Productive mats of micro-algae continue to thrive with a warmer world

Intertidal mudflats are amongst the most productive coastal ecosystems on Earth. They are widely spread worldwide supporting food webs and many ecosystem services. Their productivity mostly relies upon mats composed of benthic micro-algae called microphytobenthos (MPB). Despite their critical importance in carbon cycling and trophic cascading, the MPB response to global warming is largely overlooked in biogeochemical models. Here, we use a numerical model to simulate the response of MPB exposed to light and temperature conditions predicted by three IPCC climate change scenarios covering years 1950 to 2099. MPB undergo important phenological shifts with the increase of mud surface temperature foreseen by the end of the century. MPB bloom up to 14 days earlier in spring and 5 days later in fall expanding by 3 weeks the low-level MPB biomass summertime period in RCP 8.5. During the 21st century, MPB net primary production (NPP) continues to thrive due to the compensation of increasing/decreasing NPP during winter/summer. The ratio SP:NPP remains unaffected by changes in MPB NPP and phenology. Therefore, we suggest that low trophic levels will be resilient in a projected warmer climate, but with a cascading effect throughout the entire food-web that remains to be assessed. Regarding the role of MPB in supporting tidal mudflats ecosystems, the model ability to infer MPB response to change in irradiance and temperature brings new insights about the fate of associated ecosystem services in a warmer climate