Hard undifferentiated coral on unconsolidated substrate in very deep water

Long description

Subtidal mesophotic coral ecosystems (MCEs, i.e. low light coral ecosystems), dominated by hard coral, growing in very deep water (below 30 metres depth) on unconsolidated or intermediate substrates including boulder, gravel (i.e. cobble and pebble), sand and/or mud.

Hard corals if present are more likely to occur on boulders and gravel (e.g. coral rubble), as based on limited inventory of MCEs to date, macrobiota other than macroalgae is largely absent on mud and sand[1]. These types of MCEs of the northern Great Barrier Reef, tend to grow on ‘reefal’ substrates[1].

Mesophotic hard corals are also more likely to be heterotrophs, i.e. feeding on other biota rather than through photosynthesis[3].

Special values

Mesophotic ecosystems are potentially refugia from disturbance for coral species also found on shallow water ecosystems and include species tolerant to low light levels. Forty-five per cent of shallow reef coral species also occur in the mesophotic[2]. These ecosystems can provide protection from coral bleaching, however the mechanism for reduced bleaching at depth is complicated and appears to be related to Water temperature and/or light levels. In general, MCEs are also a refuge from the physical damage associated with storms and cyclones (Energy magnitude), apart from very intense ones.

Coral reefs and communities (including MCEs) are highly valued for their diverse flora and fauna, fish habitat values, as commercial fisheries. The values of Queensland’s coral reefs are internationally recognised in the World Heritage (Great Barrier Reef) and many MCEs are found within its boundaries. The Outstanding Universal Value of the Great Barrier Reef World Heritage area is based on four criteria (vii), (viii), (ix), (x).

Coral taxa of MCEs in the northern Great Barrier Reef have high diversity and potentially can preserve evolutionary lineages of Indo-Pacific corals[2].

Diagnostic attributes

Inundation 'Subtidal'

Benthic depth 'Very deep (>30m)'

Structural macrobiota 'Hard coral – undifferentiated'

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.

Distribution

A continuous line of submerged reefs extends along much of the shelf edge of the Great Barrier Reef in very deep waters. In the central Great Barrier Reef, surveys of mesophotic community structure on mud and sand substrates revealed either low cover of structural macrobiota, bare substrate or calcareous macrophytic algae Halimeda spp.[1]. There is very little data for MCEs south of Townsville due to limited surveys.

Deep water corals are most likely to occur in the lower latitudes. Lower latitude waters tend to have higher light levels than higher latitudes (everything else equal) due to the angle of the light and reduced path length through the water column (P. Muir, pers. comm.). Deep water corals may also occur in shaded microhabitats at higher latitudes, which also indicates the low light tolerance of these corals[2].

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

• The extent of hard coral on unconsolidated substrate in deep water is unknown.

Comments

Additional Information

What are Mesophotic Coral Ecosystems? - National Oceanic and Atmospheric Administration

Mesophotic.org

Corals of the World

Mapping the life mesophotic - Marine Biodiversity Hub

References

1. ^ a b c Bridge, TCL, Done, TJ, Beaman, RJ, Friedman, A, Williams, SB, Pizarro, O & Webster, JM (2011), 'Topography, substratum and benthic macrofaunal relationships on a tropical mesophotic shelf margin, central Great Barrier Reef, Australia', Coral Reefs, vol. 30, no. 1, pp. 143-153.
2. ^ a b c Muir, PR, Wallace, CC, Pichon, M & Bongaerts, P (19 December 2018), 'High species richness and lineage diversity of reef corals in the mesophotic zone', Proceedings of the Royal Society B: Biological Sciences. [online], vol. 285, no. 1893, p. 20181987. Available at: http://www.royalsocietypublishing.org/doi/10.1098/rspb.2018.1987 [Accessed 19 March 2019].
3. ^ Turner, JA, Babcock, RC, Hovey, R & Kendrick, GA (26 May 2017), 'Deep thinking: a systematic review of mesophotic coral ecosystems', ICES Journal of Marine Science. [online] Available at: https://academic.oup.com/icesjms/article-lookup/doi/10.1093/icesjms/fsx085 [Accessed 22 March 2019].

Last updated: 12 July 2019