Tasmanian Seamounts

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Tasmanian Seamounts
Indian Ocean laea location map.svg
Red triangle with thick white border.svg
South of Tasmania
Summit depth660 and 1,700 m (2,000 and 6,000 ft) [1]
Height300 to 600 m (1,000 to 2,000 ft) [1]
Summit area25 km (16 mi) across [2]
Location
LocationSouth of Tasmania
Country Australia
Geology
Type Seamounts (underwater volcanoes)
Age of rock ~55 million years old [3]
Last eruption 7 million years ago

The Tasmanian Seamounts (also Tasman Seamounts and Tasmania Seamounts [4] ) are a group of seamounts (underwater volcanoes) located off the southern tip of Tasmania. The seamounts were created more than 55 million years ago by the Tasman hotspot. The seamounts are ecologically important, and harbor a lush marine ecosystem, but are threatened by overfishing. For this reason, part of the Tasmanian Seamounts were incorporated into a marine reserve in 1999.

Contents

Geology

The Tasmanian Seamounts were created by the Tasman hotspot, a 4,000 km (2,000 mi) long mantle plume that is currently the active center of Mount Erebus in Antarctica. [3] The seamounts, created roughly 55 million years ago, are between 1,000 and 2,000 m (3,000 and 7,000 ft) deep, 25 km (16 mi) across, and 200 to 500 m (700 to 1,600 ft) tall. [2]

Ecology

A specimen of Solenosmilia variabeles, a species of coral that forms the base of Tasmanian Seamounts' ecosystem Stony Coral.jpg
A specimen of Solenosmilia variabeles, a species of coral that forms the base of Tasmanian Seamounts' ecosystem

The Tasmanian Seamounts are an important feature of the south Tasmanian marine environment. While oceans generally contain few nutrients, the presence of seamounts increases the flowing speed of the water current. This effect, created by the topography of the seafloor mountain, clears rocks in the area of sediments and provides food for filter feeders. The swept rocks serve as substrate for sponges and corals to attach to. Among them are some of the longest–living organisms on Earth, reaching an age of "hundreds and possibly thousands of years". [5] The Tasmanian Seamounts in particular are dominated by the stony coral Solenosmilia variabeles; these corals provide a roost and living space for benthic mollusks, echinoderms and crustaceans like stone crabs (Parclamis sp.), squat lobsters ( Munidopsis treis ), and top snails ( Trochidae sp. ), thus solidifying the seamounts' ecology. Although many of these species are also found on the continental shelf, they are never found as concentrated or lush as they are on the seamounts. [2]

The seamounts have been the site of commercial trawling for orange roughy for decades. In 1994, the Australian Geological Survey Organization mapped the south Tasmanian seafloor, including the Tasmanian Seamounts; shortly thereafter, Environment Australia (now the Department of Sustainability, Environment, Water, Population and Communities) released a report stating that the Tasmanian Seamount fauna was highly diverse, inadequately studied, and vulnerable to overfishing, and recommended that an oceanic reserve be created on the site. An interim three–year ban on trawling was declared to allow a study of the seamounts to be carried out in 1997 which found 242 distinct species of invertebrates. 26% to 44% of them could not be identified and are thus believed to be new, and about a third are seemingly present only in the seamount environment. Damage from trawling was also examined, and on the most heavily affected seamounts it had destroyed coral aggregations, removed 46% of species, and reduced net biomass by over half. [1]

Following the study, the proposed marine reserve, the Tasmanian Seamount Community or Tasmanian Seamounts Marine Reserve was created as part of the Environment Protection and Biodiversity Conservation Act 1999. [4] The reserve banned fishing, especially trawling, within an area of 370 km2 (143 sq mi). It contained 70 seamounts, a fifth of the known Tasmanian seamounts, all of which were low-trawl areas and thus still in relatively unaffected form. [6] In a 2007 audit it was merged into the Huon Commonwealth Marine Reserve. [5] A more detailed bathymetric survey the same year found a total of 123 seamounts within the reserve, many of which were previously unknown. [2]

Related Research Articles

Protected areas of Tasmania consist of protected areas located within Tasmania and its immediate onshore waters, including Macquarie Island. It includes areas of crown land managed by Tasmanian Government agencies as well as private reserves. As of 2016, 52% of Tasmania's land area has some form of reservation classification, the majority is managed by the Tasmania Parks & Wildlife Service. Marine protected areas cover about 7.9% of state waters.

<span class="mw-page-title-main">Seamount</span> Mountain rising from the ocean seafloor that does not reach to the waters surface

A seamount is a large geologic landform that rises from the ocean floor that does not reach to the water's surface, and thus is not an island, islet or cliff-rock. Seamounts are typically formed from extinct volcanoes that rise abruptly and are usually found rising from the seafloor to 1,000–4,000 m (3,300–13,100 ft) in height. They are defined by oceanographers as independent features that rise to at least 1,000 m (3,281 ft) above the seafloor, characteristically of conical form. The peaks are often found hundreds to thousands of meters below the surface, and are therefore considered to be within the deep sea. During their evolution over geologic time, the largest seamounts may reach the sea surface where wave action erodes the summit to form a flat surface. After they have subsided and sunk below the sea surface such flat-top seamounts are called "guyots" or "tablemounts".

