The Cost of Tolerance: Sensitivity of Stream Benthic Communities to Uv-B and Metals

Abstract

Abstract. The ability to tolerate disturbance is a defense strategy that minimizes the effects of damage to fitness and is essential for sustainability of populations, communities, and ecosystems. Despite the apparent benefits of tolerance, there may be an associated cost that results in a deficiency of a system to respond to additional disturbances. Aquatic ecosystems are often exposed to a variety of natural and anthropogenic disturbances, and the effects of these compound perturbations are not well known. In this investigation, we examine whether tolerance to one stressor, metals, results in a cost of increased sensitivity to an additional stressor, ultraviolet-B (UV-B) radiation.Heavy metal pollution is recognized as a major environmental problem in Rocky Mountain streams. These high-elevation, typically clear streams may be at particular risk to elevated UV-B levels associated with reduced levels of ozone. Microcosm experiments were conducted using natural stream benthic communities collected from a reference site and a site with a long-term history of heavy-metal pollution. Direct and interactive effects of heavy metals and UV-B radiation on structural and functional characteristics of benthic communities were evaluated among four treatments: control, UV-B, metals, and metal and UV-B. Communities from the metal-polluted site were more tolerant of metals but less tolerant to UV-B compared to reference communities. Increased mayfly drift and reduced metabolism in response to metal exposure were observed in reference communities but not in the metal-polluted communities. In contrast to these results, UV-B radiation significantly reduced community metabolism, total macroinvertebrate abundance, and abundances of mayflies, caddisflies, and dipterans from the metal-polluted site, but had no effects on benthic communities from the reference site. ANOSIM results demonstrated that community responses differed among treatments at both sites. Metals had the largest impact on community differences at both sites, while UV-B had greater impacts at the metal-polluted site. This research demonstrates the need to account for potential costs associated with tolerance and that these costs can result in behavioral, structural, and functional impacts to benthic communities.

Solar and atmospheric forcing on mountain lakes

“…Intensive underwater UV results in changes in aquatic productivity and species composition, and it may severely alter the ecosystem structure and functions (Häder et al, 2015). Microcrustaceans, in particular, are vulnerable to the biologically harmful UV radiation (Hansson et al, 2007) but also the macrobenthic communities are known to respond to UV-B radiation (Kashian et al, 2007). In addition to UV radiation, the impacts of solar forcing in lakes are related to its increasing effects on water temperature and light availability for the benefit of primary production (Williamson et al, 2009) that probably also contribute to the changes found in the present study lakes.…”

How do aquatic communities respond to contaminants? It depends on the ecological context

“…Interestingly, the increased tolerance for one set of stressors often results in greater susceptibility to other, novel stressors. Stream microcosm experiments have shown that metal-tolerant communities were more susceptible to acidification [37], UV-B radiation [38], and predation [35] compared with reference communities. These findings suggest that communities retain a long-term record of exposure that may persist long after a contaminant has dissipated or degraded [39].…”

Stream ecosystem integrity is impaired by logging and shifting agriculture in a global megadiversity center (Sarawak, Borneo)

“…Non-metric multidimensional scaling (NMDS) ordination was used to explore variation in the composition of shredder assemblages across sites; goodness of fit of the ordination was assessed by the magnitude of the associated stress value (a value of b 0.2 corresponds to a good ordination; Kashian et al, 2007); we tested the hypothesis of differences in assemblage composition across stream types with Analysis of Similarities (ANOSIM), based on abundance data per sample. Principal Component Analysis (PCA) was used to summarize variation in environmental, riparian and leaf litter variables; Spearman correlations were used to explore relationships between these variables and the first two PCs (which accounted for most variation); finally, we used these two PCs in GLMs to test for environmental differences across stream types.…”