The Effects of Lateral Shoreline Distance from Rivers on Mercury Concentrations in Long-Jawed Orb Weaver Spiders

Abstract

Mercury (Hg) in the environment is one of the largest environmental problems facing the world. When mercury is converted to the bioavailable form called methylmercury (MeHg), it poses a significant risk to vertebrates and can reduce reproductive success. Assessing mercury contamination in aquatic systems is challenging because the concentration of mercury in water is not representative of the bioavailable MeHg form in aquatic food webs. As a result, sentinel species are used to assess MeHg contamination in aquatic systems. Shoreline spiders, specifically long-jawed orb weavers (Tetragnathidae) have been proposed as a potential sentinel species; however, it is not currently known if spiders not collected directly off the shoreline are accurate in reflecting the aquatic MeHg concentration. The objective of this study was to test the hypothesis that mercury in shoreline spiders declines with distance from the water in a channelized river. Long-jawed orb weaver spiders were collected at different distances from the water's edge using sweep nets along the Clear Fork of the Trinity River, and these spider samples were analyzed for their mercury concentration at each of the distances. Mercury concentrations in long-jawed orb weavers did not change as the distance from the shoreline increased. The study indicates that long-jawed orb weavers can be used as sentinels up to thirty meters away from the water's edge in a channelized river.