Marine Littoral (Intertidal)

Kilmore Quay, Co. Wexford (L.Lysaght)

Habitat categories and codes
L Littoral (intertidal)	LR Littoral rock	LR1 Exposed rocky shores
		LR2 Moderately exposed rocky shores
		LR3 Sheltered rocky shores
		LR4 Mixed substrata shores
		LR5 Sea caves
	LS Littoral sediment	LS1 Shingle and gravel shores
		LS2 Sand shores
		LS3 Muddy sand shores
		LS4 Mud shores
		LS5 Mixed sediment shores

 

This section covers habitats of the seashore in the littoral or intertidal zone, defined here as the area between the upper limit of the supralittoral zone (the spray zone on rocky shores and the strandline on sediment shores) and the MLWS tide mark. There are exceptions and a number of habitats that are subject to tidal influence at the upper limit of the littoral zone have been placed in the coastland section of the classification. These include salt marshes (CM1-2) , sea cliffs (CS1-3) , lagoons and saline lakes - CW1  and tidal rivers - CW2 . Note also that the intertidal sections of any coastal constructions are considered separately under sea walls, piers and jetties - CC1 . The sublittoral fringe, or extreme lower shore between the mean and extreme low water spring tides, is not included in the littoral zone.

The term 'exposure', as used in relation to the marine environment, refers to wave action or tidal currents, and not to air. Instead, the terms 'emersion' (exposed to air) or 'submersion' (submerged by water) are used.

Littoral, or seashore, habitats are subdivided on the basis of substratum type into two broad sections: littoral rock (hard substrata colonised mainly by epibiota) and littoral sediment (unconsolidated material colonised mainly by infauna). Rock includes bedrock and accumulations of loose rocky material (boulders, cobbles and pebbles - see Table 2) that are largely stable. Sediment includes accumulations of mobile, rounded cobbles and pebbles, known as shingle, in addition to deposits of gravel, sand and mud (the silt/clay fraction). Shores with mixed substrata of rock and sediment are categorised in the littoral rock section. Intertidal peat deposits are treated as solid substrata with rock. Artificial substrata of built stone, concrete, metal, wood or plastic should be considered under sea walls, piers and jetties - CC1  in the coastland section. Note, however, that artificial substrata generally support the same communities of marine species as natural substrata.

Mudflats, sandflats and estuarine channels that are emersed at low tide are not treated as separate habitats in this classification but should be categorised on the basis of substratum type in the littoral section. Estuarine channels that retain water at low tide (freshwater or brackish) should be considered in the sublittoral section. Reedbeds in estuaries should be categorised as  reed and large sedge swamps - FS1.

Table 2: Particle size ranges for loose rocky material and sediment

Particle Type	Size range - diameter (mm)
Boulder	>256
Cobble	64-256
Pebble	16-64
Gravel	4-16
Coarse sand	1-4
Medium sand	0.25-1
Fine sand	0.063-0.25
Mud (silt/clay fraction)	<0.063

 

Littoral Rock

Littoral rock includes rocky habitats of the littoral, or intertidal zone that extends from the upper limit of the supralittoral, or spray zone, to the MLWS tide mark. The extreme lower shore, or sublittoral fringe is excluded. Rock includes bedrock, stable accumulations of loose and mainly angular rock (ranging in size from boulders to pebbles), and intertidal peats. Shores with mixed substrata of rock and sediment are included in the littoral rock section. Accumulations of rounded and mobile rocky material, or shingle, should be considered under  shingle and gravel shores - LS1 .

Rocky shores are subdivided into three main categories on the basis of wave exposure since the degree of wave action on a shore determines, to a large extent, what animal and plant communities are present. It also determines the width of the supralittoral zone because, on the most exposed shores, the effects of sea spray and wave splash can be far-reaching. Low rocky cliffs (<5 m in height), overhangs, rocky headlands and rock pools should be included in this section if they are subject to regular wetting by wave splash or sea spray, and if the cover of terrestrial vascular plant communities does not exceed 50%. Sea caves - LR5  are treated as a separate habitat, and rocky sea cliffs - CS1  (>5 m in height and sea stacks and islets - CS2  are included in the coastland section. Areas of built stone and other artificial structures in the littoral zone should be considered under  sea walls, piers and jetties - CC1.

Most rocky shores exhibit distinct zonation patterns that relate to the length of time a particular area is emersed, or exposed by the tide. Rocks of the extreme upper shore, including the supralittoral or spray zone, are typically dominated by lichens. Grey lichens ( Ramalina spp.) usually occur above yellow lichens ( Xanthoria spp.) at the top of the littoral zone. A distinctive band of the black lichen ( Verrucaria maura ), occurs below these at the bottom of the lichen zone. The width of the lichen zone varies with the degree of exposure, as does the height; both are greatest on the most exposed shores. On sheltered shores the lichen zone is usually greatly reduced. The more exposed rocky shores may support patchy cover of terrestrial vascular plant communities in the spray zone. Typical components of the vegetation include Thrift ( Armeria maritima ), Sea Aster ( Aster tripolium ) and the salt-tolerant grass, Red Fescue ( Festuca rubra ). On sheltered shores, the transition to terrestrial habitats is usually abrupt. Cover of terrestrial vascular plants should not exceed 50% for inclusion in any of the littoral rock categories.

All rocky shores may feature rock pools that remain water-filled at low tide. Rock pools support a wide variety of communities depending on their size, depth and position on the shore. Those on the upper shore are subject to variable or reduced salinity (mainly rainwater influence) and wide temperature fluctuations, and are typically dominated by ephemeral green seaweeds ( Enteromorpha and Cladophora spp.). Rock pools of the mid-shore are characterised by encrusting coralline algae and the red seaweed, Corallina officinalis. Seaweeds such as fucoids and kelps may occur in deeper rock pools on the lower shore.

Links with Annex I:  Littoral rock categories may contain examples of the annexed habitat, 'reefs (1170)'.

Exposed rocky shores LR1

Limpets - Patella sp. (R.T. Mills)

This category includes extremely exposed to exposed bedrock and boulder shores of the open coast. The effects of sea spray and wave splash are usually far-reaching and the lichen zone, described above, may be up to 30-40 m wide on the most exposed shores. At the upper extreme, these shores may support some patchy cover of terrestrial vegetation with Thrift ( Armeria maritima ), Sea Aster ( Aster tripolium ) and Red Fescue ( Festuca rubra ). Snails such as Littorina saxatilis and Melarhaphe neritoides are common in the supralittoral zone. Below this, exposed rocky shores are typically dominated by communities of Common Mussel ( Mytilus edulis ) and barnacles ( Semibalanus balanoides, Chthamalus spp.). Limpets ( Patella spp.) are common throughout. Robust algae that can tolerate the physical stresses of wave wash are often abundant on the mid- and lower shore. These include red seaweeds such as Corallina officinalis and Mastocarpus stellatus, and the brown seaweed, Thongweed ( Himanthalia elongata ). Red seaweeds can form dense turfs that are resilient to wave wash; coralline crusts are also common.

