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Celtic Sea ecosystem


Birds and mammals

Petrels (fulmar and storm-petrel) dominate the seabird populations in the west of Ireland and Celtic Sea* region but there are also large breeding colonies of kittiwake, guillemot and gannet. The iconic puffin can also be found in the Celtic Sea*.

The Celtic Sea* is home to around 75 thousand common dolphin and 36 thousand harbour porpoise (2006 estimates). It is also not uncommon to spot bottlenosed dolphins, white-beaked dolphin and white-sided dolphin over much of the shelf area

More about birds and mammals in the Celtic Sea* region

Basking shark


People and their interactions with the environment are often neglected when we think about ecosystems. But they too make a vital component of any ecosystem and should also be considered if we want to take an ecosystem approach to managing the environment.

People and the Celtic Sea* environment are intrinsically entwined – the sea is part of our cultural heritage and has shaped and allowed our coastal communities to thrive.

As this project develops, we’ll be examining the activities of each sector to build up a picture of who is doing what and where. We’ll be producing an interactive map to enable people to clearly see the extent of some major activities in the Celtic Sea*.

This project is about protecting the ecosystem – which includes people and their livelihoods.

Basking shark feeding in UK waters


The region is a spawning area for key commercial fish such as megrim, blue whiting and mackerel. On the continental shelf the main open sea species are herring, sardine, and sprat. The ground-fish community consists of over a hundred species including cod and hake. Basking sharks are seen throughout area and it is considered an important migration area.

Seafloor organisms and habitats (Benthos)

The major commercial invertebrate species is the Norway lobster or Nephrops.

Along the shelf edge and the slope, the anemone Actinauge richardi dominates, while on the continental shelf, hermit crab and other mobile invertebrates (shrimps and echinoderms) tend to dominate. The area is also rich in cold water corals including the pink sea fan.

More about cold water corals in the Celtic Sea*


Phytoplankton (minute floating aquatic plants) productivity is reasonably high on the shelf with a rapid decrease west of the shelf break. Data from the Continuous Plankton Recorder (CPR) suggest a steady increase in phytoplankton over at least the last 20 years.

Toxic algal blooms occur around Irish coasts, especially along the southwest of Ireland. The CPR data suggest an overall decline in the abundance of zooplankton (minute floating animals) in recent years. The abundance of Calanus species is used to indicate the overall abundance for zooplankton; worryingly this species is now below the long term average abundance.

More about plankton in the Celtic Sea*

Depth of the sea floor (Bathymetry)

The Celtic Sea* is located to the south of Ireland and to the south-west of England and west of France. It is bounded by the English Channel in the South and the continental slope in the west. Most of the Celtic Sea* ranges from between 100 and 200 metres in depth but travelling west from Ireland the North-East Atlantic shelf gives way to deeper sea, canyons and ridges and with that comes wildlife adapted to deeper open waters. There are also a number of relatively shallow areas to the West of Cornwall and the south east of Ireland.


Along the shelf edge there is a current which flows northwards and a weaker current which flows north from Brittany, across the mouth of the English Channel. The Irish coastal current also runs westwards in the Celtic Sea*. Several rivers discharge fresh water into the region and influence the circulation patterns – these include the river Loire in France, the Severn in the UK and the Irish rivers Lee and Blackwater.


There are three main fronts:

  • Irish Shelf front - south and west of Ireland
  • Ushant front - English Channel
  • Celtic Sea* front - southern entrance to the Irish Sea.

Source: Some information has been taken and condensed from ICES WGRED, 2007.

* includes Western Channel

Orca Fishing boat Anemone Diver underwater