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Our research goal is the study of the sea. A large share of the global economy in our country is based on the sea. Lots of people visit the littoral where they have holidays, but also from the sea come many products of commercial interest. The most relevant ones, obviously, are fish and other organisms that can be eaten. Our task is to know why the sea is the way it is, and why it works the way it does. That is the path to being able to predict where and when we will find a given species, or how human activities will affect the different organisms living at the sea.

Everything starts with the fixation of atmospheric carbon by phytoplankton, the minute microscopic algae that, together with bacteria, viruses and protozoa constitute what has been termed the microbial food web. Organic matter produced by all these organisms is degraded by bacteria which are food for protozoa. inorganic carbon uptake by phytoplankton is a process equivalent to that done by terrestrial plants and trees and is mediated by the pigments that these organisms have and that allow them to capture the energy and light from the sun. If there are enough inorganic nutrients available, the phytoplankton will grow and serve as food for protozoa (ciliates and flagellates) and zooplankton, the most conspicuous component of which are the copepods. Copepods are an essential part of the diet of larger carnivorous invertebrates, such as jellyfish, ctenophores, and krill, at the same time food for fish. Thus, all phenomena related to climate, oceanic dynamics or human-related that might affect phytoplankton will ultimately affect the invertebrates and the fish. All these growth, predation or limitation relationships occur in seawater, for us a liquid where we can easily swim, but for the microscopic organisms seawater is a very dense viscous fluid, where movement is not simple. Storms and the interaction between the atmospheric dynamics and seawater produce turbulence which may affect the movement and the feeding of the organisms and the processes by which the atmosphere and the sea interact to determine the climate and the biogeochemical cycles. The sea is a dynamic environment, affected by climate and by sea bottom topography. Thus, nutrients can enter the photic zone in some sites associated to intrusions of deep water, while in some other sites there are clear interactions with the river discharges. These factors vary along the seasonal cycle so that the trophic structure and the carbon fluxes through the plankton food web are not constant but variable.

What lives in seawater but cannot overcome marine currents is called plankton. The organisms that live on solid substrates on the seabottom is called benthos. Some benthic communities are spectacularly beautiful, like those formed by corals and gorgonids. And others have the well-known sea stars, sea urchins and sponges. But benthos cannot be considered with independence of plankton. Benthic animals feed on plankton organisms, and most benthic animals have juvenile phases in the plankton. Littoral food webs cannot be split into planktonic and benthic because the benthic suspension feeders can be secondary players but essential in the fluxes of carbon and energy in the littoral zone.

The relationships between copepods or the benthic organisms and the microbial food web can studied by diving, in large water tanks (mesocosms), in microcosms where the plankton food web is reproduced in miniature, or by means of oceanographic cruises with ships adapted for research which can be considered like mobile laboratories adapted for living and performing research. Samples obtained in these cruises and experiments are analyzed by means of a great variety of techniques: epifluorescence microscopy, flow cytometry, biochemical analyses, HPLC, molecular methods... The Department of Marie Biology and Oceanography studied both the Catalan littoral: the Ebre Delta, the beaches and submarine canyons of the Costa Brava and the Medes Islands, but also the rest of the Mediterranean. But cruises and sampling is also performed in the Salterns of the Mediterranean littoral, in the coastal waters of Galizia, in the Central Atlantic and even in the Antarctica seas, to better study the factors that determine all the processes here explained and to gather a better knowledge of the human impact on the environment. We are particularly interested in the problems related to the nutrient enrichment ("eutrophication") of the littoral, the blooming of toxic phytoplankton ("HAB") which can be toxic if humans ingest seafood that has fed upon them; or the growth of animal species that can affect the human use of the littoral and the beaches, like the jellyfish. Finally, it is important to explain that we still know very little of the true diversity of the organisms living in the sea. The study, for example, of the microbial diversity, will allow us to describe new species and follow their growth and disparation in the seas where we live.

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