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4 Assessing Interactions Among Stressors
Pages 41-58

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From page 41...
... Understanding the way exposure to any one stressor morbidity, mortality, or reproductive failure for the indimay affect marine mammal populations is challenging; vidual. If sufficient individual-level responses occur, there understanding the population-level consequences of expo can be impacts on populations and, ultimately, communities sure to multiple stressors is far more challenging.
From page 42...
... Instead, most research has focused on in which the extrinsic stressors to which marine mammals detecting deviations from additivity, usually by assessing the are exposed may interact, and explains how stressors might significance of the interaction term in an analysis of variance be prioritized for cumulative effects analysis. Finally, that (ANOVA)
From page 43...
... (2013) analyzed 623 observations from of the observed reactions of marine mammals to extrinsic controlled factorial studies of the cumulative effects of tem- stressors, this suggests that assuming the effects of individual perature and acidification on calcification, photosynthesis, stressors are additive may frequently lead to an underestimareproduction, survival, and growth in marine organisms tion of their cumulative impact.
From page 44...
... (2013) used six measures (frequency of impact, whether cumulative effects is "What combinations of dosages of the impact was direct or indirect, likelihood of mortality, stressors are likely to elevate the effect enough to pose a risk individual recovery time, reproductive impact, and spread of to populations or ecosystems?
From page 45...
... There are more than a is required to provide an adequate assessment of cumulative hundred million chemical substances known to date,1 and a effects in these locations. recent report from the Centers for Disease Control and Pre vention provides data for 265 environmental chemicals that are a potential concern for human exposure.2 People, other PREDICTING HOW MULTIPLE STRESSORS terrestrial organisms, and marine organisms are all exposed ARE LIKELY TO INTERACT to this plethora of potentially toxic substances to varying A consideration of cumulative effects has been often dis- degrees and are most often exposed to mixtures of these cussed with respect to marine mammals (Wright and Kyhn, chemicals chronically or repeatedly throughout their lives.
From page 46...
... produces an effect of complexity, the overall physiological process or pathway 1.0, more than threefold higher than the sum of the individual for an adverse health outcome should be considered. Of responses (see Figure 4.2c)
From page 47...
... with a particular exposure to a stressor could be transient, co-occurrence with other stressor effects is still likely if the Acute Mortality exposure to the stressor is chronic. A number of the stressors listed in Table 4.1 (noise, some Finding 4.3: Predicting which combinations of dosages of organic chemicals and solvents, biotoxins, microparasites, stressors are likely to elevate cumulative effects enough to prey limitation, and predation pressure)
From page 48...
... or potential chronic exposure (macroparasites) Micro- or macro- Reif et al., 2006 Some, e.g., Some, e.g., Some, e.g., parasites morbillivirus; Brucella; morbillivirus; Van Bressem et Meegan et al., Van Bressem et al., 2014 2012 al., 2014 Other stressors with potential for chronic or repeated exposure Prey limitation Rosen and Eales, 1988; Crocker et al., Brock et al., Meyer-Gutbrod Kumagai, 2008; Ayres et al., 2006 2013a; Peck et et al., 2015; Shero et al., 2015 2012; Gobush et al., 2016 Ward et al., 2009; al., 2014 Robinson et al., 2012 Perceived threat Spoon and Isojunno et al., Brock et al., French et al., Romano, 2012; Di 2016 2013b 2011 Poi et al., 2015; Champagne et al., 2012 Predation pressure Newman et al., Creel et al., 2009 Creel et al., 2007; 2013; Narayan et al., 2009; Hua et al., 2013 2014; Zanette et al., 2011 Salinity Wilson et al., 1999; Mullin et al., 2015 NOTE: Publications highlighted in bold refer to studies involving marine mammals.
From page 49...
... , no stud- and these provide the potential synergistic interactions with ies have looked at the cumulative risk of sound and other other stressors. For example, sea lions exposed to domoic stressors through the HPA axis.
From page 50...
... Persistent adverse health outcomes cetacean species following morbillivirus outbreaks after involving this pathway were reported in bottlenose dolphins the outbreak had subsided (Uchida et al., 1999; Yang et al., following the DWH oil spill (Schwacke et al., 2014a, 2014b; 2006)
From page 51...
... Ecological immunology theory predicts allocation trade-offs PRIORITIZING STRESSORS FOR between reproductive effort and immune responses under CUMULATIVE EFFECTS ANALYSIS conditions of energy limitation (Graham et al., 2011)
From page 52...
... 52 APPROACHES TO UNDERSTANDING THE CUMULATIVE EFFECTS OF STRESSORS ON MARINE MAMMALS FIGURE 4.3  A decision tree for identifying situations where studies of the possible interactions between stressors should be given a high priority when considering the effect of a focal stressor on a population. See text for a detailed description of the decision-making process.
From page 53...
... In as noted above, these approaches do not provide a rigorous these cases, analyses that are based on structural equation assessment of cumulative impacts. However, several issues modeling or some other latent state modeling may better make the estimation of exposure to multiple stressors more account for the causal pathways by which stressors impact complicated than first meets the eye.
From page 54...
... In 2010, the NMFS established a Cook Inlet Beluga   8. unauthorized take (acute physical injury)
From page 55...
... When the decision tree from Figure 4.3 is applied to While the monitoring data range from problematic to the CI beluga population, one can see that the population less than ideal for pinnipeds and sea otters, they are essenis declining, existing stressor levels are likely to get worse tially nonexistent for regional stocks of small cetaceans in the future, there is no dominant stressor, and there are a except for killer whales. Two species are common in this area number of stressors (noise, nonbiological toxins, micropara- (harbor porpoise [Phocoena phocoena]
From page 56...
... from a kelp-dominated to a as such strong debate surrounds the potential importance deforested, sea urchin–dominated coastal sea floor (Estes et of the single stressors, progress in assessing the impacts al., 1998) and various knock-on influences of this "trophic of multiple stressors on marine mammals will remain an cascade" to other species and ecological processes (Estes et elusive goal.
From page 57...
... They used a series of logistic equations to model the Application of the decision tree from Figure 4.3 indi- potential effects of all these stressors on fecundity and pup cates that the affected populations are not increasing or near survival. Although the logistic equation does not explicitly carrying capacity, that some stressor levels are likely to include an interaction term, the predicted effects of the difincrease (grey seal numbers, and therefore grey seal preda- ferent stressors are not additive.


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