Productive mats of micro-algae thrive with a warmer world

Intertidal mudflats are amongst the most productive coastal ecosys-tems on Earth. They are widely spread worldwide supporting food websand many ecosystem services. Their productivity mostly relies uponmats composed of benthic micro-algae called microphytobenthos (MPB).Despite their critical importance in carbon cycling and trophic cas-cading, the MPB response to global warming is largely overlooked inbiogeochemical models. Here, we use a numerical model to simulateover 1950-2099 the response of MPB exposed to light and tempera-ture conditions predicted by three IPCC climate change scenarios. Weshow that MPB net primary production (NPP, -1 g C m−2 dec−1)thrives with the increase of mud surface temperature foreseen by the end of the century. However, MPB undergo important phenological shifts.MPB bloom up to 14 days earlier in spring and 5 days later in fallexpanding by 3 weeks the low-level MPB biomass summertime periodin RCP 8.5. The ratio SP:NPP remains unaffected by changes in MPBNPP and phenology. Therefore, we suggest that first trophic levels willbe resilient in a projected warmer climate, but with a cascading effectthroughout the entire food-web that remains to be assessed. Regard-ing the role of MPB in supporting tidal mudflats ecosystems, the modelability to infer MPB response to change in irradiance and temperaturecould open the door to a new assessment of tidal mudflats vulnera-bility and associated numerous ecosystem services to climate change.