Pelagic respiration in the coastal zone of the southern Baltic Sea

Respiration measurements were carried out year round at two stations located in the coastal zone of the southern Baltic Sea. Study sites differed with their characteristics: first one was located in the coastal zone of the Gulf of Gdańsk near the town of Sopot (54°27′ N, 18°35′ E), second one was located in the coastal waters of the southern Baltic Sea near the town of Ustka (54°35′ N, 16°50′ E). The study reports a range of respiration rates and mean annual values, which are useful for development and parameterization of biogeochemical models. Respiration was estimated as the decrease in oxygen concentration in water confined in glass bottles. The mean annual respiration rate was 0.37 mgO2 l−1 d−1 at the study site in Sopot and 0.18 mgO2 l−1 d−1 at the study site in Ustka. In Ustka, respiration rates depended on temperature (R2 = 0.77, p = 0.0008), whereas in Sopot there was no such statistically significant dependence. At both study sites, there was no significant relationship between respiration rates and bacterial abundance. Diel oxygen consumption was compared with that measured during prolonged, five-day incubation period to detect excess resources capable of maintaining respiration rates. In Sopot respiration rates decreased during the five-day incubation period, whereas at study site in Ustka, they were generally stable during such incubation, what suggested that utilization of excess resources was prevented by top-down control of grazers.