OCEAN BLUE

Ireland's Marine Environment

Marine Environments
Coastal Environments
Marine Mammals
Marine Ducks & Seabirds
Marine Turtles
References

Location

THE island of Ireland is situated near the edge of the European continental shelf beyond which lie the deep waters of the true North Atlantic Ocean. The seabed off Ireland's Atlantic coast forms a wide shelf that slopes down gently toward the shelf edge — arbitrarily demarcated by the 200m depth contour[1] — where the water depth increases over a relatively short distance from about 200m to between 2,500-4,000m. The slopes that plunge from the shelf edge down to the deep ocean are known as "bathyal regions". At its closest, the shelf edge is only about 30-60km from the northwest coast. The marine shelf area within the 200m depth contour to the south and west of Ireland (i.e. the Celtic Sea and Atlantic seaboard) covers approximately 200,000 square kilometres.

The broad expanse of the Malin Shelf (Malin Sea) lies to the north of Ireland, and the shallow semi-enclosed Irish Sea to the east. The western Irish Sea is marked by a deep channel (> 100m), which extends the length of the region, reaching a maximum of 315m in the northern trough known as the Beauforts Dyke. It connects to the Celtic Sea via the St George's Channel in the south and to the Malin Shelf in the north through the North Channel. West of this deep channel, fringing Ireland's east coast is a narrow, shallow (< 40m) strip.

Marine Environments

Deep-sea

IT was once believed that in the open ocean beyond the continental shelf edge, the bathyal regions and deep ocean floor were deserts of sedimentary ooze that supported few life forms. However, surveys have shown that deep-sea ecosystems possess an unexpectedly high species abundance and diversity. The deep seabed off Ireland's Atlantic seaboard supports an amazing abundance and variety of life including cold-water corals, sponges, sea slugs, sea urchins, starfishes, deep-water fishes and many other benthic organisms.

Other research has gone some way to dispelling the notion that deep seabed habitats and communities are isolated from the water mass above — that there is in fact ecological continuity throughout the water column (Gage and Gordon, 1995). The existence of severe seabed currents, or "benthic storms" has been detected during research undertaken at 2,400m depth on the North Feni Ridge, west of Scotland. These submarine storms are capable of remobilising sediments and dispersing them vertically in the water column as well as horizontally across the seabed.

The bathyal regions of the Rockall Trough west of Scotland and north-west of Ireland, are thought to be among the world's most biologically rich environments, due mainly to a large number of species of microscopic mud-dwelling nematode worms and other invertebrates, most of which are new to science. Contrary to the conventional view that marine biodiversity declines with depth, maximum biodiversity occurs in these bathyal regions between 1,000-3,000m depths (Boucher and Lambshead, 1995).

In 1998, researchers from the University College Cork found cold-water coral reef structures some 350m high and several kilometres across at depths of up to 900m along the shelf edge west of Ireland.

Also in 1998, an undersea feature previously unknown to science was discovered during surveying of the deep seabed north of Shetland and west of the Hebrides (UK waters). Hundreds of seabed mounds about 5m high and 100m across with tails several hundred metres long were found. Both mounds and tails are characterised by a roughly 15-fold increase in the density of xenophyophores — giant deep ocean protozoa (single-celled animals), subsequently identified as Syringammina fragilissima, which grows up to 20cm across. The "Darwin Mounds" are at a depth of about 1,000m and are spread over 50 square kilometres of seabed composed of deep foram sand sediments (the microscopic shells from trillions of dead phytoplankton), in the northern Rockall Trough. Growing on the mounds are deep-water corals (Lophelia pertusa).

Such discoveries, and the questions they raise, emphasise that present knowledge of deep-sea ecology and physical processes is comparatively minimal.

The deep-sea comprises a habitat for many species of fish, including commercially important demersal species such as roundnose grenadier, Atlantic orange roughy; pelagic oceanic (i.e. living in water above the continental shelf edge and deep ocean) species such as albacore tuna and oceanic Atlantic redfishes (Sebastes sp.); and rays and sharks. Typically, little if anything is known about the behaviour and ecology of deep-living fish species, such as orange roughy, and their populations.

Shelf area

Ocean circulation forces cold, nutrient rich water up the continental shelf slopes to the edge where it mixes with warmer surface water. Ocean primary productivity is high at these areas known as "upwellings". The nutrients and available sunlight support abundant growth of planktonic plant organisms (phytoplankton), which in turn support both grazer and predatory planktonic animals (zooplankton), then fish, squid, and higher predators in the food chain, including tunas, sharks, marine turtles, seabirds, seals and cetaceans (porpoises, dolphins and whales).

Small shrimp-like crustaceans, such as euphausiids, copepods and amphipods, constitute the largest proportion of the zooplankton biomass; many spend their entire life-cycle floating at the surface. Other zooplankton organisms are the surface-dwelling (neustonic) eggs and larval stages of fish and bottom-dwelling worms, crustaceans and molluscs, which release millions of eggs to the water so that a few offspring may survive to disperse over a wide area before returning to the seabed as adults.

When meteorological conditions are appropriate, a thin lipid (fat) rich surface film or microlayer forms at the top of the water column. Marine surface films and microlayers, which may last for an extended period of time, are an important habitat for both phytoplankton and zooplankton.

Two dominant warm water ocean currents influence Ireland's marine environment. The first is the North Atlantic Drift (a continuation of the Gulf Stream that flows across open ocean from the Caribbean region), which warms the western coastal waters of Ireland. It brings with it an unusual faunal community including species such as the colonial hydrozoan Velella velella, also known as the "by-the-wind-sailor", and giants such as the sunfish and marine turtles, including the leatherback and loggerhead.

The second major influence is the warm water current that flows northwards along the European continental shelf edge carrying with it a planktonic community that originates in the Mediterranean Sea. This Lusitanian faunal community appears at the surface on the coasts of south, south-west and west Ireland, and is represented by adult stage animals such as the crawfish, red deadman's fingers and trumpet anemone.

Away from the warming influences of these two currents, the cooler waters to the north of Ireland support marine animals with an arctic-boreal distribution such as the stonecrab. While Ireland is at the northern limit of certain marine species with a sub-equatorial distribution, it is likewise at the southern limit of many sub-polar species.

