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Ocean warming (OW) and marine heatwaves (MHWs) rapidly transform marine
ecosystems, especially when they impact keystone or foundation species.
Foundation species such as kelps, fucoids and corals are highly sensitive
to heat stress, which threatens the future of temperate seaweed forests
and tropical reefs. However, functioning and resilience of these systems
also rely on the less conspicuous coralline algae, whose thermal
tolerances have gone largely untested. Here, we examined the sensitivity
of four temperate coralline algal morphotypes from three different species
to four realistic present-day and future OW and MHW scenarios (ambient
[16°C constant]; ambient+MHW [16°C baseline + a symmetric two-week
heatwave with a peak intensity of 18.7°C]; future [18.7°C constant];
future+MHW [18.7°C baseline + a symmetric two-week heatwave with a peak
intensity of 21.4°C]). Photo-physiology (e.g., Fv/Fm) and calcification
physiology (e.g., proxies for calcifying fluid saturation state Ω CF )
were generally unaffected by the treatments, implying a high
thermo-tolerance of our study species compared to other important marine
foundation species. We ascribe this mainly to their photosynthetic
apparatus that, unlike in other photoautotrophs, continued to function
under heat stress. Experimental evidence presented here and elsewhere
implies that coralline algae are likely to continue to play their crucial
ecological roles in a warming ocean. Yet, such predictions are fraught
with uncertainty due to the substantial gaps in our knowledge. We attempt
to highlight some of these gaps and aim to present potential physiological
underpinnings of their thermo-tolerance.
127 views reported since publication in 2022.