Cup Coral_Copyright NRW - Skomer MCZ staff

Crawfish Palinurus elephas Copyright NRW- Skomer MCZ staff

Arctica islandica with hermit crab Pagarus berhardus_Copyright NRW - Skomer MCZ staff


Marine invertebrates are extremely varied and comprise the most diverse group of animals in our seas. Ranging from the largest lobster to microscopic plankton, every marine habitat contains invertebrates, which contribute hugely to the structure and function of our marine ecosystems and provide an important food source. Many are mobile, but some form habitats of their own. Invertebrates occupy a multitude of niches from intertidal rocky crevices to deep subtidal sediments with well over 2000 species of macro-invertebrates in the Welsh marine environment.

Many of the invertebrates found in Welsh seas have a planktonic stage, where they stay in the water column for the first stage of their life cycle before they settle out on the seabed and continue life as adult invertebrates (e.g. meroplankton such as crabs and lobsters). Some organisms stay as zooplankton for their whole lifecycle (holoplankton).

Some of Wales’ most iconic and spectacular habitats are those swept by strong tides and currents, which support a range of striking sponges, bryozoans, ascidians, hydroids and anemones. Areas such as the Menai Strait, Skomer and Bardsey have high diversity of these colourful filter feeding species – long lived sponges and carpets of jewel anemones along with associated species like the colourful sea slugs – or nudibranchs.

The pink sea fan Eunicella verrucosa, is a type of coral - a colony of individual tiny anemone-like animals that share a hard skeleton attached to rocks on the seabed. They can only be found in a very few places in the UK and are at the extreme edge of their northern range in Wales in Pembrokeshire, where some individuals are thought to be 50-100 years old.

The crawfish or spiny lobster Palinurus elephas is a large and striking crustacean classified as vulnerable on the IUCN red list. It declined significantly in the 1960s and 1970s, and now survives in Wales in seas off the Llŷn Peninsula, Anglesey and Pembrokeshire, and appears to be increasing in numbers.

In contrast, some invertebrates inhabit intertidal and subtidal sediment habitats on open shores or in sheltered estuaries. From the surface of the sediment, small holes and marks on the surface give only hints to the wealth of animals that live within the sediment. The dense populations of bristle worms, crustaceans and bivalve molluscs consume detritus and food from the water column and in turn provide a large quantity of food for predators such as fish and birds.

The Ocean Quahog Arctica islandica is a large bivalve mollusc that lives buried in sediments – they are very slow growing and can live for over 500 years, possibly the longest living animal on earth!

As well as these species which all have a degree of protection, there are many more common species which you are likely to encounter on the shore. These include species such as ragworm and cockle and also those species found on the strandline, especially after storms, such as the horned wrack Flustra ceranoides, sea mouse Aphrodita aculeata and echinoderms, like the sea potato Echinocardium cordatum. Echinoderms are unique to the marine environment, no terrestrial phylum can make such a claim!

Diversity of the Welsh marine invertebrate fauna within 12 nautical miles of the coast

(compiled from multiple sources)

Marine invertebrate taxa Approximate number of species in Wales
Arthropoda - crabs / lobsters / barnacles / shrimps / sea spiders/ sandhoppers c600
Annelida - worms c560
Mollusca - gastropods / bivalves/ cephalopods c450 - 550
Cnidaria – corals, anemones, jellyfish c180
Porifera - sponges c140
Bryozoa – moss animals c100
Echinoderms – starfish, sea urchins, sea cucumbers c55
Tunicata - sea squirts c50

Conservation and protection of invertebrates in Wales

There are a number of marine invertebrates which have additional protection in Wales. Eleven invertebrates are listed on Section 7 of the Environment (Wales) Act as species of principal importance, including bivalves like the fan mussel Atrina fragilis, native oyster Ostrea edulis and ocean quahog Arctica islandica, the pink sea fan Eunicella verrucosa, crawfish Palinurus elephas and two stalked jellyfish species. Additional invertebrates form habitats which are protected under Section 7 of the Environment (Wales) Act as priority habitats, including intertidal boulder communities and biogenic reef such as the honeycomb reef Sabellaria alveolata reefs, blue mussel Mytilus edulis and horse mussel Modiolus modiolus.