To the east of Ireland, warm water enters the shallow semi-enclosed Irish Sea through the St George's Channel between County Wexford and south Wales, while a colder northern current flows south through the North Channel between Counties Antrim and Down and south-west Scotland. Where the two currents meet along a zone of "frontal mixing" across the north Irish Sea (near the Isle of Man), high densities of plankton are brought to the surface where they attract fish, including important numbers of filter-feeding basking sharks - the second largest fish in the world.

Basking sharks are frequently seen in the Irish Sea and above the continental shelf off the south and west coasts of Ireland. Though little is known about basking shark behaviour, it is thought that during autumn and winter they move offshore to deeper water; in spring they move back inshore to feed on the seasonal abundance of plankton in coastal waters, especially at frontal mixing zones. Females give birth to live young; the litter size is unknown, except for one incident where a female gave birth to six young. Basking sharks, while being long-lived, are slow to reach sexual maturity and hence their reproduction rate is low. It is not known where around Ireland and Britain female basking sharks go to give birth.

The average water depth of the Irish Sea is about 100-150m. The faunal communities of the seabed reflect the range of bottom sediments, including widespread glacial deposits, and the degree of exposure to benthic currents.

In general, seabed communities around Ireland's coasts remain poorly understood. There are estimated to be more than 15,000 benthic species in the shelf seas around Britain, reflecting the wide range of environmental conditions around those coasts (DETR, 1998).

Several North-East Atlantic populations of commercially important fish species are present in Ireland's shelf waters, either as residents or migrants. For example:

Atlantic cod is generally a demersal species (i.e. it lives and feeds at or near the seabed) that often migrates long distances to spawning and feeding grounds where it may become more pelagic in habit (i.e. living nearer to the sea surface). Though mostly found within continental shelf areas that are between 150-200m deep, Atlantic cod are widely distributed through a variety of habitats, from the near-shore to well down the continental shelf to depths of over 600m. Atlantic cod move inshore to spawn in depths generally less than 50m.

Atlantic herring inhabit coastal pelagic and semi-pelagic waters (down to 200m) of the continental shelf. They have complex feeding and spawning migrations. Depending on race, spawning takes place in coastal waters down to 200m.

Atlantic mackerel is a semi-pelagic and mesodemersal species (i.e. it lives in mid-water) that is most abundant in cold and temperate shelf areas. They over-winter in deeper waters but move inshore in spring to spawn in coastal waters.

Blue whiting is a semi-pelagic species that feeds in the Norwegian Sea on plankton in the water column at a depth below pelagic feeders. They migrate south along the shelf edge to spawn west of Scotland and off the west and northwest coast of Ireland.

Other commercially important fish occurring in Ireland's shelf waters include demersal species allied to the cod such as haddock, white pollack and hake; demersal flatfish such as halibut, plaice, sole, megrim and turbot; demersal monkfish and sand eel; pelagic neritic (i.e. living in water above the continental shelf) species such as Atlantic salmon; and rays (e.g. skate) and sharks (e.g. spur dog and spotted dogfish).

Numerous other fish species such as wrasse, conger eel, flounder and sea bass are of importance to the sea angling industry.

Populations of shrimps (prawns) and other crustaceans such as Nephrops (also called Dublin Bay prawn, Norway lobster, or scampi), crawfish, lobster and crabs, as well as molluscs — squid and shellfish such as scallops, mussels and oysters — are also of commercial importance in Irish waters.

Near-shore waters

Ireland's near-shore[2] habitats support rich and diverse communities of marine fauna and flora, and often include unusual and rare species. For example, the region of Kilkieran Bay in County Galway is renowned for its unique white beaches such as Coral Strand at Carraroe. These are formed from the remains of an unattached calcareous algae (calcified seaweed) known as Lithothamnion, maërl, or simply "coral", which wash ashore during winter storms. Maërl grows in the clear, warm and shallow bay waters to form extensive beds on the sea floor.

The maërl beds, like tropical coral reefs, provide shelter for many other marine animals, including molluscs, sea cucumbers and sea urchins. Likewise, dense beds of horse mussels provide shelter for an assemblage of other marine animals such as tubeworms, sea squirts, variegated scallops and sea cucumbers.

Strangford Lough, a large sea inlet of great conservation value in County Down, is especially important as a spawning area for fish, including sand eels, which spawn in the sandbanks near the low-water mark. Sand eels are an essential component of the marine ecosystem in many coastal waters around Ireland. They are predated by a host of larger animals and are an important part of the diet of many seabirds such as puffins, especially during the breeding season.

Coastal waters in general are important habitats for many fish species, including migratory species such as Atlantic cod, Atlantic herring, Atlantic mackerel, blue whiting and Atlantic salmon. Likewise for a diverse array of crustaceans (shrimps, lobsters, crabs), cephalopod molluscs (octopus, squid, cuttlefish), molluscan shellfish (e.g. scallops, razor shells, mussels), marine worms, jellyfish, sponges, colonial bryozoans, and other marine animal groups.

Coastal Environments

EXCLUDING offshore islands, the total length of Ireland's coastline exceeds 6,000 kilometres (3,700 miles). Its wide diversity of constituent rock types and sediments gives rise to an extensive variety of landscapes and important wildlife habitats.

The coast and its geology are exposed to different degrees of wave energy. Ireland's Atlantic seaboard is subject to high wave energy, which gives rise to characteristic cliffs, islands, rocky shores, storm beaches and wind-blown machair grasslands. On the south and east coasts the wave energy is lower and the coastal landscapes are softer, with many stretches of sand dunes, shingle and estuarine mud.

The coast is a complex interface — a zone of transition between the environments and habitats of land and sea. As a zone it contains many highly productive ecosystems in which species of fauna and flora have evolved to tolerate varying degrees of exposure to sea and brackish water or, conversely, air, salt spray and freshwater.

Intertidal zone
The intertidal, or littoral zone is between the high-water and low-water marks, i.e. that part of the shore that is covered by seawater twice a day. Beneath and beyond the low-water mark lies the sublittoral or subtidal zone. Above and beyond the high-water mark lies coastal land.

The most common intertidal habitat on the Irish coast is a low rocky shore covered with a blanket of brown macroalgae (seaweeds) such as wracks and kelps. The great mass of organic detrital material (mucus and decayed particles) produced by the seaweeds forms the basis of the web of intertidal life. Seaweeds are attached to rocks by their holdfasts and absorb nutrients directly from the surrounding seawater. In shallow, well-lit and constantly churned coastal water, seaweeds grow rapidly.

