Seagrasses of Western Australia
Encyclopedia
The Seagrasses of Western Australia are submerged flowering plants found along the coast, around islands, and in estuaries of Western Australia
. The region contains some of the largest seagrass
meadows in the world, and is the most diverse in the number of species. The variety of habitats along its western and southern coasts is often soft sands in shallow subtropical waters, ideal for these plants.
s that evolved from terrestrial grass
es to habitat in coastal waters. In contrast to seaweed
s, usually found on rocks, seagrass colonises sandy ocean beds to form dense stands and meadows.
The Western Australian coastline, along with its islands, is over 20,000 km long. These tropical to temperate waters extend from latitudes 32-34°S to 12°S. The great diversity of habitat in these coastal regions of Western Australia
are occupied by seagrasses, frequently 'engineering' habitat through colonisation of shallow ocean floors. These plants possess rhizome
s which extend under the sand, stems emerge from these with one, or many, flattened and elongated leaves. These features allow the plants to stabilise the substrate, anchor themselves against currents, and change the environment.
A colony may have one or several species of seagrass, and a large number of other species living within it.
The area covered by seagrass in Western Australian waters is equivalent to Australia's rainforest.
. Some areas of the southern coast provide suitable habitat, such as those at King George Sound
and the Archipelago of the Recherche
, the warmer water of the Leeuwin Current
contributes the diversity of these seagrass communities. The western coast contain notable and diverse seagrass beds; Cockburn Sound
and the Swan River
estuary, and the Houtman Abrolhos
, Rottnest and other islands. The Wooramel Seagrass Bank
12 species - estimated 4,500 km² of seabed - at Shark Bay
is the largest reported seagrass meadows in the world (Walker, 1989). The Timor Sea
is largely unsurveyed.
s, primarily from the ability to colonise inshore coastal sand with its roots and matted rhizome
s. These meadows are able to provide habitat to other species, especially epiphytic relationships, and are a food source for other organisms. Western rock lobsters are found as juveniles amongst seagrass, receiving food and shelter until they reach maturity. The leaves are also eaten by dugong
and other creatures.
The four families of Alismatales
includes three genera within Hydrocharitaceae
, a largely aquatic family of tape grasses, and seven other genera of marine species.
Western Australia
Western Australia is a state of Australia, occupying the entire western third of the Australian continent. It is bounded by the Indian Ocean to the north and west, the Great Australian Bight and Indian Ocean to the south, the Northern Territory to the north-east and South Australia to the south-east...
. The region contains some of the largest seagrass
Seagrass
Seagrasses are flowering plants from one of four plant families , all in the order Alismatales , which grow in marine, fully saline environments.-Ecology:...
meadows in the world, and is the most diverse in the number of species. The variety of habitats along its western and southern coasts is often soft sands in shallow subtropical waters, ideal for these plants.
Description
Marine grasses are flowering plantFlowering plant
The flowering plants , also known as Angiospermae or Magnoliophyta, are the most diverse group of land plants. Angiosperms are seed-producing plants like the gymnosperms and can be distinguished from the gymnosperms by a series of synapomorphies...
s that evolved from terrestrial grass
Grass
Grasses, or more technically graminoids, are monocotyledonous, usually herbaceous plants with narrow leaves growing from the base. They include the "true grasses", of the Poaceae family, as well as the sedges and the rushes . The true grasses include cereals, bamboo and the grasses of lawns ...
es to habitat in coastal waters. In contrast to seaweed
Seaweed
Seaweed is a loose, colloquial term encompassing macroscopic, multicellular, benthic marine algae. The term includes some members of the red, brown and green algae...
s, usually found on rocks, seagrass colonises sandy ocean beds to form dense stands and meadows.
The Western Australian coastline, along with its islands, is over 20,000 km long. These tropical to temperate waters extend from latitudes 32-34°S to 12°S. The great diversity of habitat in these coastal regions of Western Australia
Coastal regions of Western Australia
Western Australia has the longest coastline of any state in Australia, at 10,194 km or 12,889 km.-Integrated Marine and Coastal Regionalisation of Australia:...
are occupied by seagrasses, frequently 'engineering' habitat through colonisation of shallow ocean floors. These plants possess rhizome
Rhizome
In botany and dendrology, a rhizome is a characteristically horizontal stem of a plant that is usually found underground, often sending out roots and shoots from its nodes...
s which extend under the sand, stems emerge from these with one, or many, flattened and elongated leaves. These features allow the plants to stabilise the substrate, anchor themselves against currents, and change the environment.
A colony may have one or several species of seagrass, and a large number of other species living within it.