Moderately exposed rocky shores LR2

This category includes moderately exposed shores of bedrock, boulders and stable cobbles. The lichen zone is generally less extensive than on exposed rocky shores - LR1 and, within this, there may also be some limited cover of terrestrial vascular plants. Moderately exposed rocky shores are dominated by communities of barnacles and fucoids on the mid- and upper shore, or by fucoids and red seaweeds on the lower shore. Cover of fucoids is typically incomplete and is less continuous than on sheltered rocky shores - LR3 . Fucoids occur in distinct horizontal bands; the upper shore is characterised by Channel Wrack ( Pelvetia canaliculata ) and Spiral Wrack ( Fucus spiralis ), the mid-shore by Bladder Wrack ( Fucus vesiculosus ), and the lower shore by Serrated Wrack ( Fucus serratus ). Red seaweeds (including Mastocarpus stellatus, Chondrus crispus, Palmaria palmata and Corallina officinalis ) may form dense turfs of single species, or mixtures of species. The variety of other associated species depends on the influence of microtopography, salinity (inputs of freshwater) and sand scour. Communities of Common Mussel ( Mytilus edulis ), limpets ( Patella spp.), snails ( Littorina littorea, L. obtusata, Nucella lapillus ), amphipod crustaceans and crabs are common; ephemeral green and red seaweeds ( Enteromorpha, Ulva and Porphyra spp.) may also be present. The sedentary polychaete worm, Sabellaria alveolata, may form honeycomb reefs if there is a plentiful supply of sediment. The presence of boulders and cobbles on the shore increases microhabitat diversity which, in turn, may give rise to greater species richness.

Sheltered rocky shores LR3

This category includes sheltered to extremely sheltered rocky shores of bedrock, and stable accumulations of boulders, cobbles and pebbles. At the upper extreme, the lichen zone is usually compressed to a narrow band as the influence of sea spray and wave action is greatly reduced in sheltered locations. The transition to terrestrial habitats above this is usually abrupt and distinct. Sheltered rocky shores are characterised by very dense growth of fucoids. Different species form distinct zones, typically with Channel Wrack ( Pelvetia canaliculata ) above Spiral Wrack ( Fucus spiralis ) on the upper shore, Knotted Wrack ( Ascophyllum nodosum ) and/or Bladder Wrack ( Fucus vesiculosus ) on the mid-shore, and Serrated Wrack ( Fucus serratus ) on the lower shore. On the mid-shore, Knotted Wrack ( Ascophyllum nodosum ) increases in abundance with increasing shelter, and may support a dense underturf of red seaweeds such as Corallina officinalis, Mastocarpus stellatus and Chondrus crispus. Snails ( Littorina saxatilis, L. littorea, Melarhaphe neritoides ), barnacles and limpets may be present in low numbers under the dense seaweed canopy. In situations where salinity is reduced through inputs of freshwater, Horned Wrack ( Fucus ceranoides ), and ephemeral green seaweeds ( Cladophora spp.) may be common.

Mixed substrata shores LR4

This category should be used in situations where the shore comprises a mixture of rock and sediment, and where the sediment may include gravel, sand or mud. Mixed substrata shores occur in moderately exposed to sheltered locations and may support fucoid communities that are similar in composition to those of sheltered rocky coasts, but usually with less dense canopy cover, and with a reduced variety of epifaunal species. Barnacles or dense aggregations of Common Periwinkle ( Littorina littorea ) or Common Mussel ( Mytilus edulis ) may also be present. In summer months, blankets of ephemeral green and red seaweeds ( Enteromorpha, Ulva and Porphyra spp.) can dominate these shores. Horned Wrack ( Fucus ceranoides ) occurs in upper estuarine conditions and at stream outlets.

Sea caves LR5

This category includes sea caves of the littoral zone only. Fully submerged caves are not distinguished in this classification (See sublittoral rock section) and non-marine caves - EU1 are treated as a separate habitat. Caves are defined as natural recesses in rock that have a complete ceiling. Narrow gullies, ravines or fissures in coastal rock that lack complete ceilings are excluded, as are sea arches; these should be considered under the appropriate littoral rock category, or as  rocky sea cliffs - CS1 . The colonising communities are determined by the position of the sea cave on the shore with regard to tidal fluctuations, and the degree of exposure to wave action. Reduced desiccation and increased shade inside the cave allow certain species to proliferate including, in particular, bryozoans, sponges, ascidians, barnacles, calcareous tubeworms and shade-tolerant red seaweeds.

Links with Annex I: Corresponds loosely to the annexed habitat, 'submerged or partially submerged sea caves (8330)'.

