We studied the effect of climate change on the potential spawning habitats of two marine small pelagic fishes. We examined the projected changes in the potential spawning habitat of the summer-spawning anchovy ( Engraulis encrasicolus ) and round sardinella ( Sardinella aurita ) in the northwestern Mediterranean by combining the regionalized projections of RCP scenarios with an existing species distribution model (SDM). The SDM was based on a separate generalized additive model for the eggs and larvae of the two species computed from ichthyoplankton sampling that was conducted with simultaneous readings of surface temperature, salinity and chlorophyll -a values as predictor variables. The SDM was projected for the 2010 decade, which represented the present-day conditions, with these environmental variables obtained from the regionalized POLCOMS-ERSEM biogeochemical model forced by the RCP 4.5 and RCP 8.5 scenarios. The comparison of the present-day projection results with the projections for the middle and final decades of the twenty-first century showed that the suitability of the spawning habitat as defined by the anchovy eggs model was likely to increase over time under RCP4.5 or decrease slightly under RCP8.5, but the habitat for anchovy larvae was likely to decrease in all cases. Loss of habitat was projected to be particularly important in the south of the study area on the Ebre River delta continental shelf. Conversely, the probability of round sardinella occurrence will significantly increase under both scenarios. The potential habitat of this species, which is of subtropical origin, is likely to shift northwards. The limitations of the existing models to extrapolate the current results to future scenarios are discussed regarding (i) the uncertainty in the projections of driving environmental variables (e.g., chlorophyll- a ), (ii) the simplified nature of the projection models, which did not capture the dynamics of the early life stages of the fish at a small scale, and (iii) insufficient consideration of important drivers, such as larval transport or retention by mesoscale hydrographic phenomena.

中文翻译：

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地中海西北部小中上层鱼类早期生命阶段的未来分布

我们研究了气候变化对两种海洋小型远洋鱼类潜在产卵栖息地的影响。我们通过将 RCP 情景的区域化预测与现有物种分布模型 (SDM) 相结合，研究了地中海西北部夏季产卵凤尾鱼 (Engraulis encrasicolus) 和圆形沙丁鱼 (Sardinella aurita) 的潜在产卵栖息地的预测变化。SDM 基于两个物种的卵和幼虫的单独广义加性模型，该模型从浮游鱼采样计算得出，同时读取表面温度、盐度和叶绿素 -a 值作为预测变量。SDM 是针对 2010 年的十年预测的，它代表了当今的条件，这些环境变量是从 RCP 4.5 和 RCP 8.5 情景强制的区域化 POLCOMS-ERSEM 生物地球化学模型中获得的。当前预测结果与 21 世纪中期和最后几十年的预测结果的比较表明，鳀鱼卵模型定义的产卵栖息地的适宜性在 RCP4.5 或在 RCP8.5 下略有减少，但在所有情况下，鳀鱼幼虫的栖息地可能会减少。预计栖息地的丧失在埃布雷河三角洲大陆架研究区南部尤为重要。相反，在这两种情况下，圆形沙丁鱼发生的概率将显着增加。该物种的潜在栖息地是亚热带起源，很有可能向北移动。讨论了现有模型将当前结果外推到未来情景的局限性，涉及（i）驱动环境变量（例如叶绿素 a）预测的不确定性，（ii）预测模型的简化性质，这确实没有在小范围内捕捉鱼类早期生命阶段的动态，以及 (iii) 对重要驱动因素的考虑不足，例如幼虫运输或中尺度水文现象的滞留。