Maternal, temperature, and seasonal effects on yolk-sac larvae of Atlantic herring Clupea harengus in the western Baltic Sea

In marine fishes that spawn at specific times of the year, maternal effects interact with seasonal abiotic factors to influence offspring phenotypes that can affect growth, development, and survival of the early life stages. The relative importance of maternal versus abiotic processes throughout ontogeny is unclear. We incubated the progeny of 22 Atlantic herring Clupea harengus females from either early-, mid-, or late-spring spawning periods at both early- (7 °C) and late-season (13 °C) in situ temperatures. After yolk-sac larvae had hatched, changes in yolk sac area, notochord length, body depth, somatic body area, and cases of deformities were tracked until the point-of-no-return (beyond which starvation is irreversible), also allowing somatic growth rate and yolk utilization efficiency to be estimated. We then quantified the contributions of maternal effects, incubation temperature, and seasonal effects on offspring traits. Among newly-hatched larvae, the variance in body area was explained by temperature (18 %) and seasonal (12 %) but not maternal effects. As yolk-sac larvae reached maximum size, egg size and individual females together accounted for more than two-thirds (77 %) of the variance in body area, while seasonal and temperature effects did not explain additional variance. The maternal effects were, however, unrelated to female size (total length of 26.0–31.3 cm). As a result, size classes of females matched poorly (14–36 %) with those of egg and yolk-sac larval stages, while size classes of eggs matched well with those of maximum-sized larvae (59 %) and less with those of newly-hatched larvae (36 %). Furthermore, yolk-sac larvae from later in the season or from the 13 °C treatment had a relatively longer post-hatch, free-swimming yolk-sac larval stage with respect to the whole yolk period. Yolk utilization efficiency was similar and deformity percentage was low (<5.3 %) across seasonal timing and temperature treatments. In conclusion, our study revealed that the seasonal effects on offspring size at the transition period from endo- to exogenous feeding were attributed to differences in egg size, with herring females spawning earlier in the season producing larger eggs.