High individual growth and mortality rates of herring Clupea harengus membras and goby Pomatoschistus
spp. larvae were observed in the estuarine habitat of the Gulf of Riga, Baltic Sea. Both instantaneous
mortality (0.76e1.05) as well as growth rate (0.41e0.82 mm day1) of larval herring were amongst
highest observed elsewhere previously. Mortality rates of goby larvae were also high (0.57e1.05), while
first ever data on growth rates were provided in this study (0.23e0.35 mm day1). Our study also evidenced that higher growth rate of marine fish larvae did not result in lower mortalities. We suggest that
high growth and mortality rates primarily resulted from a rapidly increasing and high (>18 C) water
temperature that masked potential food-web effects. The explanation for observed patterns lies in the
interactive manner temperature contributed: i) facilitating prey production, which supported high
growth rate and decreased mortalities; ii) exceeding physiological thermal optimum of larvae, which
resulted in decreased growth rate and generally high mortalities. Our investigation suggests that the
projected climate warming may have significant effect on early life history stages of the dominating
marine fish species inhabiting shallow estuaries.