Effekten av salinitet, temperatur och födotillgång på hoppkräftan Eurytemora affinis ekologi

Climate change has already led to considerable change in the properties of the Baltic Sea. As it progresses, the Baltic Sea will likely experience changes in its temperature and salinity and an increase in eutrophication. Therefore, it is necessary to understand how species are affected by environmental factors, especially those that are projected to change. Zooplankton is the most abundant multicellular organism on earth, and among these, the copepod is the most common. In the Baltic Sea, Eurytemora affinis is among the most important copepods, and further knowledge is needed to further our understanding of E. affinis in a changing climate. In the present thesis, I conducted a field study to measure the body sizes of two E. affinis populations to determine to what extent temperature, salinity, and chlorophyll a (Chl. a) affected E. affinis ecology. Populations were sampled over approximately four months in two areas in the western Gulf of Finland with contrasting characteristics in terms of salinity, temperature, and Chl. a concentration. The study showed that E. affinis was not significantly affected by salinity but experienced significant variation in body size in relation to temperature and Chl. a. Individuals were, additionally, larger in the early summer. Interestingly, most of the variation in body size was a product of the sampling site, and the individuals sampled in the area with more extreme conditions, Pojoviken Bay, were significantly larger (151.4 μm or 21.9%) than those sampled in the other area, Storfjärden. The results strengthened the notion that E. affinis is robust against climate change, as the environmental factors had a relatively small effect. Furthermore, the results indicated that there might be unmeasured variables behind the body size variation between populations. The variation could be due to food availability acting as a buffer against the environmental factors, or conceivably due to differences in food quality. This difference could also be because of genetic adaptations, and the Pojoviken Bay population could be a sibling species. Further studies, such as multigenerational experiments and genetic analyses, are needed to determine what lies behind the substantial body size differences between these two areas