Micropollutants affect the ability of phytoplankton communities to track environmental changes

Human activities strongly influence environmental processes, and while human domination increases, biodiversity progressively declines in ecosystems worldwide. High genetic and phenotypic variability ensures functionality and stability of ecosystem processes through time and increases the resilience and the adaptive capacity of populations and communities, while a reduction in functional diversity leads to a decrease in the ability to respond in a changing environment. Pollution is becoming one of the major threats in aquatic ecosystem, and pharmaceutical and personal care products (PPCPs) in particular are a relatively new group of environmental contaminants suspected to have adverse effects on aquatic organisms. There is still a lake of knowledge on the responses of communities to complex chemical mixtures in the environment. We used an individual-trait-based approach to assess the response of a phytoplankton community in a scenario of combined pollution and environmental change (steady increasing in temperature). We manipulated individual-level trait diversity directly (by filtering out size classes) and indirectly (through exposure to PPCPs mixture), and studied how reduction in trait-diversity affected community structure, production of biomass and the ability of the community to track a changing environment. We found that exposure to PPCPs slows down the ability of the community to respond to an increasing temperature. Our study also highlights how physiological responses (induced by PPCPs exposure) are important for ecosystem processes: although from an ecological point of view experimental communities converged to a similar structure, they were functionally different.

Phytoplankton silica uptake under different artificial upwelling conditions in the Canary Islands.

Climate change is affecting pelagic ecosystems with repercussions on fish production. In particular, global change is increasing oceanic temperature and stratification with decrease in nutrient input in euphotic layer leading to a decline in primary production. The mesocosm-based project Ocean Art-Up, conducted in Gran Canaria, is aimed to increase fish production and to enhance carbon sequestration through an artificial upwelling system. Diatoms dominate the phytoplankton community in upwelling systems and they need to take up silicates to grow. The abundance and nutritional value of diatoms determine the fate of phytoplankton biomass with transport to the upper level of the pelagic food web or to the deeper layer of the ocean with potential carbon sequestration. Here, data about experiments performed in 2018 and 2019 are reported. The first mesocosm experiment investigated the differences between pulsed and continuous upwelling mode, while the second experiment was conducted with a gradient in Si:N ratio along the mesocosms. The phytoplankton community takes up and incorporate silica about at the same rate in continuous mode, while in pulsed mode its peak occurred only after the deep-water addition. The diatom silica content is not affected by mode and amount of water added but by the Si:N ratio. Diatoms grown in an environment with high Si:N ratio values show higher abundance, biogenic silica production, silica uptake and silica content than the ones that experienced low Si:N values. In addition from literature, euphotic zone rich in silicate may produce high silica containing-diatoms who will produce repercussions on copepods community regarding feeding, hatching and growth, thus continuous upwelling with high Si:N ratio favours diatoms who will tend to sink and to be converted by copepods into fecal pellet rich in silica with increasing in potential carbon sequestration. Fish production may increase with continuous artificial upwelling showing low Si:N values.