Quantifying the role of saltmarsh as a vulnerable carbon sink: A case study from Northern Portugal.

Saltmarshes play a crucial role in carbon sequestration and storage, although they are increasingly threatened by climate change-induced sea level rise (SLR). This study assessed the potential variation in Blue Carbon stocks across regional and local scales, and estimated their economic value and potential habitat loss due to SLR based on the IPCC AR6 scenarios for 2050 and 2100 in three estuarine saltmarshes in northern Portugal, the saltmarshes of the Minho, Lima and Cávado estuaries. The combined carbon stock of these saltmarshes was 38,798 ± 2880 t of organic carbon, valued at 3.96 ± 0.38 M€. Local and regional differences in carbon stocks were observed between common species, with the cordgrass Spartina patens and the reed Phragmites australis consistently showing higher values in the Lima saltmarsh in some of the parameters. Overall, the Lima saltmarsh had the highest total carbon per species cover, with S. patens showing the highest values among common species. Bolboschoenus maritimus had the highest values in the Minho saltmarsh, while the other species presented a similar carbon storage capacity. Potential habitat loss due to SLR was most evident in the Cávado saltmarsh over shorter timescales, with a significant risk of inundation even for median values of SLR, while the Lima saltmarsh was shown to be more resistant and resilient. If habitat loss directly equates to carbon loss within these saltmarshes, projected CO2 emissions may range from 22,000 to 43,449 t by 2050 and 33,000 to 130,000 t by 2100 (under the IPCC SSP5-8.5 scenario). The study shows the importance of Blue Carbon site-specific estimates, acknowledging the potential future repercussions from habitat loss due to SLR. It emphasizes the need to consider local and regional variability in Blue Carbon stocks assessments and highlights the critical importance of preserving and rehabilitating these ecosystems to ensure their continued efficacy as vital carbon sinks, thereby contributing to climate change mitigation efforts.

Unexpected nutrient influence on the thermal ecophysiology of seaweeds that recently followed opposite abundance shifts.

World's oceans are warming, and recent studies suggest that the Iberian upwelling system may be weakening. To understand the potential consequences of both trends, six intertidal seaweeds that recently followed opposite upward and downward abundance shifts in the Iberian upwelling region were exposed for six weeks to conditions simulating present and warmed scenarios, combined with nutrient treatments emulating the influence and absence of the upwelling. Unlike expectations, a high nutrient supply did not ameliorate the effects of warming. Instead, warming slowed down growth in four seaweeds and accelerated the photosynthesis of downward seaweeds only if nutrients were abundant. In a weakened upwelling scenario, nutrient limitation might more strongly influence the performance of both upward and downward seaweeds than warming. With a normally functioning upwelling, warming might be more detrimental to the performance of some downward seaweeds as they might would lose their ability to benefit from the extra nutrient input.