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Intertidal seagrass meadows dominated by unknown or unspecified growth form, which can include: Zostera muelleri subsp. capricorni*, Cymodocea rotundata, Cymodocea serrulata, Enhalus acoroides, Halodule pinifolia, Halodule uninervis, Halophila spp., Thalassia hemprichii, Thalassodendron ciliatum and Syringodium isoetifolium.
Seagrasses are not a taxonomically unified group, but rather an ecological group that arose through convergent evolution and includes several different families. They are all flowering plants that live underwater and need light to photosynthesise. They also produce seeds. They grow on muds, sands and fine gravels which may be mobile, leading to changes in seagrass composition and extent over time (see qualifiers - Period, Trend and Cover). Meadows may include other structural macrobiota, such as: encrusting algae, erect macrophyte algae, bryozoans, sponges and molluscs (e.g. bivalves, cockles, whelks, razor clam beds), together with mobile invertebrate fauna, such as: sea cucumbers, crabs (e.g. commercial sand crabs and other portunids) and polychaete worms.
*Revision of Zostera capricorni has resulted in classification to subspecies. In Queensland, Zostera capricorni has been revised to Zostera muelleri subsp. capricorni.
Seagrasses provide a wide range of services, including:
- primary production, carbon fixation and nutrient removal
- support numerous herbivore and detritivore-based food webs, including food for dugongs and green turtles (mostly H. uninervis and H. ovalis), and many fisheries species (e.g. prawns and fishes) and others (e.g. razor clam)
- fisheries habitat (e.g. food, refuge and reproduction)
- coastal protection, erosion control and sediment capture
- tourism, recreation, education and research.
The fisheries value of seagrass habitat as nursery grounds for juvenile commercial fish and prawn species in Queensland is well documented. Sea cucumbers may also be collected from seagrass meadows for commercial aquaculture. Not only do seagrass provide habitat for fish, but the proximity of seagrass meadows to other ecosystems (mangroves, coral reefs) increases their abundance in these ecosystems. This is especially important for mobile biota which move between these different seascapes for different life functions (e.g. feeding, breeding, life stages etc.).
Seagrass meadows, particularly those containing H. uninervis and H. ovalis, provide food for dugong and green sea turtles. Dugongs feed mostly on the roots of mostly H. uninervis whereas green turtles tend to graze the leaves of mostly H. ovalis. Halodule uninervis and H. ovalis  are reported to be the most nutritious seagrasses due to high nitrogen and starch content. Grazing of H. uninervis and H. ovalis has been shown to increase production of a nitrogen-rich standing crop.
Inundation 'Intertidal – Lower low', 'Intertidal – Mid low', 'Intertidal – Upper low', 'Intertidal – Low undifferentiated', 'Intertidal – Lower medium', 'Intertidal – Upper-medium', 'Intertidal – Medium undifferentiated', 'Intertidal – High', 'Intertidal – Undifferentiated', 'Intertidal – High undifferentiated', although usually occurring below mean sea level.
Structural macrobiota 'Seagrass – fern-like', Seagrass – cylindrical', 'Seagrass – other or unspecified'
Seagrass ecosystems vary in Period and Trend (seasonally and from year to year).
Seagrass meadows grow throughout the world’s coastal waters, with large areas along Queensland’s coastline. Approximately 58 species of seagrass have been recorded across the globe with about 30 recorded in Australian waters and at least 15 in Queensland.
The following relates to distribution of this ecosystem type within the Central Queensland mapping area:
- Seagrass mapping represents the maximum known extent of that ecosystem since 2000 and details concerning period and trend of each meadow are documented within the structural macrobiota attribute dataset.
- Based on the available data in the Central Queensland mapping area, intertidal seagrass meadows dominated by unknown or unspecified growth form can include: C. serrulata, H. uninervis, H. decipiens, H. ovalis, H. spinulosa, S. isoetifolium and Z. muelleri . Where mapping data is available this type typically represents H. spinulosa or S. isoetifolium.
- In Port Curtis, Z. muelleri dominated meadows on muddy sediments whereas H. uninervis dominated meadows on sandy sediments. Halophila ovalis dominated meadows adjacent to disturbance and H. decipiens and H. spinulosa dominated deeper subtidal waters only.
- Extensive seagrass meadows in Port Curtis are the only described large area of seagrass between Hervey Bay and Shoalwater Bay, and are therefore very important regionally.
- Spatial Inventory of seagrass in Hervey Bay, its tributaries/estuaries and the Great Sandy Strait was last updated in 2003 and seagrass meadows may have changed in extent since it was last mapped. Some estuarine seagrasses were mapped only once at a very broad scale 1984-88 and may or may represent the current seagrass extent.
- Baffle Creek supports estuarine seagrass as initially mapped in 2007 and confirmed by observations in 2018 (Andrew Olds and Chris Henderson pers. comm.)
- Halodule uninervis and H. ovalis provide food for dugong and green sea turtles, and both of these species were observed in Port Curtis during recent seagrass surveys.
- Thalassia hemprichii does not occur in Central Queensland.
- Mapping represents locations that seagrass has been recorded at some point in time, and therefore locations where seagrass may grow now or in the future providing environmental conditions are suitable (e.g. wave action, Water clarity, sediment stability, temperature and the presence of nutrients and other potential contaminants). The species composition, extent and biomass of seagrass meadows can vary seasonally and between years. Seasonally the extent and biomass of seagrass meadows along the Queensland east coast are typically maximal in late spring and summer, and minimal over winter.
Other relevant attributes include Water clarity, Energy magnitude and Energy source (wave) together with Sediment texture, Freshwater volume and Trace elements. Seagrasses need light to be able to photosynthesise and turbid water inhibits light penetration, thus the depth that light can penetrate is a major control. Severe storms (cyclones), and/or high rainfall, river discharge and the associated low Water clarity and high concentrations of nutrients and other potential contaminants, and sediment deposition leads to seagrass loss (see SeagrassWatch annual reports for inshore seagrass monitoring in the Great Barrier Reef Marine Park. Trace elements (nutrients N, P), herbicides and other contaminants are known to affect seagrass health and other structural macrobiota including epiphytic algae and macroalgae are indicators of high nutrients.
Marine heatwaves can also negatively impact seagrass meadows.
Seagrass – Queensland Government
Case study: Hervey Bay seagrass and dugong – Queensland Government
Seagrass – Department of Environment and Science
Saltmarshes, seagrasses and algae – Department of Agriculture and Fisheries
Seagrass-Watch: guides and manuals
Seagrasses in Queensland (pamphlet)
Seagrasses – Australian Institute of Marine Science
Seagrass – A Vulnerability Assessment for the Great Barrier Reef
Seagrass Restoration Network
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Last updated: 22 July 2019
This page should be cited as:
Department of Environment and Science, Queensland (2019) Intertidal other seagrass, WetlandInfo website, accessed 1 February 2023. Available at: https://wetlandinfo.des.qld.gov.au/wetlands/ecology/aquatic-ecosystems-natural/estuarine-marine/descriptions/15/