Intertidal and subtidal attributes

Quick Links

• Queensland Intertidal and Subtidal Ecosystem Classification Scheme
• Intertidal and subtidal mapping background
• Intertidal and subtidal mapping FAQs (including field names and alias)
• Module 1 - Introduction and implementation of intertidal and subtidal ecosystem classification
• Module 2 - Literature review of intertidal and subtidal classification frameworks and systems
• Module 3 - Attributes and qualifiers (these pages)
• Module 4 - A method for providing baseline mapping of intertidal and subtidal ecosystems in Queensland
• Fact sheet: The Queensland Intertidal and Subtidal Ecosystem Classification Scheme
• Fact sheet: Intertidal and Subtidal Habitat Mapping and Conservation Values Assessment for Central Queensland State Waters
• Fact sheet: A Method for Classifying and Mapping Intertidal and Subtidal Ecosystems in Central Queensland
• Intertidal and Subtidal Ecology (Estuarine and Marine)
• Assessment of Common Conservation Values - Intertidal and Subtidal Environs of the Baffle to Fitzroy Coast (ACCV)
• Intertidal and subtidal ecosystem types of Central Queensland
• WetlandMaps (interactive mapping)

Intertidal and Subtidal Biophysical Attributes

Ecosystems can be classified, described and defined by using measurable characteristics known as biophysical 'attributes' (biological, physical and chemical). These biophysical attributes, together with their ecosystem processes, determine how the ecosystems function and can be combined to form an ecosystem 'type'.

To classify or determine intertidal and subtidal ecosystem types requires an understanding of which attributes will shape, influence and maintain the ecosystem. The purpose of the classification (or mapping), will determine which of these attributes are used.

Key features of the attributes in the Intertidal and Subtidal Classification Scheme (scheme) include:

• the separation of benthic and water column classification (Figure 1)
• similar attributes that can be used at more than one spatial scales (levels) however:
  1. where an attribute is related to multiple levels then the categories of the attribute may vary between scales (e.g. structural macrobiota may be seagrass-dominated community at a high level such as region, but Halophila ovalis dominated community at a lower level such as habitat). Attributes used at multiple levels can be measured, thresholded and categorised independently from one another.
  2. different datasets may be used to map the same attribute at different scales.
• the use of themes to group attributes (e.g. terrain, substrate, energy, hydrology (physical/chemical) and biota).
  

Qualifiers

Qualifiers are descriptors of variability applied to an attribute: Naturalness, Trend, Period, Cover, Biotic height and Biomass. Qualifiers provide additional information for existing attributes and are similar to modifiers in other classification schemes[4]. Changes in ecosystems can be due to natural variation or from other sources, and can result in a shift of state or type of an ecosystem[7]. The nature of these changes and their influence on an attribute should be captured in classifying and mapping wherever possible. It is important to consider how natural variability influences structure (components) and functionality of ecosystems.

The ‘Naturalness’ attribute qualifier describes the extent of human-induced change. For example, if the attribute Sediment grain size is classified as 'Sand' and this was the result of deposition from dredging activity, a category of 'Modified natural’ or ‘Artificial' could be assigned to the Naturalness attribute modifier. In this way, the inherent category of the attribute does not change from 'Sand' but the additional information may be used to interpret values or to classify components differently.

Table 1 - Codes for the Naturalness qualifier

Table 2 - Attributes used in the scheme and relevance to each level showing whether they are benthic (B), water column (WC) or related to both (B/WC), and the levels to which they should apply.

Benthic Classification

Theme: Terrain

Terrain is defined here as the topography or shape of the sea floor (modified after LeCours[10]). It involves the vertical and horizontal dimensions of the sea floor surface.

Terrain attributes are primarily derived from digital elevation models (DEM) of the sea floor and relate to its structure. Terrain (and benthic depth) is a product of geomorphic processes forming sea floor geomorphic features, such as those involved in continental drift, e.g. rifting, sea floor spreading, subduction, sea level rise and fall, erosion, deposition etc. The Queensland Intertidal and Subtidal Classification Scheme does not map evolutionary processes, only their end products e.g. the terrain. Benthic depth (and terrain) also influences hydrology themes, by forming boundaries between different water masses with different conditions, circulation patterns and species pools, and is correlated to hydrological and chemical attributes such as salinity, temperature, oxygen, water clarity and exported carbon[12].

Various terrain metrics exist, but only some of these directly influence ecosystem distribution, including benthic depth, shape or morphology, slope, patterns formed by morphology, the relative relief of these patterns and roughness. Originally developed for catchment hydrology and soil prediction, terrain attributes are now routinely used to map and model sea floor ecosystems[8].

Attributes under the terrain theme include:

• Benthic depth
• Terrain morphology
• Terrain slope
• Terrain relative relief
• Terrain roughness

Theme: Substrate

Attributes relating to the composition of the substrate include the source type of rock (Sediment composition), whether it is consolidated or not (Consolidation), grain size of unconsolidated substrates (Sediment grain size), and the non-living composition of the substrate. Other substrate attributes involve complex processes, which are best explored in conceptual models, for example genesis of the substrate.

