Heatwaves during low tide are critical for the physiological performance of intertidal macroalgae under global warming scenarios

Abstract

The abundance and distribution of intertidal canopy-forming macroalgae are threatened by the increase in sea surface temperature and in the frequency and intensity of heatwaves caused by global warming. This study evaluated the physiological response of predominant intertidal macroalgae in the NW Iberian Peninsula (Bifurcaria bifurcata, Cystoseira tamariscifolia and Codium tomentosum) to increased seawater temperature during immersion and increased air temperatures during consecutive emersion cycles. We combined field mensuration and laboratory experiments in which we measured mortality, growth, maximum quantum yield and C:N content of the macroalgae. Air temperature was a critical factor in determining physiological responses and survivorship of all species, whereas high seawater temperature had sublethal effects. Cystoseira tamariscifolia suffered the greatest decreases in Fv/Fm, growth and the highest mortality under higher air temperatures, whereas C. tomentosum was the most resistant and resilient species. Two consecutive cycles of emersion under atmospheric heatwaves caused cumulative stress in all three macroalgae, affecting the physiological performance and increasing the mortality. The potential expansion of the warm-temperate species B. bifurcata, C. tamariscifolia and C. tomentosum in the NW Iberian Peninsula in response to increasing seawater temperature may be affected by the impact of increased air temperature, especially in a region where the incidence of atmospheric heatwaves is expected to increase.

Experimental Assessment of Vulnerability to Warming in Tropical Shallow-Water Marine Organisms

“…Further, these responses are manifested at different biological organization levels (Freeman et al, 2013;George et al, 2018). Slower growth, changes in phenology, and lower reproductive output have been reported in corals, seagrasses, and macroalgae (Cantin and Lough, 2014;Hughes et al, 2019;Marín-Guirao et al, 2019;Román et al, 2020), whereas the effects on coral and its symbiotic relationship were often revealed as bleaching phenomenon (Robison and Warner, 2006;Hill et al, 2011). It is assumed that physiological acclimation may, to some extent, constitute the ability of thermotolerance and that physiological responses may precede the effects on growth and reproduction (Duarte et al, 2018;Gibbin et al, 2018;Jurriaans and Hoogenboom, 2020).…”

Robots Versus Humans: Automated Annotation Accurately Quantifies Essential Ocean Variables of Rocky Intertidal Functional Groups and Habitat State

“…Mass mortality events have been reported from intertidal sites across the globe (e.g., Harley, 2008;Mendez et al, 2021), and the incidence of marine heat waves is increasing (Hobday et al, 2016). It is not clear yet what the potential consequences of these mortality events are for patterns of species distribution, biodiversity, and ecosystem services (Román et al, 2020;Vye et al, 2020).…”

Extreme heatwave drives topography‐dependent patterns of mortality in a bed‐forming intertidal barnacle, with implications for associated community structure

“…Heatwaves are considered to occur when the 90th percentile of temperature, derived from historical baseline data, is exceeded for three or more days in the case of atmospheric heatwaves (Perkins & Alexander, 2013) or five or more days in the case of marine heatwaves (Hobday et al, 2016). These events have been implicated both directly and indirectly in the mortality of many marine ectotherms, among them habitat‐forming corals (Babcock et al, 2020), macroalgae (Román et al, 2020; Wernberg et al, 2013), mussels (Harley, 2008), oysters (Scanes et al, 2020), and seagrasses (Arias‐Ortiz et al, 2018), motile fish (Genin et al, 2020) and, when concomitant with drought stress, plants in terrestrial systems (Bussotti et al, 2021; De Boeck et al, 2018). The impacts of heatwaves on organisms can affect higher levels of biological organization by altering community structure (De Boeck et al, 2018; Pansch et al, 2018; Sorte et al, 2010), increasing heterogeneity, as measured by beta diversity (Robinson et al, 2019), and driving stochastic patterns in succession and community reassembly (Kreyling et al, 2011; Seifert et al, 2015).…”