Marine Biology Commons^™

Overhauling Ocean Spatial Planning To Improve Marine Megafauna Conservation, Ana Micaela Martins Sequeira, Graeme Clive Hays, David Sims, Víctor Eguíluz, Jorge Rodríguez, Michelle Heupel, Rob Harcourt, Hannah Calich, Nuno Queiroz, Daniel Paul Costa, Juan Fernández-Gracia, Luciana Ferreira, Simon David Goldsworthy, Mark Andrew Hindell, Mary-Anne Lea, Mark Meekan, Anthony Michael Pagano, Scott Shaffer, Julia Reisser, Michele Thums, Michael Weise, Carlos Duarte

Faculty Publications, Biological Sciences

Tracking data have led to evidence-based conservation of marine megafauna, but a disconnect remains between the many 1000s of individual animals that have been tracked and the use of these data in conservation and management actions. Furthermore, the focus of most conservation efforts is within Exclusive Economic Zones despite the ability of these species to move 1000s of kilometers across multiple national jurisdictions. To assist the goal of the United Nations General Assembly’s recent effort to negotiate a global treaty to conserve biodiversity on the high seas, we propose the development of a new frontier in dynamic marine spatial management. …

Re-Examination Of The Effects Of Food Abundance On Jaw Plasticity In Purple Sea Urchins, Maya S. Devries, Summer Webb, Jennifer R. A. Taylor

Faculty Publications, Biological Sciences

Morphological plasticity is a critical mechanism that animals use to cope with variations in resource availability. During periods of food scarcity, sea urchins demonstrate an increase in jaw length relative to test diameter. This trait is thought to be reversible and adaptive by yielding an increase in feeding efficiency. We directly test the hypotheses that (1) there are reversible shifts in jaw length to test diameter ratios with food abundance in individual urchins, and (2) these shifts alter feeding efficiency. Purple sea urchins, Strongylocentrotus purpuratus, were collected and placed in either high or low food treatments for 3 months, …

Plasticity Of Foraging Behaviors In Response To Diverse Environmental Conditions, Morgan Gilmour, José Castillo‐Guerrero, Abram Fleishman, Salvador Hernández‐Vázquez, Hillary Young, Scott Shaffer

Faculty Publications, Biological Sciences

Due to rapidly changing global environmental conditions, many animals are now experiencing concurrent changes in both resource availability and the foraging cues associated with finding those resources. By employing flexible, plastic foraging strategies that use different types of environmental foraging cues, animals could adapt to these novel future environments. To evaluate the extent to which such flexibility and plasticity exist, we analyzed a large dataset of a clade (Sulidae; the boobies) of widespread aerial tropical predators that feed in highly variable marine habitats. These surface foragers are typical of many ocean predators that face dynamic and patchy foraging environments and …

Persistent Annual Migration Patterns Of A Specialist Seabird, Rachael Orben, Nobuo Kokubun, Abram Fleishman, Alexis Will, Takashi Yamamoto, Scott Shaffer, Rosana Paredes, Akinori Takahashi, Alexander Kitaysky

Faculty Publications, Biological Sciences

Specialization can make animals vulnerable to rapid environmental changes. For long-lived seabirds, foraging specialization may make individuals especially sensitive, as climatic changes are currently occurring over the course of one lifetime. The Bering Sea is a dynamic subarctic and arctic ecosystem where windblown sea ice mediates annual productivity and subsequent pathways to upper trophic levels. Red-legged kittiwakes Rissa brevirostris are endemic surface foraging seabirds specializing on myctophid fishes during reproduction. Their degree of specialization outside the breeding season is less understood. We examined their non-breeding ecology (migration, distribution, isotopic niche) during 4 winters with varying sea ice extent. Although we …

Fisheries Exploitation By Albatross Quantified With Lipid Analysis, Melinda Conners, Chandra Goetsch, Suzanne Budge, William Walker, Yoko Mitani, Daniel Costa, Scott Shaffer

