Marine Biodiversity Data Portal - NI

Correspondence with existing habitats

UK BAP broad habitat: Littoral rock

May be a component part of Annex I habitats

Description: This habitat encompasses rocky habitats in estuaries, extending from supralittoral lichens down to the subtidal circalittoral. Estuarine rocky habitats incorporate substrata types such as bedrock and stable boulders.

The rich and sheltered waters of estuaries provide nursery grounds for fish, and estuarine rocky habitats are an important component of these nursery grounds.

Conditions in estuaries are distinctly different to those on the open coast, where rocky habitats are generally more abundant. Rocky habitats in estuaries are typically located in low wave energy environments with reduced salinity, and experience accelerated tidal streams with increased turbidity and siltation. The communities present on rocky habitats are adapted to these conditions and consequently their composition and character is different to that found on similar substrata on the open coast (e.g. the cape form of the sugar kelp Saccharina latissima and the tasselled morphology of sponges such as Halichondria bowerbanki.

The rocky supralittoral supports yellow and grey lichens, with a band of the black lichen Verrucaria maura below. These bands may be unusually narrow in areas of low wave exposure. The remainder of the shore can be dominated by fucoids and kelp with an understorey of barnacles, algae, grazing molluscs and gammarids, and occasionally sponges and seasquirts. Where the topography is varied, there is added community interest – for example entangled turfs of the red algae Gelidium pusillum and Catenella caespitosa on shaded surfaces, dense covers of the seasquirt Dendrodoa grossularia on overhangs, variable salinity hydroids on shaded verticals, and green algae dominated rockpools in depressions.

The communities on subtidal estuarine rocky habitats are equally variable, and at the most diverse end of the scale, may support a rich and exceptionally abundant sessile epibiota of anemones (e.g. Metridium senile and Diadumene cincta), filter feeding sponges (e.g. Halichondria panicea, Hymeniacidon perleve, Haliclona oculata, Raspalia spp., Suberties spp. and Stelligera spp.), bryozoa (e.g. Alcyonidium diaphanum), hydroids (e.g. Sertularella gaudichaudi, Bugula spp. and Tubularia spp.) and seasquirts (e.g. Ascidiella aspersa and Dendrodoa grossularia).

Estuarine rocky habitats often display a transition of community types down the length of an estuary, reflecting the different environmental conditions i.e. those at the upper ends of estuaries being specific to ultra sheltered and low salinity to communities similar to open coast rock communities towards the mouth of estuaries.

This habitat excludes rocky habitats in areas of permanent full salinity. Some occurrences of estuarine rocky habitats may also fall within Tideswept Channels and may contain examples of the Intertidal Underboulder Community habitat. The fucoid alga Ascophyllum nodosum mackayi and the native oyster Ostrea edulis, both Northern Ireland priority species, can be associated with estuarine rocky habitats.

Examples of fucoids in reduced salinity can be found at the head of Belfast Lough.

Associated biotopes:

Some of the identified biotopes are associated with estuarine conditions only. Additional biotopes are included which may be found in estuarine conditions, but not exclusively.
• LR.LLR.FVS – Fucoids in variable salinity
• LR.LLR.FVS.PelVS – Pelvetia canaliculata on sheltered variable salinity littoral fringe rock
• LR.LLR.FVS.FspiVS – Fucus spiralis on sheltered variable salinity upper eulittoral rock
• LR.LLR.FVS.FvesVS – Fucus on variable salinity mid eulittoral boulders and stable mixed substrata
• LR.LLR.FVS.AscVS – Ascophyllum nodosum and Fucus vesiculosus on variable salinity mid eulittoral rock
• LR.LLR.FVS.Ascmac - Ascophyllum nodosum var. mackaii beds on extremely sheltered mid eulittoral mixed substrata
• LR.LLR.FVS.FserVS – Fucus serratus and large Mytilus edulis on variable salinity lower eulittoral rock
• LR.LLR.FVS.FCer – Fucus ceranoides on reduced salinity eulittoral rock
• IR.LIR.KVS.Cod – Codium spp. with red seaweeds and sparse Saccharina latissima on shallow, heavily-silted, very sheltered infralittoral rock
• IR.LIR.KVS.SlatPsaVS – Saccharina latissima and Psammechinus miliaris on variable salinity grazed infralittoral rock
• IR.LIR.KVS.SlatPhyVS –Saccharina latissima with Phyllophora spp. and filamentous green seaweeds on variable or reduced salinity infralittoral rock

• EUNIS code: A1.32, A1.321, A1.322, A1.323, A1.324, A1.325, A1.326, A1.327, A3.321, A3.322 and A3.323

Priority species: Ascophyllum nodosum, Ascophyllum nodosum var. mackayi, Ostrea edulis, Lampetra fluviatilis

Threats:

• Commercial fisheries: Communities in naturally sheltered conditions, such as those of estuarine rocky habitats, are not resilient to physical disturbance type impacts caused by mobile fishing gear.
• Water Quality: Estuaries are often major areas of urban and industrial development. As a result, estuaries and estuarine rocky habitats have experienced substantial losses through land claim, reduction in water quality (through industrial contaminants and also agricultural practices resulting in enhanced nutrient input and silt loading). Estuaries also receive disperse and point contaminant inputs from inland areas.
• Dredging: Estuaries form natural harbours and are used as safe havens for vessel traffic. With this use of estuaries is the associated need for navigational channels and dredging, with both direct and indirect impacts on estuarine rocky habitats.
• Coastal Protection: Coastal defence is widespread in estuarine environments to protect private dwellings and also industrial infrastructure. This can have immediate direct impacts on estuarine rocky habitats or indirect impacts away from the point of coastal defence.
• Non-natives: Non-native species such as Sargassum muticum can compete with and replace native species.