Potential Use of Biomarkers in Zooplankton as Early Warning Signals of Ecotoxicological Risk in the Marine Food Chain Roberta Minutoli*, Maria Cristina Fossi & Letterio Guglielmo Department of Animal Biology and Marine Ecology, University of Messina, Salita Sperone 31, S. Agata, 98166 Messina, Italy. With 1 figure Keywords: Zooplanktonic crustaceans, benthic decapods, marine environ- ment, brackish environment, biomarkers, esterases. Abstract. Zooplankton is an essential component of the marine and brackish food chains. The ecotoxicological risk of zooplanktonic communities, estimated by the mod- ern methodological approach of biomarkers, can be used as an early warning signal of ecosystem health. The aim of this project is to estimate the potential use of several bio- markers (esterases, mixed function oxidases, porphyrins) in zooplanktonic organisms. Studies were carried out with different zooplanktonic crustaceans: the copepods Acar- tia margalefi and Acartia latisetosa collected in Ganzirri Lake (Messina); the mysid Siriella clausi collected in Faro Lake (Messina); the mysids Diamysis bahirensis, Siriella armata and Mysidopsis gibbosa collected in Stagnone di Marsala (Palermo); the Antarctic euphausiids Euphausia crystallorophias and Euphausia superba; the am- phipod Streetsia challengeri and the euphausiid Meganycthiphanes norvegica collected after a shore-stranding along Messina's Ionian coast. Moreover, experiments were car- ried out with the benthic decapods Eriphia verrucosa and Pachygrapsus marmoratus from a rocky shore of Messina's Ionian coast. Acetylcholinesterase activity (AChE) was determined in homogenates of whole organisms. The key result of this project con- cerns the different AChE activity basal values of different crustacean species. Particular attention should be paid to the difference in basal activity found between the Antarctic and the Mediterranean species. Problem The modern methodological approach of biomarkers has been used in the last 20 years in order to solve one of the main objectives of ecotoxicology: the evaluation of the toxic U. S. Copyright Clearance Center Code Statement: 0173-9565/02/S2301 ± 291$15.00/0 P.S.Z.N.: Marine Ecology, 23, Supplement 1 (2002), 291±296 Ó 2002 Blackwell Verlag, Berlin ISSN 0173-9565 * Author to whom correspondence should be addressed: zooplancton@unime.it