Faculty Publications, Biological Sciences

Mortality from incidental bycatch in longline fishery operations is a global threat to seabird populations, and especially so for the albatross family (Diomedeidae) in which 15 out of 22 species are threatened with extinction. Despite the risks, fisheries remain attractive to many species of seabird by providing access to high-energy foods in the form of discarded fish and offal, target fish, and baited hooks. Current policy regarding fisheries management is increasingly aimed at discard reform, exemplified by a discard ban initiated in the European Union Common Fisheries Policy in 2014. While there is global agreement on the importance of minimizing …

Variable Utilization Of Shelf Break-Associated Habitats By Chick-Brooding Rhinoceros Auklets In The California Current System, Bradley Wilkinson, Jaime Jahncke, Pete Warzybok, Russell Bradley, Scott A. Shaffer

Faculty Publications, Biological Sciences

Identifying frequently complex and dynamic spatial distributions of marine predators via the modeling of at-sea observations can be inherently challenging, especially when attempting to predict habitats of specific populations. Remotely-sensed tracking devices provide a viable alternative way to gather this information. We collected fine-scale spatiotemporal movement data for a small seabird, the rhinoceros auklet Cerorhinca monocerata, in the California Current System. Chick-brooding adults nesting on Southeast Farallon Island were outfitted with GPS loggers during the 2015 and 2016 breeding seasons (n = 15). Along with basic movement parameters, kernel density and residence time analyses were conducted to characterize at-sea distribution …

The Political Biogeography Of Migratory Marine Predators, Autumn-Lynn Harrison, Daniel Costa, Arliss Winship, Scott Benson, Steven Bograd, Michelle Antolos, Aaron Carlisle, Heidi Dewar, Peter Dutton, Salvador Jorgensen, Suzanne Kohin, Bruce Mate, Patrick Robinson, Kurt Schaefer, Scott A. Shaffer, George Shillinger, Samantha Simmons, Kevin Weng, Kristina Gjerde, Barbara Block

Faculty Publications, Biological Sciences

During their migrations, marine predators experience varying levels of protection and face many threats as they travel through multiple countries’ jurisdictions and across ocean basins. Some populations are declining rapidly. Contributing to such declines is a failure of some international agreements to ensure effective cooperation by the stakeholders responsible for managing species throughout their ranges, including in the high seas, a global commons. Here we use biologging data from marine predators to provide quantitative measures with great potential to inform local, national and international management efforts in the Pacific Ocean. We synthesized a large tracking data set to show how …

Foraging Behavior And Energetics Of Albatrosses In Contrasting Breeding Environments, Michelle Antolos, Scott Shaffer, Henri Weimerskirch, Yann Tremblay, Daniel Costa

Faculty Publications, Biological Sciences

Animals can maximize fitness by optimizing energy acquisition through the selection of favorable foraging habitats, but trade-offs exist between time spent in preferred feeding habitats, energetic costs of travel, and reproductive constraints. For pelagic seabirds, geographic distribution of suitable breeding islands can restrict access to marine prey resources and influence foraging strategies. Laysan (Phoebastria immutabilis) and black-footed albatrosses (P. nigripes) breeding in the Northwest Hawaiian Islands, and Indian yellow-nosed albatrosses (Thalassarche carteri) breeding in the Southern Indian Ocean, utilize productive subtropical-subpolar transition zones during their breeding and non-breeding periods, but this marine feature is at a comparatively greater distance for …

Thermal History And Gape Of Individual Mytilus Californianus Correlate With Oxidative Damage And Thermoprotective Osmolytes, Lani Gleason, Luke Miller, Jacob Winnikoff

Faculty Publications, Biological Sciences

The ability of animals to cope with environmental stress depends – in part – on past experience, yet knowledge of the factors influencing an individual's physiology in nature remains underdeveloped. We used an individual monitoring system to record body temperature and valve gaping behavior of rocky intertidal zone mussels (Mytilus californianus). Thirty individuals were selected from two mussel beds (wave-exposed and wave-protected) that differ in thermal regime. Instrumented mussels were deployed at two intertidal heights (near the lower and upper edges of the mussel zone) and in a continuously submerged tidepool. Following a 23-day monitoring period, measures of …

Multimodal In Situ Datalogging Quantifies Inter-Individual Variation In Thermal Experience And Persistent Origin Effects On Gaping Behavior Among Intertidal Mussels (Mytilus Californianus), Luke P. Miller, Wesley Dowd

