Thursday, August 27, 2009
Seaweed is spreading at such an extraordinary rate that it is threatening to choke wildlife along the south coast of England. Photograph: Solent News & Photo Agency/Solent News & Photo Agency
The Solent is a stretch of sea separating the Isle of Wight from the mainland of England. It is a major shipping route for passengers, freight and military vessels. It is also an important recreational area for water sports, particularly yachting, hosting the Cowes Week sailing event annually.
The area is of great ecological and landscape importance, particularly because of the coastal and estuarine habitats along the edge of the Solent. Much of its coastline is designated as a Special Area of Conservation. It is bordered by and forms a part of the character of a number of nationally important protected landscapes including the New Forest National Park, and the Isle of Wight AONB.
Blooms of seaweed choking the waterways of the Solent have been caused by large amounts of untreated sewage and farm fertilizers dumped into the sea, according to the Environment Agency.
Extra nutrients in the pollutants combined with sunny weather have enabled the seaweed to grow out of control around Worthing in West Sussex, Ventnor in the Isle of Wight and at Langstone harbour. The excessive growth has cut off not only access to food for local birds, fish and crustaceans; but, has depleted the oxygen in the water.
Large stretches of the mudflats and saltmarshes around the Solent are designated as areas of outstanding natural beauty (AONB). They are home to more than 7,500 migratory Brent geese and tens of thousands of other local birds that visit the area throughout the year to feed on the plants and marine invertebrates such as crustaceans and molluscs.
But the biodiversity in the area's waterways and harbours is under threat from sewage and agriculture. "[Seaweed] growth is promoted by excess nutrients, mainly nitrogen, nitrates and ammonia," said Dave Lowthion, marine team leader at the Environment Agency. "We know that the two key sources to this are nitrogen in sewage discharges and nitrates runoff from agriculture into rivers and harbours."
Each year between April and November, thick mats of seaweed can grow preventing migratory birds from getting at their invertebrate meals concealed in the sediment. As the seaweed decomposes, it produces hydrogen sulphide while depleting the surrounding oxygen supply. Hydrogen sulphide can be toxic to marine life and; people, if the amount is sufficient.
Parts of the UK under threat from algae blooms caused by agriculture and sewage pollution, according to the Environment Agency.
Seaweed build-up has also affected the northern coast of France, with excess blooms covering beaches all over Brittany. Release of hydrogen sulphide on the beaches there allegedly caused the recent death of a horse, which became overwhelmed by fumes on a beach in Saint Michel de Greve. The rider, Vincent Petit, a 27-year-old vet, had to be dragged unconscious from a patch of rotting algae a metre deep. In another incident last year, two dogs died while walking near piles of algae on a beach close by.
Mounds of rotting seaweed have appeared at more than 80 locations on the coast this summer. They have a dry crust that can trap large concentrations of hydrogen sulphide, which builds up until the mound is disturbed.
Recent warm weather is also to blame for the death of thousands of fish along the coast of Cornwall. Around St. Austell Bay and Tregantle beach at Antony, near Torpoint, the Food Standards Agency closed down shellfisheries this week as blooms of microscopic red algae appeared off the shore and dead fish washed up on the beaches.
The so-called "red tide" produces toxins that are lethal to fish and shellfish and the sudden growth in the algae depletes oxygen in the water. The algae can cause skin irritation and harm pets — local authorities have warned people to avoid going into the water wherever any red algae might be present.
"When it's eaten by shellfish, the toxin can persist in the flesh and can poison people if they eat the shellfish. They can be big blooms, half the size of the English Channel, but not very often do they go right up to the shore," said Lowthion.
Posted by Pippa
Labels: deadly seaweed choking Solent