From data to knowledge: integrating observational data to trace phytoplankton dynamics in a changing world

Longobardi, Lorenzo (2022). From data to knowledge: integrating observational data to trace phytoplankton dynamics in a changing world. PhD thesis The Open University.

DOI: https://doi.org/10.21954/ou.ro.00013f13

Abstract

Phytoplankton are a fundamental component of marine systems. They are involved in the global regulation and functioning of biogeochemical and trophic processes and are strictly connected to human health and well-being through the provision of essential ecosystem services. Despite their fundamental importance, there is still no broad consensus on the mechanisms underlying their seasonal and interannual variability, while even less is known about the ecology of individual species and their response to climate variability given the scarcity of comprehensive long-term observation sets. Here, by taking advantage of high- frequency oceanographic and biological data collected over more than 25 years in a coastal pelagic Mediterranean site, I applied a set of statistical methods in order to investigate different aspects of community and individual species’ ecology, with a particular emphasis on the environmental factors and the mechanisms underlying phytoplankton phenology. Further, I analyzed long-term meteorological variations in the area and their relationships to large-scale climatic oscillation in order to address their impact on the planktonic system during the different seasons of the year. Finally, I integrated the data from 10 worldwide- distributed coastal time-series and investigated the adaptive potential of ubiquitous phytoplankton species to local conditions using a niche-based approach. The results of these analyses highlighted an impressive regularity in the annual occurrence of phytoplankton community and individual taxa despite a highly variable environment. Light was the predominant factor regulating species turnover and replacement and seemed to regulate endogenous biological processes associated with species-specific phenological patterns. Over the time series, a considerable stability was shown by individual species and the whole community, while the effects of climate fluctuation on the abiotic and biotic components revealed a strong dependence on the season. The comparison of phytoplankton niches across diverse biogeographical regions supported the idea of evolutionary adaptation, further emphasizing the importance of long-term ecological observations in the context of climate change. Overall, the results of these studies highlight the considerable resilience and the active role that phytoplankton plays under different environmental constraints, which contrasts the view of these organisms as passively undergoing external changes that occur at different temporal scales in their habitat, and show how, under certain conditions, endogenous biological processes prevail over environmental forcing.

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