Seaweeds & Algae

Seaweed_Copyright Laura Grant

Kelp and Britannia Bridge_ Copyright NRW

Kelp and sponges_Copyright NRW marine monitoring team


Marine algae is a general term which encompasses macroalgae (seaweeds), which we see on the shore to microscopic free-floating phytoplankton (microalgae), mostly invisible to the naked eye.

Phytoplankton, meaning ‘plant drifter’, encompasses many different groups (e.g. diatoms and dinoflagellates are the main two) and form the base of marine and freshwater food webs, playing a key role in the global carbon cycle and produce vast amount of oxygen vital for our existence. They can cause algal blooms as the availability of light and temperature increases.

Seaweeds dominate the rocky shores around Wales and extend into the subtidal where light levels allow growth. The more familiar ‘seaweeds’ in Wales can broadly be grouped into the following categories: brown seaweeds; red seaweeds; green seaweeds; and calcified seaweeds. They are found in a variety of habitats but are usually found attached to rocks on the seabed, either on the shore or in the shallow sea where there is enough sunlight to grow. Wales supports approximately 400 species of marine macroalgae.

Maerl is an unusual, very slow-growing hard coralline red algae, typically pink or purple in colour. It grows as unattached nodules, deposits take thousands of years to build up and forms large maerl ‘beds’. Maerl is therefore considered to be an irreplaceable resource. The Milford Haven maerl bed is the only known bed of live maerl in Wales.

Maerl - Copyright NRW

Maerl - Copyright NRW

Maerl - Copyright NRW

The role of seaweeds in ecosystem function

Seaweeds have many important roles in marine ecosystems - the oxygen in every third breath you take is from marine algae! Seaweeds support the natural ecosystem and people through primary production / carbon fixation and nutrient cycling that underpins marine food webs. Seaweeds provide and modify habitats for a wide range of organisms, including commercially targeted fish and shellfish species. The contribution to ecosystem function and services varies, with kelps and other brown seaweeds and maerl being of particular ecological importance due to their ability to provide complex structure to habitats.

Conservation / protection of seaweeds in Wales

Six algae species appear on Section 7 of the Environment (Wales) Act 2016 as species of principal importance. Maerl beds are also a habitat of principal importance (under Section 7), listed under sublittoral sediment. Kelp forests are also an OSPAR habitat.

Algal species listed on the Section 7 list

Species name Species common name Species Welsh name
Anotrichium barbatum Bearded red seaweed Gwymon coch barfog
Cruoria cruoriaeformis A red seaweed Gwymon coch
Dermocorynus montagnei A red seaweed Gwymon coch
Lithothamnion corallinoides Coral Maerl Cramen goch gwrelaidd
Padina pavonica Peacock's tail Gwymon cynffon paun
Phymatolithon calcareum Common maerl Cramen goch

There are many seaweed ‘biotopes’ which may occur within or are contained within Annex 1 features in Special Areas of Conservation, principally in the Annex 1 habitats ‘Reef’, ‘Large Shallow Inlets and Bays’ and ‘Estuaries’.

There are currently no seaweed species listed under Schedule 8 of the Wildlife and Countryside Act (rare plants which have additional protection) which would require a licence for collection.

Species in Wales

Amphibians & Reptiles



Terrestrial Mammals



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