US Long-Term Ecological Research Network

Increased frequency and/or severity of drought conditions and associated reductions in lake levels are predicted outcomes of climate change in many regions. Consequently, current and previous droughts may foreshadow potential effects of climate change on aquatic communities. Little Rock Lake experienced a 1.3-m reduction in lake level during a recent multiyear drought (Fig. 1a, blue line). This reduced the amount of coarse woody habitat (CWH) submerged in the littoral zone, which is critical habitat for many fish species. We monitored the fish community response throughout the decline in lake level and CWH reduction in 2001–2005 and 2007–2009 (Fig. 1a gray boxes). Perch were always present when CWH was abundant, but the chance of detecting prey fish was reduced to 50/50 with a 25% reduction in CWH and to zero after a 50% reduction in CWH (Fig. 1b). This was likely due to an increase in predator-prey encounter rates. Consequently, predators quickly ran out of prey fish and had to switch to less energetic prey items, which meant slower growth. When CWH (and prey) is abundant, predators take 6 years to reach the legal harvest minimum length of 14”. When CWH is low, however, predators would take 20 years to reach the same length. This result highlights a critical additional consequence of climate change (habitat availability) in addition to thermal and oxygen regimes.

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