Abstract
Climate change is driving range contractions and local population extinctions across the globe. When this affects ecosystem engineers the vacant niches left behind are likely to alter the wider ecosystem unless a similar species can fulfil them.Here, we explore the stress physiology of two coexisting kelps undergoing opposing range shifts in the Northeast Atlantic and discuss what differences in stress physiology may mean for future niche filling.We used chlorophyll florescence (F v /F m) and differentiation of the heat shock response (HSR) to determine the capacity of the expanding kelp, Laminaria ochroleuca, to move into the higher shore position of the retreating kelp, Laminaria digitata. We applied both single and consecutive exposures to immersed and emersed high and low temperature treatments, replicating low tide exposures experienced in summer and winter.No interspecific differences in HSR were observed which was surprising given the species’ different biogeographic distributions. However, chlorophyll florescence revealed clear differences between species with L. ochroleuca better equipped to tolerate high immersed temperatures but showed little capacity to tolerate frosts or high emersion temperatures.Many patterns observed were only apparent after consecutive exposures. Such cumulative effects have largely been overlooked in tolerance experiments on intertidal organisms despite being more representative of the stress experienced in natural habitats. We therefore suggest future experiments incorporate consecutive stress into their design.Climate change is predicted to result in fewer ground frosts and increased summer temperatures. Therefore, L. ochroleuca may be released from its summer cold limit in winter but still be prevented from moving up the shore due to desiccation in the summer. Laminaria ochroleuca will, however, likely be able to move into tidal pools. Therefore, only partial niche filling by L. ochroleuca will be possible in this system as climate change advances. A plain language summary is available for this article.
Highlights
The world’s oceans have warmed by 0.11°C per decade for the last 40 years while short term rapid increases in ocean and aerial temperatures have increased in frequency and duration (Christidis, Stott, Brown, Hegerl, & Caesar, 2005; Coumou & Rahmstorf, 2012; Hartmann, Tank, & Rusticucci, 2013; Lima & Wethey, 2012; Meehl & Tebaldi, 2004; Seneviratne et al, 2012)
We explore the stress physiology of two coexisting kelps undergoing opposing range shifts in the Northeast Atlantic and discuss what differences in stress physiology may mean for future niche filling
Only partial niche filling by L. ochroleuca will be possible in this system as climate change advances
Summary
The world’s oceans have warmed by 0.11°C per decade for the last 40 years while short term rapid increases in ocean and aerial temperatures (heatwaves) have increased in frequency and duration (Christidis, Stott, Brown, Hegerl, & Caesar, 2005; Coumou & Rahmstorf, 2012; Hartmann, Tank, & Rusticucci, 2013; Lima & Wethey, 2012; Meehl & Tebaldi, 2004; Seneviratne et al, 2012). Optimal growth and maximal survival temperatures of macroalgae are well studied (Bolton & Anderson, 1987; Bolton & Lüning, 1982; Hargrave et al, 2016; Lüning, 1984; Lüning & Freshwater, 1988; Orfanidis, 1991; Simonson, Metaxas, & Scheibling, 2015; Tom Dieck, 1992) but the effects of consecutive low tide exposures remain relatively unknown (but see Pereira et al, 2015) This is surprising as low tide stress has long been known to be important in determining the vertical and latitudinal distributions of intertidal organisms (Dring, 1982; Evans, 1948) and increases in aerial temperatures can cause shifts in macroalgae distributions (Harley & Paine, 2009; Harley et al, 2012; Martínez et al, 2012; Ugarte, Critchley, Serdynska, & Deveau, 2009). Understanding tolerances to consecutive low tide stress of these two species will provide important insight into how climate change can alter range edge dynamics whilst providing foresight into the future species composition of kelp- dominated communities on Northeast Atlantic rocky shores
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