The area covered by seagrass in Western Australian waters is equivalent to Australia's rainforest.
Distribution
The range extends to the temperate regions of the Southern OceanSouthern Ocean
The Southern Ocean comprises the southernmost waters of the World Ocean, generally taken to be south of 60°S latitude and encircling Antarctica. It is usually regarded as the fourth-largest of the five principal oceanic divisions...
. Some areas of the southern coast provide suitable habitat, such as those at King George Sound
King George Sound
King George Sound is the name of a sound on the south coast of Western Australia. Located at , it is the site of the city of Albany.The sound covers an area of and varies in depth from to ....
and the Archipelago of the Recherche
Archipelago of the Recherche
Archipelago of the Recherche is a group of 105 islands, and over 1200 "obstacles to shipping", off the southern coast of Western Australia. The islands, also known as the Recherche Archipelago, stretch from East to West and to off-shore....
, the warmer water of the Leeuwin Current
Leeuwin Current
The Leeuwin Current is a warm ocean current which flows southwards near the western coast of Australia. It rounds Cape Leeuwin to enter the waters south of Australia where its influence extends as far as Tasmania...
contributes the diversity of these seagrass communities. The western coast contain notable and diverse seagrass beds; Cockburn Sound
Cockburn Sound
Cockburn Sound is an inlet of the Indian Ocean on the coast of Western Australia. It extends from the south of the mouth of the Swan River at Fremantle for about 25 km to Cape Peron near Rockingham and is located at...
and the Swan River
Swan River (Western Australia)
The Swan River estuary flows through the city of Perth, in the south west of Western Australia. Its lower reaches are relatively wide and deep, with few constrictions, while the upper reaches are usually quite narrow and shallow....
estuary, and the Houtman Abrolhos
Houtman Abrolhos
The Houtman Abrolhos is a chain of 122 islands, and associated coral reefs, in the Indian Ocean off the west coast of Australia. Nominally located at , it lies about eighty kilometres west of Geraldton, Western Australia...
, Rottnest and other islands. The Wooramel Seagrass Bank
Wooramel Seagrass Bank
Wooramel Seagrass Bank is a large deposit of carbonate sediment, a sand bank, formed by diverse communities of seagrasses off the coast of Carnarvon, Western Australia. The mattes of seagrass meadows and stands consolidate a shallow platform of sandy substrate by acting as an organic baffle against...
12 species - estimated 4,500 km² of seabed - at Shark Bay
Shark Bay
Shark Bay is a World Heritage listed bay in Western Australia. The term may also refer to:* the locality of Shark Bay, now known as Denham* Shark Bay Marine Park* Shark Bay , a shark exhibit at Sea World, Gold Coast, Australia* Shire of Shark Bay...
is the largest reported seagrass meadows in the world (Walker, 1989). The Timor Sea
Timor Sea
The Timor Sea is a relatively shallow sea bounded to the north by the island of Timor, to the east by the Arafura Sea, to the south by Australia and to the west by the Indian Ocean....
is largely unsurveyed.
Ecosystem
Seagrasses are the foundation of complex ecosystemEcosystem
An ecosystem is a biological environment consisting of all the organisms living in a particular area, as well as all the nonliving , physical components of the environment with which the organisms interact, such as air, soil, water and sunlight....
s, primarily from the ability to colonise inshore coastal sand with its roots and matted rhizome
Rhizome
In botany and dendrology, a rhizome is a characteristically horizontal stem of a plant that is usually found underground, often sending out roots and shoots from its nodes...
s. These meadows are able to provide habitat to other species, especially epiphytic relationships, and are a food source for other organisms. Western rock lobsters are found as juveniles amongst seagrass, receiving food and shelter until they reach maturity. The leaves are also eaten by dugong
Dugong
The dugong is a large marine mammal which, together with the manatees, is one of four living species of the order Sirenia. It is the only living representative of the once-diverse family Dugongidae; its closest modern relative, Steller's sea cow , was hunted to extinction in the 18th century...
and other creatures.
Diversity
The seagrasses of Western Australia are the most diverse of any region in the world, 26 species in 11 genera are currently described.The four families of Alismatales
Alismatales
Alismatales is an order of flowering plants including about 2500 species. Pleants assigned to this order are mostly tropical or aquatic.-Description:...
includes three genera within Hydrocharitaceae
Hydrocharitaceae
Hydrocharitaceae is a flowering plant family that includes a number of species of aquatic plant, broadly called the Tape-grasses, and includes the well known Canadian Waterweed and Frog's Bit.The family includes both fresh and marine aquatics...
, a largely aquatic family of tape grasses, and seven other genera of marine species.
