22nd September

Why is marine biodiversity important?

Tompot Blenny. Photo Nigel Motyer

Bryan Deegan

When we look at the sea, it is usually hard to imagine what life is like and what species exist beneath the waves. We usually don't realise there is a whole different world down there, with its own mountains, valleys and animals, that only a few of us have seen and which remains largely unexplored. The Earth's tallest mountain, longest mountain range and deepest canyon are all found in the ocean.

The seas off Ireland are a fascinating world full of magical organisms from tiny microscopic plants, much smaller than the eye can see, to some of the world’s biggest animals. The variety of living things that exists in this soup of biological sea life is called marine biodiversity. Another aspect of marine biodiversity that is very important for long-term survival of a species is the different makeup of individuals within a species. This is called genetic diversity.

Globally there are more species of fish in the oceans than all the mammals, reptiles and birds combined. Many scientists believe the ocean has far more variety of species than land, because so much marine life remains undiscovered. The areas where many species are yet to be discovered lie with the smaller animals and plants and in the deep sea. Some scientists believe that there may be 10 million undiscovered species in the deep sea alone!

Human-driven extinctions of plants and animal species are now occurring at the fastest rate in the world’s history, even before the majority of species have been discovered. With this in mind there is increasing pressure to conserve our biodiversity both on land and in the sea.

Ireland’s marine biodiversity

Located on the north west of Europe, beside the largely unpolluted waters of the Atlantic Ocean, Ireland is in a very good position for a healthy marine environment and marine biodiversity. Ireland’s marine territory is over ten times our land area at 850,000 km2 and extends from the upper reaches of our muddiest estuaries, to over 600 miles west of Ireland.

Ireland’s underwater world has an amazing variety of animals and plants from the microscopic to the biggest animals ever seen on earth. Of the 7,300 animal species that have been recorded from the seabed around Ireland and the UK, 353 species are sponges, 91 species are anemones and sea slugs make up 141 species.

All creatures have a particular niche, or habitat, that they prefer and some species are more adaptable or are far more common than others. A large variety of habitats occur in the marine environment; from the murky estuaries, rocky seashores, muddy and sand seabeds to the dark world of the deep sea. Areas with the largest diversity of habitats will usually have the highest species biodiversity. The marine species that make up Ireland’s marine biodiversity can be divided roughly into the following groups; microorganisms, plankton, benthos, fish, mammals, seabirds.


Microorganisms consist primarily of bacteria, but also include yeasts, fungi and viruses. Marine bacteria are some of the smallest organisms and were the first organisms to develop on earth. The oldest fossils are of marine bacteria and are about 3.6 billion years old. These bacteria began producing oxygen, without which animal species like us would not have evolved. Their main role in the marine environment is to help break down dead plant and animal matter to simpler forms that can be reabsorbed by other plants or animals. Marine bacteria are proving to be a valuable source of antibacterial, antiviral and anticancer compounds.


Plankton from the Greek planktos meaning drifter, are very small organisms found suspended or swimming in water and sometimes can be seen by the naked eye. Planktonic organisms are unable to swim against a current and as a result generally drift in the ocean. Many marine animals and plants use the ocean to disperse their young and numerous species found in the plankton are juvenile stages of marine animals and plants. Plankton are usually divided into two groups; phytoplankton and zooplankton.

Phytoplankton are tiny marine plants, composed of only one cell. Since they need sunlight, similar to land-based plants, they are confined to the surface layers of the sea. Some phytoplankton use carbon dioxide to help build a skeleton and thus are important in reducing the world’s increase of carbon dioxide. The white cliffs of Dover on the south coast of England are made up of billions of these microscopic plant cells. Phytoplankton, like bacteria, form the bottom of the food chain. Phytoplankton are also thought to be responsible for up to 99% of the organic matter production in the marine environment.

Zooplankton are tiny marine animals also carried by the oceans’ currents. These are either young stages of larger marine creatures like fish or crabs, or are animals that spend their entire lives in the plankton like small jellyfish. Because zooplankton are not dependant on light they can be found in the deeper parts of the oceans and form an important part of the diet of deep water organisms like the cold water corals seen off the Irish coast. Zooplankton, some of which feed on phytoplankton, are the main source of food for open water fish and the early stages of many fish species.


The benthos consists of the animals and plants living near, on, or in the seabed. The marine animals and plants living in the benthos include groups that are almost entirely restricted to marine world, including sponges, sea anemones, echinoderms (sea-urchins, starfish, and sea cucumbers) sea-squirts (ascidians) and marine algae (seaweeds).

In general, in the marine environment, rocky or bedrock habitats are found in areas where there is enough waterflow or turbulence to stop sediment settling on the seashore, or on the seabed below the tides. Where there is enough light, primarily on rock and sometimes on any stable seabed, species of seaweed can grow. Almost 600 species of seaweed are found in Irish waters.