Large brown seaweeds such as serrated wrack and some Laminaria species (oarweed and kelps) dominate sheltered rocky lower-shores. On more exposed coasts, which are subject to greater wave action, these give way to shrubby red seaweeds such as carragheen.

Kelp forests, which may become exposed on low tides, are an important habitat below the low-water mark. Together with their under-storey of red seaweeds such as sea beech, dulse and Phycodrys rubens, which extends into deeper water beyond the kelps' sublittoral limits, kelp forests support a diverse and important faunal community that includes bryozoans, hydroids, sponges and colonial sea squirts. Kelp forests are also the favourite feeding ground of coastal otters.

The middle-shore is dominated by other seaweed species, including brown seaweeds such as bladder wrack, egg wrack and sea oak. Carragheen and the similar-looking Mastocarpus stellatus are red seaweeds that are more tolerant of wave exposure than the wracks. Other red seaweeds that are often abundant in middle- and lower-shore pools include Lomentaria articulata and L. clavellosa.

Green macroalgae occupy the upper and middle intertidal zone, often in pools. Sea lettuce is a green seaweed that grows over the whole shore, except for the extreme upper levels. Its growth, like that of other green algae, is kept in check by grazing species such as periwinkles and limpets.

The rocks and rock pools of rocky shores are host to an abundance of other seashore life: soft-bodied zoophytes such as anemones, sponges and colonial sea squirts; tube-footed, spiny-skinned echinoderms including starfish, brittlestars, sea urchins and sea-cucumbers; fishes including five-bearded rockling, Corkwing wrasse, common blenny, butterfish, goby, and lumpsucker; molluscs including barnacles, common mussel, common limpet, top shells, periwinkles, dog whelk, common whelk; cephalopods (a type of mollusc) including curled octopus and little cuttlefish; and crustaceans including prawns, lobster, squat lobster, hermit crabs, edible crab and green shore crab.

Rocky shore faunal communities may include some rarities such as the purple sea urchin (Paracentrotus lividus) which, apart from in the Channel Islands and a few locations in western Scotland and only extremely rarely in Devon and Cornwall, is only found in the British Isles in significant numbers on the west coast of Ireland from West Cork to Donegal. It is most abundant in County Clare, where it lives in large colonies.

The intertidal zone is an important habitat for several commercially exploited species such as lobster. During spring the adult lobsters move inshore to mate; the female returns offshore to lay her eggs in winter, where she carries them until they hatch as planktonic larvae. The common prawn likewise moves inshore in spring and early summer to breed, before moving offshore again from September to spend the winter in deepwater.

Rocky shores are vital habitats for a number of bird species. Turnstones and purple sandpipers are widespread on rocky shores along the Irish coast in winter, preferring the weed-covered boulder beaches that offer the greatest abundance and variety of invertebrate food. Rock pipits are common residents that frequent rocky coastlines. Wherever mussels grow on rocks, oystercatchers are common predators, while grey herons are commonly seen stalking for fish and crabs in weedy shallows and among rock pools at low tide.

Sandy shores also support rich and diverse faunal communities, particularly sheltered beaches with fine mixed sands, a good proportion of silt, and persistent wet areas. The lack of shelter, especially at low tide, and the absence of firm surfaces for attachment means that the animals must live within the sediment. As the tide goes out they simply retreat below the surface, to different depths depending on the species.

Characteristic species of the sandy shore include echinoderms such as the sand star, sand brittlestar and sea potato; bivalve molluscs including common cockle, razor shells, thin tellin, rayed trough shell and striped venus; gastropod molluscs including necklace shells; bristle worms (polychætes) including lugworms, ragworms and catworms; and crustaceans including masked crab, swimming crabs and common shrimps.

Sandy shores are vital habitats for several bird species. In summer, shingle shores attract a variety of breeding birds, including resident ringed plovers and oystercatchers, and summer-visiting little terns, which breed in small colonies scattered around the coast. In winter sanderlings are often found feeding along the tide line on sandy beaches.

Estuaries

Estuaries are complex environments comprising immensely important wildlife habitats that often support complex ecosystems and high species diversity. Well known Irish estuaries include Liffey Estuary (Dublin Bay), Lee Estuary (Cork Harbour), Slaney Estuary (Wexford Harbour), Nore/Barrow/Suir Estuary (Waterford Harbour), Shannon Estuary (incl. Fergus/Maigue/Deel Estuaries), Corrib Estuary (Galway Bay), Moy Estuary (Killala Bay), Erne Estuary, plus Lough Foyle and Belfast Lough, among others, in the North. As well as being rich wetland habitats, estuaries usually have a multiplicity of functions as shipping channels, fish nursery grounds, bait-digging sites, and areas for shellfish cultivation, waste disposal and recreation.

Within an estuarine environment tidal influence may extend several kilometres inland. Estuaries generally include a main waterway and conjoined river mouth, plus a number of creeks and other small inlets, rivers and streams that lead into the main waterway.

High-energy environments occur at the mouth at locations most exposed to wave and weather influences. Here, the seabed and intertidal areas consist predominantly of bedrock, coarse boulder or pebble deposits, with some finer sediment (sand) beaches. Progressively lower energy environments occur upstream, with extensive fringing areas of subtidal mud and intertidal mud banks, particularly in very sheltered environments. Consequently, estuaries comprise a wide range of aquatic habitats ranging from hard subtidal substrata through to rare saltmarsh and beds of marine grasses. Thus estuarine aquatic communities are generally very diverse and of great nature conservation value.

The soft mud of estuarine sedimentary deposition sites (sinks) may contain enormous quantities of invertebrates (worms, crustaceans, bivalve molluscs and gastropods such as Hydrobia), which comprise the staple diet of many species of wildfowl and wading birds. Beds of marine grasses are also important food resources for grazing wildfowl, especially during autumn and winter.

Estuaries are often important migration stop-off sites and wintering grounds for populations of wildfowl and waders. In late summer and early autumn, flocks of waders such as curlew leave their high moorland breeding grounds in Ireland, Scotland and Scandinavia and assemble in Irish estuaries to spend the autumn fattening-up on the abundant food resources before moving further south during winter. The chain of small estuaries along Ireland's south coast from Wexford to Cork fills with birds, including internationally important numbers of black-tailed godwit which breed in Iceland. Meanwhile, larger estuaries such as Lough Foyle and Strangford Lough in the North, and Tralee Bay and Castlemaine Harbour in the southwest, are the first landfall sites for flocks of brent geese, which fly in from staging grounds in Iceland after breeding in the Canadian high Arctic. Brent geese winter almost exclusively in Ireland, grazing on their preferred food, eelgrass — a marine flowering plant that grows in quantity in about 12 Irish estuaries.

