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NECR481 Edition 1 Seagrass in the Stour Orwell and Blackwater 2020-21 (NECR481)

Eelgrass (Zostera spp.) declined in the 20th century throughout the UK. To provide a baseline for Zostera eelgrass in the Stour, Orwell and Blackwater estuaries in north Essex and Suffolk, a survey was undertaken in summer 2021 to follow a shore-walking survey from autumn 2020. The summer 2021 survey combined shore-walking with drone surveys to capture seagrass extent and patches of Zostera marina amongst more extensive Zostera noltei. At 38 out of 40 locations Zostera seagrasses were present in the Stour and Orwell estuaries, with Z. marina seen at four of these (Lower Holbrook, Orwell Observatory, Nacton Foreshore and Strandlands in Copperas Bay).

The estimation of extent indicated 3.9 ha of Zostera in the Stour Estuary compared to 6.2 ha in the Orwell. Of the 10.1 ha of Zostera, the majority (99%) was formed of Z. noltei with only 0.1 ha of Z. marina. There were locations for Z. noltei where it was not recorded in the 1970s. Of the two sites visited for shore-walking surveys in the Blackwater Estuary, and the two further sites visited for less formal opportunistic shore-walking surveys in 2021, Z. noltei was only present in St. Lawrence Bay. Extensive widgeon grass (Ruppia spp.) was found at some sites in the Blackwater. A literature review of historical seagrass ecology across Essex and Suffolk finds seagrasses disappeared from the Blackwater and Colne earlier than some recent reports suggested.

Co-ordinated research and restoration efforts will be crucial in securing a future for Z. noltei in changing coastal environments.

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NECR481 Edition 1 Seagrass in the Stour Orwell and Blackwater 2020-21, PDF, 2.6 MB 2024/04/10


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