MEPS 482:81-92 (2013)  -  DOI: https://doi.org/10.3354/meps10266

ABSTRACT: We studied the size, distribution and viability of the egg bank of the non-indigenous cladoceran Cercopagis pengoi in different parts of the Baltic Sea. During summer, C. pengoi can attain high densities by parthenogenetic reproduction, but during most of the year, it survives as sexually produced resting eggs in bottom sediments, and yearly recruitment is dependent on the survival and hatching of these eggs. Sediments were sampled at open sea sites in the Gulf of Finland, the Gulf of Bothnia and the Baltic Proper from 2007 to 2009. C. pengoi eggs were most abundant (up to 26 × 10³ m^-2) in the Gulf of Finland, whereas farther north in the Gulf of Bothnia, the numbers were lower (up to 3 × 10³ m^-2). This reflects the invasion history of C. pengoi in the Baltic Sea, and is in agreement with its average yearly planktonic abundance. Hatching success varied substantially between sites, but at least some eggs hatched from all sites, even those suffering from persistent anoxia. However, as the incubation time needed for hatching was long (average 7 to 74 d), and some of the viable eggs were buried deep in the sediment, recruitment from the open sea sediments is possibly low, especially in the Gulf of Bothnia. C. pengoi recruitment in spring or summer originates likely from coastal sites.

KEY WORDS: Fishhook waterflea · Non-indigenous species · Resting eggs · Diapause · Hatching success · Sediments · Gulf of Finland · Gulf of Bothnia