefs found in Europe and elsewhere, and point out the unique opportunity to study these living reefs to shed light on the morphology and processes of formation of their fossilised counterparts. They also note the fragility and vulnerability of the reefs to the groundfish trawl-fishery industry. The Department of Fisheries and Oceans of Canada is currently considering the status of these reefs as potential marine protected areas (MPAs).  Conway et al. 2005 Geo-Mar Lett 25: 205; see also Conway et al. 2001 Geoscience Canada 28: 71. All photos and visuals courtesy Kim Conway, Geological Survey of Canada, Canadian Hydrographic Service, and Environment Canada
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Research study 3
 

photograph of trawling marks on glass-sponge reefAs their name implies, glass-sponge reefs are highly sensitive to mechanical damage, whether this be from fishes, mammals, or fishing gear.  Of 14 deep-water reefs mapped using multibeam bathymetry and sidescan sonar in the Georgia Basin, British Columbia, 7 of these have been visually examined by scientists in Victoria, British Columbia using video from ROV-mounted cameras.  Of the 7, three are found to be undamaged, 2 are quite badly damaged, and 2 are damaged but seem to be recovering (see photographs below).  Close scrutiny of the damaged reefs reveal tracks characteristic of those caused by bottom-dragged fishing gear (see photograph on Right).  The authors list at least 10 animal taxa associated with the reefs, and note that undamaged reefs host more adult and juvenile rockfishes than damaged ones.  Recovery from damage is slow.  With growth rates measured in just a few cm per year, recovery of a large reef may take hundreds of years.  The authors do not discuss the “conservation status” of these Georgia-Strait reefs specifically, but other glass-sponge reefs in the the province in Hecate Strait are presently identified by the Federal Ministry of Fisheries and Oceans as an “Area of Interest” for a future Marine Protected Area (MPA).  Cook et al. 2008 Mar Environmental Res 66: S80-S86. Photographs courtesy Kim Conway, Geological Survey of Canada, Canadian Hydrographic Service, and Environment Canada.


Marks photographed on one of the damaged
reefs are suggestive of scrapings made by the
large doors of bottom-trawling fishing boats

 
undamaged glass-sponge reef in the Georgia Basin complex
Example of an undamaged reef in Georgia Strait, B.C
damaged but possibly recovering glass-sponge reef in the Georgia Basin complex
Damaged but possibly recovering glass-sponge reef
damaged glass-sponge reef in the Georgia Basin complex
Damaged glass-sponge reef
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Research study 4
 

study sites for glass-sponge-reef investigationhistogram comparing reef sites for presence of juvenile rockfishesA follow-up study by the same research group shows, indeed, that glass-sponge gardens provide protective habitats for juvenile quillback rockfishes Sebastes maliger.   The reefs in question are several shallow-water ones (28-35m depth, see map) in the Strait of Georgia accessible to some extent by SCUBA-divers (see photograph) and by ROVs.  Interestingly, cloud sponges (mostly Aphrocallistes vastus) growing  directly on rocks (referred to as “sponge gardens”) host more newly recruited rockfishes than do the same sponges growing on dead and compacted sponges.  The histogram shows data for 3 types of rockfishes, but only the quillback variety is represented by new recruits; the 2 other species are represented by larger juveniles.  The difference between the 2 types of habitats appears to be in more space and food availability in the sponge-garden habitats, where biodiversity is found by the researchers to be comparatively high.  Marliave et al. 2009 Mar Biol 156: 2237.  Photographs courtesy the authors and the Canadian Hydrographic Service.

NOTE  the researchers document 106 species (from 10 phyla) in the sponge-rock habitat versus 15 species (5 phyla) in the other habitat

 
photograph of sponge gardens courtesy Marliave et al. 2009 Mar Biol 156: 2237 and Canadian Hydrographic Service
Sponge gardens at Texada Island at about 30m depth
photograph of glass-reef sponge habitat in Howe Sound courtesy  Marliave et al. 2009 Mar Biol 156: 2237 and Canadian Hydrographic Service
Glass sponge-on-dead sponges habitat in Howe Sound at 30m depth
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Research study 5
 

map showing glass reefs in the Strait of Georgiaglass sponge Aphrocallistes vastusA recent study from researchers at the University of Alberta employs ROV-mounted cameras to produce marvelous high-resolution photographic surveys of 3 glass-sponge reefs in the Strait of Georgia, Canada (see map).  The authors are able to map the reefs in 3-dimensional format with high precision.  Within a reef, the sponges grow in tightly clusterted bushes of oscula (oscula are 5-10cm in diameter), a result in large part of sideways budding from the bases of individual sponges (see photograph upper Left).  Each bud will grow into a new osculum.  Average depths of the reefs are 30-50m (depths in meters are indicated on the 3-dimensional maps below) and cover ranges from 12-26%.  The 3-dimensional growth of the sponges, up to 1m in height, provides habitat for fish and crustaceans.  The authors note that only 2 species of dyctyonine sponges Aphrocallistes vastus and Heterochone calyx comprise the reefs in the Strait of Georgia (see photographs below).  Note in these excellent visual reproductions that the reefs are not confined to the tops of ridges; rather, they occupy a wide range of slopes.  The 3 reefs featured in this study cover “several hundred thousand square meters”, but are dwarfed 1300-fold by an assemblage of large reefs in Hecate Strait in northern British Columbia (see Research Study 2 above).  Chu & Leys 2010 Mar Ecol Progr Ser 417: 97. Photographs courtesy the authors.

NOTE  glass sponges are categorised into 2 major groups: the lyssacine, with a structure of loose spicules, and the dyctyonine, with fused spicule

  photo composite of Howe Reef in Strait of Georgia courtesy Chu & Leys 2010 Mar Ecol Progr Ser 417: 97
  photo composite of Fraser Reef in Strait of Georgia courtesy Chu & Leys 2010 Mar Ecol Progr Ser 417: 97
 
photo composite of Galiano Reef in Strait of Georgia courtesy Chu & Leys 2010 Mar Ecol Progr Ser 417: 97
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