Eelgrass is most abundant in September and October, after which it dies back to form deep organic detrital deposits on the estuarine strandline. As the geese and other eelgrass grazers, such as widgeon, exhaust the eelgrass beds they begin to disperse around the coast to find other less energy-rich foods, such as green seaweeds, during the rest of the winter.

The approach of winter brings even greater numbers of birds to Ireland's estuaries as large flocks of migrant waders, including dunlin, knot and godwit, join residents such as oystercatchers and redshank. Oystercatchers feed on dense beds of shallow-burrowing common cockles and mats of common mussels. Many Irish estuaries have substantial mussel beds, which grow attached to rocks and gravel exposed to moderate, food-laden currents. Mussel beds harbour numerous other small animals and — as on the east side of Lough Foyle — may also act as a sediment trap forcing the tide to deposit fine silt along the shore.

In higher energy estuarine environments, where the shore is sandier, other waders such as sanderling and grey plover feed on tiny molluscs, crustaceans and worms at the tide's edge.

Estuaries also support important numbers of wildfowl winter visitors, including widgeon, pintail, mallard, tufted duck, goldeneye, shelduck, barnacle goose, white-fronted goose, Bewick's swan and whooper swan. Several species of gulls also over-winter in estuaries.

During prolonged periods of severe cold in Britain or continental Europe many migrant birds move west to Ireland to take advantage of its milder, damper oceanic climate. In some years Ireland's estuaries, especially along the east and south coasts, are important to the survival of large continental and British flocks of curlew, lapwing and golden plover.

Eighteen Irish estuaries regularly hold internationally important numbers of wildfowl or waders. These are sites of the utmost conservation value as they are hugely important links in the East Atlantic Flyway for migratory wildfowl and waders.

Many of Ireland's estuaries are also highly sensitive fish spawning and nursery areas. In some cases estuaries are vital breeding grounds for commercially important fish species such as halibut, herring and sea bass.

Under certain conditions (generally involving periods of high river discharge, elevated sediment loadings and warm summer temperatures), environmental conditions within estuary waters sometimes give rise to both thermal and haline stratification events (i.e. physical and chemical layering of the estuarine water column), which may inhibit natural dilution and dispersion processes within the estuary.

Bay environment

A bay is an arm or inlet of the sea extending inland, with a wide mouth. The general characteristics of bay environments are a relatively wide sea area with a shallow near-shore zone (which may extend up to several kilometres offshore), and maybe also a shallow offshore zone. Some of the best known of Ireland's numerous bays include Dundalk Bay, Dublin Bay, Wexford Bay, Youghal Bay, Roaringwater Bay, Dunmanus Bay, Bantry Bay, Kenmare River, Dingle Bay, Tralee Bay, Galway Bay, Kilkieran Bay, Killary Harbour, Clew Bay, Blacksod Bay, Killala Bay, Sligo Bay, Donegal Bay and Gweebarra Bay.

Rivers, estuaries, streams and other watercourses drain into the bay. Seasonal fluvial inputs of freshwater, with accompanying loads of terrigenous sediments as well as natural and anthropogenic nutrients (derived from of agriculture and sewage), may be high. High sediment inputs give rise to extensive intertidal sedimentary mud flats and saltmarshes in near-shore regions adjacent to estuaries, and subtidal mud and silt deposits further offshore.

Further out in the offshore zone, where fluvial influences are less, the seabed may consist predominantly of well sorted muddy-sand and gravel. During periods of elevated fluvial input and/or prolonged strong winds, the water column of both near-shore and offshore zones can become enriched with suspended or re-suspended sedimentary material.

Bays — especially shallow ones — are often recognised as having high conservation value in respect of their marine and coastal environments. Bays often hold important spawning and nursery sites for fish, including offshore demersal and pelagic fish, and shellfish species. Within the bay there may be important commercial harvests from populations of flatfish such as halibut, plaice, sole and turbot, and other fish such as sea bass and sandeel, as well as shellfish such as mussel, cockle and edible periwinkle, and bait species such as ragworm and lugworm.

Compared to estuaries and other more enclosed water bodies, the study of bay environmental fluxes and dynamics — factors such as tidal and current flushing, fluvial influence, sedimentation, and seasonal thermal and haline stratification events — is often poor (Sherwin et al., 1994). When a seasonal thermal and/or haline stratification event does occur, such as when normal current-driven mixing processes collapse, the bay water column is divided into a warm, brackish surface-water component and a cold, more saline (more dense) bottom-water component. Reduced exchange and mixing across the interface between the two components limits, or prevents, vertical mixing and dilution.

The dynamics of freshwater discharge from river systems into coastal waters, especially bays, are also significant, and in particular the close relationship between river-borne nutrients, algal blooming and high oxygen demand by bacteria (eutrophication), which can give rise to hypoxia (oxygen depletion) and anoxia (oxygen absence) in well-stratified coastal waters. It is evident that in such circumstances high anthropogenic nutrient loading from agriculture and sewage can easily overwhelm the natural equilibrium of coastal marine ecosystems, leading to high levels of net productivity and seasonally significant mortalities of bottom-dwelling marine species such as common whelk, dogfish, razor shells and starfish (Deere-Jones, 1995 & Justic et al., 1993).

If currents are weak, together with seasonal onset of thermal stratification and elevated saline stratification of the bay water column, it may be that the exchange and flushing of bay water to the open sea are also seasonally weak. There is, therefore, growing concern that many bay marine environments around the Irish coast are already under significant stress.

Sea cliffs and coastal land

Coastal land is that which lies above the high tide mark. This encompasses a variety of geomorphologic features and habitat types.

Sea cliffs that provide suitable ledges for nesting are vital habitats for seabirds such as gannets, razorbills, guillemots, kittiwakes and fulmars, and for other birds such as peregrine falcons and rock doves. Cliff tops and scree slopes provide habitat for puffins, storm petrels and Manx shearwaters, which nest in burrows. Cliffs also support assemblages of salt- and wind-exposure tolerant plants such as sea campion, scurvy grass, rock samphire and thrift. Sometimes, as in the cliffs of Slieve League in County Donegal, the sheer height of the cliffs and exposure also make them an important habitat for a range of unusual and rare arctic-alpine plants.