Benthic zone Ecological region at the lowest level of a body of water

The benthic zone is the ecological region at the lowest level of a body of water such as an ocean, lake, or stream, including the sediment surface and some sub-surface layers. The name comes from ancient Greek, βένθος (bénthos), meaning "the depths." Organisms living in this zone are called benthos and include microorganisms as well as larger invertebrates, such as crustaceans and polychaetes. Organisms here generally live in close relationship with the substrate and many are permanently attached to the bottom. The benthic boundary layer, which includes the bottom layer of water and the uppermost layer of sediment directly influenced by the overlying water, is an integral part of the benthic zone, as it greatly influences the biological activity that takes place there. Examples of contact soil layers include sand bottoms, rocky outcrops, coral, and bay mud.

<span class="mw-page-title-main">Bottom trawling</span> Fishing method for fishing trawlers

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.

<span class="mw-page-title-main">Demersal fish</span> Fish that live and feed on or near the bottom of seas or lakes

Demersal fish, also known as groundfish, live and feed on or near the bottom of seas or lakes. They occupy the sea floors and lake beds, which usually consist of mud, sand, gravel or rocks. In coastal waters they are found on or near the continental shelf, and in deep waters they are found on or near the continental slope or along the continental rise. They are not generally found in the deepest waters, such as abyssal depths or on the abyssal plain, but they can be found around seamounts and islands. The word demersal comes from the Latin demergere, which means to sink.

Lord Howe Rise Deep sea plateau from south west of New Caledonia to the Challenger Plateau, west of New Zealand

The Lord Howe Rise is a deep sea plateau which extends from south west of New Caledonia to the Challenger Plateau, west of New Zealand in the south west of the Pacific Ocean. To its west is the Tasman Basin and to the east is the New Caledonia Basin. Lord Howe Rise has a total area of about 1,500,000 square km, and generally lies about 750 to 1,200 metres under water. It is part of Zealandia, a much larger continent that is now mostly submerged, and so is composed of continental crust.

The South Tasman Rise is an area of seafloor that lies 550 km south of Hobart, Tasmania in the Southern Ocean where water depths are about 1,500 metres. The South Tasman Rise is also known as the Tasmania Ridge or South Tasmania Ridge. The South Tasman Rise is a sunken landbridge that used to connect Tasmania to Antarctica.

DEntrecasteaux Channel Water between Bruny Island and Tasmania

The D'Entrecasteaux Channel is a body of water located between Bruny Island and the south-east of the mainland of Tasmania, Australia. The channel is the mouth for the estuaries of the Derwent and the Huon Rivers and empties into the Tasman Sea of the South Pacific Ocean. It was sighted by Abel Tasman in 1642 and surveyed in 1792 by Bruni d'Entrecasteaux.

<span class="mw-page-title-main">Environmental impact of fishing</span>

The environmental impact of fishing includes issues such as the availability of fish, overfishing, fisheries, and fisheries management; as well as the impact of industrial fishing on other elements of the environment, such as bycatch. These issues are part of marine conservation, and are addressed in fisheries science programs. According to a 2019 FAO report, global production of fish, crustaceans, molluscs and other aquatic animals has continued to grow and reached 172.6 million tonnes in 2017, with an increase of 4.1 percent compared with 2016. There is a growing gap between the supply of fish and demand, due in part to world population growth.

Huon Commonwealth Marine Reserve is a 9,991 km2 marine protected area within Australian waters. The former Tasmanian Seamounts Marine Reserve created in 1999 was incorporated into the Huon reserve in 2007, and is part of the South-east Commonwealth Marine Reserve Network.

Cobb–Eickelberg Seamount chain Range of undersea mountains formed by volcanic activity of the Cobb hotspot in the Pacific Ocean

The Cobb-Eickelberg seamount chain is a range of undersea mountains formed by volcanic activity of the Cobb hotspot located in the Pacific Ocean. The seamount chain extends to the southeast on the Pacific Plate, beginning at the Aleutian Trench and terminating at Axial Seamount, located on the Juan de Fuca Ridge. The seamount chain is spread over a vast length of approximately 1800 km. The location of the Cobb hotspot that gives rise to these seamounts is 46° N—130° W. The Pacific plate is moving to the northwest over the hotspot, causing the seamounts in the chain to decrease in age to the southeast. Axial is the youngest seamount and is located approximately 480 km west of Cannon Beach, Oregon. The most studied seamounts that make up this chain are Axial, Brown Bear, Cobb, and Patton seamounts. There are many other seamounts in this chain which have not been explored.

