Like coral reefs, sponge reefs serve an important ecological function as feeding, breeding and nursery habitats for demersal fish and invertebrates but are currently threatened by the commercial fishery, offshore oil and gas industries.[3][4] Attempts are being made to protect these unique ecosystems through fishery closures and potentially the establishment of Marine Protected Areas (MPAs) around the sponge reefs.[3]
Characteristics of hexactinellid sponges
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.[3] 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 20–30minutes, but will stop again if the irritation is still present.[3]
Hexactinellids are exclusively marine and are found throughout the world in deep (>1000 m) oceans.[5] Individual sponges grow at a rate of 0–7cm/year, and can live to be at least 220years old.[6] 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.[5]
There are no known predators of healthy reef sponges.[6] This is likely because the sponges possess very little organic tissue; the siliceous skeleton accounts for 90% of the sponge body weight.[5]
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.
The primary frame-building sponges are all members of the order Hexactinosa, and include the species Chonelasma/Heterochone calyx (chalice sponge), Aphrocallistes vastus (cloud sponge), and Farrea occa.[6] Hexactinosan sponges have a rigid scaffolding of "fused" spicules that persists after the death of the sponge.
Other sponge species abundant on sponge reefs are members of the order Lyssactinosa (Rosselid sponges) and include Rhabdocalyptus dawsoni (boot sponge), Acanthascus platei, Acanthascus cactus and Staurocalyptusdowlingi.[6] Rosselid sponges have a "woven" or "loose" siliceous skeleton that does not persist after the death of the sponge, and are capable of forming mats, but not reefs.[3]
Location of sponge reefs
Sponge reefs can only be found off a small part of the northwest coast of North America
Although hexactinellid sponges are found worldwide in deep seawater, the only place that they are known to form reefs is between south east Alaska and off Grays harbor.[2][7][3][5] Communities of Rosselid sponges called "sponge mats" are widely distributed; they are found in canyons in the North Atlantic, in the Canadian Arctic and on Antarctic continental shelves.[5] There is also a reef formed of siliceous Demospongiae species off of Axel Heiberg Island in the Arctic Ocean.[8]
Four hexactinellid reefs were discovered in the Queen Charlotte Basin (QCB) in 1987–1988.[2] Three more reefs were reported in the Georgia Basin (GB) in 2005.[7] The QCB reefs are found 70–80km from the coastline in water 165–240m deep.[6] These reefs cover over 700km² of the ocean floor.[5]
Sponge reefs require unique conditions, which may explain their global rarity. They are found only in glacier-scoured troughs of low-angle continental shelf. The seafloor is stable and consists of rock, coarse gravel, and large boulders.[5] Hexactinellid sponges require a hard substrate, and do not anchor to muddy or sandy sea floors.[6]
They are found only where sedimentation rates are low, dissolved silica is high (43–75μM), and bottom currents are between 0.15 and 0.30m/s.[5] Dissolved oxygen is low (64–152μM), and temperatures are a cool 5.5-7.3°C at the reefs.[5] Surface temperatures range between 6°C in April and 14°C in August.[6]
Downwellings are common in Hecate Strait and Queen Charlotte Sound, especially in winter, but there is an occasional summer upwelling.[5] These upwellings bring nutrient-rich waters to the sponge reefs.
Structure of sponge reefs
Generalised food web for sponge reefs
Each living sponge on the surface of the reef can be over 1.5m tall. The reefs are composed of mounds called "bioherms" that are up to 21m high, and sheets called "biostromes" that are 2–10m thick and may be many kilometers wide.[5]
Each sponge in the order Hexactinosa has a rigid skeleton that persists after the death of the animal. This provides an excellent substrate for sponge larvae to settle upon, and new sponges grow on the framework of past generations. The growth of sponge reefs is thus analogous to that of coral reefs. The tendrils of new sponges wrap around spicules of older, deceased sponges. The tendrils will later form the basal plate of the adult sponge that firmly anchors the animal to the reef.
