Water striders ( family Gerridae): mercury sentinels in small freshwater ecosystems Timothy D. Jardine a,b, * , Tom A. Al a,c , Kerry T.B. MacQuarrie a,d , Charles D. Ritchie e , Paul A. Arp e , Antu Maprani a,c , Richard A. Cunjak a,b,e a Canadian Rivers Institute, University of New Brunswick, Fredericton, New Brunswick, Canada b Department of Biology, University of New Brunswick, Fredericton, New Brunswick, Canada c Department of Geology, University of New Brunswick, Fredericton, New Brunswick, Canada d Department of Civil Engineering, University of New Brunswick, Fredericton, New Brunswick, Canada e Faculty of Forestry and Environmental Management, University of New Brunswick, Fredericton, New Brunswick, Canada Received 30 April 2004; accepted 2 July 2004 Water striders accurately reflect the entry of mercury in food chains of small freshwater systems. Abstract To circumvent some of the previous limitations associated with contaminant-monitoring programs, we tested the suitability of the water strider (Hemiptera: Gerridae) as a mercury sentinel by comparing total mercury concentrations in water striders and brook trout (Salvelinus fontinalis) from a variety of stream sites in New Brunswick, Canada. There was a strong association between the two variables across sites (r 2 Z 0.81, P ! 0.001) in systems where both atmospheric deposition and a point source (an abandoned gold mine) were likely contributing to ambient mercury levels. In a small stream draining the gold mine tailings pile, water striders had mercury concentrations an order of magnitude higher than those from reference locations. Temporal variation at three southern New Brunswick stream sites was non-significant. These results suggest that water strider mercury levels accurately quantify food chain entry of the element. The use of sentinel species holds great potential for expanding contaminant-monitoring programs. Ó 2004 Elsevier Ltd. All rights reserved. Keywords: Sentinel; Brook trout; Streams; Gold mine; Atmospheric deposition 1. Introduction Given that concentrations of contaminants, such as mercury, have increased in certain areas of the world over the past century (Schuster et al., 2002), there is a growing need to identify geographic areas of concern and associated ecological pathways (Pilgrim et al., 2001). To achieve these goals, it is necessary to have consistent measurement indices, allowing comparisons to be made locally, regionally, and globally. One approach to unifying otherwise diverging monitoring efforts is through the use of sentinel species (Beeby, 2001). Sentinel species accurately reflect ambient con- taminant concentrations, and can be routinely and conveniently collected and analyzed as part of monitor- ing programs. In this regard, invertebrate species are commonly used as environmental sentinels, as exempli- fied by extensive monitoring of contaminant levels in marine bivalves (O’Connor, 1998; Rebelo et al., 2003). In freshwater, shellfish have also been employed to measure contaminant concentrations along perceived * Corresponding author. University of New Brunswick, Loring Bailey Hall, Fredericton, New Brunswick, Canada, E3B 5A3. Tel.: C1-506-458-7148; fax: C1-506-453-3583. E-mail address: tim.jardine@unb.ca (T.D. Jardine). 0269-7491/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.envpol.2004.07.006 Environmental Pollution 134 (2005) 165–171 www.elsevier.com/locate/envpol