Changes in cladoceran assemblages from tropical high mountain lakes during periods of recent climate change

The Andes Mountain range of South America is one of the most rapidly warming regions in the world. Alpine lakes from Cajas National Park (Ecuador) have shown evidence of increased thermal stratification and associated shifts in algal communities in recent decades, consistent with regionally warmer air temperatures and reduced wind speeds. Here, we use paleolimnological approaches to examine the impacts of recent climate change on Cladocera (Crustacea, Branchiopoda) in three equatorial alpine lakes. Each lake experienced a shift in abundance from the small pelagic grazer Bosmina spp. to larger Daphnia spp. In two of the lakes, Daphnia spp. increased from an average of ~5 to 35–40% relative abundance within the last ~20 years. Meanwhile, in the third lake, Daphnia spp. increased to ~50% relative abundance in the ~1970s, but subsequently declined to background levels within the following decade. We show that cladoceran assemblages have undergone marked shifts during a period of rapid climate change in this region, but unlike comparable work on algal indictors, the response has been more complicated. We conclude that climate is likely affecting these keystone aquatic invertebrates, and may begin to impact higher level predators such as fish, which often rely on cladocerans as a food source.