Deep ocean currents carry fine sediments that are captured by the scaffolding of sponge reefs. A sediment matrix of silt, clay, and some sand forms around the base of the sponge bioherms. The sediment matrix is soft near the surface, and firm below one metre deep.[6] Dead sponges become covered in sediment, but do not lose their supportive siliceous skeleton.[6] The sponge sediments have high levels of silica and organic carbon. The reefs grow parallel to the glacial troughs, and the morphology of reefs is due to deep currents.[7]
In the fossil record
Hexactinellids first appeared in the fossil record during the Late Proterozoic, and the first hexactinosans were found in the Late Devonian.[6] Hexactinellid sponge reefs were first identified in the Middle Triassic (245-208million years ago). The sponges reached their full extent in the late Jurassic (201-145million years ago) when a discontinuous reef system 7,000km long stretched across the northern Tethys and North Atlantic basins.[6] This chain of sponge reefs is the largest known biostructure to have ever existed on Earth.[6]
The sponge reefs declined throughout the Cretaceous period as coral and rudist reefs were becoming prominent.[6] It is theorized that the spread of diatoms may have been detrimental to the sponges, as diatoms compete with hexactinellid sponges for silica.[5]
It is estimated through radiocarbon dating of reef cores that the reefs have been living on the continental shelf of Western Canada for 8,500–9,000years.[2]
Ecological significance
Sponge reefs provide structure on the otherwise relatively featureless continental shelf. They provide habitat for fish and invertebrates, and may serve as an important nursery area for these animals. More research is required to determine the full ecological importance of these reefs.[2][3]
Observations by crewed submersible indicate that the fauna of sponge reefs differs from surrounding areas.[2] Organisms found in and around sponge reefs include annelid worms, bryozoans, spider crab, King crab, shrimp, prawns, and euphausids. Echinoderms, especially sea urchins and sea stars, were abundant in areas of the reef where the sponges were dying or deceased, and can be used as an indicator of sponge reef health.[6] Rockfish, especially Sebastes species, live in openings and in between sponges.[6] Gravid and juvenile rockfish were observed, suggesting that the reefs are being used as a nursery area.[5]Foraminiferans are abundant around the reefs, and diatoms are scarce. The consortium of organisms living in and around sponge reefs has changed very little since the Jurassic.[6]
Destruction of sponge reefs
Bottom trawling, in which a net is dragged along the sea floor, is particularly damaging to sponge reefs
The reefs are susceptible to damage by fishing, especially bottom trawling and dredging. In typical groundfish trawling, a large net is dragged across the ocean floor, its mouth held open by two 2tonne doors called otterboards. The siliceous skeleton of the sponges is fragile, and these organisms are easily broken by physical impact. The impacts of bottom trawling have been observed in three of the reefs in the QCB.[3] Trawling damage appears as parallel tracks 70–100 m apart that may extend for several kilometers. Each trawl track is 10cm deep, 20cm wide, and occurs at depths of 210–220m. Sponges in the vicinity of trawl tracks are shattered or completely removed.
While less harmful, hook and line fishing as well as crustacean trapping may also damage the reefs. When the fishing gear is hauled to the surface, the lines and traps drag along the ocean floor and have the potential to break corals and sponges. Broken sponge "stumps", as well as those with abraded sides, were found in regions where line and trap fishing took place.[3]
Breakage of reef sponges may have dire consequences for the recruitment of new sponges, as sponge larvae require the siliceous skeletons of past generations as a substrate.[6] Without a hard substrate, new sponges cannot settle and regrow broken parts of the reef. It has been estimated that broken sponge reefs may take up to 200years to recover.[3]
In addition, offshore oil and gas exploration threatens the reefs. The government of British Columbia has lifted a moratorium preventing exploratory drilling and tanker traffic in Hecate Strait and Queen Charlotte Sound, and the area has been leased by the oil and gas industry.[3] Even if exploratory drilling is not done on or immediately adjacent to the reefs, it may still have a negative impact by increasing the amount of sediment in the seawater, or through hydrocarbon pollution.[4]
Protection
In 1999, Fisheries and Oceans Canada requested that groundfishtrawlers voluntarily avoid the sponge reefs. In 2002, following reports of new reef damage sustained since 1999, the ministry initiated regulated closures of groundfish trawling and voluntary closures of shrimp trawl fishing in areas where sponge reefs were known to inhabit.[3]
Protection of the four sponge reefs in Hecate Strait and Queen Charlotte Sound was included as a "management issue" in the 2005/06 groundfish trawling management plan.[10] The management plan recommended that an additional 9km (5.6mi) buffer zone around the reefs be added to the existing groudfish trawl closures.[3] The reefs were also being considered as locations for future Marine Protected Areas (MPAs).[3] Although MPAs may be more effective than fishery closures for long-term protection of the reefs from bottom trawling, the oil and gas industry would still pose a threat.[10]
In 2008, the issue of preserving sensitive underwater ecosystems along the North Coast of British Columbia were consolidated within the Pacific North Coast Integrated Management Area. The goal was to develop a plan to conserve this relatively undeveloped region, while fostering sustainable economies on the coast, which promised to make Canada a world leader in marine conservation. However, in 2011, the ministry withdrew support for the process in favour of greater consistency with ocean planning on the other coasts of Canada.
