Seagrasses of Western Australia

Last updated April 13, 2024

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.

Description

Marine grasses are flowering plants that evolved from terrestrial grasses to habitat in coastal waters. In contrast to seaweeds, 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.^[1] 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 rhizomes 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.^[2]

Distribution

The range extends to the temperate regions of the Southern Ocean. 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 Seais largely unsurveyed.

Ecosystem

Seagrasses are the foundation of complex ecosystems, primarily from the ability to colonise inshore coastal sand with its roots and matted rhizomes. 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.

Diversity

The seagrasses of Western Australia are the most diverse of any region in the world, 26 species in 11 genera are currently described.^[2]

The four families of Alismatales includes three genera within Hydrocharitaceae, a largely aquatic family of tape grasses, and seven other genera of marine species.^[3]

Hydrocharitaceae
- Enhalus acoroides (L.f.) Royle
- Halophila australis Doty & B.C.Stone
- Halophila decipiens Ostenf.
- Halophila minor (Zoll.) Hartog
- Halophila ovalis (R.Br.) Hook.f.
- Halophila spinulosa (R.Br.) Asch.
- Thalassia hemprichii (Ehrenb.) Asch.
Cymodoceaceae
- Amphibolis antarctica (Labill.) Sonder et Aschers. ex Aschers. (Wire weed, Sea Nymph)
- Amphibolis griffithii (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
Posidoniaceae
- Posidonia angustifolia Cambridge and J.Kuo
- Posidonia australis Hook.f. (Ribbon weed)
- Posidonia coriacea Cambridge and J.Kuo
- Posidonia denhartogii J.Kuo and Cambridge
- Posidonia kirkmanii J.Kuo and Cambridge
- Posidonia ostenfeldii den Hartog
- Posidonia robertsoniae J.Kuo and Cambridge
- Posidonia sinuosa Cambridge and J.Kuo
Zosteraceae
- Heterozostera nigricaulis J.Kuo
- Heterozostera polychlamys J.Kuo
- Zostera muelleri Asch.
- Zostera muelleri subsp. mucronata (Hartog) S.W.L.Jacobs

Notes

↑ "Coastline Lengths". Geoscience Australia. Commonwealth of Australia. 16 October 2008. Archived from the original on 18 June 2009. Retrieved 2008-10-27.
1 2 Morrison, Sue; Storrie, Ann (1999). Wonders of Western Waters: The Marine Life of Western Australia. Department of Conservation and Land Management. ISBN 0-7309-6894-4.
↑ "Marine Plants of Western Australia". FloraBase . Retrieved 2008-09-19.

Related Research Articles

Seagrasses are the only flowering plants which grow in marine environments. There are about 60 species of fully marine seagrasses which belong to four families, all in the order Alismatales. Seagrasses evolved from terrestrial plants which recolonised the ocean 70 to 100 million years ago.

Shark Bay is a World Heritage Site in the Gascoyne region of Western Australia. The 23,000-square-kilometre (8,900 sq mi) area is located approximately 800 kilometres (500 mi) north of Perth, on the westernmost point of the Australian continent. UNESCO's listing of Shark Bay as a World Heritage Site reads:

Zostera is a small genus of widely distributed seagrasses, commonly called marine eelgrass, or simply seagrass or eelgrass, and also known as seaweed by some fishermen and recreational boaters including yachtsmen. The genus Zostera contains 15 species.

Zosteraceae 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 aquatic environment and ribbon-like leaves that lack stomata. Seagrasses are herbaceous and have prominent creeping rhizomes. A distinctive characteristic of the family is the presence of characteristic retinacules, which are present in all species except members of Zostera subgenus Zostera.

A seagrass meadow or seagrass bed is an underwater ecosystem formed by seagrasses. Seagrasses are marine (saltwater) plants found in shallow coastal waters and in the brackish waters of estuaries. Seagrasses are flowering plants with stems and long green, grass-like leaves. They produce seeds and pollen and have roots and rhizomes which anchor them in seafloor sand.

Cymodoceaceae is a family of flowering plants, sometimes known as the "manatee-grass family", which includes only marine species.

