The study analyses the environmental conditions that regulate phytoplankton species succession in the Vigo estuary
The University of Vigo has collaborated with a team from the Vigo Oceanographic Centre of the Spanish Institute of Oceanography (IEO-CSIC) to present a new conceptual model that improves understanding of the dynamics and succession of phytoplankton communities in the Rías Baixas, a key component for the balance of marine ecosystems. The work stems from a PhD thesis within the DoMar Programme and uses data from the REMEDIOS project, led by CIM researcher Bea Mouriño.
Until now, studies on seasonal phytoplankton succession in the Rías Baixas treated these changes as homogeneous processes throughout the water column. However, this new approach, based on high spatial and temporal resolution observations, shows that phytoplankton dynamics are far more complex, varying over time and with depth, especially in response to coastal upwelling events typical of the region.
A new approach
The study, published in Progress in Oceanography, analyses phytoplankton communities by depth layers and reveals that different communities can coexist simultaneously at different levels of the water column. Based on these findings, the authors propose a new hypothesis describing strong connectivity between three main layers—surface, high-level and deep—whose interaction is directly shaped by upwelling events. During these events, a vertical circulation system is established that reverses direction depending on oceanographic conditions, functioning similarly to a conveyor belt that transports organisms between layers.
This publication is derived from the PhD thesis of Esther Velasco Senovilla, supervised by Enrique Nogueira at the Vigo Oceanographic Centre and defended at the University of Vigo in June 2025 within the Marine Sciences, Technology and Management Doctoral Programme “DoMAR”.
The observations come from specific samples designed within the REMEDIOS project, led by Bea Mouriño (CIM), and included seasonal weekly monitoring. Esther Velasco Senovilla’s predoctoral (FPI) contract was linked to this project.
A reservoir or “seed bank” of species
During spring and summer, increased solar radiation promotes stratification of the water column. Under these conditions, a two-layer circulation system develops between the estuary and offshore waters (continental shelf), driven by wind: a surface layer and a bottom layer moving in opposite directions, separated by an intermediate layer with its own characteristics. Changes in prevailing wind direction—and thus circulation—disrupt the fragile dynamic balance between species, potentially triggering new succession patterns.
One key finding is the role of the intermediate layer, where a subsurface chlorophyll maximum forms and acts as a reservoir or “seed bank” of species. From this zone, species can be transported both upwards and downwards, facilitating continuous exchange between communities. For this reason, ecologists identify this intermediate layer as a “hub” layer—a central connection point regulating species distribution and succession throughout the water column.
“The spatio-temporal variability of phytoplankton communities and the adaptive strategies of the species that compose them are essential to understand how marine ecosystems function and to anticipate changes in the goods and services they provide to society, especially in the context of toxic phytoplankton, climate change, resource overexploitation and pollution”, explains Esther Velasco Senovilla, author of the study. “In other words, it is about anticipating which species may be winners and which may be losers in the competitive dynamics under changing environmental conditions”, she concludes.
CIM holds the CIGUS recognition awarded by the Xunta de Galicia, which certifies the quality and impact of its research, and its activity is co-funded by the European Union through the ERDF 2021–2027 Programme.
Source: DUVI
