Skip to main content


Title: The identification and investigation of a dinoflagellate bloom in Mounts Bay, Cornwall
Author: R Grantham
Document Type: Monograph
On Thursday 3 August 1989 Penvith District Council Environmental Health Department received reports of large numbers of dead sea urchins and lugworrn on the shore at Long Rock, Marazion in Cornwall and that this appeared to be associated with a reddish-brown discolouration of the sea. The South West Water Rivers Unit was informed on the afternoon of Saturday 5 August 1989 and consequently visited the area that evening. Staff from the Rivers Unit and Scientific Services of South West Water worked throughout the weekend to assess the water quality of inputs to the bay and the receiving waters, and to establish the nature of the discolouration. Die Tidal Waters Unit of the SWWRU visited the area and the adjacent beaches of Newlyn, Praa Sands, Per ran Sands and Penzance Harbour on 7 August 1989 and again the next day. The 'red tide' could only be seen in the waters at the extreme north of Mounts Bay and affected an area that stretched from Penzance Harbour to the Long Rock and Marazion beaches. The waters concerned were highly turbid, of a red clay colouration and occurred to a depth of at least one metre. A large number of dead sea urchins were present and a few lugworm were found to be under stress. Samples were collected to verify those results obtained from the samples taken on the Saturday. Close collaborative work with the Plymouth Marine Laboratories identified a predominance of the Dinoflagellate species Gyrodinium aureolum. South West Water Scientific Laboratories' algologists also identified the presence of the algae, Glenodinium. The dominant species has been known to bloom in the area in the past, giving the observed reddish/brown discolouration and mortalities of benthic species. Dinoflagellates are algae type microorganisms that bloom under favourable conditions including elevated temperature, high illumination and the supply of limiting materials. A prolonged dry spell and settled conditions prior to the bloom are likely to be the primary causative factors for the predominance of Qyrodinium aureolum. The Chemical anallyses of the inputs and waters within the bay showed levels in the order that would be expected of the various water types within the region.
Publisher: National Rivers Authority
Publication Date: 1989
Publication Place: Exeter
Subject Keywords: AlgaeWater qualitySamplingBeachesCoastal managementCoastsAlgal blooms
Geographic Keywords: CornwallWest Cornwall and the Fal catchment
Total file downloads: 295

Download PDF    Display PDF in separate tab