In 1981, UNESCO recognised the importance of Dublin Bay by designating North Bull Island as a Biosphere because of its rare and internationally important habitats and species of wildlife. To support sustainable development, UNESCO’s concept of a Biosphere has evolved to include not just areas of ecological value but also the areas around them and the communities that live and work within these areas. There have since been additional international and national designations, covering much of Dublin Bay, to ensure the protection of its water quality and biodiversity.

To fulfil these broader management aims for the ecosystem, the Biosphere was expanded in 2015. The Biosphere now covers Dublin Bay, reflecting its significant environmental, economic, cultural and tourism importance, and extends to over 300km². Over 300,000 people live within the newly enlarged Biosphere.


Dublin Bay Biosphere contains three different zones, which are managed in different ways:

  • The core zone of Dublin Bay Biosphere comprises 50km² of areas of high natural value. Key areas include the Tolka and Baldoyle Estuaries, Booterstown Marsh, Howth Head, North Bull Island, Dalkey Island and Ireland’s Eye.
  • The buffer zone comprises 82km² of public and private green spaces such as parks, greenbelts and golf courses, which surround and adjoin the core zones.
  • The transition zone comprises 173km² and forms the outer part of the Biosphere. It includes residential areas, harbours, ports and industrial and commercial areas.

Nature and biodiversity

As the days shorten and the temperatures drop in autumn the first Brent Geese arrive in Dublin Bay after a 5,000 kilometre migration from Arctic Canada. Like many of the geese and swans, the young birds stay with their parents over winter, following them on migration and learning from them about the best places to feed. The long lines of geese that fly daily across the city are moving from overnight roosts on the Bull Island to daytime feeding areas. Normally, one of the experienced adults takes the lead in these daily commuting flights with the younger birds falling in behind. Brent Geese are essentially vegetarians and they need to graze more or less continuously during daylight hours to maintain their body in suitable condition for the long migration to the arctic breeding grounds. When they first arrive the geese feed on green seaweeds and other plants on the shoreline. However, as the population wintering in Ireland has grown steadily, the amount of intertidal feeding habitat in Dublin Bay has been exceeded and the geese have gradually moved on to feeding on coastal grasslands, including parks, sports pitches and other open spaces all around Dublin City.


Plants of the mudflats

Green seaweeds are abundant on some of the mudflats, especially in the northern part of Dublin Bay. Typical species are Sea Lettuce and Intestine Weed although a total of 32 species of green seaweeds have been recorded from the Dublin Bay mudflats. They grow abundantly during summer months and die back or get eaten by waterbirds such as Brent Geese in winter. These are algae that are related to the brown seaweeds growing on rocks and harbour walls around the bay. The green seaweeds probably depend on anaerobic mud beneath them for their nutrient supply. This influenced the design of the new Ringsend treatment works, which greatly reduces the release of particulates into Dublin Bay. As the tide rises most of the seaweed mat floats free from the mud surface and drapes its long fronds around any obstacle such as a post. Whilst many records of algal biomass with season are available, the detailed ecology of each species has yet to be worked out.