Sumner Beach - Christchurch
![]() The Press | Monday, 07 January 2008 The curse of the summer sea- lettuce bloom is back to irritate Christchurch beach-goers. Sea lettuce from the Avon- Heathcote Estuary has broken free from its usual habitat and is landing in clumps on Sumner Beach. Avon-Heathcote Estuary Ihutai Trust chairman Alex Drysdale said sea lettuce always flourished where humans spread waste – the estuary being the end point for Christchurch's treated sewage. "It is a little unusual but not unknown,"
Drysdale said of the recent Sumner invasion. "Given the hot weather and
the conditions, sea lettuce would not normally make its way to Sumner
Beach unless there had been a storm and it broke off, but there have
been a few high winds here lately." Drysdale said the quantity of
lettuce was just a symptom of the long-term pollution in the estuary
which would be eased after the city's ocean sewage outfall was
completed. "Everything that can be done has been done and it will be
several years before nutrients in the estuary fall enough to inhibit
sea-lettuce growth. http://www.stuff.co.nz/4346664a10.html |
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What is Sea Lettuce?
Sea lettuce is a bright green marine macro algae found around the world on rocks along sheltered rocky coasts and in shallow estuaries. The sea lettuces are collectively grouped under the category of Ulva species. Ulva is a macrophyte algae (as opposed to a planktonic algae), which grows in sheets two cells thick usually less than 30cm in diameter. Ulva is rich in nutrients such as vitamin A and B. Early Maori used the completely edible sea lettuce in cooking. Sea lettuce is still eaten today in salads and stews around the world. It is a very vigorous grower which adapts readily to changing conditions. Rotting Sea Lettuce - Why such a problem? Sea lettuce can grow very fast when nutrients, temperature and light conditions are favourable. Biomass can increase at a rate of up to 20% per day. Wave action causes the organism to break off from its growth beds and be washed ashore where it rots. The smell can be very offensive because of the high sulphur content of sea lettuce. The offensive smell can occur intermittently between late November and early April. What Factors Influence Sea Lettuce Growth? Increased levels of nitrogen and phosphorous in coastal waters in particular agricultural runoff is often carried down to the sea in the rivers. Sea lettuce grows more in spring. Growth rates are linked to temperature with growth decreasing below 15oC and above 20oC. Growth is light sensitive so the lack of light with increasing depth means that the algae prefers shallow water. More information on the problem is available from the http://www.envbop.govt.nz website. use the 'search website' feature to look for 'sea lettuce'. |