Manuel Vivanco-Bercovich

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.

Kelp forests are under increasing threat from ocean warming and marine heatwaves. In this context, assisted adaptation techniques emerge as promising tools for optimizing conservation and restoration strategies. One such technique is the cross-generational induction of stress memory by thermal priming, which aims to stimulate the thermal tolerance of kelps in the face of warming. However, research into these processes is still in its infancy. Here, we evaluated whether sublethal warming (priming) applied to gametophytes (23°C for 25 days) enhances the thermotolerance of the resulting juvenile sporophytes of Macrocystis pyrifera and Eisenia arborea. After the priming phase, we compared the biological performance of juvenile sporophytes derived from primed and non-primed gametophytes at two temperatures: a severe warming (25 °C for five days) that simulates regional marine heatwave conditions, and a control temperature of 17 °C. Under severe warming, sporophytes derived from non-primed gametophytes experienced complete mortality in both species, whereas sporophytes derived from primed gametophytes survived, maintained physiological function and grew. These sporophytes exhibited similar or even higher photosynthetic capacities than those at 17°C and did not show evidence of oxidative damage. Overall, these findings prove that applying thermal priming to gametophyte stage can increase thermotolerance in subsequent sporophyte generations, preventing mortality and improving physiological performance at temperatures that would otherwise be lethal. The present study provides initial evidence that the induction of cross-generational memory stress can be applied to M. pyrifera and E. arborea, paving the way for the development of future conservation and restoration strategies.

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 Northeast 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), while 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 analyses revealed a distinct transition from tolerance to functional breakdown near 26.5 °C, suggesting a physiological tipping point only 5–6 °C above current summer maxima in the area of the studied population. Our findings demonstrate that intensifying MHWs may rapidly erode the thermal safety margin of temperate seagrasses, pushing foundational coastal ecosystems toward metabolic instability and potential regime shifts under continued ocean warming. Highlight: Extreme marine heatwave disrupts photosynthesis, nitrogen metabolism, and carbon balance in the seagrass Phyllospadix scouleri , suggesting a narrow thermal safety margin in the face of ocean warming.

The ongoing environmental crisis, driven by biodiversity loss and climate change, raises concerns about the impacts on marine systems and human well-being. These environments provide crucial ecosystem services valued at approximately USD 74.5 trillion·year⁻¹ globally. Seagrasses support fisheries, protect coasts, help mitigate climate change, maintain biodiversity, provide food security, and enhance water quality. However, comprehensive assessments of seagrass ecosystem services (SESs) and their impacts are lacking. Focusing on the Brazilian southwest Atlantic, our aim is to bridge this gap and identify key research areas for improved management decisions. Our literature search employed n = 19 paired terms for seagrass in Brazil. We screened 30,351 search returns for 394 relevant documents. Research on SESs has grown over time, and most research has focused on provisioning and supporting ecosystem services: 79.7% of documents mentioned at least one SES, while 24.5% of the documents provided evidence of observed SESs; 31.5% only provided information on expected SESs. Provisioning services were the most observed and expected. Coastal urbanization (54%) and marine food provisioning (17%) were the main drivers impacting SESs. Terrestrial food and material provision (9%) and climate change (8%) were also significant drivers. This study provides key recommendations aimed at fostering further research and management strategies to consider the complete ensemble of ecosystem services for a range of seagrass bioregions, to better understand the provision of and impacts to seagrass services and human well-being at the global scale.