Abstract
Global warming was reported to cause growth reductions in tropical shallow water corals in both, cooler and warmer, regions of the coral species range. This suggests regional adaptation with less heat-tolerant populations in cooler and more thermo-tolerant populations in warmer regions. Here, we investigated seasonal changes in the in situ metabolic performance of the widely distributed hermatypic coral Pocillopora verrucosa along 12° latitudes featuring a steep temperature gradient between the northern (28.5°N, 21–27°C) and southern (16.5°N, 28–33°C) reaches of the Red Sea. Surprisingly, we found little indication for regional adaptation, but strong indications for high phenotypic plasticity: Calcification rates in two seasons (winter, summer) were found to be highest at 28–29°C throughout all populations independent of their geographic location. Mucus release increased with temperature and nutrient supply, both being highest in the south. Genetic characterization of the coral host revealed low inter-regional variation and differences in the Symbiodinium clade composition only at the most northern and most southern region. This suggests variable acclimatization potential to ocean warming of coral populations across the Red Sea: high acclimatization potential in northern populations, but limited ability to cope with ocean warming in southern populations already existing at the upper thermal margin for corals.
Highlights
Global warming was reported to cause growth reductions in tropical shallow water corals in both, cooler and warmer, regions of the coral species range
Calcification rates were higher in the northern Red Sea, while they were higher in the southern Red Sea in winter (Fig. 2a)
C-I curves generally revealed an increase of calcification with light intensity, albeit with a few exceptions (Fig. 4; see C-I compared to P-I curves, Supplementary Information Fig. S2)
Summary
Global warming was reported to cause growth reductions in tropical shallow water corals in both, cooler and warmer, regions of the coral species range. We investigated seasonal changes in the in situ metabolic performance of the widely distributed hermatypic coral Pocillopora verrucosa along 126 latitudes featuring a steep temperature gradient between the northern (28.56N, 21–276C) and southern (16.56N, 28–336C) reaches of the Red Sea. Surprisingly, we found little indication for regional adaptation, but strong indications for high phenotypic plasticity: Calcification rates in two seasons (winter, summer) were found to be highest at 28–296C throughout all populations independent of their geographic location. The Red Sea, constitutes a unique natural laboratory to study the effect of different temperature and nutrient regimes in situ, including conditions considered detrimental in other geographic regions under global change scenarios[24]. We hypothesized that coral populations are adapted to prevailing local conditions, which should be reflected in a low latitudinal pattern in coral performance and a differentiation in the genetic composition from north to south
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