Anthropogenic impacts

The functional integrity of marine ecosystems and the sustainable management of their natural resources are frequently threatened, especially in heavily polluted areas, such as the Mediterranean Sea, subject to historical anthropogenic impacts (deforestation, river damming, etc.). Diminishing the effect of pollution on organisms and ecosystems constitute nowadays one of the key topics to improve quality of life in developed countries. Changes induced in marine ecosystems as a consequence of human activity and its influence on organisms can have important effects on the abundance and quality of natural resources and therefore on the economic development, since they can alter both biodiversity and the functioning of ecosystems and their carrying capacity.

Biodiversity in the Mediterranean has been undergoing significant changes as a result of anthropogenic and climatic influences (Bethoux et al., 1999). Many changes concern additions of species mainly through Lesseptian migrating from the Red Sea (more than 300 new species have already migrated and become established in the eastern basin), although exotic species have also arrived by means of accidental introductions into the western basin. The shallow soft-bottom sediments on the coasts of Catalonia are continuously stressed by man-made disturbances such as trawling fisheries, dredging and

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recreation activities and offshore construction, so the associated communities are permanently affected.

Eutrophication in polluted coastal areas tends to reduce species richness, while climatic warming is favoring the development of a more tropical fauna (Galil, 1993). These biological changes concern both fish and phytoplankton that produce nuisance and toxic blooms with concomitant socio-economic consequences for fishing industry and tourism. Growing concern about human influence on marine ecosystems conflicts with our inability to separate manmade impacts from natural change (Duarte et al., 1992).

Environment managers need, as a consequence, new tools or criteria to properly monitor and manage the health status of marine ecosystems, in order to find measures to minimize risks and impacts.

Mediterranean coastal waters suffer the deepest ecological problems since they concentrate the major part of human activities, such as maritime traffic, mineral and marine sources extraction, recreational activities, chemical effluents, and urbanization of the coast. Fishing activities are often an important impact on marine communities. Soft bottoms of continental shelves are highly disturbed by trawl fishing (Gray et al., 2006). Many of these habitats might be essential fish habitats that are important for refuge, feeding, growth and recruitment of commercial species, or sensitive habitats that support highly vulnerable organisms which are often of biological interest (de Juan et al., 2011). Although the fishing activities can determine the main impacts on sea communities, the increase of human population and human activities exert a strong pressure on marine communities (pollution, large scale impacts determined by climate change, changes in water masses and wrong management of hydrological resources) with evident effects not only on coastal ecosystems but also on deep sea.

Knowledge of species composition changes at different time scales is crucial to understanding the dynamics of marine communities. Due to the scarceness of a previous historic data baseline on ecosystems functioning, trials to evaluate human impact on marine systems are often extremely difficult

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to be successfully applied. Thus, studies focused in anthropogenic impact on the marine ecosystem should take into account the basic knowledge of ecosystems natural dynamics.

The rivers that discharge near the cities are highly polluted, and most of the waste discharged by them accumulates in the nearshore area. This situation is aggravated by the sewers discharging along the city littoral. Domestic wastewater treatment plants do not contribute to improving the quality of the littoral waters. Many of the contaminants are associated with sludge and river particles, so the transport and fate of the contaminants are also associated with the transport and deposition of the suspended particulate matter (SPM) discharged into the sea (Palanques and Diaz, 1994). After sedimentation, contaminants and waste can be resuspended either by bioturbation or by physical erosion. The final situation is the effect of a dynamic interaction between anthropogenic input and natural processes.

Thus, continental shelves influenced by densely populated coastal areas and located off rivers mouths experience complex interactions between continental influences, marine processes and direct and indirect anthropogenic impacts. Studies around the world have demonstrated that changes in the fluvial discharge and human activities modify the oceanographic conditions of the shelf waters and the accumulated seafloor sediments (Dounas et al., 2007;

Hartwell, 2008). The Barcelona continental shelf, off the Barcelona city, is a good area to study these complex relationships, since it is under the influence of two typical Mediterranean rivers, Llobregat and Besòs, the second being the sampling area of this thesis. About five million people live in the Barcelona metropolitan area (World Gazetteer, 2012). The major sources of metals on this continental shelf are the Besòs River, the littorals sewers and the pipeline of the Barcelona-Besòs wastewater treatment plant (Palanques, 1994). The

The persistent organic pollutants (POPs) are ubiquitous marine pollutants reaching the marine environment through rivers and continental runoff in coastal zones and in the open sea by atmospheric deposition. They have four main basic features: their toxicity, their persistence, their capacity for long-range

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transport and their capacity to bioaccumulate in throphic chains. Once in the marine environment, these hydrophobic substances are absorbed by organisms or adsorved in suspended particles that will deposit in the bottom sediments and will accumulate in benthic organisms, entering again in the food chain (Nhan et al., 1997). Halogenated aromatic hydrocarbons (HAHs), such as polychlorinated biphenyls (PCBs), polychlorinated dibenzodioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs), enter the environment from a number of potential sources. These hydrophobic chemicals are highly persistent in the environment and have a strong affinity with sediments and a high potential for accumulating in biological tissues (Eljarrat et al., 2001).

The contamination of sediments may also pose a severe risk to aquatic organisms, which tend to bioaccumulate PCDDs, PCDFs, PCBs and polycyclic aromatic hydrocarbons (PAHs), and to wildlife and humans through the ingestion of contaminated fish and sellfish. Following a sampling study done in the north-western Mediterranean, PCBs were detected in sediments at concentrations ranging from 1.1 to 311 ng/g dry weight, whereas PAHs concentrations ranged between 13.4 ng/g d.w. and 17ng/g d.w., being the Besòs area the most contaminated (Eljarrat et al., 2001). Furthermore, although the use and production of some organohalogen compounds have been restricted (chlorinated paraffins (CPs)) or banned (polychlorinated napthalenes (PCNs)), Castells et al. (2008) reported levels of PCNs and CPs in all the marine sediments analyzed in the Barcelona coast, especially near the submarine emissary, showing their ubiquity in the north-western Mediterranean coastal area, and suggesting a diffuse but uniform inputs of these pollutants to the marine environment.

Nevertheless, there is still poor knowledge on dynamic processes (e.g. in terms of persistence or bioaccumulation) or ways followed by different pollutants of anthropogenic origin until they accumulate in tissues of fish and other marine predators. Likewise, detailed knowledge about trophic fluxes in marine ecosystem is still scarce, and not only in deep water, but also in shallow (continental shelf) ecosystems (Grémare et al., 1997).

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