## 4 Discussion
In the German Southern Bay (North Sea) [36], due to the high summer temperature, higher salinity, and sufficient food concentration, _Pseudocalanus elongatus_ have three to four generations per year; similarly in the northern part of the North Sea three generations are usually described [41]. While [PERSON] [42] described four to six generations of that species in coastal waters of Northumberland (also North Sea). However, in the Southern Baltic, due to lower salinity only one full generation per year for _P. acuspes_ is observed [43]. Such a discrepancy of results is a result of the females' physiological abilities, due to slower growth and differences in the body size which are related to lower salinity. This is a well-known phenomenon concerning many organisms from the Baltic Sea, including copepods;Comparison of the estimated values of secondary production of crustaceans from other regions shows that that copepod production in the Gulf of Gdarsk is relatively low. The maximum estimated average value of _P. acuspes_ was 0.2 mgC m\({}^{-2}\) day\({}^{-1}\) in the summer of 2007, while [PERSON] [44] described it as 26.2 mg C m\({}^{-2}\) day\({}^{-1}\) in June. Such a large difference in the obtained values is probably due to differences in hydrological factors leading to differences in metabolic rates [36]. [PERSON] and [PERSON] [36] have shown that the rate of North Sea _P. elongatus_ population development is \(\sim\)3-5 times higher and the growth rate is up to 10 times higher than the _P. acuspes_ population from the Baltic Sea, which translates \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Name** & **Explains \%** & **pseudo-F** & \(\mathbf{p}\) \\ \hline Temperature (T) & 11.8 & 15.6 & 0.001 \\ Dissolved oxygen (O\({}_{2}\)) & 5.0 & 7.0 & 0.002 \\ Chlorophyll \(a\) & 4.5 & 6.6 & 0.005 \\ Salinity (S) & 0.5 & 0.8 & 0.442 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Conditional term effects of particular environmental variables for redundancy analysis (RDA). Explained variability and \(p\)-values of particular environmental variables. Figure 21: Ordination plot from redundancy analysis (RDA) on secondary production of development stages of _Acartia_ spp., _Temora longicornis_, and _Pseudocalanus acuspes_ (N—nauplii; CI–CV—copepodites of respective stage) and their relation to chlorophyll \(a\) and dissolved oxygen. directly into the higher production of _P. elongatus_. Results reported by [PERSON] [45] from the North Sea show that the secondary production of _T. longicornis_ and _Acartia clausi_ fluctuated between 22 and 16 mgC m\({}^{-2}\) between May and September. In the brackish waters of the Western Scheldt Estuary, the estimated maximum average secondary production of _Acartia tonsa_ oscillated around 25 mgC m\({}^{-3}\) in August; the second peak was recorded in September with the value of 8 mgC m\({}^{-3}\). The presence of maxima of secondary production in these months is consistent with the seasonality of production observed for these species from genus Acartia in the Gulf of Gdarsk. Production values, as in the case of _P. acuspes_, were, however, lower than those recorded in the North Sea. Differences in the value of secondary production can also be caused by the use of different calculation methods and wet mass converters for the copep from various sources of literature. In the perspective of the observed progressing warming of the Baltic Sea, which is particularly noticeable in its northern region (the air temperature in the spring increased by \(\sim\)1.5 \({}^{\circ}\)C over the period of 1871 to 2011 [46]. The ecosystem of the southern Baltic, which is much more productive and biodiverse, is more susceptible to the negative effects of such changes. Due to the currently observed restructuring of unicellular plankton and the shift of phenological phases [47], further comprehensive research on biological production in ecosystems is needed, combining the research on primary phytoplankton production and the production of zooplankton.