Cliff bases, including the rocky shore intertidal zone, also support birds such as rock pipits and turnstones, and provide resting and nesting sites for species such as black guillemot and eider.

Maritime grassland that is grazed provides ideal feeding conditions for choughs and other birds of the coast, such as rock dove, which require open ground to forage for seeds and invertebrates.

Ireland has the largest population of choughs in Western Europe, making them of special conservation importance. They are distributed around the coast from the Great Saltee island off County Wexford, around the west coast to Rathlin Island, County Antrim. Choughs nest on both sea and inland cliffs, as well as in quarries and ruins.

Mature sand dune systems are rich and diverse habitats that support a large number of species. The ecological succession of plant and animal communities progresses with dune maturity (usually represented by distance inland), from the strandline/high-water mark of the sandy or sand-shingle shore, through unstable fore-dunes, dunes stabilised first by marram grass then other colonising plants, to mature back-dunes with a developing soil structure that eventually supports old-growth plant assemblages that include mature trees. The hollows in-between various mid-dunes and mature back-dunes may be waterlogged, either seasonally or permanently. These "dune slacks" add a further important wetland habitat type. The relatively deep water in dune slacks allows the rare natterjack toad — found in only a few coastal locations in County Kerry — to forage and spawn. Dune slacks also provide an important source of fresh drinking water for birds and mammals, including badgers and foxes.

There are many important sand dune systems around Ireland's coasts. Some of the geomorphologic features associated with dune systems include spits such as those at Inch and Castlegregory on the Dingle Peninsula in County Kerry, and coastal lagoons such as those on the south coast of County Wexford where a number of lagoons are linked together by barrier beaches. At one of these, Lady's Island Lake, the unstable dune habitat — where the shingle barrier is frequently overwashed by the sea on high tides backed by an onshore wind — is the only known location of one of Ireland's rarest coastal plants, the cotton weed, which is at the northern limit of its European range.

Another feature is the 18-kilometre long shingle beach known as the Murrough in County Wicklow. In July its distinctive shingle beach floral community includes some rare plants such as the oyster plant, which was once widespread on the east coast but is now restricted to just a few more northerly shingle beaches. The sand and shingle of the Murrough provide habitats for birds such as ringed plovers that nest there in early summer.

The northwest coasts from Inishowen Peninsula in County Donegal to Galway Bay have a unique kind of sandy plain or machair, best developed in the northwest corner of County Mayo around the Mullet Peninsula. This habitat is unique to the Atlantic fringes of Ireland and Scotland, where the shelly sands have been blasted into a flat plain by high winds. These machair grasslands are rich in plant species and are of special importance to nesting waders such as lapwing, ringed plover and dunlin.

Marine Mammals

Eurasian otter

THOUGH the Eurasian otter is an aquatic rather than a truly marine mammal, we shall include it here because a significant proportion of Ireland's population inhabits the coastal zone, where they spend part of their lives on land and the remainder at sea, whilst depending on both.

With their webbed toes, streamlined body and dense waterproof coat of fur, otters are well adapted to an aquatic way of life. They feed on a variety of aquatic prey, including fish, eels, crabs and other crustaceans, and to a lesser extent frogs and birds. Much of Ireland's extensive low rocky shore environment provides ideal habitats for coastal otter populations, which often breed and rear their cubs (usually two per litter) within easy reach of the shore.

Pinnipeds (seals)

The common seal, sometimes referred to as the harbour seal, is a coastal species that inhabits sheltered waters around Ireland. It occurs most frequently along the north, east and southwest coasts, being less abundant in the west. They prefer to feed on fish, both bottom-dwelling and free-swimming, and some invertebrates in narrow channels near the mouths of bays. At low tide they haul out onto skerries (rocky islets and reefs) or sand banks to rest and digest their food. Common seals are gregarious, preferring to live in groups, probably made up of related animals. Around Ireland, common seals give birth during June and July. The single pup, which is able to swim within just a few minutes after its birth, suckles for between 3-6 weeks.

The grey seal is also a coastal species, though it may forage further out at sea than the common seal. It is sparsely distributed around Ireland and widely dispersed outside the breeding season. Grey seals feed on a wide variety of fish and some invertebrates. Adults congregate to form herds during the late summer to autumn breeding season. One of Ireland's largest herds (about 200 individuals) hauls out to breed on the Blasket Island group in County Kerry, especially the White Strand (An Trá Bhán) on the Great Blasket Island, and on the shores of Beginish. The other main Irish breeding group is centred on the remote Inishkea islands off the coast of northwest County Mayo, while other much smaller rocky shore breeding sites are dotted around the coast.

Unlike common seals, the single grey seal pup is born in white lanugo (natal coat). Lactation lasts for 2-3 weeks before the mother abandons the pup, around which time it begins to moult its lanugo. The pup spends another two weeks or so on land while it moults before entering the sea when it must learn to forage efficiently before its body fat reserves are depleted. Recent research by the UK Sea Mammal Research Unit suggests that grey seal pup mortality is high, with approximately 50 per cent of newborn pups dying during the first year (Seal Conservation Society, 1998).

Cetaceans (porpoise, dolphins and whales)

Twenty-three cetacean species have so far been identified in Irish waters, of which eleven are frequently recorded.

The harbour porpoise is considered to be the most abundant species and has been recorded on all coasts but is especially abundant off southwest Ireland, where an estimated 20,000 may occur in summer (Leopold et al., 1992). This, together with a population in the southern Irish Sea, represents an important part of the overall North-East Atlantic population, which is considered to be vulnerable (Simmonds et al., 1997). Sightings made in deeper waters above the Rockall and Faroe Banks show that the species is not just restricted to shallow shelf waters, as was previously thought. A survey conducted in July 1994 confirmed that the harbour porpoise is present throughout most of the Celtic Sea shelf area.

There is considerable genetic and other evidence to indicate that harbour porpoises live in discrete populations with little movement between them (Simmonds et al., 1997). The harbour porpoise is relatively short-lived (average life span is only nine years). They are known to calve off the southwest and east coasts of Ireland between June and September (Irish Whale and Dolphin Group, 1993). Their low reproductive rate, typical of all cetaceans, makes them especially vulnerable to threats.

