Abstract
Recently, increased attention is being paid to the importance of environmental history in species’ responses to climate-change related stressors, as more variable and heterogeneous environments are expected to select for higher levels of plasticity in species tolerance traits, compared to stable conditions. For example, organisms inhabiting environments with highly fluctuating thermal regimes might be less susceptible to the increasing frequency and intensity of marine heatwaves (MHWs). In this study, we assessed the metabolic and calcification responses of the rhodolith-bed forming Phymatolithon lusitanicum, from a coastal region that is strongly influenced by frequent changes between upwelling and downwelling conditions, to a simulated MHW scenario, with and without prior exposure to a moderate thermal stress. This allowed determining not only the influence of the species’ long-term thermal history on its resilience against MHWs, but also the rhodoliths capacity for short-term thermal stress memory and its importance during posterior MHW-exposure. Our findings indicate that the rhodoliths experienced negative impacts on daily net primary production (DNP) and calcification (DNC) during the MHW. The effect on the former was only temporary at the beginning of the MHW, while DNC was highly impacted, but exhibited a quick recovery after the event, suggesting a high resilience of the species. Furthermore, prior exposure to a moderate temperature increase, such as those occurring frequently in the natural habitat of the species, mitigated the effects of a subsequent MHW on DNP, while promoting a faster recovery of DNC after the event. Thus, our findings (1) support the hypothesis that benthic organisms living in nearshore habitats may benefit from the natural short-term temperature fluctuations in these environments with an increased resistance to MHW impacts and (2) provide first-time evidence for thermally induced stress memory in coralline algae.
Highlights
Benthic organisms that are sessile in nature cannot escape, but must respond to or endure fluctuating surroundings and diverse environmental challenges
Our results demonstrate that a fluctuating environment preconditions the free-living coralline species P. lusitanicum to cope better with thermal stress, such as that experienced during marine heatwaves (MHWs)
While the rhodoliths may experience some negative impacts on daily net primary production and calcification during a MHW event, the effect on DNP are rather short-lived and the larger impact on daily net calcification (DNC) is compensated by a high rate of recovery, suggesting a high resilience of the species
Summary
Benthic organisms that are sessile in nature cannot escape, but must respond to or endure fluctuating surroundings and diverse environmental challenges. Natural environmental variability can essentially influence the responses of marine organisms to changing conditions, such as related to the ongoing climate change (Boyd et al, 2016), as (1) marine provinces differ strongly in their environmental heterogeneity (Zhao et al, 2020), (2) organisms from more heterogeneous environments may have an increased phenotypic plasticity (Vargas et al, 2017; Miller et al, 2020), and (3) the inclusion of natural environmental fluctuations in experimental climate-change simulations has been shown to yield different outcomes from those that do not (Oliver and Palumbi, 2011; Cornwall et al, 2013, 2018; Roleda et al, 2015; Schoepf et al, 2015; Britton et al, 2016; Johnson et al, 2021) In view of the latter, a common expectation for studies, examining the effects of climate change-related stressors, is that environmental heterogeneity and variability will select for higher levels of plasticity in specific tolerance traits compared to stable environments. The effects of highly fluctuating thermal regimes on organisms’ thermotolerance received increased attention in recent years (Putnam et al, 2010; Oliver and Palumbi, 2011; Schoepf et al, 2015; Safaie et al, 2018; Hughes et al, 2019; McCoy and Widdicombe, 2019)
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