Multidecadal spatial reorganisation of plankton communities in the North East Atlantic

Changes in the spatial distribution of plankton populations are thought to have a profound effect on the oceanic ecosystem across all levels. This study aims to address how the spatial distribution of different plankton assemblages has changed over a multidecadal period. The multivariate structure on the CPR dataset is analysed using a technique called sparse principal component analysis. We identify functional groups of species and show that there have been changes in the ecoregions in the North East Atlantic over a multidecadal period. This technique is data-driven and can be used to identify biologically defined ecoregions based on dominant assemblages from the dataset without relying on prior knowledge. Whilst there is a change in ecoregions across time for both zooplankton and diatoms, the nature of the changes differs for the two assemblages. For zooplankton species there has been a shift in the ecoregions towards higher latitudes, implying that cold water zooplankton have moved further into arctic waters. For species that were previously restricted to the south of the region, these have been identified with increasing frequency further north. The change in spatial distribution for different species assemblages can be attributed to different factors. For example, the primary driver of zooplankton abundance across all spatial locations appears to be temperature. It is speculated that the observed northward movement of zooplankton species is a response to rising sea surface temperatures. The abundance of diatom species is instead highly correlated with the Atlantic Multidecadal Oscillation (AMO), with the spatial patterns becoming more clearly defined in its positive phase. For the diatom species, changes may be cyclic and so mean reverting to a certain extent, but for the zooplankton, continued changes can be expected if the current warming trend continues.