Littoral Sediment

This section covers habitats of the seashore in the littoral, or intertidal zone where the substratum comprises mainly unconsolidated material: shingle (mobile cobbles and pebbles), gravel, sand or mud, or mixtures of sediments of different grades. Habitats are classified according to sediment type since this determines the water-holding properties of the substratum and reflects, to some extent, the conditions of wave exposure. Both factors are important in influencing species distributions. Note, however, that making distinctions between the various different sediment categories, particularly the finer sands and muds, can be difficult in practice.

The littoral zone is taken as the area between the uppermost limit of the strandline and the MLWS tide mark. It includes the supralittoral zone which is subject to wetting by sea spray and wave splash, and excludes the sublittoral fringe, or extreme lower shore. The strandline is a zone on the upper shore where organic debris from the sea (mainly decaying seaweed) is deposited by the falling tide. Strandlines, at their upper limit, may support open communities of terrestrial vascular plants. Note that all other coastal or intertidal habitats that are characterised by terrestrial vascular plants should be considered elsewhere in the classification. Littoral sediment does not include   salt marshes (CM1-2) , sand dune systems ( CD1-6 ), shingle and gravel banks - CB1 , or sedimentary sea cliffs - CS3.

Estuarine sediments of the littoral zone that are emersed at low tide are included in this section. Note that  tidal rivers - CW2, lagoons and saline lakes - CW1, and reed and large sedge swamps - FS1  are categorised as separate habitats. Any estuarine channels that remain occupied by water at low tide should be considered on the basis of substratum type under sublittoral sediments.

Shingle and gravel shores LS1

Shingle Shore, Co. Galway (J. Fossitt)

This category includes exposed or moderately exposed shores with accumulations of loose, coarse but usually rounded and mobile rocky material. Sediments comprise mainly shingle and gravel, where particle sizes are generally larger than coarse sand and smaller than boulders (mostly 4-256 mm in diameter). Shell fragments may also be common. Coastal accumulations of dead maerl, so-called 'coral beaches', are included in this category. The strandline at the upper limit of the shore may be characterised by open communities of terrestrial vascular plants including Annual Sea-blite ( Suaeda maritima ), oraches ( Atriplex spp.), Sea Sandwort ( Honkenya peploides ), Sea Beet ( Beta vulgaris ) and Sea Mayweed ( Tripleurospermum maritimum ). Two rare perennial plants, Sea-kale ( Crambe maritima ) and Oysterplant ( Mertensia maritima ), are associated with shingle shores. Note that elevated ridges and banks of shingle and gravel are treated as a separate habitat in the coastland section (See shingle and gravel banks - CB1 ). Coarse, mobile sediments typically support little marine life other than opportunist amphipod and isopod crustaceans and oligochaete worms. Ephemeral green seaweeds ( Enteromorpha spp.) may also be present in summer months.

Links with Annex I: This category may contain examples of the annexed habitat, 'annual vegetation of drift lines (1210)'.

Sand shores LS2

This category includes exposed to sheltered shores of coarse, medium or fine-grained sand, usually with a very small proportion of gravel and mud (<10%). Most of the sediment particles should range from 0.063-4 mm in diameter for inclusion in this category but scattered shells or stones may occur on the surface. Bedrock and loose rock may also be exposed in places. Intertidal sandflats and strandlines are considered as part of the sand shore, but note that any ridges and mounds of sand should be considered under embryonic dunes - CD1 . Strandlines may support open communities of annual terrestrial vascular plants such as oraches ( Atriplex spp.), Sea Rocket ( Cakile maritima ), Saltwort ( Salsola kali ) and Annual Sea-blite ( Suaeda maritima ). There may also be some sparse cover of Sand Couch ( Elymus juncea ), Lyme-grass ( Leymus arenarius ), Sea Sandwort ( Honkenya peploides ) and Sea-holly ( Eryngium maritimum ). Lines of decaying seaweed are characterised by communities of beach fleas and sand hoppers. Mobile sand of the upper shore is typically impoverished of animal and plant life. The lower shore is characterised by amphipod ( Pontocrates spp., Bathyporeia spp., Haustorius arenarius ) and isopod ( Eurydice pulchra ) crustaceans, with some polychaete worms ( Scolelepis squamata, Nephtys cirrosa, Lanice conchilega ) and bivalve molluscs ( Angulus tenuis ). Eelgrasses ( Zostera spp.) may colonise sand along the lower seashore.

