Hard non-branching coral on unconsolidated substrate in shallow to deep water

Long description

Subtidal non-branching hard corals in shallow (0 to 10 metres) to deep water (10 to 30 metres) on unconsolidated or intermediate substrates including boulder, gravel (i.e. cobble and pebble), sand, mud and/or coffee rock. Non-branching corals include massive, submassive, plate/table, bushy, vase/foliose or encrusting growth forms. Growth forms of coral are influenced by biophysical factors including depth, light and currents. Generally, non-branching corals tolerate more turbid waters than branching corals[2]. Non-branching coral ecosystems can have high species diversity, particularly within the subtropics where both tropical and temperate species co-occur at the limit of their range[1].

Many substantial Great Barrier Reef fringing reefs originally began thousands of years ago by hard corals colonising unconsolidated substrates such as clay (mud)/sand (e.g. Dunk Island, Great Palm Island) or gravel/boulder[5]. Similar rubbly coral areas exist today. The difference between these communities and those on consolidated substrate is that they are vulnerable to mechanical movement (e.g. wave action throwing unconsolidated particles up onto the shores, and may never become permanently established (Smithers pers. comm.)).

This ecosystem resembles undifferentiated coral on unconsolidated substrate in shallow to deep water (type 94), except that it is a non-branching form starting to create the beginnings of a calcareous framework. Depending on whether branching corals, hard corals or octocorallians* are dominant, this ecosystem may switch back and forth between type 78 (branching coral on unconsolidated), 94 (undifferentiated coral on unconsolidated) and 70 (hard undifferentiated coral on unconsolidated) and not be a distinct ecosystem in itself.

Refer to type 70 (undifferentiated corals on unconsolidated) for comments concerning the origin of many Great Barrier Reef fringing reefs on unconsolidated sediments[5].

*Octocorallia is a subclass of the class Anthozoa in the phylum Cnidaria, and include soft corals, gorgonians, sea whips, sea pens, sea fans and octocorals. Like some of the many other anthozoans, octocorallians are sessile polyp-bearing animals with a mobile larval phase. Octocorallians are distinguished by the eight (i.e. octo) tentacles in each polyp. Most octocorallians do not deposit a rigid calcium carbonate exoskeleton, and therefore tend to attach to reefs rather than contribute to reefal frameworks as per the reef building Scleractinian (hard) corals[3].

Special values

The values of Queensland’s coral reefs are internationally recognised in the World Heritage and Ramsar conventions. The Outstanding Universal Value of the Great Barrier Reef World Heritage area is based on four criteria (vii), (viii), (ix), (x). The Ramsar convention also includes coral reefs as one of its wetland types which make up part of a site’s ecological character (a combination of the ecosystem components, processes and services of the wetland). The Great Sandy Strait Ramsar wetland also includes coral reefs (e.g. Woody and Round Island reefs, coral communities at Little Woody Island, and soft corals on coffee rock reefs). Shoalwater and Corio Bays Ramsar wetland and the Moreton Bay Ramsar wetland also includes fringing coral reefs.

Non-branching hard corals growing on unconsolidated substrates provide the beginnings of calcareous reefal framework at a finer scale, providing structure for the attachment of other flora and fauna (e.g. sponges, other invertebrates, macroalgae etc.) and providing nooks and crannies and food for corallivorous fish (e.g. angelfish) or algal farmers such as damselfish. Corally, gravelly, rubbly substrates can be productive areas for gastropod molluscs (e.g. cowries, cones and murex).

Diagnostic attributes

Inundation 'Subtidal'

Benthic depth 'Shallow (0-10m)', 'Deep (10-30m)'

Structural macrobiota 'Hard coral – non-branching'

Consolidation 'Unconsolidated', 'Intermediate', 'Unknown'

Qualifiers

Potentially Naturalness qualifiers are relevant. Being able to be shifted by mechanical action means that these ecosystems can be potentially modified by trawling or dredging.

Period and Trend qualifiers are relevant as wave action from storms or cyclones can move these colonies about on the sea floor, or waves can deposit them in the intertidal area (see Energy source and magnitude).

Distribution

Potentially non-branching corals may occur on unconsolidated substrate in the proximity of consolidated coral ecosystems on the inner shelf.

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

• Rubbly non-branching coral areas exist today, for example ‘pre-reefal’ Goniopora spp. on Gravel Patches at Dundowran near Hervey Bay, and patches of Turbinaria spp. growing laterally on rubble surrounding Hervey Bay reef[6].

Comments

Inventory on gravelly substrates may expand the distribution of this ecosystem type. Consideration of scale is important as these ecosystems may not exist at a seascape scale. This ecosystem type can be part of a succession on unconsolidated substrate, ultimately leading to consolidated calcareous reef (i.e. types 70 (undifferentiated coral on unconsolidated), 94 undifferentiated coral on unconsolidated), 86 (non-branching hard on unconsolidated), 98 (soft coral reefal gardens on unconsolidated), and then to consolidated types 90 (undifferentiated coral), 82 (non-branching hard), 74 (branching hard) etc.).

Water temperature is critical to all corals as they are sensitive to extremes of heat and cold, resulting in bleaching due to the loss of endosymbiotic dinoflagellates (e.g. zooxanthellae) and therefore the ability to photosynthesise[4].

Additional Information

Protecting the Great Barrier Reef - Queensland Government

Coral - Department of Environment, Science and Innovation

Coral reefs - Queensland Museum

The Reef - Great Barrier Reef Marine Park Authority

Corals of the World

Great Barrier Reef - UNESCO

Nationally (DIWA) and internationally important (Ramsar) wetlands - WetlandInfo

Coral Indicators for the 2017 Gladstone Harbour Report Card - Australian Institute of Marine Science

Reef Report Card 2016 - Queensland Government

Great Barrier Reef Outlook Report - Great Barrier Reef Marine Park Authority

Monitoring inshore reefs - Australian Institute of Marine Science

Reef Check Methods - Reef Check Australia

Coral reefs - Museum of Tropical Queensland

Remote Sensing Research Centre - The University of Queensland

References

1. ^ Beger, M, Sommer, B, Harrison, PL, Smith, SDA & Pandolfi, JM (2014), 'Conserving potential coral reef refuges at high latitudes', Diversity and Distributions, vol. 20, no. 3, pp. 245-257, Wiley Online Library.
2. ^ Butler, IR (2015), Flood response and palaeoecology of the high-latitude, terrigenoclastic influenced coral reefs of Hervey Bay, Queensland, Australia. PhD thesis, School of Biological Sciences The University of Queensland.
3. ^ Fabricius, K (2010), 'Octocorallia', in Encyclopedia of Modern Coral Reefs, pp. Chapter-35.
4. ^ Hoegh-Guldberg, O (1999), 'Climate change, coral bleaching and the future of the world's coral reefs', Marine and Freshwater Research. [online], vol. 50, no. 8, p. 839. Available at: http://www.publish.csiro.au/?paper=MF99078 [Accessed 11 June 2019].
5. ^ a b Smithers, SG, Hopley, D & Parnell, KE (2006), 'Fringing and nearshore coral reefs of the Great Barrier Reef: episodic Holocene development and future prospects', Journal of Coastal Research, pp. 175-187.
6. ^ Zann, M (2012), The use of remote sensing and field validation for mapping coral communities of Hervey Bay and the Great Sandy Strait and implications for coastal planning policy, The University of Queensland.

Last updated: 12 July 2019