Crossing thermal limits: functional collapse of the surfgrass Phyllospadix scouleri under simulated extreme marine heatwave

Authors:
Publisher website
Google Scholar
Abstract
Marine heatwaves (MHWs) are intensifying under climate change, yet the physiological limits that constrain seagrass resilience remain poorly defined. We experimentally tested the responses of the surfgrass Phyllospadix scouleri, a foundation species of the north-east Pacific coast, to simulated MHWs of contrasting intensity. In a 27-day mesocosm experiment, plants were exposed to fluctuating temperatures representing a severe MHW (23.5±1.5 °C) and an extreme MHW (26.5±1.5 °C), and photosynthetic performance, respiration, nitrogen metabolism, oxidative stress, and growth were monitored during and after warming. Phyllospadix scouleri maintained photosynthetic capacity and carbon balance under severe warming but exhibited pronounced physiological disruption at extreme temperatures, including sustained photoinhibition, reduced nitrate assimilation, elevated respiration, and negative daily productivity. These effects persisted after heat stress, leading to reduced growth and indicating incomplete recovery. Multivariate analysis revealed a transition from tolerance to functional breakdown near 26.5 °C, suggesting a potential physiological tipping point only 5–6 °C above current summer maxima in the area of the studied population. Our findings indicate that intensifying MHWs may rapidly erode the thermal safety margin of temperate seagrasses, pushing foundational coastal ecosystems toward metabolic instability under continued ocean warming.
Funding Information
  • Secretaría de Ciencia, Humanidades, Tecnología e Innovación
  • CONACYT) (A1-S-8382)
  • Rufford Foundation (43604-1)
  • NextGenerationEU (CN00000033)
  • Fundação para a Ciência e a Tecnologia (UIDB/04326/2020)
  • Fundação para a Ciência e a Tecnologia (UIDP/04326/2020)
  • Fundação para a Ciência e a Tecnologia (LA/P/0101/2020)

This publication has 79 references indexed in Scilit: