Phytoplankton Dynamics in Mediterranean Coastal Ecosystems

Phytoplankton communities in Mediterranean coastal zones are shaped by a complex interplay of physical drivers, nutrient availability and biological interactions. Seasonal stratification and vertical mixing determine the supply of inorganic nutrients from deeper waters to the euphotic zone, fuelling pulses of primary production that typically peak in spring and, to a lesser extent, in autumn. Along narrow continental shelves and in semi‐enclosed gulfs, wind‐driven upwelling and riverine inputs generate localised hotspots of productivity, while extreme events such as marine heatwaves can disrupt successional trajectories and shift systems towards heterotrophy. Community composition ranges from picoplanktonic cyanobacteria and picoeukaryotes to larger diatoms and haptophytes, with size structure strongly influenced by light, temperature and grazing pressure. Coastal phytoplankton are central to regional carbon cycling, underpinning food‐web support for fisheries and mediating fluxes of organic carbon to both the atmosphere and the seabed. Long‐term time series, high‐resolution mesocosm experiments, radar‐tracked advection studies and ecosystem modelling have together advanced understanding of how Mediterranean coastal phytoplankton respond to natural variability and to anthropogenic pressures such as warming, stratification changes and nutrient loading.

Research from Nature Portfolio

Recent experimental mesocosm work has quantified how sequential heatwaves alter coastal plankton processes. The first imposed marine heatwave enhanced gross primary production, respiration, chlorophyll‐a concentrations and both phytoplankton growth and loss rates, whereas a second heatwave shifted the system towards net heterotrophy and restructured succession, favouring cyanobacteria and chlorophytes at the expense of haptophytes. High‐frequency coastal radar data integrated with long‐term plankton time‐series at a gulf observatory have revealed that physical advection from coastal and offshore waters modulates local species succession, while horizontal mixing dampens dominance of fast-growing taxa and promotes diversity by importing and diluting plankton populations. Foundational work on nanoplanktonic diatoms in the northwestern Mediterranean has exposed a massive spring bloom of previously overlooked small diatom species, demonstrating that these cells can contribute significantly to carbon export via rapid sinking and challenging conventional size-based models of phytoplankton–food-web interactions.

Phytoplankton Dynamics in Mediterranean Coastal Ecosystems publication trend

The graph below shows the total number of articles in phytoplankton dynamics in mediterranean coastal ecosystems across all publications each year (not limited to Nature Index journals).

Technical terms

Phytoplankton: Photosynthetic microorganisms inhabiting the sunlit upper layers of aquatic systems, forming the base of marine food webs.

Primary production: The rate at which phytoplankton convert inorganic carbon into organic matter via photosynthesis.

Mesocosm experiment: A controlled outdoor enclosure that simulates natural water bodies to study ecological processes under manipulated conditions.

Upwelling: The upward movement of nutrient‐rich deep water to the surface, driven by wind or density gradients, enhancing local productivity.

Stratification: The formation of distinct water layers in the ocean or a coastal basin due to differences in temperature or salinity, affecting vertical mixing.

References

1. Functional and structural responses of plankton communities toward consecutive experimental heatwaves in Mediterranean coastal waters. Scientific Reports (2023).
2. Time series and beyond: multifaceted plankton research at a marine Mediterranean LTER site. Nature Conservation (2019).
3. Nanoplanktonic diatoms are globally overlooked but play a role in spring blooms and carbon export. Nature Communications (2018).
4. The Spatiotemporal Variability of Marine Plankton Ecosystem Services at the Regional Scale: A Combined Approach Using a Systematic Review and Network Analysis. Sustainability (2025).
5. Phytoplankton dynamics in relation to seasonal variability and upwelling and relaxation patterns at the mouth of Ria de Aveiro (West Iberian Margin) over a four-year period. PLOS ONE (2017).