Hexactinellid sponges are sponges with a skeleton made of four- and/or six-pointed siliceous spicules, often referred to as glass sponges. They are usually classified along with other sponges in the phylum Porifera, but some researchers consider them sufficiently distinct to deserve their own phylum, Symplasma. Some experts believe glass sponges are the longest-lived animals on earth; these scientists tentatively estimate a maximum age of up to 15,000 years.
Trawling is an industrial method of fishing that involves pulling a fishing net through the water behind one or more boats. The net used for trawling is called a trawl. This principle requires netting bags which are towed through water to catch different species of fishes or sometimes targeted species. Trawls are often called towed gear or dragged gear.
Venus' flower basket is a species of marine glass sponge found in the deep waters of the Pacific Ocean, usually at depths below 500 m (1,600 ft). Like other sponges, they feed by filtering sea water to capture plankton and marine snow. Similar to other glass sponges, they build their skeletons out of silica, which forms a unique lattice structure of spicules. The sponges are usually between 10 cm (3.9 in) and 30 cm (12 in) tall, and their bodies act as refuge for their mutualist shrimp partners. This body structure is of great interest in materials science as the optical and mechanical properties are in some ways superior to man-made materials. Little is known regarding their reproduction habits, however fluid dynamics of their body structure likely influence reproduction and it is hypothesized that they may be hermaphroditic.
Hecate Strait is a wide but shallow strait between Haida Gwaii and the mainland of British Columbia, Canada. It merges with Queen Charlotte Sound to the south and Dixon Entrance to the north. About 140 kilometres (87 mi) wide at its southern end, Hecate Strait narrows in the north to about 48 kilometres (30 mi). It is about 260 kilometres (160 mi) in length.
Bottom trawling is trawling along the seafloor. It is also referred to as "dragging". The scientific community divides bottom trawling into benthic trawling and demersal trawling. Benthic trawling is towing a net at the very bottom of the ocean and demersal trawling is towing a net just above the benthic zone. Bottom trawling can be contrasted with midwater trawling, where a net is towed higher in the water column. Midwater trawling catches pelagic fish such as anchovies and mackerel, whereas bottom trawling targets both bottom-living fish (groundfish) and semi-pelagic species such as cod, squid, shrimp, and rockfish.
Biogenic silica (bSi), also referred to as opal, biogenic opal, or amorphous opaline silica, forms one of the most widespread biogenic minerals. For example, microscopic particles of silica called phytoliths can be found in grasses and other plants.
Siliceous ooze is a type of biogenic pelagic sediment located on the deep ocean floor. Siliceous oozes are the least common of the deep sea sediments, and make up approximately 15% of the ocean floor. Oozes are defined as sediments which contain at least 30% skeletal remains of pelagic microorganisms. Siliceous oozes are largely composed of the silica based skeletons of microscopic marine organisms such as diatoms and radiolarians. Other components of siliceous oozes near continental margins may include terrestrially derived silica particles and sponge spicules. Siliceous oozes are composed of skeletons made from opal silica SiO2·nH2O, as opposed to calcareous oozes, which are made from skeletons of calcium carbonate (CaCO3·nH2O) organisms (i.e. coccolithophores). Silica (Si) is a bioessential element and is efficiently recycled in the marine environment through the silica cycle. Distance from land masses, water depth and ocean fertility are all factors that affect the opal silica content in seawater and the presence of siliceous oozes.
The habitat of deep-water corals, also known as cold-water corals, extends to deeper, darker parts of the oceans than tropical corals, ranging from near the surface to the abyss, beyond 2,000 metres (6,600 ft) where water temperatures may be as cold as 4 °C (39 °F). Deep-water corals belong to the Phylum Cnidaria and are most often stony corals, but also include black and thorny corals and soft corals including the Gorgonians. Like tropical corals, they provide habitat to other species, but deep-water corals do not require zooxanthellae to survive.
