Population dynamics and ecoparasitological surveys of Corophium volutator in coastal waters in the Bay of Mecklenburg (southern Baltic Sea)

The population dynamics of Corophium volutator (Pallas, 1766) were studied at 2 stations in virtually tideless water in the Bay of Mecklenburg (southern Baltic Sea). Particular attention was given to temperature, the main factor affecting reproductive and development processes. Infestation by parasites was one of various factors which was considered for explanation of variations in abundance in the course of the year. At both stations 2 generations were present during the reproduction period. These were called the spring generation and summer generation (with cohorts I and II) in accordance with their occurrence. The greatest increase in abundance coincided with the appearance of the spring generation. Most of the overwintering individuals originated from summer generation I in both populations. Although reproductive activity was the same at both stations, the variations in abundance were completely different; the population at one station collapsed almost completely. Ecoparasitological analysis revealed that mortality in the extremely heavily infested spring generation was unusually high, and this had a direct impact on subsequent reproductive processes. The much more severe infestation at one station than at the other was found to be caused by a 4-fold higher abundance of the wadden snail Hydrobia spp., which is the primary intermediate host of the larval trematodes found in C. volulator in these waters. The studies showed that parasite infestation is a factor that can affect population development. Therefore, ecoparasitological phenomena should be taken into account when interpreting data relating to population dynamics.