Green Seaweed Ulva species growing on the rocky shore at West Dale Bay, Pembrokeshire.

An algal bloom formed by phytoplankton off the west coast of Ireland. It can be seen as a light blue band all along the left side of the image. © Nasa.

Preserved specimen of a Torgoch or Arctic Charr (Salvelinus alpinus). Collected from Llyn Peris in 1978.

This is a Sea-Lettuce (Ulva lactuca) from Amgueddfa Cymru's scientific collection. We have around 5,000 algae specimens comprising macroalgae (seaweeds) and charophytes (stoneworts).

Porphyra

, the seaweed used to make Laverbread, is shown here growing on a rocky shore...

... and here as a herbarium specimen in Amgueddfa Cymru.

Algal blooms develop when algae or bacteria living in the sea or freshwater occur in vast numbers. Algal blooms can become big enough to be visible from space.

What are Algal Blooms?

This is when algae or bacteria living in the sea or freshwater occur in vast numbers. Algal blooms can become big enough to be visible from space. Many different kinds of algae and bacteria can form blooms. Two important groups are green seaweeds and blue-green bacteria (cyanobacteria).

Why do they occur?

Algal blooms occur when conditions are just right, usually where there are high nutrient levels, warm temperatures and slow water currents. Pollution from our homes, sewage plants, fertilisers and manure from farms can result in high nutrient levels in lakes and the sea.

If the global climate warms up, then so will water temperatures. This means algal blooms are likely to occur more frequently. They have already become more common around the UK in the last 30 years.

What are the effects?

As the algal bloom grows it blocks out light to plants in the water, which begin to die and decompose. Bacterial decomposition reduces oxygen levels in the water, which in turn causes marine animals to die.

As the bloom decomposes, the algae also release poisonous hydrogen sulphide gas.

Some algae and cyanobacteria also create toxins that can kill other wildlife in the water. In some cases these toxins can build up in shellfish such as cockles, making them poisonous for us to eat.

Can we prevent it from happening again?

Although algal blooms are natural phenomena, our activities can cause them to occur more frequently. Tighter controls on the use of fertilisers in farming and better treatment of waste water can help to reduce them. The only way to protect people from harm once an algal bloom has formed is to keep them away from the water. Wildlife cannot be protected that easily.

Seaweed Blooms

Sea-Lettuces (Ulva species) are green seaweeds that can form algal blooms. In summer 2009, vast blooms of green seaweed were reported in southern UK and northern France.

In this case it is not the seaweed itself but the hydrogen sulphide gas that is poisonous to humans on the beach. However, the only casualty reported in 2009 was an unfortunate horse, which broke through the crust on a deep pile of weed and was poisoned by the release of hydrogen sulphide.

Fortunately, Sea-Lettuces do not usually grow to such huge proportions. They are common on rocky shores around the UK and, as their name suggests, resemble thin, bright green lettuces.

Toxic Cyanobacteria

In the summer of 2009 a cyanobacteria (Anabaena spiroides) formed a potentially toxic algal bloom in Llyn Padarn, north Wales. This is one of only three lakes where the Torgoch, or Arctic Charr (Salvelinus alpinus), is found in Wales. The population of this rare fish was threatened by the lack of oxygen. There was also an impact on the local economy as people were prevented from visiting the lakeside.

What you can do

We can all help to reduce the chance of algal blooms this summer by using less washing liquids and powders in our homes. The phosphates in these products are washed down our drains and into lakes and the sea where they become nutrients for algae. They can form as much as 25% of the nutrients released in sewage. Look out for environmentally friendly products that contain less phosphate.

Did you know?

The Welsh dish known as Laverbread is made from a type of red seaweed. These seaweeds are called Porphyra, commonly known as laver. Porphyra seaweeds are also known as nori in Asia and are processed in a different way to make the seaweed into sheets used in sushi.

Seaweeds and the Museum

There are three main groups of seaweeds: green seaweeds, red seaweeds and brown seaweeds. The Sea-Lettuces that can cause problems in the UK and France are green seaweeds, and are placed in the genus Ulva by taxonomists.

Taxonomists are scientists that study the classification and evolution of organisms. At Amgueddfa Cymru our taxonomists study many different groups. To do this they use the Museum's extensive scientific collections of animals and plants. These collections provide an invaluable resource for accurate identification and a sound taxonomic foundation. At Amgueddfa Cymru we hold approximately 5,000 algae specimens, which are constantly being added to.

Seaweeds are included in a broad group known as the algae. Our oldest and perhaps the most important algae collection is that of Lewis Weston Dillwyn, who was an important figure in Welsh history. Many of the specimens he collected were from or near Swansea where he lived. The collection contains algae specimens that are 200 years old. They are part of the original material used by Dillwyn in the preparation of his pioneering 1809 work British Confervae.

This work, a rare copy of which is housed at Amgueddfa Cymru, contains beautiful colour drawings of algae and was a significant advance for algology. Before its publication, only 34 species of algae had been described; this rose to 177 described species after its publication.