The spatial dimension of climate-driven temperature change in the Baltic Sea and its implication for cod and sprat early life stage survival

Throughout the last decades there has been a world-wide, general warming trend. In this study, we use the example of the Baltic Sea to resolve the overall estimated temperature trend into smaller, meso-scale spatial units. Afterwards, we investigate the spatially resolved potential impact of the temperature trend on larval survival for two important fish species, cod and sprat. We used two different sets of hydrographic data: (i) long-term temporally and depth-resolved data measured in situ originating from one geographic position and (ii) long-term horizontally resolved data, originating from a circulation model. In contrast to basin-wide integrated results, our modelling approach revealed different results related to smaller spatial scales. In shallow and coastal areas non-significant long-term temperature trends were observed. In some cases even decreasing temperature trends were found. Average distribution maps (1973–2010) of cod and sprat eggs and larvae confirmed the higher importance of central, deep basins as nursery grounds. Applying the temperature trends when calculating cod larval window of opportunity values, resulted in decreased durations of 1–3 days (~ 3–13%) in most areas. Sprat larval window of opportunity values mainly increased up to 4 days (~ 45%), indicating a potential reproduction advantage of sprat over cod under anticipated future temperature increase.

► We resolve the overall positive temperature trend in the Baltic into meso-scale spatial units and investigate the impact on larval survival for two important fish species, cod and sprat.
► In shallow and coastal areas non-significant or even negative temperature trends occurred.
► Cod larval window of opportunity values decreased by 1–3 days (~ 3–13%).
► Sprat larval window of opportunity values increased up to 4 days (~ 45%).
► Sprat will have a reproduction advantage over cod under anticipated future temperature change.