## 3 Results
### Secondary Production  
Considering the entire research period, interannual and seasonal variability of secondary production of _Acartia_ spp., _T. longicornis_, and _P. acuspes_ was visible. Obtained results showed that the highest average secondary production was recorded during 2006 and 2007, while the lowest  
Figure 4: Interannual (**a**) abundance and (**b**) biomass monthly mean and anomaly of _Tomona longicornis_. Figure 5: Interannual (**a**) abundance and (**b**) biomass monthly mean and anomaly of _Pseudocalanus acuspes_. values were observed from 1998 to 2000. During each of the years, the summer season was characterized by the highest values of production rates (Figure 6). During the first research period, the average production rate for _Acartia_ spp. reached the highest value in the summer of 2000, almost 4 mg C m\({}^{-2}\). In the second study period (2006-2007), there was a large variation in the production rate. In summer 2007 it was more than four times higher (\(\sim\)16 mg C m\({}^{-2}\)) than recorded in the previous year. In the last years of research, a downward tendency in production was observed, from \(\sim\)8 mg C m\({}^{-2}\) in the summer of 2010, to \(\sim\)6 mg C m\({}^{-2}\) the following year, and finally \(\sim\)4 mg C m\({}^{-2}\) in summer 2012 (Figure 6). The secondary production of _T. longicornis_ was lower than for _Acartia_ spp. In the first years of the study, from 1998 to 2000, the average maximum value in the summer fluctuated around 1 mg C m\({}^{-2}\). During the second time interval, similarly to _Acartia_ spp., significant variations in production values were observed, reaching \(\sim\)2 mg C m\({}^{-2}\) in summer 2006, and \(\sim\)6 mg C m\({}^{-2}\) a year later. In following years of research, the highest average production rates were observed in spring-summer periods. In 2010 it fluctuated between 2 mg C m\({}^{-2}\) in spring to 1.8 mg C m\({}^{-2}\) in summer, while in 2011 and 2012 noted values were 1.7 mg C m\({}^{-2}\) in spring and 2 mg C m\({}^{-2}\) in summer (Figure 6). Among the investigated copepods, _P. acuspes_ was characterized by the lowest secondary production values. In the 1998 to 2000 period, the average values of production rates of the species did not exceed 25 \(\mu\)g C m\({}^{-2}\) (summer 2000). During the second period of our research, two production peaks were observed during each year. In 2006, the first was recorded in summer with an average value of \(\sim\)175 \(\mu\)g C m\({}^{-2}\), and the second in autumn-\(\sim\)80 \(\mu\)g C m\({}^{-2}\). In 2007 these values were similar: in the summer the average production was 150 \(\mu\)g C m\({}^{-2}\) and in autumn it reached approximately 50 \(\mu\)g C m\({}^{-2}\). During the last research period even lower production rate values were observed. In 2010 and 2012, the average values did not exceed 50 \(\mu\)g C m\({}^{-2}\), and the maximum was observed in the summer of 2011, reaching 70 \(\mu\)g C m\({}^{-2}\) (Figure 6). Obtained production values show significant differences between each designated season (winter, spring, summer, and autumn) (ANOSIM, \(p\) = 0.001, global R = 0.454), which is quite clearly visible on the nMDS plot (Figure 7). There is, however, a visible connection between spring and autumn groups, which overlap partially (\(p\) = 0.001, global R = 0.089). The largest differences in production rates were recorded between summer and winter (\(p\) = 0.01, global R = 0.841). Figure 6: Mean secondary production rates (\(\pm\) standard deviation) of for (**a**) _Acartia_ spp., (**b**) _Temora longicornis_, and (**c**) _Pseudocalanus acuspes_ in the Gulf of Gdánsk during particular seasons. Generally, production rates of _Acartia_ spp. for all stages were the highest in summer season (Figure 8). Also, the range of production rates was highest in case of this taxon. _T. longicornis_ showed a similar trend, but during spring, production values were even higher than in summer, especially for the youngest copepites (CI-CIII). What is more, _T.