Here are some projects I have worked on...
Estimating human consumption of domoic acid in the Pacific Northwest
I am quantifying realistic, chronic, low-level DA exposure estimates for human shellfish consumers. Chronic low level exposure to domoic acid (DA) has been connected to such toxic effects as renal toxicity, increased toxin susceptibility and impaired mitochondrial function in laboratory studies, placing coastal communities at risk due to their high levels of shellfish consumption. Razor clams (Siliqua patula), in particular, are a commonly harvested shellfish that can retain DA up to one year, exposing human consumers to chronic low levels of DA (below the regulatory limit of 20 ppm). The results of this study will directly inform management policies protecting the health of human shellfish consumers from environmental toxins. Photo credit: Washington Department of Fish and Wildlife
I am quantifying realistic, chronic, low-level DA exposure estimates for human shellfish consumers. Chronic low level exposure to domoic acid (DA) has been connected to such toxic effects as renal toxicity, increased toxin susceptibility and impaired mitochondrial function in laboratory studies, placing coastal communities at risk due to their high levels of shellfish consumption. Razor clams (Siliqua patula), in particular, are a commonly harvested shellfish that can retain DA up to one year, exposing human consumers to chronic low levels of DA (below the regulatory limit of 20 ppm). The results of this study will directly inform management policies protecting the health of human shellfish consumers from environmental toxins. Photo credit: Washington Department of Fish and Wildlife
Evaluating trophic and non-trophic effects of shellfish aquaculture in Puget Sound
Expansion of the shellfish aquaculture industry has the potential to affect the structure and dynamics of coastal estuarine food webs. To better understand food web trade-offs, we incorporated both trophic and non-trophic interactions (e.g. habitat facilitation and predator refuge) into a food web model of central Puget Sound to predict the effects of an increase in geoduck (Panopea generosa) aquaculture. At a basin scale, the food web can support at least 120% increased geoduck aquaculture, above current production levels (landings of 10, 546 kg in 2012), with only minor changes in individual species’ biomass and/or metrics of ecosystem resilience. The non-trophic effects of increased geoduck aquaculture, related to the influence of anti-predator structure, had a stronger influence on the food web than the trophic role of cultured geoducks as filter-feeders and prey to other species. Increased geoduck culture caused substantial increases in biomass densities of surfperch, nearshore demersal fish, and small crabs, and decreases in seabirds, flatfish, and certain invertebrates (e.g. predatory gastropods and small crustaceans). This study identifies species that should be a priority for additional empirical research and monitoring related to bivalve aquaculture interactions, including demersal fish, small crustaceans, and seabirds. It also provides insights into the benefits and challenges of incorporating habitat-related data into a food web model. Understanding these relationships can inform management decisions by clarifying trade-offs in ecosystem functions and services in Puget Sound and facilitates estimation of direct and cumulative effects of bivalve aquaculture at a food web scale.
Expansion of the shellfish aquaculture industry has the potential to affect the structure and dynamics of coastal estuarine food webs. To better understand food web trade-offs, we incorporated both trophic and non-trophic interactions (e.g. habitat facilitation and predator refuge) into a food web model of central Puget Sound to predict the effects of an increase in geoduck (Panopea generosa) aquaculture. At a basin scale, the food web can support at least 120% increased geoduck aquaculture, above current production levels (landings of 10, 546 kg in 2012), with only minor changes in individual species’ biomass and/or metrics of ecosystem resilience. The non-trophic effects of increased geoduck aquaculture, related to the influence of anti-predator structure, had a stronger influence on the food web than the trophic role of cultured geoducks as filter-feeders and prey to other species. Increased geoduck culture caused substantial increases in biomass densities of surfperch, nearshore demersal fish, and small crabs, and decreases in seabirds, flatfish, and certain invertebrates (e.g. predatory gastropods and small crustaceans). This study identifies species that should be a priority for additional empirical research and monitoring related to bivalve aquaculture interactions, including demersal fish, small crustaceans, and seabirds. It also provides insights into the benefits and challenges of incorporating habitat-related data into a food web model. Understanding these relationships can inform management decisions by clarifying trade-offs in ecosystem functions and services in Puget Sound and facilitates estimation of direct and cumulative effects of bivalve aquaculture at a food web scale.
Salmon growth as an indicator of marine pelagic ecosystems
We measured insulin-like growth factor 1 (IGF1) concentrations (a proxy for growth rate) from juvenile coho (Oncorhynchus kisutch), sockeye (O. nerka), chum (O. keta), and Chinook salmon (O. tshawytscha) collected in eight regions of British Columbian coastal waters, in June of 2009, 2010, and 2011. We found annual differences in IGF1 for all four species of salmon, and species-specific regional differences in IGF1 concentrations in coho, chum and sockeye salmon. These results demonstrate that salmon growth responds to local environmental variability on a scale of several hundred kilometers. IGF1 levels provide a mechanism linking local environmental conditions to variable salmon growth rates.