• Genesis of the substrate (e.g. organic, inorganic, terrigenous, siloclastic etc.) tells the story of origin and formation of the substrate, including processes and drivers. The story of the genesis of the Great Barrier Reef (GBR) and its various reef types are best described through conceptual models and specialist typologies. For example most modern coral reefs grow on the bones of their ancestors, so it is important to distinguish what is the antecedent substrate within the GBR. Processes involve thousands of years of sea level rise and fall, position on the continental shelf, width of the continental shelf, erosion, sediment transport, deposition and calcification. The depth of the growing reef and its resultant shape modify energy patterns of sediment transport, erosion and deposition[9].

The following characteristics describe a change or variability in the substrate and apply to several substrate attributes (e.g. Lithology, Consolidation, Sediment grain size). Note that sediments usually occur in mixtures of different grain sizes termed 'sediment texture'. These qualifiers include:

• Hardness/compaction of the substrate is important to burrowing fauna or for flora growing on its surface. Compaction or hardness is a result of soil- and rock-forming processes involving primary and secondary chemical and/or physical compaction. For example:
  • chemical percolation of dissolved iron and aluminium oxides that solidify as an indurated layer, or overburden of material weighing down on the substrate below.
  • cementation of unconsolidated substrates can be irregular, including nodules or concretions, or form regular bands of rock such as beach rock or coffee rock.
• Voids or interstitial spaces are available to be occupied by fauna, and substrate permeability may be inferred from substrate grain size. Importantly, porewater/groundwater/seawater filters through permeable substrates, driving groundwater–seawater movements and interactions through a variety of processes including wave, tidal, and hydraulic action[14]
• Layering of the substrate (e.g. a thin veneer of sand over clay) may be inferred from percentage composition of the Sediment grain size attribute.

Attributes under the substrate theme include:

• Substrate consolidation
• Substrate grain size (incorporating sediment texture)
• Substrate composition

Theme: Hydrology - Physical

Energy of the sea interacts with sea floor terrain which may be modified by the energy[17]. Energy source, magnitude and exposure influence sediment transport, erosion and accretion, resulting in changes to the terrain itself. There is a feedback loop between energy and morphology[9][3]. For example, the width of the continental shelf and its steepness, together with the degree of enclosure of a reef, influences the magnitude of energy exposure on coral reefs. This can be seen where tidal currents are forced through gaps in the ribbon reefs, and nutrients are transported in upwellings to Halimeda sp. macroalgal beds[17].

Energy also influences physical and chemical properties of water types and water masses, including the extent of tidal inundation, degree of mixing between different water masses and layers, suspension of particles, light penetration, temperature and salinity, nutrients and primary production. Ultimately these water column factors affect the benthos[16]. A map of dynamic attributes is a model, for example hydrodynamic models animate water movement in response to energy. Models are validated by field inventory, such as IMOS stations. Hydrodynamic models may provide metrics of the energy attributes of water, for example the GBR Hydrodynamic Model.

When capturing metrics of non-enduring attributes, consideration of timing, persistence, duration, periodicity and variability is required over relevant intervals such as tidal, diurnal, weekly, tidal fortnight, tidal month, seasonal, annual, interannual (e.g. SOI), decadal (e.g. Pacific Decadal Oscillation), centuries, episodic or other specific periods (e.g. 40-60 day weather bands such as the Madden-Julian Oscillation). Several regime metrics may exist for the same attribute. For example water regime applies to freshwater and tidal inundation[2].

Attributes under the 'hydrology' theme include:

• Inundation
• Energy Magnitude

Theme: Biota

Biotic attributes become more applicable at seascape, habitat and community scales. Some biotic attributes are also important at higher scales (e.g. the biotic attribute of ‘Coral’ shapes reef complexes at the subregional level, and the GBR and its lagoon at a regional level).

Biotic attributes are focused on species that provide structural and mappable features[1][11]. While surface biota is mappable, infaunal (organisms living largely within the substrate) presence is usually only confirmed during inventory, however future inventory methods may enhance their detection.

Although five to ten years is a nominated interval for identifying persistent biotic habitats, many biotic habitats also experience natural temporal variability. This requires a consideration of timing, persistence, duration, periodicity and variability over relevant intervals, such as tidal, diurnal, weekly, tidal fortnight, tidal month, seasonal, annual, interannual (e.g. Southern Oscillation Index), decadal (e.g. Pacific Decadal Oscillation), centuries, episodic and other specific periods such as 40-60 day weather bands (e.g. Madden-Julian Oscillation). ‘Stability of benthic substrates’, ‘ecological succession’, ‘disturbance’, ‘resilience’, ‘alternative stable states’ and ‘phase-shifts’ (e.g. change from coral to algae[5][6]) are all concepts related to ‘drivers’ and do not form part of this classification. Repeated application of typology and mapping may detect key changes in ecosystems required to inform monitoring programs.

