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Scientists say mangroves have room to spread further in Tauranga harbour

For immediate release: Tuesday 8 February 2005

Mangroves have more than doubled in extent in Tauranga harbour since the 1940s - and still have plenty of room to spread further, according to research by Environment Bay of Plenty.

Senior environmental scientist Stephen Park told the council’s regulation and monitoring committee recently that large areas currently free of mangroves have the potential to grow them.

As examples, he showed maps defining the native plant’s habitat limits in Welcome Bay and Waikaraka Estuary at Te Puna. Welcome Bay, in particular, had a higher potential for mangrove spread because of the estuary’s mud content. “And there is a clear link between the amount of mud in an estuary and mangrove cover,” he said.

Mr Park has also studied changes in mangrove extent over the past 60 years. Mangrove canopy cover had generally increased exponentially, with about 240ha recorded in 1943, 375ha in 1974 and 545 in 1999. However, mangrove spread was more rapid in some estuaries than others. One of the most quickly changing areas is just north of Tanners Point along the open harbour margin. In 1943 that area had only 0.2ha of mangrove canopy cover. By 2003, it was 26ha. Nearby Tuapiro Estuary also shows a very high rate of increase between 1980 and 2003.

Mr Park’s report on mangrove distribution and abundance is part of a wider project studying the impacts of urbanisation and other development on the ecology of Tauranga harbour. Its intention is to fill data gaps and “to help us and the community to understand the overall picture”, he explained.

The regulation and monitoring committee’s deputy chairman, Robin Ford, said mangrove expansion in Tauranga harbour is a contentious topic. “Mangroves are a native plant and grow naturally in the harbour. But, over the past few decades, they have spread widely, partly because of the increased sedimentation from historic land clearance and development. This has caused considerable conflict.

The full report is available on www.envbop.govt.nz under Recent Council Reports.

ENDS

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