The bottlenose dolphin is the other most frequently sighted cetacean in Irish waters. They are most commonly seen in coastal waters, though they are frequently reported further out at sea, especially in the Celtic Sea shelf area. Anecdotal evidence suggests that, historically, bottlenose dolphins used to frequent various Irish estuaries and other inshore waters where they are now no longer (or very rarely) seen. It has been suggested that a major decline in the species, dating from as early as the 19th century, may have occurred. As the human population has increased (accompanied by industrial pollution, expanding fisheries, coastal development and habitat disturbance), so bottlenose dolphin populations seem to have declined (Simmonds et al., 1997).

Work by researchers in the UK suggests that bottlenose dolphins in European waters typically form well-established groups of some 130 individuals, comprising several sub-pods. A bottlenose dolphin group off Cornwall and Devon has been found to have a large home range of several hundred kilometres of coastline, which may be typical. This group also appears to travel more in the spring and summer than at other times.

The discovery of this extensive range ... has very significant implications for their conservation as it challenges the view that their conservation can be simply addressed via small "protected areas". (Simmonds et al., 1997)

Bottlenose dolphins are known to calve in Irish coastal waters, including the funnel-like mouth of the Shannon Estuary, which is a clearly identified home range, summer calving and nursery ground for a group of about 100 bottlenose dolphins. Consequently, the Mouth of the Shannon is of very high European conservation importance.

Both the harbour porpoise and bottlenose dolphin are listed in Annex II of the EU Habitats Directive as species that not only require strict protection but also warrant designation of Special Areas of Conservation (SAC).

Other "small cetaceans" in Irish waters are usually animals that are oceanic in habit and hardly ever come into inshore waters. The common dolphin is one of the most abundant cetacean species found off the south and southwest coasts and is frequently observed in the Irish Sea and on the Celtic Sea shelf.

The white-beaked dolphin and Atlantic white-sided dolphin frequently occur offshore where they feed on a variety of pelagic fish species. White-beaked dolphins may move closer to shore in summer, although they are most usually found over the continental shelf area. Atlantic white-sided dolphins have been shown to calve off the southwest coast during early summer. Their distribution seems to be closely related to that of blue whiting — an important prey species for them.

In recent years there has been an increase in sightings of the striped dolphin in Irish waters. This species prefers warmer waters and the increase in sightings may relate to changes in the warm water currents of the North Atlantic Drift.

Risso's dolphin has a wide distribution, mainly off the west coast of Ireland, though they are occasionally reported in the Irish Sea. This largely oceanic dolphin has been shown to calve in Irish waters in late spring and early summer.

The long-finned pilot whale is the most commonly observed "whale" species in Irish waters (though it is technically a "small cetacean" because it does not yet come under formal International Whaling Commission jurisdiction). Although mainly inhabiting waters of the deep open ocean, where they feed principally on squid, large numbers have been recorded along the edge of the continental shelf west of Ireland. The waters off southwest Ireland are thought to be an important breeding ground for this species (Evans, 1980).

The orca, or killer whale is a frequently recorded species in Irish waters, being observed in small numbers, especially off the west coast.

Of the baleen whales, the minke whale and fin whale are the most frequently observed in Irish waters. The minke whale is widely distributed along the Atlantic seaboard and is reported sporadically in the Irish Sea. It is the baleen whale most frequently seen from land. Minke whales that over-winter in warmer waters, such as near the Azores, may regularly return to feed in Irish waters where they may also breed. Others pass through Irish waters on migration to the rich sub-arctic summer feeding grounds. Fin whales also migrate through Irish waters along the edge of the continental shelf from breeding grounds at lower, warmer latitudes to summer feeding grounds in the sub-arctic. It is thought that some fin whales (possibly a genetically discrete sub-population) may in fact breed off the south coast of Ireland.

Other baleen whales reported or believed to transit through Irish waters on migration along the shelf edge are the sei whale, humpback whale, the rare blue whale and possibly the even rarer northern right whale.

As for the toothed whales, the deep-sea to the west of the continental shelf provides suitable habitats for deep-diving species such as the sperm whale and various beaked whales (Ziphiidae). There is evidence that sperm whales may be occurring more frequently off the Irish coast (Berrow et al., 1993), but many of the beaked whales, apart from the northern bottlenose whale, have never been seen alive and are known only from stranded carcasses. Six of the nine European records of True's beaked whale are from the west coast of Ireland and a recent stranding of a Gervais' beaked whale was only the second record for Europe (Bruton et al., 1989).

The northern bottlenose whale inhabits deep ocean waters and is very occasionally seen in Irish territorial waters along the continental shelf edge where they feed on squid and other deep-sea animals. The International Whaling Commission classifies the North-East Atlantic population as a Protection Stock due to its depletion (by commercial whaling) and continued vulnerability.

Commercial whaling by Europeans and Scandinavians from the late 16th century through to the 20th century — peaking in the late 19th century with the introduction of modern whaling technology such as harpoon cannon, exploding harpoons, steam then diesel driven catcher vessels and factory motherships — has depleted most North-East Atlantic populations of "great whales" and some small cetacean species.

The North-East Atlantic populations of blue, fin, sei, humpback, right and sperm whales were further depleted between 1908 and 1923 by commercial whaling operations in Irish waters undertaken from Norwegian owned shore stations in County Mayo. Commercial whaling operations for northern bottlenose whales by Norwegian vessels are thought to have continued in waters to the northwest of Ireland until 1973. In recent years, whaling interests in the Faroe Islands have sought to establish a commercial hunt of between 200-400 northern bottlenose whales annually.

Long-finned pilot whales, including those which transit through offshore Irish territorial waters, continue to be subject to a drive-fishery in the Faroe Islands with as yet undetermined long-term consequences to the overall North-East Atlantic population and constituent, genetically discrete sub-populations.

Likewise the North-East Atlantic minke whale population is subject to an increasingly large-scale commercial whale hunt by Norway during the summer whaling season. Some of these minke whales may seasonally migrate through Irish waters — either along the Atlantic seaboard or else through the Irish Sea. In 2002 Norwegian whalers caught 634 minke whales from a self-allocated quota of 671; the 2003 self-allocated quota is 711 minke whales. Whaling interests in Norway are currently pushing for quotas approaching 2,000 minke whales annually, plus government-approval for takes of other species, including fin whales. During 2002, Iceland rejoined the International Whaling Commission; it has expressed its long-term aim to resume hunting minke, sei and fin whales, and has even mentioned taking humpback and blue whales once their North Atlantic populations have "recovered"!

