Blood Oxygen Depletion Is Independent of Dive Function in a Deep Diving Vertebrate, the Northern Elephant Seal

Although energetics is fundamental to animal ecology, traditional methods of determining metabolic rate are neither direct nor instantaneous. Recently, continuous blood oxygen (O2) measurements were used to assess energy expenditure in diving elephant seals (Mirounga angustirostris), demonstrating that an exceptional hypoxemic tolerance and exquisite management of blood O2 stores underlie the extraordinary diving capability of this consummate diver. As the detailed relationship of energy expenditure and dive behavior remains unknown, we integrated behavior, ecology, and physiology to characterize the costs of different types of dives of elephant seals. Elephant seal dive profiles were analyzed and O2 utilization was classified according to dive type (overall function of dive: transit, foraging, food processing/rest). This is the first account linking behavior at this level with in vivo blood O2 measurements in an animal freely diving at sea, allowing us to assess patterns of O2 utilization and energy expenditure between various behaviors and activities in an animal in the wild. In routine dives of elephant seals, the blood O2 store was significantly depleted to a similar range irrespective of dive function, suggesting that all dive types have equal costs in terms of blood O2 depletion. Here, we present the first physiological evidence that all dive types have similarly high blood O2 demands, supporting an energy balance strategy achieved by devoting one major task to a given dive, thereby separating dive functions into distinct dive types. This strategy may optimize O2 store utilization and recovery, consequently maximizing time underwater and allowing these animals to take full advantage of their underwater resources. This approach may be important to optimizing energy expenditure throughout a dive bout or at-sea foraging trip and is well suited to the lifestyle of an elephant seal, which spends > 90% of its time at sea submerged making diving its most “natural” state

A retrospective study of ecosystem effects of the 1976/77 regime shift in the eastern Pacific warm pool

Physical processes in surface ocean circulation are critical in shaping pelagic communities. On spatial scales that include entire ocean basins, climate oscillations drive changes in ocean physics that in turn shape biological production. The El Nin̋o Southern Oscillation (ENSO), for example, persists for 6 to 18 months, spatially enveloping physical changes in the tropical and eastern Pacific. On the other hand, the Pacific Decadal Oscillation (PDO), while having a similar spatial fingerprint, has "regimes" lasting 20 to 30 years. Changes in these regimes, or regime shifts, can happen abruptly (within a year), affecting pelagic ecosystems by altering processes regulating nutrient supply that in turn drive biological production (bottom-up forcing). With the benefit of hindsight, we now recognize that regime shifts have impacted ecosystems in the eastern Pacific, particularly in extra-tropical regions. Despite covering the largest portion of the worlds oceans, few long-term ecological data sets exists for tropical oceanic ecosystems. Thus, there is a lack knowledge as to how tropical open ocean systems react to regime shifts. In this dissertation, I retrospectively built physical and biological data sets to test hypotheses linking the 1976/ 77 Pacific Ocean regime shift to bottom-up effects of ecosystem change in a tropical and oceanic system, the eastern Pacific warm pool. I approached my research goals by analyzing three components of the eastern Pacific warm pool ecosystem during the 1960-2006 time period. First, I used historical hydrographic data from the World Ocean Database 2009 to characterize trends in thermocline depth and water column stratification in the upper 200 meters. Second, I tested hypotheses linking the 1976/77 Pacific Ocean regime shift to bottom-up control of ecosystem change in the eastern Pacific warm pool for mid-trophic- level organisms and apex predators. For the mid-trophic- level organisms I used ichthyoplankton samples collected during historical and contemporary expeditions to the eastern tropical Pacific. For the apex predators I used carbon and nitrogen stable isotope ratios measured from seabird feathers of a suite of ecologically and phylogenetically diverse seabird species collected in the eastern Pacific warm pool in 1960-2006 to gauge diet variability during this time period. I found evidence suggesting that multidecadal changes occurred in the thermal structure of the upper 200 meters in the eastern Pacific warm pool. Furthermore, I found evidence suggesting that organisms from two trophic levels responded differently to these environmental changes. Temoral variability in species assemblages of mid-trophic organisms, ichthyoplankton, appeared to be higher in regions of the study area where upwelling is prevalent, while assemblages from oceanic regions with less or no upwelling were stable. In contrast to variability of mid trophic-level organisms, the carbon and nitrogen stable isotope proxy for diet of apex predators, seabirds, showed little variation over time. These results are in agreement with the notion that physical forcing shapes nutrient fluctuations driving biological production and that lower trophic levels are more likely to respond to these fluctuations than long-lived apex predators. However, stable isotope proxy data and biological survey of apex predators in the northeastern Pacific have shown fluctuations coherent with ocean warming and the 1976/77 regime shift. The eastern tropical Pacific supports a unique multispecies community of apex predators comprised of around 50 resident seabird species and 30 cetacean species including several endemics and the world's largest yellowfin tuna fishery. The most recent regime shift is thought to have occurred in 1998/99. Future research should focus on more robust data sets that can further improve our knowledge of ecosystem effects of regime shifts in tropical system