Marine invertebrates on the Section 7 list - species

Species name Species common name Welsh species name
Alkmaria romijni Tentacled lagoon worm Llyngyren dentaclog
Arctica islandica Icelandic cyprine or Ocean quahog Cocosen fawr
Atrina fragilis Fan mussel Cragen adain
Edwardsia timida Burrowing anemone Anenome dyllu
Eunicella verrucosa Pink sea-fan Môr-wyntyll binc
Haliclystus auricula A stalked jellyfish Slefren goesynnog
Lucernariopsis campanulata A stalked jellyfish Sglefren fôr goesynnog
Ostrea edulis Native oyster Wystrysen
Palinurus elephas Crayfish, crawfish or spiny lobster Cimwch coch
Tenellia adspersa Lagoon sea slug Môr-wlithen y morlyn

Marine invertebrates on the Section 7 list - habitats

Habitat name
Welsh habitat name
Musculus discors beds (Musculus discors)
Gwelyau o fisglod gwyrdd
Blue mussel beds Gwelyau o fisglod glas
Horse mussel beds Gwelyau o farchfisglod
Fragile sponge & anthozoan communities on subtidal rocky habitats Cymunedau bregus o sbyngau ac anthosoaid ar gynefinoedd creigiog islanw
Sabellaria alveolata reefs
Riffiau Sabellaria alveolata
Intertidal boulder communities Cymunedau ar glogfeini yn y gylchfa rhyng-lanw

There are three additional habitats which are on the OSPAR threatened and declining list; Oyster Ostrea edulis beds, Sabellaria spinulosa and Seapens and burrowing megafauna.

Many of these species are also listed under various sections of Section 9 of the Wildlife and Countryside Act, which protect against killing and taking, possession, disturbance, selling or advertising. These invertebrates include, tentacled lagoon worm Alkmaria romijni, lagoon sea slug Tenellia adspersa, pink sea fan and fan mussel.

There are no marine invertebrates included on Annex II of the EC Habitats & Species Directive. However, many invertebrates are noted as important species associated with Annex 1 habitats, such as ‘Reef’, many of them comprising biogenic reefs.

Unlike many terrestrial invertebrates e.g. butterflies and dragonflies, there are fewer dedicated societies recording these marine species groups. However, there are societies who focus on different groups (e.g. the Conchological Society are interested in molluscs) and volunteer organisations like Seasearch operate in Wales and, along with the public and statutory bodies, record presence of marine invertebrate species, building up a valuable picture of their distribution.

Netted Dogwhelk Tritia reticulata eggs_Copyright Laura Grant

Anemone Sargartiogetan undatus _Copyright Laura Grant

Sabellaria Alveolata Honeycomb worm Copyright NRW

Sponges_Copyright NRW - Skomer MCZ staff

Blue-rayed limpet Patella pellucida_Copyright Laura Grant

Flat periwinkle Littorina obtusata_Copyright Laura Grant

Sand mason worms Lanice conchilega_Copyright Laura Grant

Mytilus edulis Blue mussel_Copyright NRW - Paul Brazier

Arctica islandica_Copyright NRW - Skomer MCZ staff

Pink sea fan Eunicella verrucosa Copyright NRW Marine Conservation Zone

Snakelocks anemone Anemonia viridis_Copyright Laura Grant

Lined seaslug at Skomer Copyright NRW- Skomer MCZ staff

Action for marine invertebrates

A number of the iconic marine invertebrates have targeted conservation projects focussed on restoration and / or improving management.

Pink Sea Fan

As a southern species, pink sea fans are at the extreme northern edge of their range in Wales in Pembrokeshire and their numbers are declining. Welsh Marine Treasures project (part of Natur am Byth!) is a Heritage Lottery and Welsh Government funded project being led by NRW. It unites nine environmental NGOs with NRW to deliver Wales’ largest natural heritage and outreach programme to save species from extinction and to reconnect people to nature.

Natur am Byth! will build on the existing monitoring by the Skomer Team within the Skomer Marine Conservation Zone (MCZ) and seek to protect the pink sea fan population around Skomer MCZ by engaging with sea-users and communities about the vulnerability of this iconic species. The human impacts on pink sea fans will be explored and will identify voluntary measures which can be put in place to support its conservation.

Native Oyster

The Wales Native Oyster Restoration Project led by Natural Resources Wales is a three-year European Maritime and Fisheries Fund project, administered by the Welsh Government, investigating questions around the approach and feasibility of restoring the native oyster Ostrea edulis in the Milford Haven waterway. The main focus of the project is to address fundamental restoration questions relating to survivability, recruitment and stocking density, while also considering potential impacts of the oyster disease Bonamia and non-native species.

Also as part of Welsh Marine Treasures, there will be a test and scaling up of the restoration of native oyster beds in Milford Haven, building on the Welsh Native Oyster action plan.

Another project working to restore native oysters is The Wild Oysters Project. This project is being run by Zoological Society London (ZSL), Blue Marine Foundation (BLUE) and British Marine and is working with local delivery partners in Wales delivering restoration hubs (in Conwy).

Species in Wales

Amphibians & Reptiles



Terrestrial Mammals



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