Biomarker responses in the copepod Acartia tonsa of the Venice lagoon

Zooplankton is an essential component of the aquatic food chain, and the evaluation of the ecotoxicological risk to this community, using a biomarker approach, represents an early warning signal of potential alterations to the health of an ecosystem. Moreover, the calanoid copepod, Acartia tonsa, is recognised as an important marine test species, widely used in toxicity tests. In this study, A. tonsa has been chosen as a sentinel organism in the Venice lagoon ecosystem, due to its wide distribution, short life cycle and high reproductive potential. As in most estuarine and brackish environments, this species represents the most important genus from a quantitative point of view. A. tonsa was never observed before 1980 in the Mediterranean Sea. Then, in 1992, its presence was reported in the inner area of the Venice lagoon (Palude della Rosa), with very high abundance values (maximum of about 85,000 ind/m3). In 2004 a monthly study was undertaken to evaluate the copepod health condition. Samples were collected from May to December in three selected sites, representative of the variety of habitats subjected to contamination (S. Giuliano, Marghera and Palude della Rosa). Metallothionein (MT), acetylcholinesterase (AchE) and total protein content were measured. Additional parameters were also considered to better understand the biomarker responses: species abundances, hydrochemical and biological data.