Seaweed is divided into three groups: green, red and brown. Like many other marine creatures, certain seaweeds are only found in particular places or habitats. Some species of seaweed are edible and others are used in the manufacture of fertiliser, medicine and food products.

The rocky seashore is a very difficult place to survive, as both plants and animals are exposed to varying quantities of water and air depending where they are located on the shore. Exposure to air for varying lengths of time on a rocky shore means that any organism must be able to withstand a wide range of air temperatures, desiccation, freshwater and must have the ability to hold on while waves break on the shore.

As a result, the organisms fixed to the rock usually divide themselves into different zones going up the shore. Where there is not enough light or where animals have dominated over the seaweed, the rocky seashore or seabed is covered with animal species. On the rocky shore this will usually be with barnacles, mussels or limpets. Below the low tides on the seabed animal species that live on the rocky surface are usually softer and include sponges, anemones, starfish, sea cucumbers, tube worms and soft or in rare occasions hard corals.

In areas of the marine environment where sediment gathers, totally different species from rocky areas are found. The most obvious of these species on the sandy seashore is the lugworm that leaves casts on the surface of the sand. Below the tides, generally the species here are different and the diversity is greater. In shallow areas where light levels are high and pollution is low important habitats like eel grass grow on sediment. Here amongst the long grass diverse communities including juvenile fish thrive.

As you go deeper, even within the types of sediment from fine mud, sand and gravel completely different groups of species exist. Very fine muds are usually found in sheltered areas, while gravels are found where strong currents or waves keep the fine silt from settling. In contrast to the rocky habitats, many species live or burrow within the sediment. These species include anemones, razor clams the Dublin Bay prawn and fish species like the sand eel.


From the whole North Atlantic Ocean nearly 1100 species of fish are known, with 331 recorded from Irish waters. They are usually divided into two habitat groups: those associated with and feeding in and around the seabed are called demersal (meaning bottom dwelling) species and those found in the open water are called pelagic species. Fish are also divided between those that have a bony skeleton; those that have a skeleton of cartilage (sharks and rays) and the primitive jawless fish e.g. lampreys. The vast majority of fish species (95%) have a bony skeleton. The plankton eating basking shark is the biggest fish in Irish waters and can grow up to 10m long!


A significant number of marine mammals can be seen in Irish waters. Some of these are resident species and others are just passers by. Probably the most readily seen marine mammals are seals. There are two resident seal species, the common and grey seal and these are protected under law.

To date, of the 32 species of cetacean (whales and dolphins) recorded in the Atlantic Ocean, 24 have been recorded in Irish waters. Regularly seen species in Ireland include the bottlenose, common, striped and Risso’s dolphins, harbour porpoise and long finned pilot whales. Fin and humpback whales are now being seen regularly off the south coast and seasonal patterns are now emerging.


Twenty six species of seabird nest on the coast of Ireland. Coastal habitats such as mud flats, beaches, and sand dunes are important feeding areas for both resident and migrating birds. Ireland has an extensive coastline offering a wide range of nesting habitats from shingle beaches, dunes, and high cliffs to offshore islands that lack predators like foxes and rats. The rocky islands and sea cliffs, which are common around the coast, support many internationally important breeding colonies of gulls, cormorants, storm petrels and gannets, and burrowing species like the manx shearwater and puffins. Peregrine falcons and the chough also use coastal cliffs as nest sites. Important migrating species of swans, geese, ducks and waders come to Ireland every winter to feed on our rich shores.

Human impacts


  • Fish stocks in the shallower waters are declining, mainly due to overfishing
  • Fishing activity in the deeper waters is now increasing
  • Other species, are caught (up to 50% of catch) while fishing and are discarded
  • Fishing gear can also impact greatly on the seabed and the organisms living in it
  • Governments now starting to develop a more ecosystem based approach to conserve stocks
  • Fish (Atlantic salmon& Rainbow trout) and shellfish (mussels, oysters & clams) farming
  • Fish and shellfish farming require a good healthy environment
  • Fish farming uses feeds that are mostly made up of other fish species
  • Eight to ten tons of wild fish are needed to produce one ton of farmed fish
  • There are concerns that escapees from fish farms can breed with wild fish stocks
  • Parasites of farmed salmon including sea lice attach themselves to wild fish

Introduction of non-native invasive species

$1·     The most common way of introduction is by shipping (on hulls or in ballast water)

$1·     Sargassum muticum − an invasive seaweed was introduced with juvenile oysters

$1·     Bonamia − a parasite that devastates native oyster populations was also introduced with oysters.

