Trends in functional group richness and trait composition
The simplest approach to defining functional diversity is thefunctional group richness (FGR). To calculate the FGR for the samples, species were divided into basic functional groups . Functional groups were defined by combining higher level taxonomic classification (mostly Class) with the feeding mode. The prominent groups Cladocera and Copepoda were further classified into ‘large’ and ‘small’. Values of a relatively simple set of functional traits was assigned to more frequently encountered zooplankton taxa (species or higher) in order to analyse the shifts in functional composition of communities in further detail (Table 1).
Table 1 . Functional traits used in this paper, and organization of trait table. Trait values are shown for 10 most frequent taxa in Gulf of Riga. “Complexity” is a four-level proxy for the complexity (body size, reproduction) of the organism: ‘1’ – rotifers; ‘2’ – cladocerans, ‘3’ – copepods; ‘4’ – other (more complex) organisms (e.g. Polychaeta, Meroplankton, Mollusca). Filtering and predation: 1 = yes, 0 = no.