We measured insulin-like growth factor 1 (IGF1) concentrations (a proxy for growth rate) from juvenile coho (Oncorhynchus kisutch), sockeye (O. nerka), chum (O. keta), and Chinook salmon (O. tshawytscha) collected in eight regions of British Columbian coastal waters, in June of 2009, 2010, and 2011. We found annual differences in IGF1 for all four species of salmon, and species-specific regional differences in IGF1 concentrations in coho, chum and sockeye salmon. These results demonstrate that salmon growth responds to local environmental variability on a scale of several hundred kilometers. IGF1 levels provide a mechanism linking local environmental conditions to variable salmon growth rates.
Regional variations in mercury concentrations in tuna
Mercury (Hg) concentrations in high trophic level fish, such as bigeye tuna (Thunnus obesus) and yellowfin tuna (Thunnus albacares), can often exceed consumption advisories. Here we sampled 444 yellowfin and bigeye tuna to determine whether tuna Hg concentration varies regionally in the eastern and central Pacific Ocean and whether this variation corresponds to environmental characteristics that promote the bioavailability of Hg. Of the five regions sampled, we found significantly higher Hg concentrations in the eastern equatorial region (5°S–5°N; 110°W–120°W) for both species. Hg concentrations in this region were elevated by 0.22 and 0.17 µg/g for yellowfin and bigeye tuna, respectively, compared with Hg concentrations in the other regions. Tuna selenium concentrations, which may alter the toxicity of Hg, did not vary by region. Oceanographic data indicated that the eastern equatorial region had elevated chlorophyll a concentrations and shallow minimum oxygen depths, both of which promote Hg methylation. These findings suggest that methylation - promoting mechanisms may translate into regional variation in the Hg concentrations of highly mobile, high trophic level fish.
Mercury (Hg) concentrations in high trophic level fish, such as bigeye tuna (Thunnus obesus) and yellowfin tuna (Thunnus albacares), can often exceed consumption advisories. Here we sampled 444 yellowfin and bigeye tuna to determine whether tuna Hg concentration varies regionally in the eastern and central Pacific Ocean and whether this variation corresponds to environmental characteristics that promote the bioavailability of Hg. Of the five regions sampled, we found significantly higher Hg concentrations in the eastern equatorial region (5°S–5°N; 110°W–120°W) for both species. Hg concentrations in this region were elevated by 0.22 and 0.17 µg/g for yellowfin and bigeye tuna, respectively, compared with Hg concentrations in the other regions. Tuna selenium concentrations, which may alter the toxicity of Hg, did not vary by region. Oceanographic data indicated that the eastern equatorial region had elevated chlorophyll a concentrations and shallow minimum oxygen depths, both of which promote Hg methylation. These findings suggest that methylation - promoting mechanisms may translate into regional variation in the Hg concentrations of highly mobile, high trophic level fish.
Tracking the fate of and flow of mercury through different food webs
Large pelagic predators in the marine environment accumulate relative high levels of mercury (Hg), yet it is difficult to identify the ecological factors that control the fate and flow of contaminants in marine systems, in part due to the difficulty in experimenting with large, dynamic ecosystems. Here we developed coupled contaminant-trophic mass balance models to describe the fate and flow of mercury (Hg) through the eastern tropical Pacific (ETP) and central north Pacific (CNP) pelagic food webs. We use the models to estimate Hg concentrations or Hg-elimination rates for the species groups in each region finding generally higher Hg concentrations in the ETP model. Specifically we found Hg concentrations of yellowfin, skipjack, bigeye, and albacore tunas increased by factors of two to four. Regional differences in tuna Hg concentrations can be solely explained by differences in diets of tuna and their prey, although changes in Hg input at the base of the food web can strongly influence Hg concentrations in top predators as well. These models foster network analysis on the scale of large, pelagic food webs that would not be possible through diet analysis alone. Our ability to draw firm conclusions regarding causal effects underlying known differences in Hg levels across ocean regions is restricted by data limitations that led to different assumptions made to construct the food web models.
Large pelagic predators in the marine environment accumulate relative high levels of mercury (Hg), yet it is difficult to identify the ecological factors that control the fate and flow of contaminants in marine systems, in part due to the difficulty in experimenting with large, dynamic ecosystems. Here we developed coupled contaminant-trophic mass balance models to describe the fate and flow of mercury (Hg) through the eastern tropical Pacific (ETP) and central north Pacific (CNP) pelagic food webs. We use the models to estimate Hg concentrations or Hg-elimination rates for the species groups in each region finding generally higher Hg concentrations in the ETP model. Specifically we found Hg concentrations of yellowfin, skipjack, bigeye, and albacore tunas increased by factors of two to four. Regional differences in tuna Hg concentrations can be solely explained by differences in diets of tuna and their prey, although changes in Hg input at the base of the food web can strongly influence Hg concentrations in top predators as well. These models foster network analysis on the scale of large, pelagic food webs that would not be possible through diet analysis alone. Our ability to draw firm conclusions regarding causal effects underlying known differences in Hg levels across ocean regions is restricted by data limitations that led to different assumptions made to construct the food web models.