Davidson Seamount Underwater volcano near California

Davidson Seamount is a seamount located off the coast of Central California, 80 mi (129 km) southwest of Monterey and 75 mi (121 km) west of San Simeon. At 26 mi (42 km) long and 8 mi (13 km) wide, it is one of the largest known seamounts in the world. From base to crest, the seamount is 7,480 ft (2,280 m) tall, yet its summit is still 4,101 ft (1,250 m) below the sea surface. The seamount is biologically diverse, with 237 species and 27 types of deep-sea coral having been identified.

Destructive fishing practices are practices that easily result in irreversible damage to aquatic habitats and ecosystems. Many fishing techniques can be destructive if used inappropriately, but some practices are particularly likely to result in irreversible damage. These practices are mostly, though not always, illegal. Where they are illegal, they are often inadequately enforced.

<span class="mw-page-title-main">Fishing industry in the United States</span>

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.

<span class="mw-page-title-main">Hotspot Ecosystem Research and Man's Impact On European Seas</span> International multidisciplinary project that studies deep-sea ecosystems

Hotspot Ecosystem Research and Man's Impact On European Seas (HERMIONE) is an international multidisciplinary project, started in April 2009, that studies deep-sea ecosystems. HERMIONE scientists study the distribution of hotspot ecosystems, how they function and how they interconnect, partially in the context of how these ecosystems are being affected by climate change and impacted by humans through overfishing, resource extraction, seabed installations and pollution. Major aims of the project are to understand how humans are affecting the deep-sea environment and to provide policy makers with accurate scientific information, enabling effective management strategies to protect deep sea ecosystems. The HERMIONE project is funded by the European Commission's Seventh Framework Programme, and is the successor to the HERMES project, which concluded in March 2009.

Tasman Fracture Commonwealth Marine Reserve is a 42,502 km2 marine protected area within Australian waters located off the coast of south-west Tasmania. It extends to the southerly limits of the Australian exclusive economic zone in the Indian Ocean and encompasses the Tasman Fracture. The reserve was established in 2007 and is part of the South-east Commonwealth Marine Reserve Network.

South Tasman Rise Commonwealth Marine Reserve is a 27,704 km2 marine protected area located at the southerly limit of Australia's exclusive economic zone near Tasmania. The reserve was established in 2007 and is part of the South-east Commonwealth Marine Reserve Network.

Freycinet Commonwealth Marine Reserve is a 57,942 km2 marine protected area within Australian waters located off the east coast of Tasmania. It extends to the outer limits of the Australian exclusive economic zone in the Tasman Sea. The reserve was established in 2007 and is part of the South-east Commonwealth Marine Reserve Network. It is the largest reserve of the South-east Network, the area covered is approximately equivalent to about 86% of the land area of Tasmania.

Flinders Commonwealth Marine Reserve is a 27,043km2 marine protected area within Australian waters located off the coast of north-east Tasmania. It extends to the outer limits of the Australian exclusive economic zone in the Tasman Sea. The reserve was established in 2007 and is part of the South-east Commonwealth Marine Reserve Network.

The Norfolk Marine Park is an Australian marine park located in the waters immediately offshore of Norfolk Island, an external territory of Australia. The marine park extends 700 km (430 mi) in a north–south direction and covers an area of 188,444 km2 (72,759 sq mi). The park is assigned IUCN category IV and is one of 8 parks managed under the Temperate East Marine Parks Network.

References

  1. 1 2 3 J. A. Koslow; K. Gowlett-Holmes; J. K. Lowry; T. O’Hara; G. C. B. Poore; A. Williams (4 April 2011). "Seamount benthic macrofauna off southern Tasmania: community structure and impacts of trawling" (PDF). Marine Ecology Progress Series . 213: 111–125. doi: 10.3354/meps213111 . Retrieved 27 October 2011.
  2. 1 2 3 4 "Seamount ecosystems conserved in the Huon Commonwealth Marine Reserve" (PDF). June 2007. Retrieved 26 October 2011.
  3. 1 2 Seach, John. "Tasman Seamounts Reserve - John Seach". Volcanolive. Retrieved 27 October 2011.
  4. 1 2 "Tasmanian Seamounts". Department of Sustainability, Environment, Water, Population and Communities. 20 June 2011. Retrieved 27 October 2011.
  5. 1 2 "Huon Commonwealth Marine Reserve". Department of Sustainability, Environment, Water, Population and Communities. 29 June 2011. Archived from the original on 3 November 2011. Retrieved 27 October 2011.
  6. "Fact Sheet: Discovering Seamounts". CSIRO Marine and Atmospheric Research. 11 December 2008. Retrieved 27 October 2011.

Coordinates: 44°18′S147°00′E / 44.300°S 147.000°E / -44.300; 147.000