Temperature increase due to climate change has caused shifts in the range distribution of several organisms globally. In coastal intertidal environments most organisms have an amphibious life cycle and their poleward range limits may be delimited by their thermal tolerance during the pelagic larval stages. Fiddler crabs are key species in intertidal environments and their early larval stages occur in coastal waters. We evaluated the mean and monthly minimum sea surface temperature (SST) gradient over the South American coast and compared it to the minimum and maximum critical thermal limits (CT_min and CT_max) of the first larval stage of eight fiddler crab species to assess whether temperature delimits their distributional ranges. We found a clinal decrease in mean SST of 0.28 °C per latitudinal degree along the distribution of fiddler crabs in South America. Cold tolerance differed among the larvae of fiddler crab species, which corresponds to the latitudinal temperature gradient observed in their poleward range limits. Thus, our results suggest that cold water temperature can define the poleward range limits of South American fiddler crabs. The CT_max cannot explain the northern poleward range limits of the fiddler crabs. Fiddler crabs larvae showed a similar tolerance to high temperatures (mean 40.5 °C) regardless of species (except Leptuca uruguayensis) and these are higher than environmental temperatures observed in South America. We also observed an increase in mean SST of 0.9 °C in the last 37 years. This increase in water temperature may explain the recent poleward range expansion of one South American fiddler crab species, Leptuca cumulanta. Therefore, we showed that differential thermal responses at the early larval stage have consequences on the geographic range limits of the fiddler crab species. Our findings allow us to hypothesize that fiddler crabs’ poleward range limits may expand to higher latitudes in the future due to global warming.

气候变化导致的温度升高导致全球几种生物的范围分布发生变化。在沿海潮间带环境中，大多数生物具有两栖生命周期，它们的极地范围限制可能受远洋幼虫阶段的热耐受性限制。招潮蟹是潮间带环境中的关键物种，它们的早期幼虫阶段发生在沿海水域。我们评估了南美海岸的平均和每月最低海面温度 (SST) 梯度，并将其与最小和最大临界热极限（CT _min和 CT _max) 的八个招潮蟹物种的第一个幼虫阶段，以评估温度是否界定了它们的分布范围。我们发现，沿着南美洲招潮蟹的分布，每纬度度数的平均海温在临床上下降 0.28 °C。招潮蟹幼虫的耐寒性不同，这与在极地范围限制中观察到的纬度温度梯度相对应。因此，我们的结果表明冷水温度可以定义南美招潮蟹的极地范围限制。CT_最大值不能解释招潮蟹的北极范围限制。招潮蟹幼虫对高温（平均 40.5 °C）表现出相似的耐受性，无论物种如何（Leptuca uruguayensis除外）) 并且这些温度高于在南美洲观察到的环境温度。我们还观察到在过去 37 年中平均 SST 增加了 0.9 °C。水温的这种升高可以解释最近一种南美招潮蟹物种Leptuca cumulanta向极地扩张的原因。因此，我们表明早期幼虫阶段的差异热响应会对招潮蟹物种的地理范围限制产生影响。我们的发现使我们能够假设，由于全球变暖，招潮蟹的极地范围限制可能会在未来扩展到更高的纬度。