Seasonal and interannual variation in the phytoplankton community in the north east of Scotland

In 1997 a monitoring site was established 5 km offshore from Stonehaven (56° 57.8′ N, 02° 06.2′ W) in the north east of Scotland to examine the effects of physical and chemical parameters on the plankton community in this region. Analysis of the first 10 years of data show that, in common with trends in the NE Atlantic, there was an increasing trend in temperature and salinity at the site. Nutrients were typical of unimpacted waters in this region, with nitrate being the main limiting nutrient over the summer months. The phytoplankton community composition showed strong seasonality with low phytoplankton biomass in the winter, diatoms dominating in spring and early summer and dinoflagellates appearing in mid to late summer. Two different regimes were recognised: from 1997–2000 and 2005–2006, where the chlorophyll concentration peaked in the early part of the year (mid month values ranging from 2.6–4.1 μg l− 1) and a period from 2001–2004 where chlorophyll mid month values did not exceed 2.5 μg l− 1. A decreasing trend in the abundance of dinoflagellates, including members of the genus Ceratium, was observed from 2003–2006. In addition, from 1997–2001, the diatom genus Chaetoceros was the dominant species in the spring bloom, but post 2001 Skeletonema spp. became more abundant. The study highlights the variability that exists in time series data and emphasises the need for long term time series to determine the long term trends and impacts of the phytoplankton community on the marine ecosystem.