- HydrocharitaceaeHydrocharitaceaeHydrocharitaceae is a flowering plant family that includes a number of species of aquatic plant, broadly called the Tape-grasses, and includes the well known Canadian Waterweed and Frog's Bit.The family includes both fresh and marine aquatics...
- Enhalus acoroides (L.f.) Royle
- Halophila australis Doty & B.C.Stone
- Halophila decipiens Ostenf.
- Halophila minor (Zoll.) Hartog
- Halophila ovalisHalophila ovalisHalophila ovalis is a seagrass in the family Hydrocharitaceae, a common name is paddle weed. It is a small herbaceous plant that occurs in sea beds and other saltwater environments....
(R.Br.Robert Brown (botanist)Robert Brown was a Scottish botanist and palaeobotanist who made important contributions to botany largely through his pioneering use of the microscope...
) Hook.f. - Halophila spinulosa (R.Br.) Asch.
- Thalassia hemprichii (Ehrenb.) Asch.
- Cymodoceaceae
- Amphibolis antarcticaAmphibolis antarcticaAmphibolis antarctica, commonly known as Wire weed or Sea Nymph, is a seagrass found in coastal waters of southern and western Australia.-Description:...
(Labill.) Sonder et Aschers. ex Aschers. (Wire weed, Sea Nymph) - Amphibolis griffithiiAmphibolis griffithiiAmphibolis griffithii is a seagrass found in waters along the southwestern coasts of Western Australia. -Description:A common marine herb, the rhizomatous plant forms meadows which stabilise sands; the intertwining roots and leaves protects the substrate from ocean currents...
(J.Black) den Hartog - Cymodocea angustata Ostenfeld
- Cymodocea serrulata (R.Br.) Asch. et Magnus
- Halodule pinifolia (Miki) den Hartog
- Halodule uninervis (Forsk.) Aschers.
- Syringodium isoetifolium (Aschers.) Dandy
- Thalassodendron ciliatum (Forrsk.) den Hartog
- Thalassodendron pachyrhizum den Hartog
- Amphibolis antarctica
- Posidoniaceae
- Posidonia angustifolia Cambridge and J.Kuo
- Posidonia australisPosidonia australisPosidonia australis is a species of seagrass that occurs in the southern waters of Australia. It is sometimes referred to as Fibreball Weed. The marine plant forms large meadows that are considered to be of high importance to the environmental conservation of the region...
Hook.f. (Ribbon weed) - Posidonia coriaceaPosidonia coriaceaPosidonia coriacea is a species of seagrass that occurs in the southern waters of Australia.-Description:A species of Posidonia. A perennial rhizomatous herb that appears as stands in marine habitat. This species is found at depths from 1 to 30 metres on white sands, in areas subject to intense...
Cambridge and J.Kuo - Posidonia denhartogii J.Kuo and Cambridge
- Posidonia kirkmanii J.Kuo and Cambridge
- Posidonia ostenfeldiiPosidonia ostenfeldiiPosidonia ostenfeldii is a species of seagrass that occurs in the southern waters of Australia.-Description:A species of Posidonia. A perennial rhizomatous herb that appears as clumps on sand in marine habitat. It is found at depths between 1 and 15 metres. The leaf blades are 6-12 mm...
den Hartog - Posidonia robertsoniaePosidonia robertsoniaePosidonia robertsoniae is one of the seagrasses of Western Australia, submerged flowering plants that occurs in the southern coastal waters.-Description:...
J.Kuo and Cambridge - Posidonia sinuosa Cambridge and J.Kuo
- ZosteraceaeZosteraceaeZosteraceae is a family of marine perennial flowering plants found in temperate and subtropical coastal waters, with the highest diversity located around Korea and Japan. Most seagrasses complete their entire life cycle under water, having filamentous pollen especially adapted to dispersion in an...
- Heterozostera nigricaulis J.Kuo
- Heterozostera polychlamys J.Kuo
- Zostera muelleri Asch.
- Zostera muelleri subsp. mucronata (Hartog) S.W.L.Jacobs
Further reading
- Thomson, Carolyn (1997) Discovering Shark Bay Marine Park and Monkey Mia Como, W.A. Department of Conservation and Land Management. ISBN 0-7309-6854-5 pp. 46–47 - includes mention mainly of wireweed and ribbon weed.
- Walker, D.I. (1990) Seagrass in Shark Bay, Western Australia. In: "Research in Shark Bay: Report of the France-Australe Bicentenary Expedition Committee." (Eds. P.F. Berry, S.D. Bradshaw, B.R. Wilson) (Western Australian Museum, Perth). p. 101-6