Data on the variation of physicochemical parameters, biomass and growth of green macroalgae (mostly Enteromorpha) collected between January 1993 and January 1997 in the Mondego Estuary (western coast of Portugal) was analysed with the aim to identify the factors that control opportunistic macroalgal abundance in the system.The annual biomass of Enteromorpha spp. is strongly dependent on the amount of fresh water that enters the system during winter and spring. In turn, the input of fresh water is regulated by precipitation and by river management practices. The optimization of the rice crops from the upstream valley depends on their water level, which determines the number of days and hours per day during which sluice gates remain open in winter and spring. River flow has significant impacts on salinity, N:P ratios, current velocities and light extinction coefficients within the system. The interaction of all these factors controls macroalgal growth and biomass loss processes.In winters and springs during which sluice gates are often closed due to water deficiency of the rice fields (dry winter and spring or dry winter followed by rainy spring), little fresh water enters the system and consequently, salinity remains high, N:P ratios around 20, light penetration increases, and current velocities fall. These conditions facilitate macroalgal fixation, enhance their growth and spring blooms occur. On the contrary, during winters and springs when fresh water is in excess of rice fields' needs (rainy winters and springs), sluice gates remain open for long periods of time. High input of fresh water to the system causes salinity and light penetration to decrease, while N:P ratios and current velocities increase. These conditions contribute both to reduced Enteromorpha growth and higher loss of macroalgal biomass from the system to the ocean.The present work shows that the inter-annual variation of macroalgal biomass in the Mondego Estuary is controlled by hydrodynamics, which in turn depends on precipitation and on river management, according with the water needs of the upstream rice crop. Academic Press
Marine macrophytes are the foundation of algal forests and seagrass meadows-some of the most productive and diverse coastal marine ecosystems on the planet. These ecosystems provide nursery grounds and food for fish and invertebrates, coastline protection from erosion, carbon sequestration, and nutrient fixation. For marine macrophytes, temperature is generally the most important range limiting factor, and ocean warming is considered the most severe threat among global climate change factors. Ocean warming induced losses of dominant macrophytes along their equatorial range edges, as well as range extensions into polar regions, are predicted and already documented. While adaptive evolution based on genetic change is considered too slow to keep pace with the increasing rate of anthropogenic environmental changes, rapid adaptation may come about through a set of non-genetic mechanisms involving the functional composition of the associated microbiome, as well as epigenetic modification of the genome and its regulatory effect on gene expression and the activity of transposable elements. While research in terrestrial plants demonstrates that the integration of non-genetic mechanisms provide a more holistic picture of a species' evolutionary potential, research in marine systems is lagging behind. Here, we aim to review the potential of marine macrophytes to acclimatize and adapt to major climate change effects via intraspecific variation at the genetic, epigenetic, and microbiome levels. All three levels create phenotypic variation that may either enhance fitness within individuals (plasticity) or be subject to selection and ultimately, adaptation. We
Eutrophication of European estuaries due to massive nutrient loading from urban areas and diffuse runoff from extensively cultivated land areas is analysed. Consequences for the ecology of estuaries, namely changes in plant species composition, which also affects heterotrophic organisms, are approached based on examples showing that the result is often a fundamental structural change of the ecosystem, from a grazing and/or nutrient controlled stable systems to unstable detritus/mineralisation systems, where the turnover of oxygen and nutrients is much more dynamic and oscillations between aerobic and anaerobic states frequently occur. Several relevant aspects are examined, namely the influence of rooted macrophytes on nutrient dynamics, by comparing bare bottom sediments with eelgrass covered sediments, primary production and the development of organic detritus, and hydrodynamics and its relations to the spatial distribution of macrophytes in estuarine systems.
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