Climate Change

  • Ireland’s climate has a strong bearing on both terrestrial and marine biodiversity
  • Medium term theory is that the oceans around Ireland could warm by 2.5˚C by 2050
  • Warming waters will lead to less boreal (northern) and more Lusitanian (southern) species
  • Long term theories include the breakdown the North Atlantic Drift with longer colder winters leading to colder sea temperatures and a significant change in marine biodiversity


  • The majority of human wastes, whether put into freshwater, land or air, will end in the sea eventually
  • The gathering effect of ground water, rivers and rain, release wastes into the sea
  • Wastes include litter, nutrients, hydrocarbons, hazardous chemicals, radioactive materials, oxygen demanding materials and microorganisms
  • The loss of sensitive habitats is one of the first signs of a reduction in water quality. Reductions in sensitive habitats like eel grass beds, can result in a loss to species diversity
  • Stringent laws are now coming into place across Europe that will dramatically reduce the amount of waste entering the marine environment directly and indirectly. 

Offshore energy

  • Concerns have been raised that in the process of finding and putting the structures in place for oil, gas and wind farms resources, habitat destruction, pollution and disturbance of wildlife are taking place

Disturbance of wildlife and habitats

  • The coastal zone is an important area for birds and nursery areas for marine species
  • 80% of the human population live close to the coast, resulting in significant potential for the disturbance and destruction of marine habitats
  • The areas behind the coastal zone also provide habitats for terrestrial plants and animals
  • Increased development of housing and industry, places additional pressure on the marine environment
  • Increased recreation and tourism activities in the coastal zone can also result in the disturbance of wildlife and habitats


  • The Birds Directive requires each EU member state to designate ‘Special Protection Areas’ (SPAs) for birds
  • The Habitats Directive aims to create a network of Special Areas of Conservation (SAC’s) called ‘Natura 2000’. About 5-20% of each country will become part Natura 2000
  • The Oslo Paris Convention for the Protection for the North East Atlantic (OSPAR) guides international cooperation on the protection of the marine environment of the North-East Atlantic and is concerned with all human activities and pollution from land based sources, offshore installations that can have an adverse effect on the protection and conservation of the ecosystems and the biological diversity
  • The EU Water Framework Directive aims at maintaining ‘high status’ of waters where it already exists, preventing any deterioration in the existing status of waters and achieving at least ‘good status’ in relation to all waters by 2015
  • The Bonn Convention aims to improve the status of all threatened migratory species through national action and international Agreements
  • The Bern Convention on the conservation of European wildlife and natural habitats aims to ‘conserve wild flora and fauna and their natural habitats’; to promote co-operation between countries and their conservation efforts, and to give ‘particular emphasis to endangered and vulnerable species, including endangered and vulnerable migratory species.’

Research projects

  • BioMar-LIFE project: the largest survey of the marine animals and plants in the benthos was completed in 1997. The information gathered from this survey has been used to help select areas of conservation importance
  • The Irish National Seabed Survey, which is the biggest mapping project of national waters in the world, is currently mapping the entire Irish seafloor and will assist in the understanding of marine biodiversity and habitats
  • Deep water corals were also investigated under EU-funded projects like ACES and Hermes. Hermes also studied deep-sea biological hotspots, including life in canyons, in areas where oxygen is almost non-existent and areas high in sulphur where little life was to exist

How to get involved

Marine Biodiversity is not just important at a very local level. It is important to conserve it on a global scale. The easiest and possibly most important way to get involved is to get interested and conserve marine biodiversity where you live. Other ways include becoming a member of an organisation involved in the conservation of marine biodiversity. In Ireland these include the Irish Whale and Dolphin Group, Birdwatch Ireland and Coastwatch Ireland. If you are very enthusiastic you could always become a marine biologist!

Additional Sources of Information on:

Irish Marine Biodiversity

Irish Whale and Dolphin Group: www.iwdg.ie

Birdwatch Ireland: www.birdwatchireland.ie

National Parks and Wildlife Service: www.npws.ie

Irish Wildlife Trust: www.iwt.ie

Marine Institute: www.marine.ie

Irish Marine Digital Atlas: http://mida.ucc.ie/

Encyclopaedia of Marine Life of Britain and Ireland: http://www.habitas.org.uk/marinelife/index.html?item=about

European Marine Biodiversity

Biodiversity in the EU: http://europa.eu.int/comm/environment/nature/home.htm

OSPAR: www.ospar.org

Council of Europe: www.coe.int 

Bonn (of CMS) Convention: http://www.cms.int

Bern Convention: http://www.coe.int/T/E/Cultural_Co-operation/Environment/Nature_and_biological_diversity/Nature_protection/

WWF marine health check: www.wwf.org

General Sites on Marine Biodiversity

Marine Conservation Society: http://www.mcsuk.org/

Joint Nature Conservation Committee: www.jncc.gov.uk/marine

Centre for Marine Conservation: www.cmc-ocean.org

Fish Species: http://www.fishbase.org/home.htm

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