Phenology of flight of сhironomid flies (Diptera: Chironomidae) in Taganrog Bay of the Sea of Azov

Being predominant in the benthic communities of the north-east part of the Taganrog Bay, Chironomidae determine seasonal shifts in quantitative characters of zoobenthos in this area. Changes in chironomids’ abundance are related to their turning from larval into imaginal stage, therefore studying fluctuations of their quantity and biomass in marine ecosystems is of certain interest. Present research was carried out in spring and summer periods of 2011–2012 at four stations in the Don river estuary and the adjacent part of the Taganrog Bay, within the depth range of 2.7 to 3.4 m. Sampling was performed by the modified Petersen grab with sampling surface 0.034 m2; three samples at each station were taken. Chironomid larvae were predominant in all studied sites. Number of generations and therefore number of recurrent seasonal fluctuations of biomass and abundance are determined mainly by the sum of active temperatures. Not only weather characteristics of regarded period play important role, but also those of the previous period as well. In 2011 early summer, the clear decrease of abundance and biomass was distinguished in population dynamics of the genus Chironomus. Winter generation imago’s flight started at reaching average daily temperature of water near +7 °C, near-bottom layer temperature being +5... 6 °C. Solitary specimens were registered even at water temperature +4... 5 °C. Mass flight was recorded in the end of April – first days of May, at warming of water over 8–9 °C. Summer generation’s flight extended for all the summer period. In winter period of 2011–2012, abnormally heavy ice conditions occurred in the Sea of Azov. Due to this, time of imago flight shifted to May and its duration reduced. In April 2012, low quantity and biomass of Chironomidae, not typical for this period, were recorded. At low temperature, larvae of large thermophilic chironomids including imago of the genus Chironomus failed to complete their development cycle due to metabolism decrease; part of individuals possibly died due to the lack of food in a cold period.