Intertidal low energy over mud below mean sea level

Long description

Intertidal low to very low wave energy over mud banks below mean sea level (MSL). Mud banks, open coastal shorelines or river banks below the mangrove line (approximately MSL). Muddy sands are regarded as muds in this ecosystem type.

Burrowing infauna are prevalent in intertidal low energy mud ecosystems where the mud retains sufficient structure to permit burrowing (see Infauna utilisation attribute). Fauna may include: burrowing crabs, bivalve molluscs, polychaetes (e.g. tubeworms), other worms (e.g. other annelids, sipunculids, phoronids etc.), ascidians and anthozoans (e.g. anemones). Depending on the proportions of mud to sand, and the compactness of the mud for burrowing, there may be fiddler crabs (e.g. the fiddler crab Uca longidigita or close to very low tide Uca seismella), and in the soft deep mud close to low waterline sentinel crabs (Macrophthalmus spp.)[6]. Sessile epifauna is usually sparse but may have a high species diversity including sponges and emergent infauna, including tubeworms and anemone species (e.g. Cerianthus spp., Stoichactis haddoni).

Special values

Habitat for non-filtering feeding infauna (bottom feeding detritus such as polychaete worms) and habitat for filter-feeders in highly riverine or strong current areas with slightly clearer water.

Intertidal mud banks can be productive areas for invertebrate infauna and for shorebird feeding habitat[4]. Many shorebirds Environment Protection and Biodiversity Conservation Act 1999-listed species (EPBC).

Low energy muddy substrates provide habitat for recreationally and commercially important fishes and crustaceans (e.g. mud crabs) particularly in association with adjacent mangroves and saltmarshes.

These areas are likely to contain unmapped areas of sparse seagrass which are potential habitat for dugong and green turtles. Although more an issue in higher energy muddy ecosystems, re-suspension of mud or silt in the water column can also be problematic for photosynthetic biota such as seagrasses in low energy ecosystems. Seagrasses need Water clarity to enable light penetration required to make food, and suspended sediment can also settle on the seagrass ecosystems causing mortality[1]. Extreme events such as rainfall runoff and flood plumes are known to impact seagrass ecosystems[5][2].

Diagnostic attributes

Inundation 'Intertidal – Lower low', 'Intertidal – Mid low', 'Intertidal – Upper low', 'Intertidal – Low undifferentiated', 'Intertidal – Lower medium', 'Intertidal – Upper-medium', 'Intertidal – Medium undifferentiated'

Energy magnitude (wave) 'Low', 'Very low'

Sediment texture 'MUD', 'gravelly MUD', 'muddy SAND', '(slightly gravelly) sandy MUD', '(slightly gravelly) MUD', 'sandy MUD' (note that the dominant grain size is capitalised)

Qualifiers

Includes the intertidal sections of mapped modified ecosystems that have modified Benthic depth and Terrain morphology including dredged channels, boat harbours, depressions near boat ramps etc. Although unmapped, Period and Trend qualifiers are also relevant as the Energy magnitude may also vary seasonally and episodically with respect to wave action.

Distribution

Common up and down the Queensland coast, particularly in association with river mouths along protected coastlines in protected waters, such as bays and inlets. Wind action resuspends muddy sediments where they are found in the Great Barrier Reef lagoon[1].

The following relates to distribution of this ecosystem type within the Central Queensland mapping area:

• Large areas in the Central Queensland mapping area, including the Port Curtis area, and parts of the Great Sandy Strait. These ecosystems provide good fiddler crab habitat with a variety of species based on height on the shoreline. In very productive rivers, close to the shoreline Uca seismella is an indicator of a healthy river habitat (in the Mary River catchment they are only found in the Susan River, southern-most range). Outputs from agriculture (such as chemicals) can modify water and sediment quality (eutrophication, very fine mud) and there are now no U. seismella. Once abundant in the Burnett estuary but replaced by a rock wall (M. Zann pers. comm.).
• The mouth of the Fitzroy River estuary provides important shorebird feeding habitat with high biomass infauna. Slope and degree of tidal emergence determine how much habitat is available for the shorebirds to feed on at certain times[3]. See the Aquatic Conservation Assessment (ACA) for further information.
• In the Gladstone area, there can be ‘outbreaks’ of pink ascidians across the intertidal mud banks, however this is a very rare occurrence (S. McKenna pers. comm.).

Comments

Standardising wave models between local and national scales is problematic and may result in mis-matches in Energy magnitude (wave) mapping. Incorporating the attribute of Energy source by creating a typology of other forms of energy such as riverine and current to form a benthic stress model would more accurately model areas where mud is likely to be resuspended within the water column.

Additional Information

Intertidal mud flats - Queensland Museum

Reef 2050 Water Quality Improvement Plan - Australian Government

References

1. ^ a b Australian Government (2019), 'How does sediment affect the Great Barrier Reef?', Reef 2050 Water Quality Improvement Plan. [online] Available at: https://www.reefplan.qld.gov.au/resources/explainers/how-does-sediment-affect-the-gbr [Accessed 5 June 2019].
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. ^ Choi, CY, Coleman, J, Klaassen, M, Moffitt, DJ, Rogers, D, Skilleter, GA & Fuller, RA (2017), Final Report: Migratory Shorebird Monitoring - Understanding Ecological Impact (CA12000284), Uniquest, University of Queensland, Queensland, Australia.
4. ^ Department of Environment and Science, QG (2019f), Assessment of Common Conservation Values - Intertidal and Subtidal Environs of the Baffle to Fitzroy Coast, Version 1.1., Department of Environment and Science, Queensland Government., Brisbane, Queensland.
5. ^ 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.
6. ^ Zann, C (1979), The spatial distribution and sociological factors influencing spacing in five ocypodid crab species (Decapoda : branchyura) on the eastern Australian coast.. [online], p. 76, University of Queensland. Available at: https://trove.nla.gov.au/work/19172165?selectedversion=NBD3905821.

Last updated: 22 July 2019