Conclusions
The essence of using functional traits is to characterize organisms by properties that capture essential aspects of diversity, rather than to analyse individual species. In the current paper, we have used traits to determine how the zooplankton community is associated with environmental gradients in a highly eutrophicated gulf. The benefit of looking into traits have revealed systematic changes in the current community – the long-term decrease of copepods, increase of rotifers and dominance shift. On the other hand, the proportion of simpler organisms have increased in spring, whereas the proportion of more complex organisms have increased in late summer. Salinity did not have a clear effect on our functional traits, which could be due to the fairly small fluctuations in the Baltic Sea salinity. Neither oxygen concentrations affected traits significantly, which may depend on the fact that oxygen was fairly stable in the used time series; planktonic organisms are also very much able to move away from hypoxic areas. Our data also suggest that organisms of low complexity will benefit from the climate-induced warming of the environment, whereas salinity and oxygen levels seem to have minor effect on the planktonic community in the Baltic Sea, here exemplified by Gulf of Riga basin.