Subtidal low energy over gravel

Long description

Subtidal low to very low energy gravels (including cobbles and pebbles) with or without low density structural macrobiota. Gravels can be of various Substrate compositions, such as terrigenous (i.e. fragments of decomposed rock or stones washed out of substrates) and carbonate (i.e. coarse shellgrits and coral rubble and fragments).

Biota are highly variable, including very low densities of isolated hard and soft corals, other octocorallians* and sponges, that are insufficiently dense to map as a biota ecosystem.

Carbonate gravels composed of shell or coral rubble are habitats for a variety of invertebrates (e.g. gastropod molluscs including cowries, cones and murexes, or burrowing bivalve molluscs).

*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[1].

Special values

Where biota grows on gravels, these can be biodiverse areas with a wide variety of taxa. Coral rubble areas in and surrounding coral reef lagoons. Mobile crustaceans such as Moreton Bay bugs (Thenus orientalis) occur in deep waters.

Diagnostic attributes:

Inundation 'subtidal'

Benthic depth 'shallow (0-10m)', 'deep (10-30m)', 'very deep (>30m)'

Sediment texture 'Gravel', 'muddy Gravel, 'sandy Gravel', '(muddy) sandy Gravel'

Qualifiers

The Naturalness qualifier may be relevant in areas of trawl or dredge fisheries.

Distribution

Low energy subtidal gravels occur throughout Queensland waters in the nearshore area and on the continental shelf.

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

• The western coastline of the Great Sandy Strait where the Elliott Formation geology meets the coast, nodules of iron and aluminium oxide from the duricrust layer form gravel beds subtidally and intertidally
• Gravel Pits at Dundowran west of Gatakers Bay, Point Vernon, Hervey Bay includes a mixed community of sparse hard corals, soft corals and macro-algae (Asparagopsis) growing on gravels, including cobbles and pebbles of coral rubble and shelly fragments
• Deep gravelly shellgrit and rubbly areas exist between subtidal dunes west of Rooney’s Point in Hervey Bay are potentially biodiverse areas.

Comments

Substrate composition and Morphology are relevant.

References

1. ^ Fabricius, K (2010), 'Octocorallia', in Encyclopedia of Modern Coral Reefs, pp. Chapter-35.

Last updated: 11 July 2019