Seagrass species, such as Posidonia oceanica, are particularly susceptible to ocean warming and have undergone extensive thermal stress, mortality, and range contraction over recent decades. The Mediterranean has experienced rapid warming, 2–3 times faster than the average global ocean over the past three decades. Marine heatwaves have impacted central populations of P. oceanica and studies have predicted the functional extinction of the species by 2050.

Predicting the thermal sensitivity of species and determining whether thermal performance varies between populations is critically important to predict and manage climate change impacts.

We collaborated with researchers from the Global Change Research Group, Institut Mediterrani d’Estudis Avançats (CSIC-UIB), Centre d’Estudis Avançats de Blanes (CEAB-CSIC), Universitat de Barcelona, and University of New South Wales, Sydney, among others, to evaluate the ecological response and recovery of P. oceanica populations to thermal stress across different regions.

We conducted a 12-month translocation experiment across its geographical range (western to eastern Mediterranean Sea), to compare the performance of geographically distant populations under common, relatively natural ecological settings. Trans-Mediterranean translocation of P. oceanica fragments took place between Catalunya – Spain (‘cool-edge’ populations), Mallorca – Spain (‘centre’ populations) and Cyprus (‘warm-edge’ populations) during July 2018 and was monitored until July 2019.

The study aimed to compare whether warm-edge populations are more sensitive to climatewarming than central and cool-edge populations. Transplants in central and warm-edge locations experienced temperatures over 29°C, representing thermal anomalies > 5°C above long-term maxima for cool-edge populations, 1.5°C for central and < 1°C for warm-edge populations. Cool-edge populations did not differ from warm-edge populations under common conditions and performed significantly better than central populations in growth and survival, suggesting that thermal performance does not necessarily reflect the thermal geography of a species. Warm-edge populations were also less sensitive to thermal stress than cooler, central populations. These findings provide hope for greater resilience to warming in Mediterranean seagrasses than previously recognized.

The article has been published in the journal New Phytologist and can be found in the link: https://doi.org/10.1111/nph.17885