Marine Ducks & Seabirds

IN addition to the numerous wildfowl and waders supported by the shore, estuarine and freshwater coastal environments already mentioned in the text, Ireland's seas and coasts provide habitats for regionally and internationally important numbers of marine ducks and seabirds, which may be resident, summer or winter visitors, or else passage migrants. They include:

Ducks

The mallard is both a freshwater and marine species that may be seen resting on the open sea. The long-tailed duck is essentially a marine bird, often seen well out to sea even in rough weather. The red-breasted merganser is a resident that is commonly seen on coastal waters in winter, diving for fish and invertebrates, along with winter visiting goldeneye. Scaup is a predominantly marine species, while eider and common scoter are exclusively marine. Eiders are residents, breeding on the north and northwest coasts of Ireland where they feed by diving for mussels and other molluscs. Common scoter feed by diving for crustaceans, cockles, mussels, larvae and benthic worms; though principally a winter visitor, they may be seen offshore year-round, and a few birds breed on the Irish coast. Less common is the winter-visiting velvet scoter.

Divers and grebes

The great northern diver and red-throated diver are common winter visitors to Irish coastlines, while the black-throated diver is a much more rare winter visitor. All are found on open coastal waters, bays and sometimes harbours, where they dive for fish and marine invertebrates. In winter, great crested grebes may also be found in open coastal waters and harbours, as well as the less common Slavonian grebe.

Gulls

The herring, common, great black-backed, lesser black-backed and black-headed gulls are resident breeding birds of sea and coast, as is the kittiwake. Other gulls found around Ireland's coasts are the uncommon winter visiting Mediterranean, glaucous, Iceland and little gulls. Occasionally, the mainly pelagic Sabine's gull is blown inshore during its migration to/from the high Arctic regions of Canada, Greenland and Spitzbergen. Gulls generally feed on a wide range of food including fish, molluscs, worms, crustaceans, offal and carrion.

Fulmar, shearwaters and petrels

The fulmar is a member of the family that includes the mainly southern hemisphere albatrosses. It breeds on all suitable cliffs around Ireland's coast and is otherwise strictly pelagic, often following fishing vessels to feed on offal, though it principally feeds on a variety of fish, molluscs and crustaceans.

Four species of shearwaters (sooty, great, Mediterranean and Manx) are visitors to Irish waters in late summer-early autumn. Sooty and great shearwaters are birds of the open ocean, where they feed on a wide range of marine life including fish, squid, molluscs, crustaceans and offal from trawlers. Both species breed in the southern hemisphere. The Mediterranean shearwater breeds in the western Mediterranean. The Manx shearwater is a common, but infrequently seen, seabird which travels long distances to feed far out at sea on small fish, molluscs and offal. They only come ashore during the breeding season to nest in burrows, mainly on offshore islands. Birds arrive and leave the burrow in the dark to avoid predation by gulls. There are several important breeding colonies scattered around the Irish coast.

Petrels occurring around Ireland are the tiny storm petrel, a strictly sea-going bird which feeds on small fish and plankton, that comes ashore only to breed; and Leach's petrel, which breeds on some remote islands off the west coast.

Skuas

Sightings of piratical and predatory skuas (Arctic, long-tailed, pomarine and great skua), which are spring and autumn passage migrants off Ireland's coasts, usually only occur during onshore gales. All but the long-tailed skua feed by chasing and harassing gulls and terns, pursuing them until they drop or disgorge their food, though they will also variously feed on fish, small mammals, birds and eggs, carrion and offal.

Auks

The razorbill, guillemot, black guillemot and puffin are some of the most familiar seabirds around Ireland's coasts. Razorbills nest in close association with guillemots on cliffs and stacks, with foraging and resting birds sometimes forming large "rafts" on the sea. Outside the breeding season they disperse out at sea where they over-winter. Razorbills and guillemots feed on a wide variety of prey including fish, worms, molluscs and crustaceans by diving (swimming underwater by flapping the wings).

Usually seen at sea or resting on rocks, the black guillemot breeds in small groups around Ireland's coasts and offshore islands, nesting under boulders and in caves, holes and crevices. The puffin breeds in grassy cliff top (rabbit and shearwater) burrows in places scattered around Ireland's coasts. Puffins feed on a wide variety of marine prey, with sand eels forming an important part of the diet especially during the breeding season. During winter, which is spent far out at sea, the puffin's bill changes shape and dulls in colour. The little auk, which also winters at sea, is occasionally seen, usually only when blown inshore by gales.

Terns

The common, Arctic, roseate, little and Sandwich terns are summer visitors to Ireland's coasts, where they breed. They feed for fish by plunge-diving after a mid-air hover; Arctic, Sandwich and little terns also feed on marine invertebrates. The rarest of these is the roseate tern. The largest and most successful roseate tern breeding colony in Europe, and the centre of the Irish Sea population, is on the tiny island of Rockabill off County Dublin, where the terns nest in the shelter of tree mallow and other dense vegetation such as lyme grass. The arctic tern is an impressive long-distance migrant. Ireland is near the limit of its world breeding distribution.

The little tern is relatively scarce. After migrating from its African wintering grounds in spring, it prefers to nest in small colonies at a few traditional mainland sites on the east coast such as Baltray Dunes, County Louth, Kilcoole Beach, County Wicklow and Raven Point, County Wexford. On the west coast there are little tern colonies on offshore islands such as the Aran Islands, County Galway, and the Inishkea Islands, County Mayo. Their main habitat requirements are a shingle beach that is relatively free from human disturbance and close proximity to shallow coastal water or a lagoon for fishing.

Gannet

The gannet is Europe's largest seabird. It is almost always airborne, resting on the water only briefly after feeding on fish, which it does by plunge-diving from up to 30m high with half-folded wings. Gannets breed in colonies on cliffs and stacks, mainly on offshore islands. In summer the island cliffs of the Skellig Rocks off County Kerry are home to one of Europe's largest gannet colonies. Over 22,000 pairs of gannets nest on the Little Skellig while razorbills and guillemots nest on the Great Skellig Rock. The Great Saltee island off County Wexford also has an important gannet colony, with about 1,200 pairs of gannets breeding on the rugged southern cliffs. Situated in the southeast, the Great Saltee is also an important first landfall for spring migrants such as swallows arriving from their African wintering grounds. There are other gannet colonies on the Bull Rock in County Cork, and on Clare Island in County Mayo. The most recently established gannet colony, where the first breeding pairs arrived in 1989, is on a sea stack off Ireland's Eye close to the fishing port of Howth, County Dublin. In autumn gannets migrate (en masse, in strings of several birds, often visible from headlands) to warmer southern seas to over-winter.