Sea-holly - Eryngium maritimum  (L. Lysaght)

Links with Annex I:  Sand shores may contain examples of the annexed habitats, 'mudflats and sandflats not covered by sea water at low tide (1140)' and 'annual vegetation of drift lines (1210)'.

Muddy sand shores LS3

This category includes shores where most of the sand is medium or fine ( <1 mm in diameter ) and where muds ( the silt/clay fraction ) make up 10-30% of the sediment. Muddy sand usually occurs as gently sloping flats in sheltered areas and these remain water-saturated throughout the tidal cycle. Characteristic components of the fauna include communities of lugworms ( Arenicola marina ) and bivalve molluscs ( particularly Macoma balthica and Cerastoderma edule ). Mudflats may also support beds of eelgrasses ( Zostera spp.), vascular plants that stabilise sediments and provide a colonising surface for other marine species. Muddy sand shores frequently occur at the seaward edge of salt marshes and may support open or discontinuous stands of cord-grasses ( Spartina spp.) and glassworts ( Salicornia spp.). Dense stands of any of these plants should be considered under lower salt marsh - CM1. At low tide, any channels that remain occupied by water, including estuarine channels with freshwater, should be considered under sublittoral sediments.

Links with Annex I:  This category may contain examples of the annexed habitat, 'mudflats and sandflats not covered by sea water at low tide (1140)'.

Mud shores LS4

Mud shores are formed primarily of very fine sediment and usually occur along the most sheltered sections of coastline. The silt/clay fraction of the sediment (particle sizes of <0.063 mm in diameter) should be at least 30%. Small amounts of coarser material, mainly gravel and pebbles, may also be present. This category includes some sandy muds (with 20-70% sand and 30-80% silt/clay), in addition to soft mud shores (>80% silt/clay) that are typically found in the upper reaches of estuaries. They are subject to variable, reduced or low salinity conditions. Mud shores are often characterised by elevated mudflats that are dissected by networks of shallow channels associated with flooding and drainage. They support communities of polychaete worms ( Hediste diversicolor, Nephtys hombergii, Pygospio elegans ), bivalve molluscs ( Macoma balthica, Scrobicularia plana, Cerastoderma edule, Mya arenaria ), mud snails ( Hydrobia spp.) and amphipod crustaceans ( Corophium spp.). Oligochaete worms are also characteristic if there is a significant freshwater influence. Mud shores may support open or discontinuous stands of glassworts ( Salicornia spp.), and this may indicate the pioneer formation of salt marsh. Cord-grasses ( Spartina spp.) may also be present. Dense stands of either of these two plants should be considered under lower salt marsh - CM1  in the coastland section.

Links with Annex I:  Mud shores may contain examples of the annexed habitat, 'mudflats and sandflats not covered by sea water at low tide (1140)'.

Mixed sediment shores LS5

This category should be used for sheltered shores that comprise poorly sorted mixtures of sediments of different grades, including pebbles, gravel, sand and mud. Larger stones and cobbles may be present and these often support some cover of fucoids (particularly Fucus spp.) or ephemeral green seaweeds ( Cladophora spp.). Depending on substratum type, mixed sediment shores may support communities of polychaete worms ( Hediste diversicolor, Scoloplos armiger, Pygospio elegans ), bivalve molluscs ( Cerastoderma edule, Mytilus edulis, Mya arenaria, Macoma balthica ), oligochaete worms, amphipod crustaceans and mud snails ( Hydrobia spp.).