Exposure to simulated heatwave scenarios causes long-term reductions in performance in Saccharina latissima

Abstract

Kelps are important foundation species in many cold-temperate coastal systems, and the loss of these organisms is a threat to ecosystem structure and function. The abundance of sugar kelp Saccharina latissima has recently declined in Northern Europe, which has been explained by increasing water temperature. We tested heat tolerance of sugar kelp exposed to simulated heatwave scenarios of 15, 18, 21 and 24°C for 3 wk, followed by a 2 wk recovery period at 15°C. Growth rate and photosynthetic performance decreased significantly with increasing temperature, while mortality remained low among treatments except at 24°C, where > 90% of the algae died within a few days. Although exposure to 18 and 21°C had limited effect on mortality, kelps exposed to these temperatures had negative growth and continued to show impaired photosynthesis during the subsequent recovery period. Reductions in growth were strongly correlated to reduced carbon acquisition and, hence, photosynthetic performance, which was strongly correlated to heat-related changes in pigmentation. We suggest that reduced performance after exposure to elevated but non-lethal temperatures was caused by oxidative stress resulting from a discrepancy between light absorption and photosynthesis. Our results show that exposure to high but sub-lethal temperatures can have significant long-term effects, which may cause loss of biomass and leave sugar kelp susceptible to other stressors.

Elevated Temperature Affects Phenotypic Plasticity in the Bull Kelp (Nereocystis luetkeana, Phaeophyceae)

“…In kelps, new blade growth, initially narrow at the intercalary meristem at the base of the blade, widens as it is pushed distally (Kain Jones 1987). Elevated temperatures are known to physiologically disrupt kelps (Simonson et al 2015, Nepper-Davidsen et al 2019, and an inability to widen could indicate a disruptive effect of thermal stress on cell division or expansion perpendicular to the long axis of the blade. In low-flow conditions, where the development of wider blades is favored, being unable to widen would be especially conspicuous.…”

“…2015, Nepper‐Davidsen et al. 2019), and an inability to widen could indicate a disruptive effect of thermal stress on cell division or expansion perpendicular to the long axis of the blade. In low‐flow conditions, where the development of wider blades is favored, being unable to widen would be especially conspicuous.…”

Seascape Genomics of the Sugar Kelp Saccharina latissima along the North Eastern Atlantic Latitudinal Gradient

“…“Seascape genetics” aims to uncover signs of local adaptive responses at both historical and recent time scales. This is of particular relevance considering that there is increasing evidence that the physical and biochemical changes in the seascape due to global warming are threatening the long-term persistence of many kelp forests, especially at the marginal areas of their distribution [ 24 , 82 ]. Here, we examined how geographical variation in three major abiotic parameters (temperature, salinity, and light) might interact with the genetic diversity of S. latissima and assessed how this may have influenced historical and recent local adaptive processes.…”

Seascape Genomics of the Sugar Kelp Saccharina latissima Along the North Eastern Atlantic Latitudinal Gradient

“…"Seascape genetics" aims to uncover signs of local adaptive responses at both historical and recent time scales. This is of particular relevance considering that there is increasing evidence that the physical and biochemical changes in the seascape due to global warming are threatening the long-term persistence of many kelp forests, especially at the marginal areas of their distribution [21,82]. Here, we examined how geographical variation in three major abiotic parameters (temperature, salinity and light) might interact with the genetic diversity of S.…”