The Archipelago of the Recherche, known locally as the Bay of Isles, is a group of 105 islands, and over 1200 "obstacles to shipping", off the south coast of Western Australia. The islands stretch 230 km (140 mi) from east to west and to 50 km (31 mi) off-shore encompassing an area of approximately 4,000 square kilometres (1,544 sq mi). The western group is near Esperance and the eastern group at Israelite Bay. They are located in coastal waters, part of which is designated the Recherche Archipelago Nature Reserve.

Amphibolis griffithii is a seagrass found in waters along the southwestern coasts of Western Australia, extending to Encounter Bay in South Australia.

Amphibolis antarctica is a species of flowering plant in the family Cymodoceaceae. It is referred to by the common names wire weed or sea nymph, and is a seagrass found in coastal waters of southern and western Australia.

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Posidonia is a genus of flowering plants. It contains nine species of marine plants ("seagrass"), found in the seas of the Mediterranean and around the south coast of Australia.

Thalassia testudinum, commonly known as turtlegrass, is a species of marine seagrass. It forms meadows in shallow sandy or muddy locations in the Caribbean Sea and the Gulf of Mexico. Turtle grass and other seagrasses form meadows which are important habitats and feeding grounds. The grass is eaten by turtles and herbivorous fish, supports many epiphytes, and provides habitat for juvenile fish and many invertebrate taxa.

Zostera marina is a flowering vascular plant species as one of many kinds of seagrass, with this species known primarily by the English name of eelgrass with seawrack much less used, and refers to the plant after breaking loose from the submerged wetland soil, and drifting free with ocean current and waves to a coast seashore. It is a saline soft-sediment submerged plant native to marine environments on the coastlines of northern latitudes from subtropical to subpolar regions of North America and Eurasia.

Cymodocea nodosa is a species of seagrass in the family Cymodoceaceae and is sometimes known as little Neptune grass. As a seagrass, it is restricted to growing underwater and is found in shallow parts of the Mediterranean Sea and certain adjoining areas of the Atlantic Ocean.

Halodule wrightii is an aquatic plant in the Cymodoceaceae family. It is referred to by the common names shoal grass or shoalweed, and is a plant species native to seacoasts of some of the warmer oceans of the world.

Halodule uninervis is a species of seagrass in the family Cymodoceaceae. It is native to the western Pacific and Indian Oceans. Common names include narrowleaf seagrass in English and a'shab bahriya in Arabic.

Thalassodendron ciliatum, the sickle-leaved cymodocea, is a species of plant in the Thalassodendron genus of seagrasses in the family Cymodoceaceae.

Zostera novazelandica Setchell is a species of seagrass in the family Zosteraceae found on the shores of New Zealand. It is regarded as a distinct species by some authors but considered as a synonym of Zostera muelleri Irmisch ex Ascherson by others. The Maori names for Zostera novazelandica are karepō, nana, rehia, and rimurehia.

Zostera muelleri is a southern hemisphere temperate species of seagrass native to the seacoasts of South Australia, Victoria and Tasmania. and New Zealand. Today, Zostera muelleri can be found in regions of Australia, New Zealand, and Papua New Guinea, as well as areas of the eastern Indian Ocean, and the southwest and western central Pacific Ocean. Zostera muelleri is a marine angiosperm, and is commonly referred to as eelgrass or garweed. It is a fast growing and readily colonizing species that serves as a feeding ground for wading birds and aquatic animals, and a breeding ground for juvenile fish and shrimp species.

Posidonia australis seagrass meadows of the Manning-Hawkesbury ecoregion is an endangered ecological community, listed under the EPBC Act of the Commonwealth of Australia on 7 May 2015

References

Rippey, Elizabeth; Rowland (Reinette), Barbara (2004) [1995]. "Seagrasses". Coastal plants: Perth and the south-west region (2nd ed.). Perth: University of Western Australia Press. pp. 243–247. ISBN 1-920694-05-6.
van Keulen, Mike (25 October 2005). "Seagrasses of Western Australia" . Retrieved 2008-09-19.
New combinations in Australasian Zostera (Zosteraceae). Telopea 11(2) 127-128
Poiner, I. R.; Peterken, C. "Seagrasses: Seagrasses of Western Australia". State of the Marine Environment Report for Australia: The Marine Environment - Technical Annex: 1. CSIRO (Division of Fisheries). Cockburn Sound ... by 1978, 97% of the original 34 km2 of seagrass had been lost (Cambridge & McComb 1984).

External links