Plankton are the microscopic plants and animals that inhabit the pelagic realm and form the base of the entire marine food web. The word plankton comes from the Greek planktos meaning drifter as plankton cannot swim against a tide or current. There are two main types of plankton – phytoplankton which are plants and zooplankton which are animals. The Plankton assessment is based on data from a number of sources including the Marine Scotland Science Scottish Coastal Observatory (SCObs) fixed point sites, the Marine Biological Association Continuous Plankton Recorder (CPR) Scottish survey routes, the Lorn Pelagic Observatory and the SEPA WFD monitoring programme. These show that significant changes have occurred in the plankton community in some marine regions in recent decades.