Development of Acartia bifilosa (Copepoda: Calanoida) eggs in the northern Baltic Sea with specialreference to dormancy

First evidences of <i>Acartia bifilosa</i> resting eggs in sediments of the Urdaibai estuary (Bay of Biscay): abundance and hatching success

“…However, we recorded smooth-surface eggs considered subitaneous but not the morphologically distinct spiny form described by Castro-Longoria and Williams (1999) as the diapause egg type for A. bifilosa. Katajisto (2003) deduces that A. bifilosa does not produce diapause eggs in the Baltic Sea, and suggests that this species presents different strategies consisting in producing diapause eggs only in areas where the planktonic population is totally absent at any time of the year. According to this, the selection pressure for the production of diapause forms in A. bifilosa will be lacking in the Urdaibai estuary, where a perennial species is found.…”

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“…Accumulation of the dormant stages of plankton in the seafloor not only buffers against unfavorable periods or catastrophic events but also substantially extends the generation time and modifies the outcome of selection in plankton communities (Ellner and Hairston 1994). Emergence from the seafloor is strongly species-specific and often seasonally restricted, but it may essentially contribute to pelagic populations, as demonstrated for copepods (De Stasio 1990;Katajisto et al 1998;Hairston et al 2000) and cladocerans (Kankaala 1983;Onbé 1985;Cá ceres 1998). Investment in a benthic egg or seed bank is not, however, a risk-free strategy: feeding and burrowing of zoobenthos may strongly influence the dormant life stages of plankton (e.g., Albertsson and Leonardsson 2001;Giangrande et al 2002;Viitasalo 2007).…”

“…The two most abundant calanoid copepods, Acartia bifilosa and Eurytemora affinis, are present in plankton throughout the year, albeit in low numbers in winter, whereas benthic resting eggs form the only quantitatively important means of overwintering in cladocerans and rotifers, which practically disappear from the water column in late autumn (Viitasalo et al 1995). The Baltic populations of A. bifilosa rely solely on the production of subitaneous eggs (Katajisto 2003), capable of hatching whenever conditions are favorable. The benthic eggs of E. affinis and all rotifers and cladocerans, in turn, are of the diapause type (i.e., they must complete a refractory phase before the development may be resumed; Kankaala 1983;Katajisto 2006).…”

“…The Baltic populations of A. bifilosa rely solely on the production of subitaneous eggs (Katajisto 2003), capable of hatching whenever conditions are favorable. The benthic eggs of E. affinis and all rotifers and cladocerans, in turn, are of the diapause type (i.e., they must complete a refractory phase before the development may be resumed; Kankaala 1983;Katajisto 2006).…”

“…A. bifilosa lays and releases eggs solitarily in the water, most of which probably reach the bottom (Katajisto et al 1998). Females in E. affinis, in turn, carry subitaneous eggs with them until hatching, and only diapause eggs, produced later in the season, sink to the seabed.…”