INTRODUCED GRASS, KILLING MARINE LIFE

Press, 15 October 1976, Page 13

INTRODUCED GRASS, KILLING MARINE LIFE

JOHN KEAST, looking around the Pleasant Point Domain, finds—see picture--an area of .. .

Spartina grass, introduced into New Zealand in 1913 by a Manawatu farmer, has now become as much a pest as rabbits or the common house fly. Originally considered a cheap method of raising inter-tidal areas so as to assist land reclamation, the grass has proved almost impossible to control. It now poses a serious threat to the natural flow of coastal streams and the biological production of estuarine areas. The grass, which has spread to most areas in New Zealand, is common in Christchurch. Species

have been found in the Avon-Heathcote estuary and it is estimated there may be 26 acres of spartina in New Brighton's Pleasant Point Domain. In 1970 there was only one acre of the grass there, according to Craig Batchelor, a wildlife officer for the Department of Internal Affairs. He said that the Heathcote estuary now contained about 13 hectares of spartina. It was destroying the natural habitat of wading birds such as oyster catchers. After the grass’s introduction it was distributed to New’ Zealand farmers for 40 years as a

land reclaimant. Now, said Mr Batchelor, the grass ■was reaching epidemic proportions. Many fish, molluscs and Crustacea depend on estuaries for existence during critical stages of their life, and rely on estuaries to act as spawning grounds, provide food and give protection from predators. Now the main hazard is spartina which, left unchecked, will choke the life in estuarine areas and upset the ecology. Over many years the plant’s roots collect silt and mud, gradually raising stream and estuary beds, until, as was the case in Invercargill, mud-flats become grasslands.

Estuaries are thought to be the most productive areas on earth, and their yield is almost double that of most forms of agriculture. Wildlife officers are now understandably concerned at the damage the grass can do to marine life. New Zealand conditions are favourable for the plant which thrives in deep, soft and fertile mud — like that in the Pleasant Point Domain. The spread of spartina in New Zealand is thought to be entirely vegetative, as few records of viable seed exist and most spread has been by the

expansion of established clumps. In Invercargill’s Oreti River estuary the sedimentation rate has been measured at 2cm a year; and in England, where the plant is also causing concern, its accretion rate has been measured at 12cm annually. Once established, the plant — common in two species in New Zealand. S. Townsendii and S. Alterniflora — is extremely hard to kill. A chemical, 2,2-DPA, has been found to give the best results, but it is slow. Mr A. R. Greenland, a research officer with the Christchurch Drainage

Board, said that spartina had been sprayed in the Pleasant Point Domain after complaints from local people. He said that the board had been urged to dig out the plant initially. "It wouldn’t have worked, we would have spread more than we removed," said Mr Greenland. The Drainage Board has estimated that it would cost $50,000 to clear a I.6km x 40m area of spartina by dredging.

Mr Greenland said that the board was now annually spraying the Pleasant Point Domain and that the area of spartina had been greatly reduced.