The marine laboratories in Plymouth have sampled at two principle sites in the Western English Channel for over a century in open-shelf (station E1; 50° 02'N, 4° 22'W) and coastal (station L4; 50° 15'N, 4° 13'W) waters. These stations are seasonally stratified from late-April until September, and the variable biological response is regulated by subtle variations in temperature, light, nutrients and meteorology. Station L4 is characterized by summer nutrient depletion, although intense summer precipitation, increasing riverine input to the system, results in pulses of increased nitrate concentration and surface freshening. The winter nutrient concentrations at E1 are consistent with an open-shelf site. Both stations have a spring and autumn phytoplankton bloom; at station E1, the autumn bloom tends to dominate in terms of chlorophyll concentration. The last two decades have seen a warming of around 0.6°C per decade, and this is superimposed on several periods of warming and cooling over the past century. In general, over the Western English Channel domain, the end of the 20th century was around 0.5°C warmer than the first half of the century. The warming magnitude and trend is consistent with other stations across the north-west European Shelf and occurred during a period of reduced wind stress and increased levels of insolation (+20%); these are both correlated with the larger scale climatic forcing of the North Atlantic Oscillation.

Datasets contain depth profiles of the mean abundance of groups of plankton as cells per millilitre, measured using flow cytometry. The groups quantified are divided into phytoplankton and heterotrophs. Phytoplankton groups quantified are: Synechococcus sp. (cyanobacteria) (Syn), picoeuakryotes (smaller than 2 µm) (Peuk), cryptophytes (Crypto), coccolithophores (Cocco), small dinoflagellates (<30 µm) (Dino), Phaeocystis sp. (Pcystis) and nanoeukaryotes (Neuk) not already mentioned (2-20 µm). Heterotrophs quantified are: heterotrophic nanoflagellates (HNAN), bacteria with relatively high nucleic acid content (HNA) and bacteria with relatively low DNA. Samples were collected and analysed in duplicate (heterotrophs) or triplicate (phytoplankton) from the sea surface, 10 m, 25 m and 50 m depth. In 2007 the Secchi depth was sampled instead of the 10 m depth. 3 replicates for phytoplankton, 2 for HNAN, HNA, LNA.