Parasites and Pollution: Why Both Matter to Marine Bird Conservation in the North

Wild animals are exposed to a number of factors ber of ways, including sensory disturbances and loss of that can affect both individuals and populations. muscle coordination (Liu et al., 2012). Habitat and food availability, disease, paraIn captive populations of birds, high Hg exposure has sites, and environmental pollutants all have the potential been associated with lower reproductive efforts, increased to influence their health and reproductive success (Heinz, deformities in developing young, and behavioral changes 1975; Hudson, 1986; Descamps et al., 2012; Vincenzi et al., (Heinz, 1979; Braune et al., 2012). In wild birds, increased 2013). Knowledge of how biotic and abiotic factors, such levels of Hg have also been linked with neurological as parasites and contaminants, can jointly influence indichanges, reduced reproduction, and decreased fat stores vidual reproduction is crucial to understanding what drives (Wayland et al., 2002; Burgess and Meyer, 2008; Scheu changes in individual health and populations; thus, it has a hammer et al., 2008), all of which indicate a decline in bearing on appropriate evidence-based wildlife conservafitness. Collectively, these changes can not only affect indi tion and management options (Wayland et al., 2002; Reed viduals of a species, but also have the potential, in highly et al., 2008). polluted areas, to affect species at the population level. Mercury (Hg) is of particular interest because of its A model using Hg burdens among free-living Common known negative impacts on organisms and the increasing Loons (Gavia immer) in highly polluted areas of eastern levels detected recently in the Canadian Arctic (Riget et al., North America found that Hg was likely having an impact 2011). Mercury is a trace metal that is found naturally in on local loon populations by lowering their reproductive the environment, but it is also released through the burnefforts (Meyer, 2005). ing of fossil fuels and other industrial processes (Munthe et In addition to environmental pollutants such as Hg, al., 2011). It is estimated that approximately 65% of global parasites can also affect wildlife species. Parasites are airborne Hg emissions originate in Asia (Munthe et al., naturally a part of every ecosystem, and by definition ulti 2011). Large atmospheric depositions of Hg occur in northmately compete with hosts for resources (Hatcher and ern Nofth America because global circulation patterns Dunn, 2011). Parasites can thus either cause hosts to have carry gaseous Hg across the Pacific (Jaffe et al., 2005). As reduced reserves, or impose the need for hosts to acquire a result, Hg concentrations in some regions of the Canadian more resources in order to compensate for the nutrient Arctic continue to rise even though Hg emissions have been drain (Hatcher and Dunn, 2011). Captive populations have reduced in North America (Munthe et al., 2011; Riget et al., demonstrated that parasites can have a range of negative 2011). effects on avian hosts. Breeding American Kestrels {Falco Most of the Hg deposited from atmospheric sources into sparverius) experimentally infected with nematodes {Trich the terrestrial, aquatic, and marine ecosystems is in the inellapseudospiralis) were found to have a decline in flying form of gaseous elemental Hg. Once elemental Hg is deposactivity and an increase in stress behaviours such as gaping ited, methylmercury (MeHg) is formed by bacterial methyland scratching (Saumier et al., 1991). Parasites can influ ation in both freshwater and marine environments (Barkay ence reproductive success as well as affecting individual et al., 2011; Lehnherr et al., 2011). Methylmercury is then health. For example, nematodes {Trichostrongylus tenius) accumulated and biomagnified through the food chain, and have been found to reduce fecundity of female Red Grouse high concentrations occur within the tissues of organisms {Lagopus lagopus scoticus), which can lead to population at upper trophic levels (Campbell et al., 2005). regulation (Hudson and Dobson, 1991). Increased burdens of MeHg have been found to influence Parasites do not act on host condition and health in iso animal health and reproduction, and MeHg is considered lation, but are also influenced by other external factors, toxic (Dietz et al., 2013). For example, MeHg can act as an such as pollutants. Parasites and contaminants can lead to enzyme inhibitor and may irreversibly disrupt a number of a decline in host health and reproduction independently of metabolic processes (Hoffman et al., 2002). Methylmercury each other, but when both are present, their interactions exposure can also cause oxidative cellular injury, in which may be complex (Marcogliese and Pietrock, 2011; Min it disrupts receptor signaling pathways associated with the guez et al., 2012). Either parasites or contaminants can endocrine system and thereby disrupts gene regulation of alter immune functions and thus influence how a host is the body's protective mechanisms (Ung et al., 2010). Thus, affected by the other. A host exposed to parasites typically Hg not only causes direct damage to cells, but also can have mounts an immune response, which may be energetically an indirect effect on metabolic pathways, leaving cells open costly (reviewed by Bulte et al., 2012). In turn, the presence

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