It is often easier to measure abiotic surrogates (e.g. terrain, substrate, physical/chemical hydrology) to model the distribution of biotic ecosystems, than to map the biotic ecosystems themselves. Frequently, biota may not consistently respond to the same attributes, responding to other patterns and life processes not captured by these attributes[13][15]. Critical biotic attributes of species richness and abundance can often be modelled, but are difficult to reliably scale-up to habitat maps. The limitation of available biota inventory data is that it is often focussed on an ecosystem of interest (e.g. seagrass, mangroves, coral etc.) and may apply different survey standards, analysis method, output and spatial attribute, at varying spatial scales.

See more on the Structural macrobiota composition attribute under the Biota theme.

Pages under this section

References

1. ^ Aquatic Ecosystems Task Group (AETG) (2013), Interim Australian National Aquatic Ecosystem Classification (ANAE) Estuarine - Marine Attribute Workshop Summary Report, Auricht Projects.
2. ^ Aquatic Ecosystems Task Group (2012), Aquatic Ecosystems Toolkit, Module 2: Interim Australian National Aquatic Ecosystem (ANAE) Classification Framework, Australian Government Department of Sustainability, Environment, Water, Population and Communities, Canberra..
3. ^ Brinkman, R, Herzfeld, M, Andrewartha, J, Steinberg, C & Spagnol, S (2010), 'Hydrodynamics at the whole of GBR scale', Proceedings of the 2010 Marine and Tropical Sciences Research Facility Annual Conference, pp. 18-20.
4. ^ Cowardin, LM, Carter, FC & LaRoe, ET (1979), 'Classification of wetlands and deepwater habitats of the United States.', Fish an dWildlif Service, vol. FWS/OBS-79131, Fish and Wildlife Services, Washington, DC.
5. ^ Done, TJ (1992), 'Phase shifts in coral reef communities and their ecological significance', in The Ecology of Mangrove and Related Ecosystems, Springer, pp. 121-132.
6. ^ Done, TJ (1995), 'Ecological criteria for evaluating coral reefs and their implications for managers and researchers', Coral Reefs, vol. 14, no. 4, pp. 183-192, Springer.
7. ^ Done, TJ (1999), 'Coral community adaptability to environmental change at the scales of regions, reefs and reef zones', American Zoologist, vol. 39, no. 1, pp. 66-79, The Oxford University Press.
8. ^ Harris, PT & Baker, E (2011), 'Seafloor geomorphology as benthic habitat: GeoHab Atlas of seafloor geomorphic features and benthic habitats', in P T Harris & E K Baker (eds), Seafloor geomorphology as benthic habitat: GeoHab Atlas of seafloor geomorphic features and benthic habitats, Elsevier, p. 871.
9. ^ a b Hopley, D, Smithers, SG & Parnell, K (2007), The geomorphology of the Great Barrier Reef: development, diversity and change, Cambridge University Press.
10. ^ Lecours, V, Brown, CJ, Devillers, R, Lucieer, VL & Edinger, EN (2016a), 'Comparing Selections of Environmental Variables for Ecological Studies: A Focus on Terrain Attributes', PLoS One, vol. 11, no. 12, p. e0167128, Public Library of Science.
11. ^ Mount, R, Bricher, P & Newton, J (2007), National Intertidal/Subtidal Benthic (NISB) Habitat Classification Scheme., Australian Coastal Vulnerability Project. National Land and Water Resources Audit, Hobart, Tasmania.
12. ^ Pitcher, CR, Lawton, P, Ellis, N, Smith, SJ, Incze, LS, Wei, CL, Greenlaw, ME, Wolff, NH, Sameoto, JA & Snelgrove, PVR (2012), 'Exploring the role of environmental variables in shaping patterns of seabed biodiversity composition in regional‐scale ecosystems', Journal of Applied Ecology, vol. 49, no. 3, pp. 670-679, Wiley Online Library.
13. ^ Richmond, S & Stevens, T (2014), 'Classifying benthic biotopes on sub-tropical continental shelf reefs: How useful are abiotic surrogates?', Estuarine, Coastal and Shelf Science, vol. 138, pp. 79-89.
14. ^ Santos, IR, Eyre, BD & Huettel, M (2012), 'The driving forces of porewater and groundwater flow in permeable coastal sediments: A review', Estuarine, Coastal and Shelf Science, vol. 98, pp. 1-15, Elsevier.
15. ^ Sutcliffe, PR, Mellin, C, Pitcher, CR, Possingham, HP & Caley, MJ (2014), 'Regional‐scale patterns and predictors of species richness and abundance across twelve major tropical inter‐reef taxa', Ecography, vol. 37, no. 2, pp. 162-171, Wiley Online Library.
16. ^ Webster, IT, Brinkman, R, Parslow J, Prange J, Stevens ADL & Waterhouse J (2007), Review and Gap Analysis of Receiving-Water Water Qualty Modelling in the Great Barrier Reef. Report to Department of Environment, Water, Heritage and the Arts., CSIRO Water for a Healthy Country Flagship.
17. ^ a b Wolanski, E (2001), Oceanographic Processes of Coral Reefs. Physical and Biological Links in the Great Barrier Reef, CRC Press, Boca Raton, ed. E Wolanski.

Last updated: 27 October 2021