Subtidal fern-like seagrass

Long description

Subtidal seagrass meadows dominated by the fern-like Halophila spinulosa. These ecosystems typically occur in slightly deeper water with higher tolerance to low light Halophila spinulosa[16]. Often co-occurs with other seagrasses, particularly the other ‘deep water’ species of Halophila ovalis, Halophila decipiens, Halophila tricostata and Halophila capricorni.

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.

Structural macrobiota in seagrass meadows potentially include encrusting algae, erect macrophyte algae, bryozoans, sponges and molluscs (e.g. bivalves, cockles, whelks, razor clam beds). Other invertebrate fauna includes sea cucumbers, crabs (e.g. commercial sand crabs and other portunids) and polychaete worms. Sea cucumbers may be collected for commercial aquaculture.

Deep water seagrasses provide feeding habitat for dugong and potentially a refuge if nearshore seagrasses are impacted by runoff, low light / poor water quality, high nutrients causing algal overgrowth. In Western Australia, deep water meadows provide dugong habitat with evidence of long deep dives to feed on rhizomes with high nutrient content. H. spinulosa has large fleshy rhizomes similar to those known to contain abundant starch in other members of the genus and it is suggested that carbohydrate-rich rhizomes might compensate for the higher costs of foraging in deep water. Dugongs travelled along the deeper sea floor feeding on seagrass during long-distance movements from Burrum Heads to Breaksea Spit in winter, only coming to the surface to breathe[14]

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, 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 and stabilisation
• tourism, recreation, education and research[10][14][8].

The fisheries value of seagrass habitat as nursery grounds for juvenile commercial fish, prawn, crab and crayfish species in Queensland is well documented[12][15]. 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[6][11].

Potentially a deep water refuge when shallower seagrasses are impacted by nearshore flood events.

Diagnostic attributes

Inundation 'Subtidal'

Structural macrobiota 'Seagrass - fern-like'

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[1][5][13].

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 (SeagrassWatch). Most tropical and sub-tropical species are found in water less than 10 metres deep, however several Halophila species also grown in deeper water with lower light.

Of the 13 species identified in north-eastern Queensland[9] 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 including 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[3].

Seagrasses form dynamic communities of mixed species. Enhalus acoroides, Thalassia hemprichii and Thalassodendron ciliatum are considered persistent whereas Cymodocea spp. and Syringodium isoetifolium are considered opportunistic, Zostera muelleri and Halodule uninervis are considered colonising to opportunistic. Wide strap seagrasses are typically more enduring than early colonising species of Halophila spp., with Zostera spp. 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[8].

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
• Very large areas mapped in the Central Queensland
• 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[9] and may either be absent or not represent current seagrass extent
• Thalassia hemprichii does not occur in Central Queensland.

Comments

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. Other relevant attributes include Water clarity, Sediment texture, and Trace elements, together with Energy magnitude, Energy source (wave) and Freshwater volume however deeper seagrass tend to be less influenced by energy and freshwater except in a severe storm. 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[10][2]). 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[4][10]. Deeper subtidal meadows are generally less susceptible to air and surface temperature than shallow subtidal and intertidal seagrasses[7].

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 Trace elements (the presence of 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

Seagrasses in Queensland (pamphlet)

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

1. ^ 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/.
2. ^ 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.
3. ^ 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].
4. ^ Collier, CJ, Ow, YX, Langlois, L, Uthicke, S, Johansson, CL, O'Brien, KR, Hrebien, V & Adams, MP (23 August 2017), 'Optimum Temperatures for Net Primary Productivity of Three Tropical Seagrass Species', Frontiers in Plant Science. [online], vol. 8. Available at: http://journal.frontiersin.org/article/10.3389/fpls.2017.01446/full [Accessed 5 April 2019].
5. ^ Danaher, K, Rasheed, M & Thomas, R (2005), The intertidal wetlands of Port Curtis, Department of Primary Industries and Fisheries.
6. ^ 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].
7. ^ 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.
8. ^ a b Kilminster, K, McMahon, K, Waycott, M, Kendrick, GA, Scanes, P, McKenzie, L, O'Brien, KR, Lyons, M, Ferguson, A & Maxwell, P (2005), 'Unravelling complexity in seagrass systems for management: Australia as a microcosm', Science of the Total Environment, vol. 534, pp. 97-109, Elsevier.
9. ^ 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].
10. ^ a b c McKenzie, LJ, Collier, CJ, Langlois, LA, Yoshida, RL, Smith, N & Waycott, M (2018), Marine Monitoring Program: Annual Report for inshore seagrass monitoring 2016-2017. Report for the Great Barrier Reef Marine Park Authority. [online], p. 248pp., Great Barrier Reef Marine Park Authority, Townsville. Available at: http://elibrary.gbrmpa.gov.au/jspui/handle/11017/3398.
11. ^ 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.
12. ^ 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..
13. ^ 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].
14. ^ a b 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.
15. ^ 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].
16. ^ York, PH, Carter, AB, Chartrand, K, Sankey, T, Wells, L & Rasheed, MA (October 2015), 'Dynamics of a deep-water seagrass population on the Great Barrier Reef: annual occurrence and response to a major dredging program', Scientific Reports. [online], vol. 5, no. 1. Available at: http://www.nature.com/articles/srep13167 [Accessed 18 March 2019].

Last updated: 19 July 2019