High thermal plasticity and vulnerability in extreme environments at the warm distributional edge: the case of a tidepool shrimp

Abstract

1Climate change threatens the resilience of species, especially at their warm 2 distributional edge in extreme environments. However, not much is known about the 3 thermal vulnerability of marine intertidal species at this edge. We investigated the 4 thermal vulnerability of the tidepool shrimp, Palaemon elegans in the fast-warming 5 southeastern Mediterranean, its warm distributional edge. Tidepool organisms 6 experience strong and fast thermal fluctuations. This might make them more resilient 7 to change, but also bring them closer to their thermal limits during extreme conditions. 8To test the shrimp's resilience, we tested three hypotheses: (1) P. elegance in the 9 southeast Mediterranean has higher critical thermal maximum (CTMax) than in cooler 10 regions, (2) the shrimp possess seasonal acclimatization, but (3) long exposure to 11 extreme summer temperatures might erode its thermal performance making it 12 vulnerable to future climate change. We characterized the shrimp's thermal 13 environment and population dynamics, determined CTMax and tested diverse 14 physiological performance attributes (respiration, digestion, activity, growth) under a 15 wide range of temperatures during winter and summer. P. elegans has a wide optimum 16 performance range between 20-30°C during summer and its CTMax is 38.1°C, higher 17 than its Atlantic counterparts. However, its warming tolerance is only 0.3°C, indicating 18 low capacity for dealing with further warming in pools compared to northeast Atlantic 19 populations that have wider tolerance. Prolonged exposure to current mean summer 20values in open water (~ 32°C) would also significantly reduce its performance and 21 increase mortality. This suggests that its population viability may be reduced under 22 continuous regional warming and intensification of extreme events. 23 24