Cysts and sediments: Gonyaulax Polyedra (Lingulodinium Machaerophorum) in Loch Creran

The distribution of Lingulodinium machaerophorum and a calcareous Scrippsiella cyst were investigated in Loch Creran (west coast of Scotland) in comparison with the distribution of fine grained sediments. A water-column survey showed the abundance of Gonyaulax polyedra (the motile thecate stage) to be highest in the upper loch and at the head of the lower loch. In the region of this high thecate cell abundance, cyst densities in the sediment showed no relation to grain size distribution, remaining uniformly high. In the other areas of the loch, sediment cyst densities increased with increasing amounts of the fine grained fraction in the sediment with a plateau of cyst numbers when 50–60% of the sediment was less than 63 pm. The calcareous Scrippsiella cyst showed a similar distribution but no plateau of numbers was reached. Numbers of whole Lingulodinium machaerophorum calculated for the whole loch (250 × 10⁹ cysts in the top 1 cm) is higher than previously estimated, further emphasizing the size of the cyst pool in Loch Creran.