Abstract
Abstract. The evolution of environmental changes during the last decades and the impact on the living biomass in the western part of Amvrakikos Gulf was investigated using abundances and species distributions of benthic foraminifera and lipid biomarker concentrations. These proxies indicated that the gulf has markedly changed due to eutrophication. Eutrophication has led to a higher productivity, a higher bacterial biomass, shifts towards opportunistic and tolerant benthic foraminifera species (e.g. Bulimina elongata, Nonionella turgida, Textularia agglutinans, Ammonia tepida) and a lower benthic species density. Close to the Preveza Strait (connection between the gulf and the Ionian Sea), the benthic assemblages were more diversified under more oxygenated conditions. Sea grass meadows largely contributed to the organic matter at this sampling site. The occurrence of isorenieratane, chlorobactane and lycopane supported by oxygen monitoring data indicated that anoxic (and partly euxinic) conditions prevailed seasonally throughout the western part of the gulf with more severe oxygen depletion towards the east. Increased surface water temperatures have led to a higher stratification, which reduced oxygen resupply to bottom waters. Altogether, these developments led to mass mortality events and ecosystem decline in Amvrakikos Gulf.
Highlights
Coastal development, pollution and a range of anthropogenic activities including extensive agriculture, aquaculture, urban and industrial wastes are main causes of decline and loss of coastal habitats observed over the last decades (Airoldi and Beck, 2007; Diaz and Rosenberg, 2008).Amvrakikos Gulf, located in northwestern Greece, is a semi-enclosed embayment characterized by a complex lagoonal system and an extensive delta (Kapsimalis et al, 2005)
Eutrophication has led to a higher productivity, a higher bacterial biomass, shifts towards opportunistic and tolerant benthic foraminifera species (e.g. Bulimina elongata, Nonionella turgida, Textularia agglutinans, Ammonia tepida) and a lower benthic species density
Despite the efforts, which have been made for the protection and conservation of this unique area, the western part of the gulf is suffering from seasonal hypoxia, whereas the eastern part is affected by seasonally anoxic conditions (Kountoura and Zacharias, 2011)
Summary
Pollution and a range of anthropogenic activities including extensive agriculture, aquaculture, urban and industrial wastes are main causes of decline and loss of coastal habitats observed over the last decades (Airoldi and Beck, 2007; Diaz and Rosenberg, 2008).Amvrakikos Gulf, located in northwestern Greece, is a semi-enclosed embayment characterized by a complex lagoonal system and an extensive delta (Kapsimalis et al, 2005). The gulf is protected under the international Ramsar Convention as Wetlands of International Importance In addition it is designated as a Special Protection Area (SPA), according to the European Union Directive 79/409/EU, and it is included in the Natura 2000 Network. Despite the efforts, which have been made for the protection and conservation of this unique area, the western part of the gulf is suffering from seasonal hypoxia (oxygen concentrations < 2 mg L−1), whereas the eastern part is affected by seasonally anoxic conditions (oxygen concentrations < 0.5 mg L−1) (Kountoura and Zacharias, 2011) This was caused by the excessive use of fertilizers, the increase in animal stocks, intensive fish farming and domestic effluents for the last 20 to 30 yr (Ferentinos et al, 2010; Kountoura and Zacharias, 2011).
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