Statistically-based
methods that use patterns of Hg bioaccumulation to estimate consumption rates
We developed an approach to estimate consumption rates by applying statistical methods to coupled
bioenergetics and individual-based mercury (Hg) mass balance models, applied to bigeye (Thunnus obesus), yellowfin (Thunnus albacares), skipjack (Katsuwonus pelamis), and albacore (Thunnus alalunga) tunas. Direct measurement of consumption rates for these highly migratory species involves laborious and infrequent point estimates, while individual bioenergetics or contaminant-based models are biased by errors in parameter estimation due to a lack of data. We linked bioenergetics and Hg mass balance models by using consumption rate estimates produced from the former as inputs into the latter and determined
whether the model could predict observed Hg-at-age. Consumption rate estimates derived from conventional bioenergetics and Hg mass balance models diverged considerably and the coupled bioenergetics-Hg mass balance model, based on default parameters, could not predict patterns of Hg accumulation. The statistical estimation approach (we found maximum likelihood estimates of metabolic expenditures related to swimming and the Hg concentration in tuna diets) generated biologically plausible daily consumption rates (yellowfin: 5.8–9%, skipjack: 4.5–6.7%, bigeye: 9.4–13% body weight for a 10 kg tuna), but failed to fit the albacore Hg data. Statistically based methods that use patterns of Hg bioaccumulation hold promise to advance our ability to estimate consumption rates, but are limited by high variance in Hg-at-size data and uncertainty in prey Hg data.
We developed an approach to estimate consumption rates by applying statistical methods to coupled
bioenergetics and individual-based mercury (Hg) mass balance models, applied to bigeye (Thunnus obesus), yellowfin (Thunnus albacares), skipjack (Katsuwonus pelamis), and albacore (Thunnus alalunga) tunas. Direct measurement of consumption rates for these highly migratory species involves laborious and infrequent point estimates, while individual bioenergetics or contaminant-based models are biased by errors in parameter estimation due to a lack of data. We linked bioenergetics and Hg mass balance models by using consumption rate estimates produced from the former as inputs into the latter and determined
whether the model could predict observed Hg-at-age. Consumption rate estimates derived from conventional bioenergetics and Hg mass balance models diverged considerably and the coupled bioenergetics-Hg mass balance model, based on default parameters, could not predict patterns of Hg accumulation. The statistical estimation approach (we found maximum likelihood estimates of metabolic expenditures related to swimming and the Hg concentration in tuna diets) generated biologically plausible daily consumption rates (yellowfin: 5.8–9%, skipjack: 4.5–6.7%, bigeye: 9.4–13% body weight for a 10 kg tuna), but failed to fit the albacore Hg data. Statistically based methods that use patterns of Hg bioaccumulation hold promise to advance our ability to estimate consumption rates, but are limited by high variance in Hg-at-size data and uncertainty in prey Hg data.
Environmental Indicators
An online survey of coastal practitioners, followed by personal interviews, was conducted to examine the potential of environmental indicators as tools in the management of estuaries along the Washington and Oregon coasts (U.S.A.). Specifically, the perceptions of coastal practitioners regarding current uses of indicators and factors limiting indicator use were explored. Results show that the organizations we surveyed generally do not use indicators to their full potential. Indicator use and factors limiting their use vary across both levels of government (Local, State, Federal) and job functions (Administration, Research, Planning & Development, Management, Education & Outreach). Limiting factors include lack of resources and unfamiliarity with indicators, especially in local management. These results demonstrate that while indicators are potentially beneficial management tools, realizing these benefits likely requires tailoring to the specific needs and limitations of intended users. The scientific community is well aware that a single set of environmental indicators can not be applied across all geographic or ecological scales. This study demonstrates that it is also necessary to recognize the breadth of the spectrum of user groups and management contexts, and how their individual characteristics may affect the applicability of environmental indicators, for them to be truly useful to management.
An online survey of coastal practitioners, followed by personal interviews, was conducted to examine the potential of environmental indicators as tools in the management of estuaries along the Washington and Oregon coasts (U.S.A.). Specifically, the perceptions of coastal practitioners regarding current uses of indicators and factors limiting indicator use were explored. Results show that the organizations we surveyed generally do not use indicators to their full potential. Indicator use and factors limiting their use vary across both levels of government (Local, State, Federal) and job functions (Administration, Research, Planning & Development, Management, Education & Outreach). Limiting factors include lack of resources and unfamiliarity with indicators, especially in local management. These results demonstrate that while indicators are potentially beneficial management tools, realizing these benefits likely requires tailoring to the specific needs and limitations of intended users. The scientific community is well aware that a single set of environmental indicators can not be applied across all geographic or ecological scales. This study demonstrates that it is also necessary to recognize the breadth of the spectrum of user groups and management contexts, and how their individual characteristics may affect the applicability of environmental indicators, for them to be truly useful to management.