Subtidal narrow strap seagrass

Long description

Subtidal seagrass meadows dominated by the narrow strap seagrass Halodule uninervis. These meadows can also include seagrasses with other growth forms such as Zostera muelleri subsp. capricorni*, Cymodocea rotundata, Cymodocea serrulata, Enhalus acoroides, Thalassia hemprichii, Thalassodendron ciliatum, Halophila spp. and Syringodium isoetifolium. Halodule uninervis also includes a wide strap growth form, see type (12).

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. Meadows may include 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[9].

Special values

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 Halophila ovalis), and many fisheries species (e.g. prawns and fishes) and other Structural macrobiota (e.g. shellfish reefs of razor clams)
• fisheries habitat (e.g. food, refuge and reproduction)
• coastal protection, erosion control and sediment capture
• tourism, recreation, education and research[13][9][10].

The fisheries value of seagrass habitat as nursery grounds for juvenile commercial fish, prawn, crab and crayfish species in Queensland is well documented[17][21]. Sea cucumbers may also be collected for commercial aquaculture. Not only do seagrasses provide habitat for fish, but the proximity of seagrass meadows to other ecosystems (mangroves, coral reefs) increases their abundance in these ecosystems[7][14].

Seagrass meadows, particularly those containing H. uninervis and H. ovalis, provide food for dugong[20] and green sea turtles[11]. Dugongs feed mostly on the roots of mostly H. uninervis whereas green turtles tend to graze the leaves of mostly H. ovalis. Halodule uninervis[20] and H. ovalis[15] 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[15][1][11].

Diagnostic attributes

Inundation 'Subtidal'

Structural macrobiota 'Seagrass - strap narrow'

Qualifiers

Seagrass ecosystems vary in Period and Trend (seasonally and from year to year). The species composition, extent and biomass of seagrass meadows can vary seasonally and between years. The extent and biomass of seagrass meadows along the Queensland east coast are typically maximal in late spring and summer, and minimal over winter[2][6][19].

Distribution

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[16].

Most tropical and sub-tropical species are found in water less than 10 metres deep and narrow strap seagrasses are typically found in shallow water and the intertidal area (coastal areas and within estuaries). Of the 13 species identified in north-eastern Queensland[12] all occurred in water depths less than 6 metres below mean sea level (MSL) and only four occurred in water more than 20 metres below MSL. Three general depth zones of seagrass species composition for tropical waters have been observed a shallow zone less than 6 metres deep with high species diversity, likely to include all species found in a region; a zone between 6 and 11 metres where the most commonly found seagrasses were the pioneering Halodule and Halophila species; and a zone deeper than 11 metres where only species of the genus Halophila were commonly found[4].

Seagrasses form dynamic communities of mixed species. Enhalus acoroides, T. hemprichii and T. ciliatum are considered persistent whereas Cymodocea spp. and S. isoetifolium are considered opportunistic, Z. muelleri and H. uninervis are considered colonising to opportunistic.

Halodule uninervis is typically more enduring than early colonising species of Halophila, but is considered a colonising and opportunistic seagrass forming both transitory and enduring meadows. Transitory meadows increase and decrease in extent and biomass seasonally, and can re-establish following complete loss through sexual reproduction. Enduring meadows may fluctuate but generally remain to some extent through seasons and years. More colonising species typically have fast shoot turnover, short lifespan, fast sexual maturation and development of a (dormant) seed bank. They have low physiological resistance to disturbance but a rapid ability to recover[10].

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
• Halodule uninervis can have a narrow growth form but is not mapped in the Central Queensland area as available data did not distinguish between the wide and narrow growth form, with all H. uninervis allocated to narrow
• Seagrass meadows, particularly those containing H. uninervis and H. ovalis, provide food for dugong[20] and green sea turtles[11]. Both of these species were observed in Port Curtis during recent seagrass surveys[18]
• Halodule-dominated meadows have been mapped around Burrum Heads and along the western side of the Great Sandy Strait. Dugongs travel along this shore to feed, with tagging studies showing movements from Burrum Heads to Kauri Creek where there is a big persistent meadow
• 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 (excluding Baffle Creek) were mapped only once at a very broad scale 1984-88[12] and may either be absent or not represent current seagrass extent
• Thalassia hemprichii does not occur in Central Queensland.

Comments

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 Benthic 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[13][3]). Trace elements (nutrients N, P), herbicides and other contaminants are known to affect seagrass health and other Structural macrobiota. This includes epiphytic algae and macroalgae which are indicators of high nutrients.

Water temperature is also relevant. Marine heatwaves can also negatively impact seagrass meadows[5][13]. Zostera is particularly susceptible to temperature stress. The optimal temperature for primary production of Zostera is 24 degrees Celsius, with deficient primary production (i.e. energy loss) above 35 degrees Celsius, compared to 40 degrees Celsius for deficient primary production in H. uninervis and C. serrulata[5]. Deeper subtidal meadows are generally less susceptible to air and surface temperature than shallow subtidal and intertidal seagrasses[8].

Mapping represents locations where 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 Trace elements (nutrients and other potential contaminants)).