A retrospective study of ecosystem effects of the 1976/77 regime shift in the eastern Pacific warm pool

Physical processes in surface ocean circulation are critical in shaping pelagic communities. On spatial scales that include entire ocean basins, climate oscillations drive changes in ocean physics that in turn shape biological production. The El Nin̋o Southern Oscillation (ENSO), for example, persists for 6 to 18 months, spatially enveloping physical changes in the tropical and eastern Pacific. On the other hand, the Pacific Decadal Oscillation (PDO), while having a similar spatial fingerprint, has "regimes" lasting 20 to 30 years. Changes in these regimes, or regime shifts, can happen abruptly (within a year), affecting pelagic ecosystems by altering processes regulating nutrient supply that in turn drive biological production (bottom-up forcing). With the benefit of hindsight, we now recognize that regime shifts have impacted ecosystems in the eastern Pacific, particularly in extra-tropical regions. Despite covering the largest portion of the worlds oceans, few long-term ecological data sets exists for tropical oceanic ecosystems. Thus, there is a lack knowledge as to how tropical open ocean systems react to regime shifts. In this dissertation, I retrospectively built physical and biological data sets to test hypotheses linking the 1976/ 77 Pacific Ocean regime shift to bottom-up effects of ecosystem change in a tropical and oceanic system, the eastern Pacific warm pool. I approached my research goals by analyzing three components of the eastern Pacific warm pool ecosystem during the 1960-2006 time period. First, I used historical hydrographic data from the World Ocean Database 2009 to characterize trends in thermocline depth and water column stratification in the upper 200 meters. Second, I tested hypotheses linking the 1976/77 Pacific Ocean regime shift to bottom-up control of ecosystem change in the eastern Pacific warm pool for mid-trophic- level organisms and apex predators. For the mid-trophic- level organisms I used ichthyoplankton samples collected during historical and contemporary expeditions to the eastern tropical Pacific. For the apex predators I used carbon and nitrogen stable isotope ratios measured from seabird feathers of a suite of ecologically and phylogenetically diverse seabird species collected in the eastern Pacific warm pool in 1960-2006 to gauge diet variability during this time period. I found evidence suggesting that multidecadal changes occurred in the thermal structure of the upper 200 meters in the eastern Pacific warm pool. Furthermore, I found evidence suggesting that organisms from two trophic levels responded differently to these environmental changes. Temoral variability in species assemblages of mid-trophic organisms, ichthyoplankton, appeared to be higher in regions of the study area where upwelling is prevalent, while assemblages from oceanic regions with less or no upwelling were stable. In contrast to variability of mid trophic-level organisms, the carbon and nitrogen stable isotope proxy for diet of apex predators, seabirds, showed little variation over time. These results are in agreement with the notion that physical forcing shapes nutrient fluctuations driving biological production and that lower trophic levels are more likely to respond to these fluctuations than long-lived apex predators. However, stable isotope proxy data and biological survey of apex predators in the northeastern Pacific have shown fluctuations coherent with ocean warming and the 1976/77 regime shift. The eastern tropical Pacific supports a unique multispecies community of apex predators comprised of around 50 resident seabird species and 30 cetacean species including several endemics and the world's largest yellowfin tuna fishery. The most recent regime shift is thought to have occurred in 1998/99. Future research should focus on more robust data sets that can further improve our knowledge of ecosystem effects of regime shifts in tropical system