Cormorant and shag

The cormorant and the shag are common residents around Ireland's coasts. The shag is normally a strictly marine species, frequenting open water off rocky coasts rather than the more sheltered waters and estuaries frequented by the cormorant. Shags breed colonially on rocks and in sea caves, and some birds disperse along the coasts in winter. The cormorant, also a colonial nester, breeds on rocks on the coast and trees inland. Though its coastal distribution is similar to the shag, cormorants are increasingly common on inland rivers and lakes. Both feed on a variety of fish, jumping clear of the water before diving.

Breeding seabird numbers

Ireland has 22 species of breeding seabird, including nearly 220,000 auks and at least 224,000 pairs of other species. This total does not include the huge, but virtually unknown numbers of storm petrels which nest unseen in burrows and crevices in at least 28 colonies around the Irish coast. On the four outermost Blasket Islands off County Kerry, storm petrels nest in the tens of thousands among the precipitous scree slopes, from sea level to the summits. The Irish colonies of Manx shearwater, storm petrel and gannet make up a sizeable part of the European populations of these birds.

Seabird lifespan

Recent evidence suggests that some seabirds may naturally live long lives. British Trust for Ornithology reports on the recovery of ringed birds show a number of longevity records for waders and seabirds, including 18 years for the ringed plover, 26 years for the bar-tailed godwit and 33 years for the common tern. Storm petrels have been shown to live to at least 32 years, Manx shearwaters to 35 years, gannets to 36 years and fulmars to nearly 41 years.

Marine Turtles

FIVE of the world's seven turtle species occur in Irish and British waters. The most frequent visitor is the leatherback turtle, followed by the loggerhead turtle. Both are usually seen regularly in late summer. The others are the Kemp's ridley turtle, hawksbill turtle and green turtle, which are only rarely seen, and most usually dead.

Leatherbacks and loggerheads have been reported every year in Ireland particularly off the west and southwest coasts, usually from August to October when the sea is at its warmest. Official sightings from sea observatories on the west coast report both individuals and groups of turtles moving past during this time.

Leatherbacks are partially warm-blooded, enabling them to survive in cooler water and at temperatures that other marine turtles may not tolerate for long. Loggerhead turtles are also cold-tolerant to some extent. In stormy conditions young loggerheads may be found cold-stunned on the coast of Ireland and Britain.

The exact origin of leatherbacks and loggerheads in the North-East Atlantic is not fully understood, but in 1997 a turtle found drowned in Wales had a tag that had been fitted on a breeding beach in French Guyana on the north coast of South America. Other breeding beaches are in the Caribbean and Gulf of Mexico. From here the clockwise currents of the Atlantic Ocean gyre bring animals east on the Gulf Stream/North Atlantic Drift. One recent estimate suggests that there may be fewer than 35,000 breeding female leatherbacks in the world, and they are known to be declining in many places.

Marine turtles feed on a variety of prey items, particularly jellyfish. Leatherbacks are known to feed on deep-sea jellyfish at depths exceeding 1,000m. They are potentially threatened by entanglement in fishing gear (nets, lines and pots), which leads to drowning, and from ingestion of marine debris — especially plastic bags which are eaten because they resemble jellyfish — leading to death from suffocation or gastro-intestinal blockage.

References

Berrow, S.D., et al., 1993. An analysis of sperm whale Physeter macrocephalus stranding and sighting records, from Britain and Ireland. Journal of Zoology (London) 230: 333-337.

Boucher, G. and Lambshead, J., 1995. In: New Scientist, 16/9/95 p.8.

Bruton, T., et al., 1989. Gulf Stream beaked whale Mesoplodon europaeus (Gervais). Irish Naturalists' Journal 23(4): 156.

Deere-Jones, T., 1995. Marine Environmental Implications of Proposed Developments: Tenby Waste Water Treatment Works — Addendum 3: Carmarthen Bay: STS, ROFI, and Hypoxic Events. Tenby Campaign for Clean Seas, April 1995.

DETR, 1998. Cleaner Seas: Natural Processes. Department of the Environment, Transport and the Regions, web page 21/9/98.

Evans, P.G.H., 1980. Cetaceans in British Waters. Mammal Review 10(1): 1-52.

Gage, J. and Gordon, J., 1995. In: New Scientist, 26/8/95 p.4.

Irish Whale and Dolphin Group, 1993. Ireland — A Sanctuary for Whales and Dolphins; A discussion document prepared by the Irish Whale and Dolphin Group, April 1993.

Justic, D., et al., 1993. Seasonal Coupling Between Riverborne Nutrients Net Productivity and Hypoxia. Marine Pollution Bulletin 26(4): 184-189.

Leopold, M.F., et al., 1992. The elusive harbour porpoise exposed: strip transects off southwest Ireland. Netherlands Journal of Sea Research 29(4): 395-402.

Seal Conservation Society, 1998. Unexpected results from study of UK grey seal pup survival. Seal Conservation Society web page, 26/9/98.

Sherwin, T.J., et al., 1994. The Impact of Ambient Stratifications on Marine Outfall Studies in British Waters. Marine Pollution Bulletin 28(9): 526-533.

Simmonds, M., Irish, R. and Moscrop, A., 1997. The Dolphin Agenda — a report to the Whale and Dolphin Conservation Society. Conservation Research Group of the University of Greenwich, January 1997.

Footnotes

1. Also taken by the OSPAR Commission to be the arbitrary "division" between Region III (Celtic Seas) and Region V (Wider Atlantic).

2. We use the term "near-shore" to denote coastal waters from the intertidal zone down to a depth of about 50m. The term "inshore" refers to coastal waters out to the 12 nautical mile territorial seas limit; "offshore" refers to waters from the 12 nautical mile territorial sea limit out to the 200 nautical mile Exclusive Economic Zone limit and/or Continental Shelf designated area limit (up to 350 nautical miles).