Additional Information

Seagrass-Watch

Seagrass - Queensland Government

Seagrass (Case study: Hervey Bay seagrass and dugong) - Queensland Government

Saltmarshes, seagrasses and algae - Department of Agriculture and Fisheries

Seagrass-Watch: guides and manuals

Seagrass - Department of Environment, Science and Innovation

Seagrasses - Australian Institute of Marine Science

A Vulnerability Assessment for the Great Barrier Reef (Seagrass) - Great Barrier Reef Marine Park Authority

Seagrass Restoration Network

References

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2. ^ Bruinsma, C & Danaher, K (2001), Queensland Coastal Wetland Resources: Round Hill Head to Tin Can Inlet.. [online], vol. QI99081, Department of Primary Industries, Queensland Government., Brisbane. Available at: http://era.daf.qld.gov.au/id/eprint/3545/.
3. ^ Campbell, SJ & McKenzie, LJ (2004), 'Flood related loss and recovery of intertidal seagrass meadows in southern Queensland, Australia', Estuarine, Coastal and Shelf Science, vol. 60, no. 3, pp. 477-490, Elsevier.
4. ^ Coles, R, Lee Long, W, Squire, B, Squire, L & Bibby, J (1987), 'Distribution of seagrasses and associated juvenile commercial penaeid prawns in north-eastern Queensland waters', Marine and Freshwater Research. [online], vol. 38, no. 1, p. 103. Available at: http://www.publish.csiro.au/?paper=MF9870103 [Accessed 5 April 2019].
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6. ^ Danaher, K, Rasheed, M & Thomas, R (2005), The intertidal wetlands of Port Curtis, Department of Primary Industries and Fisheries.
7. ^ Gilby, B, Olds, A, Connolly, R, Maxwell, P, Henderson, C & Schlacher, T (8 February 2018), 'Seagrass meadows shape fish assemblages across estuarine seascapes', Marine Ecology Progress Series. [online], vol. 588, pp. 179-189. Available at: http://www.int-res.com/abstracts/meps/v588/p179-189/ [Accessed 15 March 2019].
8. ^ Great Barrier Reef Marine Park Authority (GBRMPA) (2012), Great Barrier Reef Coastal Ecosystems Assessment Framework. [online], GBRMPA, Townsville. Available at: http://www.gbrmpa.gov.au/__data/assets/pdf_file/0003/28254/Coastal-Ecosystems-Assessment-Framework.pdf.
9. ^ a b Jacobs, S & Les, D (26 October 2009), 'New combinations in Zostera (Zosteraceae)', Telopea. [online], vol. 12, no. 3, pp. 419-423. Available at: http://plantnet.rbgsyd.nsw.gov.au/emuwebnswlive/objects/common/webmedia.php?irn=55023&reftable=ebibliography [Accessed 25 March 2019].
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11. ^ a b c Kuiper-Linley, M, Johnson, CR & Lanyon, JM (2007), 'Effects of simulated green turtle regrazing on seagrass abundance, growth and nutritional status in Moreton Bay, south-east Queensland, Australia', Marine and Freshwater Research. [online], vol. 58, no. 5, p. 492. Available at: http://www.publish.csiro.au/?paper=MF06241 [Accessed 5 April 2019].
12. ^ a b Lee Long, W, Mellors, J & Coles, R (1993), 'Seagrasses between Cape York and Hervey Bay, Queensland, Australia', Marine and Freshwater Research. [online], vol. 44, no. 1, p. 19. Available at: http://www.publish.csiro.au/?paper=MF9930019 [Accessed 5 April 2019].
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14. ^ Olds, AD, Connolly, RM, Pitt, KA & Maxwell, PS (2012), 'Primacy of seascape connectivity effects in structuring coral reef fish assemblages', Marine Ecology Progress Series, vol. 462, pp. 191-203, Inter-Research, Nordbuente 23 Oldendorf/Luhe 21385 Germany.
15. ^ a b Preen, AR, Long, WJL & Coles, RG (1995), 'Flood and cyclone related loss, and partial recovery, of more than 1000 km 2 of seagrass in Hervey Bay, Queensland, Australia', Aquatic Botany, vol. 52, no. 1, pp. 3-17, Elsevier.
16. ^ Queensland Government, Seagrasses in Queensland. [online], Department of Primary Industries and Fisheries. Available at: https://www.seagrasswatch.org/wp-content/uploads/Resources/Brochure-Poster/Brochure/PDF/Seagrasses_in_Queensland_Fisheries_Info_Pamphlet.pdf.
17. ^ Rasheed, MA, Lee Long, WJ, McKenzie, LJ, Roder, CA, Roelofs, AJ & Coles, RG (1996), Port of Karumba: seagrass monitoring baseline surveys, Dry-season (Oct.) 1994 - Wet-season (Mar.) 1995, Ports Corp. of Queensland, Brisbane, Qld..
18. ^ Rasheed, MA, Thomas, R, Roelofs, AJ, Neil, KM & Kerville, SP (2003), Port Curtis and Rodds Bay Seagrass andBenthic Macro-Invertebrate Community Baseline Survey.
19. ^ Sheaves, M (2005), 'Nature and consequences of biological connectivity in mangrove systems', Marine Ecology Progress Series. [online], vol. 302, pp. 293-305. Available at: http://www.int-res.com/abstracts/meps/v302/p293-305/ [Accessed 15 March 2019].
20. ^ a b c Sheppard, JK, Preen, AR, Marsh, H, Lawler, IR, Whiting, SD & Jones, RE (2006), 'Movement heterogeneity of dugongs, Dugong dugon(Müller), over large spatial scales', Journal of experimental marine biology and ecology, vol. 334, no. 1, pp. 64-83, Elsevier.
21. ^ Watson, R, Coles, R & Lee Long, W (1993), 'Simulation estimates of annual yield and landed value for commercial penaeid prawns from a tropical seagrass habitat, Northern Queensland, Australia', Marine and Freshwater Research. [online], vol. 44, no. 1, p. 211. Available at: http://www.publish.csiro.au/?paper=MF9930211 [Accessed 8 April 2019].

Last updated: 19 July 2019