Intertidal low energy over consolidated substrate

Long description

Intertidal low to very low wave energy over rocky headlands, platforms, pavements, river banks and rock bars with geology of mineral rock or chemical origin (i.e. terrigenous or land-based). The Lithology or rock type may influence the shape, chemistry and nature of the biota growing on these ecosystems. They may occur along the open coastline, on islands and reefs, in estuaries and beside and within tidal river systems. Rock bars towards the upper limits of tidal rivers may act as natural barriers to the passage of tidal waters where these limits have not been hydrologically modified.

The alternate exposure to air and to salt water is reflected by a pronounced zonation that reflect the tidal planes and their inundation, although narrower than on high energy rocky shores because there is no splash zone. Potentially low energy rocky reef ecosystems have a suite of algae, coral and other encrusting fauna (octocorallians*). Typical patterns from the high tide mark downward is a littorinid zone (periwinkles), a barnacle zone around mean high water, an oyster zone around mean sea level, and macroalgae near the low tide levels (occasionally also mussels). There is no tubeworm zone, and the lower low tide area may include zoanthids and corals (hard and soft). Fauna includes grazing molluscs (periwinkles e.g. Littorina scabra), limpets and nerites) and crabs (e.g. rock crabs)[3][5]. See types 21 (corals), 20 and 116 (molluscs) and 22 (other biota) for further information about special values.

*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[4].

Special values

Tidal pools form above the water mark and provide submerged habitat for typically subtidal species[1]. Rocky shores provide habitat for a wide range of sessile flora and fauna. Rock bars towards the upper limits of tidal influence are natural controllers of tidal waters.

Ridges and channels of the rocky shore may provide shape for the construction of fish traps, creating high tide pools. Through the placement of stones, Traditional Owners have used fish traps for thousands of years to capture traditional food.

Rocky substrates are important feeding habitats for popular recreational fish. For example, at high tide, low energy rocky shores are a preferred habitat of bream, which feed on molluscs and crabs, and for herbivorous fish (e.g. luderick, drummer).

Shorebird feeding habitat for resident species such as the beach stone curlew and sooty oyster catcher[2].

Diagnostic attributes

Inundation 'Intertidal – Lower low', 'Intertidal – Mid low', 'Intertidal – Upper low', 'Intertidal – Low undifferentiated', 'Intertidal – Lower medium', 'Intertidal – Upper-medium', 'Intertidal – Medium undifferentiated', 'Intertidal – High', 'Intertidal – Undifferentiated', 'Intertidal – High undifferentiated'

Consolidation 'Consolidated'

Energy magnitude (wave) 'Low', 'Very low'

Qualifiers

Can also include ecosystem types with modified Consolidation such as subtidal parts of boat ramps, jetties, port infrastructure (e.g. bunds, weirs and dams) which also modify tidal inundation. The biota growing on these modified ecosystems would be very different from that growing on natural rocky ecosystems. Artificial tidal barriers can shorten the tidal prism, modifying the Energy source (riverine and current), Sediment texture and Water clarity. Tidal barriers provide impediments to the movement of diadromous fish, that is, those that need to move from freshwater to estuaries to reproduce (or vice versa).

The attributes of Consolidation, Substrate grain size and Inundation may be modified by fish traps.

Distribution

There are low energy rocky headlands, platforms and pavements up and down the Queensland coast, interspersed with sandy beaches and muddy bays. K'gari (Fraser Island) is the northern-most limit of high energy rocky shorelines, forming a barrier to wave energy together with the Great Barrier Reef. Mostly low energy shorelines occur behind those barriers from about 25 degrees latitude northward to the tropics. From Point Vernon (Hervey Bay) northward, typically ‘northern’ species occur and the zonation pattern differs substantially from high energy rocky shores with their more typical ‘southern’ biota[3][5]. Low energy rocky shores from Point Vernon northward were dominated by an oyster zone in the upper half of the intertidal region and a barnacle zone in the lower half of the intertidal area[3]. Low energy rocky shores also occur in the Great Sandy Strait and further south in Moreton Bay. See types 21 (corals), 20 and 116 (molluscs) and 22 (other biota) for further information.

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

• In the Central Queensland mapping area, there are low energy rocky shores within Port Curtis, in Rodds Harbour, Agnes Water and Woongarra, along Point Vernon in Hervey Bay and on Woody and Little Woody Islands in the Great Sandy Strait. Rock bars occur within many of the estuaries and tidal rivers, notably in Worthington Creek, Baffle Creek and tributaries of the Burrum River.
• The Lithology or rock type may influence the shape, chemistry and nature of the biota growing on these ecosystems. For example, the granite around Rodds Peninsula will differ from that of the Agnes Water volcanics and Woongarra coastal basaltic communities.
• Ensure that high energy and low energy rocky shorelines are viewed in conjunction with the naturalness qualifier, to identify human modified ecosystem types including boat ramps, jetties and port infrastructure. In some cases jetties are both intertidal and subtidal, extending into deep water that normally would not have an intertidal component.

Comments

Relevant additional attributes include Substrate composition, Energy source and Energy magnitude, Lithology. The Terrain slope, Terrain roughness and Terrain morphology are indicative of the shape of the substrate, e.g. steep sided cliffs to platforms, rock bars and pools and crevices for potential shelter of biota. Freshwater influence is relevant in tidal estuaries and rivers. Tidal range changes may influence the extent of tidal zonation and species present.

Additional Information

Rocky shore - Queensland Government

Intertidal rocky shores - Queensland Museum

Intertidal rocky shores - Museum of Tropical Queensland

Indigenous Fish Traps and Weirs of Queensland

References

1. ^ Bennett, I & Dakin, WJ (1992), Australian seashores, Collins/Angus & Robertson, Pymble, N.S.W..
2. ^ Driscoll, P (1995), Survey of wader and waterbird communities along the central Queensland coast, Queensland Ornithological Society Inc.
3. ^ a b c Endean, R, Kenny, R & Stephenson, W (1956), 'The Ecology and Distribution of Intertidal Organisms on the Rocky Shores of the Queensland Mainland', Marine and Freshwater Research. [online], vol. 7, no. 1, p. 88. Available at: http://www.publish.csiro.au/?paper=MF9560088 [Accessed 30 April 2019].
4. ^ Fabricius, K (2010), 'Octocorallia', in Encyclopedia of Modern Coral Reefs, pp. Chapter-35.
5. ^ a b Poloczanska, ES, Smith, S, Fauconnet, L, Healy, J, Tibbetts, IR, Burrows, MT & Richardson, AJ (2011), 'Little change in the distribution of rocky shore faunal communities on the Australian east coast after 50years of rapid warming', Journal of experimental marine biology and ecology, vol. 400, no. 1, pp. 145-154, Elsevier.

Last updated: 22 July 2019