Long-term survival of marine planktonic diatoms and dinoflagellates in stored sediment samples

Sediment samples from Scottish coastal sites, taken over the last 9 years, were stored in closed containers at 5 degrees C. Slurry cultures were used to determine the survival of phytoplankton in these sediments. A range of d iatom and dinoflagellate species survived for at least 27 months in these s tored samples. A number of species grew for which no resting stage has yet been described: Thalassiosira angulata, T.pacifica, T.punctigera, T.eccentr ica, T.minima and T.anguste-lineata. Notable results were survival times of 73 months for Skeletonema costatum, 96 months for Chaetoceros socialis, C. didymus and C.diadema, 109 months for Scrippsiella sp. and 112 months for L ingulo-dinium polyedrum. A single sample was stored and repeatedly cultured for diatoms over a period of 16 months. The number of species cultured fro m the sediment declined over this time. Lingulo-dinium polyedrum cysts isol ated from sediments collected at least 18 months previously gave a hatching success of 97% and cysts isolated from a 9-year-old sample gave a hatching success of 3%. The study indicates the potential importance of coastal sed iments as a source of phytoplankton to their overlying waters. The validity of using marine planktonic diatoms and dinoflagellates for modelling geolo gical events is discussed.