To understand how living beings respond to environmental changes, it is necessary to know well what the natural response of ecosystems is to these changes when there is no impact due to human activities. The only useful method is to study what happened in the past, before significant human impacts occurred. For this, the main tool is paleoenvironmental reconstruction, that is, the reconstruction of what happened in the past through the study of proxies or paleontological indicators (“fossils”) that persist over time and allow information to be obtained about the environment in which they lived, the changes that occurred in living beings and relate them to oscillations in the environment, such as temperature, sea level or precipitation. This is the field of work of the Paleobotany Laboratory of the Marine Research Center of the University of Vigo (CIM-UVIGO), in which palynomorphs are microscopically analyzed, that is, resistant structures produced by various plant organisms (vegetation, fungi, microalgae and dinoflagellates) that accumulate at the bottom of the estuary and can last a long time (even thousands of years) in the sediments. The different studies carried out in this field by researchers from the University of Vigo have allowed us to identify, for example, changes in phytoplankton productivity in the last 200 years, caused, among other factors, by climate change, pollution, the construction of reservoirs or the massive production of mussels.
Paleohydrology, a very promising technique
The distribution of palynomorphs varies depending on various environmental parameters, such as temperature or rainfall, and also the availability of nutrients in the water column, in the case of marine algae. Thus, their study allows us to reconstruct the plant landscape, marine productivity and the prevailing environmental conditions at the time these microfossils were deposited, as well as their variability over time. Specifically, the research staff of the XM-3 research group of CIM-UVIGO is developing work focused on the study of dinoflagellate cysts (dinocysts) accumulated in sediments to reconstruct conditions in the marine environment (paleohydrology). As the researchers explain, a collaboration with the Marine Palynology Laboratory of the University of Victoria (Canada) helped to improve the techniques of identification and paleoenvironmental interpretation from dinocysts that were being carried out in the Paleobotany Laboratory of the University of Vigo. The result of this collaboration was a work that allowed the high-resolution reconstruction of the changes that have occurred in the ecosystems of the Vigo estuary in the last two centuries based on the study of marine dinocysts and other “microalgae” of continental origin.
Alterations in phytoplankton productivity caused by climate change or rafts
Dinoflagellates are one of the main components of microphytoplankton and their composition and variability depend on the temperature regime, fluvial contributions and nutrient availability, among other factors. The study of dinocysts in a sedimentary record of the Vigo estuary that has been accumulated during the last decades has helped to reconstruct the main changes that occurred in the hydrology of the estuary and to identify the factors that caused them. For example, a transition phase (1855-1910 AD) has been identified from the final stages of the Little Ice Age (1400-1900), towards the warmer and wetter conditions that would govern most of the 20th century. Strong changes in phytoplankton productivity and species distribution have also been detected, which are mainly attributed to recent climate change, different types of pollution, changes in the fluvial regime and habitat destruction.
It has been found, for example, that pollution, the construction of reservoirs or the massive production of mussels are having effects on phytoplankton productivity. One of the most relevant effects is the increase in certain heterotrophic species, which were previously very scarce, due to the increase in the contributions of nutrients and organic matter as a result of the discharge of sewage, among other causes. “We also observed a general decrease in autotrophic dinoflagellates (decrease in the primary productivity of dinoflagellates) probably due to the increase in turbidity (lower light penetration) and/or the decrease in the availability of oxygen in the water”, indicates Iria García Moreiras, from the XM-3 group.
The researchers also obtained new data on the distribution of some species of dinoflagellates, such as Peridinium ponticum, which until now was considered exclusive to the Black Sea. “Thanks to this new study, we have shown that this species has been present in Galician waters naturally since at least 1830,” says Iria García Moreiras, who adds that they have also linked “the massive growth of some potentially toxic species (such as Lingulodinium polyedrum) to certain environmental factors; it seems that the increase in rainfall and, as a consequence, in river discharges, provide extra nutrients that favor the proliferation of these dinoflagellates.”
Fonte:duvi
