Long-term shifts in trait composition
The significance of long-term variability was judged from the deviance explained by the GAM curves. Only the coastal community in August did not change over time, when judging from the GAM fit on A1 and A2 as a function of year (Figs. 3c, g). In all other cases (open gulf in August, and both open and coastal areas in May), pronounced long-term variability occurred both in A1 (mostly reflecting the feeding type) and A2 (mostly reflecting the complexity).
Most conspicuous trends in functional composition were the shift towards negative values of A1 indicating a shift from filtering organisms to mixed feeders and predators in the open sea late summer communities during the 1980s to early 2000 (August: Fig. 3d), although this trend reversed in early 2000 simultaneously with a shift towards more complex organisms (until 2000). Also in both areas in May (Figs. 3a, b), the long term trend was towards increasing share of mixed or predatory feeding type.
Significant long-term variability was also evident in A2 values. In the spring communities (May), the prominent long-term shift in complexity was towards higher share of simpler organisms (Figs. 3e, f). In August, the functional composition of both coastal and open area communities remained almost unchanged.