Impact of marine heatwaves on the physiological health of two fucoid species

Abstract

Marine Heatwaves (MHWs) are periods of high-water temperature that have become an increasingly significant threat to marine ecosystem biodiversity in recent decades with rising anthropogenic carbon driving greater severity of MHW events. The two intertidal fucoid species, Fucus serratus and Fucus vesiculosus, are keystone primary producers supporting an extensive biodiverse community of associated flora and fauna. As intertidal species, fucoids are adapted to cope with high atmospheric temperatures during exposure at low tide, however, are prone to changes in abundance, distribution, and life cycles during MHW events. Changes to fucoid communities resulting in reduced primary production and habitat biomass will have knock-on impacts to higher trophic levels. This study aims to identify the impact of MHWs of varying intensity on the eco-physiology of F. serratus and F. vesiculosus in the South-West (SW) of the United Kingdom (UK). The objectives were to conduct MHW experiments on F. serratus and F. vesiculosus taken from Firestone Bay, Plymouth, under two MHW intensities chosen based on realistic MHW temperatures for the region. These intensities were the control (14°C), as ambient seawater temperature for the region, a moderate MHW treatment (18°C) and an extreme MHW treatment (22°C), over a duration of one month. Results showed healthy Fv/Fm values and significant growth for both species throughout the experiment period. Overall, no clear evidence of physiological stress induced by the MHW treatments was found, showing a high tolerance to temperature over a onemonth duration. The findings from this study contribute to the growing understanding of how MHW events have the capacity to impact key marine species in an intertidal environment, building knowledge on a topic with still limited scientific understanding.