Abstract
The small pelagic sprat (Sprattus sprattus) is a key ecologic player in the Baltic Sea. However, there is long-term variability in recruitment which is thought to be influenced by fluctuations in abiotic and biotic conditions experienced during the early life stages. This study concentrates on the influence of different ambient salinities on sprat egg development, egg buoyancy and survival as well as early yolk sac larval morphometric traits. Egg buoyancy significantly decreased with increasing salinity experienced during fertilization and/or incubation experiments. Field egg buoyancy measurements in 2007 and 2008 exhibited annual and seasonal differences in specific gravity, potentially associated with changes in adult sprat vertical distribution. Neither egg development time nor the duration of the yolk sac phase differed among salinity treatments. At eye pigmentation, larval standard length exhibited high variance among individuals but did not differ among treatments. The largest ecological impact of salinity experienced during spawning was the modification the buoyancy of eggs and yolk sac larvae, which determines their vertical habitat in the Baltic Sea. There are strong thermo- and oxyclines in the Baltic Sea, and thus salinity can indirectly impact
Highlights
The population dynamics of sprat (Sprattus sprattus) are driven by large variability in recruitment caused by fluctuations in abiotic (Grauman and Yula, 1989; Köster et al, 2003) and biotic (e.g. Köster and Möllmann, 2000) conditions experienced by early life stages (ELS)
For the situation of sprat in the Central Baltic Sea, reduced egg development time could be beneficial for survival due to a high predation pressure on eggs by clupeids (Köster and Möllmann, 2000)
Egg buoyancy thresholds may be exceeded if winddriven advection transports eggs eastward into low salinity regions where eggs would sink and die due to low oxygen conditions at depth
Summary
The population dynamics of sprat (Sprattus sprattus) are driven by large variability in recruitment caused by fluctuations in abiotic (Grauman and Yula, 1989; Köster et al, 2003) and biotic (e.g. Köster and Möllmann, 2000) conditions experienced by early life stages (ELS). Baltic sprat can have a prolonged spawning season lasting from March to August (Aro, 1989) and display diel vertical migration through thermo- and haloclines (Stepputtis, 2006). Due to these factors, different batches of eggs probably experience markedly different abiotic conditions. Previous studies have quantified the influence of temperature on the survival and development rate of sprat eggs and larvae (Nissling, 2004; Petereit et al, 2008), no studies have evaluated the impact of salinity The latter is surprising given that salinity has been shown to be a critical factor influencing the reproductive success of other Baltic Sea fish species, such as Atlantic cod (Gadus morhua), due to the impacts of salinity on egg buoyancy (Nissling and Westin, 1991b)
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