The dataset presented here is from the long-term monitoring of phytoplankton at 12 coastal water positions (stations) in south-west Ireland: Eight within Roaringwater Bay / Long Island Bay, and four from 1.5 km to 17.5 km offshore in open waters south of Sherkin Island, Co. Cork, Ireland.

Stations were visited approximately every 12 days from April to October each year, within a period from 1980-2014. Water samples were taken at set depths for each station and phytoplankton counts were recorded. Where water depth allowed, stations were usually sampled at the following depths: 0m, 2.5m, 5m, 10m, 15m, 20m, 25m, 30m, and 50m, ranging from a maximum depth of 5m in three stations to a depth of 50m in four stations. An additional depth of 7.5m was sampled at one station.

The dataset includes standardized phytoplankton counts together with recorded location, date, water depth, water temperature, salinity, conductivity, Secchi disc estimate, tide height at time of sampling, sea conditions and weather conditions.

Standard air temperature records from the manual weather station at Sherkin Island Marine Station covering the same time period, together with records from the automated weather station from 2004, offer comparisons with the marine records for climate-related studies (available from Met Éireann : The Irish Meteorological Service).