Green abalone, Haliotis fulgens infected with the agent of withering syndrome do not express disease signs under a temperature regime permissive for red abalone, Haliotis rufescens

All California abalone species have been shown to be susceptible to infection with the bacterial agent of abalone withering syndrome (WS), although expression of signs of the disease may vary between species and with environmental conditions. We examined thermal modulation of WS expression in green abalone Haliotis fulgens at temperatures mimicking El Niño (18.0°C) and La Niña (14.2°C) events in southern California. In contrast to results obtained from previous experiments with red abalone, H. rufescens, the higher temperature did not result in higher infection intensities of the causative agent of the disease nor increase in clinical signs of disease. These results demonstrate clear differences in thermal regulation of disease expression between abalone species, and provide further data suggesting that green abalone should be a target species of recovery efforts in southern California, where WS is endemic

Blood oxygen depletion is independent of dive function in a deep diving vertebrate, the northern elephant seal.

Although energetics is fundamental to animal ecology, traditional methods of determining metabolic rate are neither direct nor instantaneous. Recently, continuous blood oxygen (O2) measurements were used to assess energy expenditure in diving elephant seals (Mirounga angustirostris), demonstrating that an exceptional hypoxemic tolerance and exquisite management of blood O2 stores underlie the extraordinary diving capability of this consummate diver. As the detailed relationship of energy expenditure and dive behavior remains unknown, we integrated behavior, ecology, and physiology to characterize the costs of different types of dives of elephant seals. Elephant seal dive profiles were analyzed and O2 utilization was classified according to dive type (overall function of dive: transit, foraging, food processing/rest). This is the first account linking behavior at this level with in vivo blood O2 measurements in an animal freely diving at sea, allowing us to assess patterns of O2 utilization and energy expenditure between various behaviors and activities in an animal in the wild. In routine dives of elephant seals, the blood O2 store was significantly depleted to a similar range irrespective of dive function, suggesting that all dive types have equal costs in terms of blood O2 depletion. Here, we present the first physiological evidence that all dive types have similarly high blood O2 demands, supporting an energy balance strategy achieved by devoting one major task to a given dive, thereby separating dive functions into distinct dive types. This strategy may optimize O2 store utilization and recovery, consequently maximizing time underwater and allowing these animals to take full advantage of their underwater resources. This approach may be important to optimizing energy expenditure throughout a dive bout or at-sea foraging trip and is well suited to the lifestyle of an elephant seal, which spends > 90% of its time at sea submerged making diving its most "natural" state

Blood oxygen depletion is independent of dive function in a deep diving vertebrate, the northern elephant seal.

