Octocorallians in very deep water

Long description

Octocorallians occurring as part of a mesophotic ecosystem in very deep water (greater than 30 metres) including the octocorallian genus Dendonepthya in deep holes on the sea floor (T. Stevens, pers. comm.). 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 (i.e. attached) 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[2].

Special values

Mesophotic ecosystems are potentially refugia for species also found on shallow water ecosystems.

Mesophotic ecosystems are popular recreational fishing spots.

Diagnostic attributes

Inundation 'Subtidal'

Benthic depth 'Very deep' greater than 30m

Structural macrobiota 'Soft coral – octocorallians'

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

Poorly known distribution in Queensland waters.

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

• The sole known representative is from the 25 fathom hole in Hervey Bay (northern Mary River paleochannel, Great Sandy Marine Park).
• Mesophotic ecosystems of Central Queensland are very poorly known, both in their nature, extent and biophysical influences. For example there is speculation as to whether the holes in which this ecosystem occurs is a wonky hole or freshwater influenced groundwater dependent ecosystem[5].
• Palaeochannels are important for the cross-shelf transport of sediments and biota and the regulation of currents and climate[4][3] showed that the deep nutrient rich saline bottom water of Hervey Bay travelled across the shelf and was periodically discharged off Fraser Island, transporting the sediment that had travelled northward from Victoria by longshore drift, over the continental slope into the abyssal plain[1]. The saline bottom water also drove the circular current patterns of Hervey Bay.
• Mapping is based on one example in the 25 Fathom Hole, part of the Mary River palaeochannel. Its limited extent is based on very sparse bathymetry for the deeper parts of Hervey Bay. Palaeochannels also occur in the north of the CQ mapping region, i.e. the Fitzroy River palaeochannel passes to the north of the Capricorn Bunker Group.

Comments

Not differentiated on Consolidation, these ecosystems may also fall within type 94 (undifferentiated coral not on consolidated in very deep water) and type 95 (undifferentiated coral on consolidated in very deep water). Other relevant attributes are Terrain morphology (channels, pits). Deep water ecosystems are only found in the south of the mapping region, in Hervey Bay. Other deep holes in the area that are along palaeochannels include Southern Gutters (to the south of 25 Fathom Hole) and African Gutters (to the north, potentially part of the Burnett palaeochannel). With further inventory, potentially may expand in range including other palaeochannels e.g. Fitzroy (north of Curtis).

Additional Information

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

Mesophotic.org

Reef corals and coral communities in the mesophotic zone - Corals of the World

Mapping the life mesophotic - Marine Biodiversity Hub

References

1. ^ Boyd, R, Ruming, K, Goodwin, I, Sandstrom, M & Schröder-Adams, C (2008), 'Highstand transport of coastal sand to the deep ocean: A case study from Fraser Island, southeast Australia', Geology, vol. 36, no. 1, pp. 15-18, Geological Society of America.
2. ^ Fabricius, K (2010), 'Octocorallia', in Encyclopedia of Modern Coral Reefs, pp. Chapter-35.
3. ^ Gräwe, U, Wolff, JO & Ribbe, J (2010), 'Impact of climate variability on an east Australian bay', Estuarine, Coastal and Shelf Science, vol. 86, no. 2, pp. 247-257, Elsevier.
4. ^ Ribbe, J, Wolff, JO, Staneva, J & Gräwe, U (2008), 'Assessing water renewal time scales for marine environments from three-dimensional modelling: A case study for Hervey Bay, Australia', Environmental Modelling & Software, vol. 23, no. 10, pp. 1217-1228, Elsevier.
5. ^ Stieglitz, T (2005), 'Submarine groundwater discharge into the near-shore zone of the Great Barrier Reef, Australia', Marine pollution bulletin, vol. 51, no. 1, pp. 51-59, Elsevier.

Last updated: 22 July 2019