As with other countries, the 200 nautical miles (370 km) exclusive economic zone (EEZ) off the coast of the United States gives its fishing industry special fishing rights. It covers 11.4 million square kilometres, which is the second largest zone in the world, exceeding the land area of the United States.
Chatham Sound is a sound on the North Coast of British Columbia, Canada, bordering on Alaska, United States. It is located between the Dundas and Stephens Islands and the Tsimpsean Peninsula, it is part of the Inside Passage and extends from Portland Inlet in the north to Porcher Island in the south.
The cloud sponge(Aphrocallistes vastus) is a species of sea sponge in the class Hexactinellida. It is a deep-water reef-forming animal. The species was first described by F.E. Schulze in 1886.
Spicules are structural elements found in most sponges. The meshing of many spicules serves as the sponge's skeleton and thus it provides structural support and potentially defense against predators.
The Pacific North Coast Integrated Management Area is one of five Large Ocean Management Areas (LOMAs), areas of high ecological, social and economic importance, that have been identified by Fisheries and Oceans Canada (DFO) as priority regions for marine planning as part of Canada’s Oceans Action Plan.
Monorhaphis is a monotypic genus of siliceous deep sea Hexactinellid sponges. The single species is the type species Monorhaphis chuni, a sponge known for creating a single giant basal spicule (G.B.S.) to anchor the sponge in the sediments. The species was described by Franz Eilhard Schulze in 1904 from specimens collected by the German Deep Sea Expedition in 1898–1899. Monorhaphis is also the only genus in the monotypic family Monorhaphididae.
The Pacific Biological Station is a Research station in Departure Bay, Nanaimo, British Columbia, Canada. Established in 1908, with the Rev. George William Taylor as its first director and sole employee, it is the oldest fisheries research centre on the Pacific coast. Operated by Fisheries and Oceans Canada, the station forms a network with eight other scientific facilities.
Sponge grounds, also known as sponge aggregations, are intertidal to deep-sea habitats formed by large accumulations of sponges, often dominated by a few massive species. Sponge grounds were already reported more than 150 years ago, but the habitat was first fully recognized, studied and described in detail around the Faroe Islands during the inter-Nordic BIOFAR 1 programme 1987–90. These were called Ostur by the local fishermen and this name has to some extent entered the scientific literature. Sponge grounds were later found elsewhere in the Northeast Atlantic and in the Northwest Atlantic, as well as near Antarctica. They are now known from many other places worldwide and recognized as key marine habitats.
The silica cycle is the biogeochemical cycle in which biogenic silica is transported between the Earth's systems. Silicon is considered a bioessential element and is one of the most abundant elements on Earth. The silica cycle has significant overlap with the carbon cycle and plays an important role in the sequestration of carbon through continental weathering, biogenic export and burial as oozes on geologic timescales.
Hecate Strait and Queen Charlotte Sound Glass Sponge Reefs Marine Protected Area is a 2,410-square-kilometre marine protected area located in Hecate Strait and Queen Charlotte Sound off the North Coast of British Columbia, Canada. The marine protected area was established in February 2017 with the goal of conserving the biological diversity, structural habitat, and ecosystem function of four glass sponge reefs. These reefs were the first discovered living specimens and are the largest glass sponge reefs in the world.
Bolosoma is a genus of pedunculated siliceous sponges belonging to the family Euplectellidae. This genus lives in deep-sea environments and provides a habitat for a plethora of other benthic species, giving Bolosoma an incredibly important ecological role in the ecosystems it is a part of.
1 2 3 4 5 6 Hexactinellid sponge reefs on the British Columbia continental shelf: Geological and biological structure (Report). DFO Pacific Region Habitat Status Report. Department of Fisheries and Oceans. February 2000.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 Jamieson, G.S.; Chew, L. (2002). Hexactinellid sponge reefs: Areas of interest as marine protected areas in the north and central coast areas (Report). Can Sci Adv Sec Res Doc. Vol.12.
1 2 3 Conway, K.; Barrie, J.; Krautter, M. (2005). "Geomorphology of unique reefs on the western Canadian shelf: sponge reefs mapped by multibeam bathymetry". Geo-Mar Lett. 25 (4): 205–213. doi:10.1007/s00367-004-0204-z. S2CID129356194.
↑ Eluik, L. (1991). "Siliceous sponge communities, biological zonation, and recent sea-level change on the Arctic margin: Ice Island results: Discussion". Can J Earth Sci. 28 (3): 459–462. doi:10.1139/e91-040.
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