Tesis doctoral de Estela Romero Sotoca
Coastal areas play a fundamental role in the functioning of marine ecosystems. These are strategic areas, transition zones in which terrestrial, atmospheric and oceanic factors come together and whose dynamics determines a wide variety of natural resources. Unlike what happens in vast regions of the ocean, where planktonic organisms exhibit recurring seasonal cycles and a clear synchrony with the physical forcing, coastal planktonic communities show a strong temporal and spatial variability. Seasonal patterns are not always visible and the dynamics of the community is oftentimes dependent on specific local processes. In recent decades, the step-up of urban pressure along the coast and the growing impact of human populations have increased the influence of terrestrial factors on coastal waters, pressing the need to understand the singularities and the functioning of coastal ecosystems. in this context, the present thesis addresses the variability of plankton in an urbanized coastal area, placing special emphasis on (1) the various time scales at which physical forcing factors operate and their different effects on the organisms, (2) the divergence between coastal plankton dynamics and the variations observed in open ocean regions, (3) the heterogeneity of coastal waters, which integrate different geomorphological, oceanographic and land use properties that are key to understand the response of the organisms to environmental perturbations. broadly speaking, the significance of seasonal patterns is examined through a multi-year series of monthly samplings. in barcelona, as in other parts of the mediterranean, there is an annual chlorophyll maximum between late winter and early spring. It is a recurrent pattern, although it represents only a small fraction of the annual variability; on one hand, the chlorophyll maximum values vary significantly from year to year; on the other, terrestrial inputs can induce chlorophyll peaks of similar magnitude during other periods of the year. The comparison with nearby coastal areas, less exposed to human disturbances but subject to similar climatological and hydrological conditions showed that beyond smoothing the seasonal cycles, the city exerts a continuous pressure which modifies the structure and the response of the planktonic community. We identified two key aspects: first, the composition of urban inflows, particularly enriched in ammonia and organic matter; second, the decoupling between nutrient inputs and turbulence. both factors seem to sustain a background community where the smallest plankton abounds and the microbial loop is kept very active. The fast growth of small planktonic organisms ultimately limits the response of microphytoplankton, whose proliferation appears to be strongly influenced by the availability of nitrate and the concurrence with mixing processes. the influence of turbulence and the composition of nutrients, particularly the nitrogen source, on the structure and dynamics of plankton was also assessed experimentally. In the laboratory, under controlled conditions, it is possible to distinguish more clearly the effects of specific factors; the experimental results were consistent with the observations at sea and stressed the importance on the coast, not only of nutrient loading, but especially of its relative composition and the coupling with turbulence. finally, we examine the effects of an intense episode of atmospheric deposition. Atmospheric inputs, in particular saharan dust, are a prominent source of variability in the mediterranean coast. The study analyzes in detail the increase of nutrients in the water column, the sequence and interactions among organisms and the differences in the biological response depending on the severity of the episodes.
Datos académicos de la tesis doctoral «Sources of plankton variability in an urbanized coastal ecosystem«
- Título de la tesis: Sources of plankton variability in an urbanized coastal ecosystem
- Autor: Estela Romero Sotoca
- Universidad: Politécnica de catalunya
- Fecha de lectura de la tesis: 22/09/2010
Dirección y tribunal
- Director de la tesis
- Francesc Peters
- Tribunal
- Presidente del tribunal: celia Marrase
- paul Tett (vocal)
- Antonio Tovar sanchez (vocal)
- maurizio Ribera d¿alcala (vocal)