Although energetics is fundamental to animal ecology, traditional methods of determining metabolic rate are neither direct nor instantaneous. Recently, continuous blood oxygen (O2) measurements were used to assess energy expenditure in diving elephant seals (Mirounga angustirostris), demonstrating that an exceptional hypoxemic tolerance and exquisite management of blood O2 stores underlie the extraordinary diving capability of this consummate diver. As the detailed relationship of energy expenditure and dive behavior remains unknown, we integrated behavior, ecology, and physiology to characterize the costs of different types of dives of elephant seals. Elephant seal dive profiles were analyzed and O2 utilization was classified according to dive type (overall function of dive: transit, foraging, food processing/rest). This is the first account linking behavior at this level with in vivo blood O2 measurements in an animal freely diving at sea, allowing us to assess patterns of O2 utilization and energy expenditure between various behaviors and activities in an animal in the wild. In routine dives of elephant seals, the blood O2 store was significantly depleted to a similar range irrespective of dive function, suggesting that all dive types have equal costs in terms of blood O2 depletion. Here, we present the first physiological evidence that all dive types have similarly high blood O2 demands, supporting an energy balance strategy achieved by devoting one major task to a given dive, thereby separating dive functions into distinct dive types. This strategy may optimize O2 store utilization and recovery, consequently maximizing time underwater and allowing these animals to take full advantage of their underwater resources. This approach may be important to optimizing energy expenditure throughout a dive bout or at-sea foraging trip and is well suited to the lifestyle of an elephant seal, which spends > 90% of its time at sea submerged making diving its most "natural" state

Blood oxygen depletion is independent of dive function in a deep diving vertebrate, the northern elephant seal.

Although energetics is fundamental to animal ecology, traditional methods of determining metabolic rate are neither direct nor instantaneous. Recently, continuous blood oxygen (O2) measurements were used to assess energy expenditure in diving elephant seals (Mirounga angustirostris), demonstrating that an exceptional hypoxemic tolerance and exquisite management of blood O2 stores underlie the extraordinary diving capability of this consummate diver. As the detailed relationship of energy expenditure and dive behavior remains unknown, we integrated behavior, ecology, and physiology to characterize the costs of different types of dives of elephant seals. Elephant seal dive profiles were analyzed and O2 utilization was classified according to dive type (overall function of dive: transit, foraging, food processing/rest). This is the first account linking behavior at this level with in vivo blood O2 measurements in an animal freely diving at sea, allowing us to assess patterns of O2 utilization and energy expenditure between various behaviors and activities in an animal in the wild. In routine dives of elephant seals, the blood O2 store was significantly depleted to a similar range irrespective of dive function, suggesting that all dive types have equal costs in terms of blood O2 depletion. Here, we present the first physiological evidence that all dive types have similarly high blood O2 demands, supporting an energy balance strategy achieved by devoting one major task to a given dive, thereby separating dive functions into distinct dive types. This strategy may optimize O2 store utilization and recovery, consequently maximizing time underwater and allowing these animals to take full advantage of their underwater resources. This approach may be important to optimizing energy expenditure throughout a dive bout or at-sea foraging trip and is well suited to the lifestyle of an elephant seal, which spends > 90% of its time at sea submerged making diving its most "natural" state

Assessing ecological correlates of marine bird declines to inform marine conservation.

Identifying drivers of ecosystem change in large marine ecosystems is central for their effective management and conservation. This is a sizable challenge, particularly in ecosystems transcending international borders, where monitoring and conservation of long-range migratory species and their habitats are logistically and financially problematic. Here, using tools borrowed from epidemiology, we elucidated common drivers underlying species declines within a marine ecosystem, much in the way epidemiological analyses evaluate risk factors for negative health outcomes to better inform decisions. Thus, we identified ecological traits and dietary specializations associated with species declines in a community of marine predators that could be reflective of ecosystem change. To do so, we integrated count data from winter surveys collected in long-term marine bird monitoring programs conducted throughout the Salish Sea--a transboundary large marine ecosystem in North America's Pacific Northwest. We found that decadal declines in winter counts were most prevalent among pursuit divers such as alcids (Alcidae) and grebes (Podicipedidae) that have specialized diets based on forage fish, and that wide-ranging species without local breeding colonies were more prone to these declines. Although a combination of factors is most likely driving declines of diving forage fish specialists, we propose that changes in the availability of low-trophic prey may be forcing wintering range shifts of diving birds in the Salish Sea. Such a synthesis of long-term trends in a marine predator community not only provides unique insights into the types of species that are at risk of extirpation and why, but may also inform proactive conservation measures to counteract threats--information that is paramount for species-specific and ecosystem-wide conservation