Abstract
To examine the extent to which human activities near the Ria Formosa coastal lagoon influence the accumulation of trace elements (TE) in Ruditapes decussatus, individuals were transplanted from a natural bank located in the lower lagoon to three sites located in clam growth grounds under the influence of a small city (Faro), a fish farming centre (Olhão) and a site near the lagoon inlet (Lavajo). Concentrations were determined in substrate of the clam grounds and in the digestive gland, gills, mantle plus siphons, and remaining tissues of clams in four periods of the year. These measurements were accomplished with the monthly survey of the gametogenic stages, condition index, proteins, glycogen, total lipids, pH and osmolarity of hemolymph. Arsenic, Cu, Mn, V, Cr and Pb were preferentially linked to the digestive gland, while Cd was linked to the gills. TE concentrations in the digestive gland and remaining tissues were higher in winter, most likely reflecting additional inputs associated with rain. The lack of disruptions in biological parameters and the prolonged period of spawning and gonad recovery in clams suggest that the current TE availability in the lagoon has a minor influence on the reproductive cycle and hence on clam production.
Highlights
Coastal lagoons are among the most productive ecosystems supporting habitats for wildlife and commercially explored species (Costanza et al 1997)
The objective of this work was to examine whether human activities in Ria Formosa and the surrounding region have a major influence on the trace element partitioning in the clam Ruditapes decussatus produced on inter-tidal flats, superimposed on changes related to metabolic processes
This lagoon is a paradigmatic example of an ecosystem with ecological and economic importance it is under stress from human activities and displays alterations of its morphology reflecting its fragility to extreme natural conditions, such as sea storms (Cunha et al 2005, Guimarães et al 2012, Vila-Concejo et al 2002)
Summary
Coastal lagoons are among the most productive ecosystems supporting habitats for wildlife and commercially explored species (Costanza et al 1997). These services are often at risk due to the increasing stress caused by contaminants from activities related to urbanization, industrialization, intensive agriculture in the watershed, massive tourism, and intensive aquaculture Organisms exposed to trace elements may accumulate them in tissues leading to various inductive responses, such as production of metallothioneins to sequestrate toxic metals (Bebianno and Langston 1993), and triggering antioxidant defence systems to prevent the formation of reactive oxygen species and their deleterious effects (Ivanina et al 2013, Lushchak 2011). According to Mantel and Farmer (1983), metal exposure may alter the fluid ion level in clams, causing the decrease of Na+, Cl– and K+ contents as a compensatory process in the internal osmolarity regulation
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