Faculty Publications, Biological Sciences

In complex habitats, environmental variation over small spatial scales can equal or exceed larger-scale gradients. This small-scale variation may allow motile organisms to mitigate stressful conditions by choosing benign microhabitats, whereas sessile organisms may rely on other behaviors to cope with environmental stresses in these variable environments. We developed a monitoring system to track body temperature, valve gaping behavior and posture of individual mussels (Mytilus californianus) in field conditions in the rocky intertidal zone. Neighboring mussels' body temperatures varied by up to 14°C during low tides. Valve gaping during low tide and postural adjustments, which could theoretically lower …

Quantifying The Top-Down Effects Of Grazers On A Rocky Shore: Selective Grazing And The Potential For Competition, Diana Lascala-Gruenewald, Luke Miller, Matthew Bracken, Bengt Allen, Mark Denny

Faculty Publications, Biological Sciences

The effect of grazers on the diversity, distribution, and composition of their principal food source has rarely been described for the high intertidal zone of rocky shores, a model system for studying the potential effects of climate change. Along rocky, wave-swept shores in central California, the microphytobenthos (MPB) supports diverse assemblages of limpets and littorine snails, which, at current benign temperatures, could potentially partition food resources in a complementary fashion, thereby enhancing secondary productivity. Two limpet species in particular, Lottia scabra and L. austrodigitalis, may partition components of the MPB, and are likely to affect the composition of the …

Long-Term, High Frequency In Situ Measurements Of Intertidal Mussel Bed Temperatures Using Biomimetic Sensors, Brian Helmuth, Francis Choi, Allison Matzelle, Jessica Torossian, Scott Morello, K.A.S. Mislan, Lauren Yamane, Denise Strickland, P. Szathmary, Sarah Gilman, Alyson Tockstein, Thomas Hilbish, Michael Burrows, Anne Marie Power, Elizabeth Gosling, Nova Mieszkowska, Christopher Harley, Michael Nishizaki, Emily Carrington, Bruce Menge, Laura Petes, Melissa Foley, Angela Johnson, Megan Poole, Mae Noble, Erin Richmond, Matt Robart, Jonathan Robinson, Jerod Sapp, Jackie Sones, Bernardo Broitman, Mark Denny, Katharine Mach, Luke P. Miller, Michael O'Donnell, Philip Ross, Gretchen Hofmann, Mackenzie Zippay, Carol Blanchette, J. Macfarlan, Eugenio Carpizo-Ituarte, Benjamin Ruttenberg, Carlos Peña Mejía, Christopher Mcquaid, Justin Lathlean, Cristián Monaco, Katy Nicastro, Gerardo Zardi

Faculty Publications, Biological Sciences

At a proximal level, the physiological impacts of global climate change on ectothermic organisms are manifest as changes in body temperatures. Especially for plants and animals exposed to direct solar radiation, body temperatures can be substantially different from air temperatures. We deployed biomimetic sensors that approximate the thermal characteristics of intertidal mussels at 71 sites worldwide, from 1998-present. Loggers recorded temperatures at 10–30 min intervals nearly continuously at multiple intertidal elevations. Comparisons against direct measurements of mussel tissue temperature indicated errors of ~2.0–2.5 °C, during daily fluctuations that often exceeded 15°–20 °C. Geographic patterns in thermal stress based on biomimetic …

Individual-Level Variation And Higher-Level Interpretations Of Space Use In Wide-Ranging Species: An Albatross Case Study Of Sampling Effects, Sarah Gutowsky, Marty Leonard, Melinda Conners, Scott A. Shaffer, Ian Jonsen

Faculty Publications, Biological Sciences

Marine ecologists and managers need to know the spatial extent of at-sea areas most frequented by the groups of wildlife they study or manage. Defining group-specific ranges and distributions (i.e., space use at the level of species, population, age-class, etc.) can help to identify the source or severity of common or distinct threats among different at-risk groups. In biologging studies, this is accomplished by estimating the space use of a group based on a sample of tracked individuals. A major assumption of these studies is consistency in individual movements among members of a group. The implications of scaling up individual-level …

Wintering North Pacific Black-Legged Kittiwakes Balance Spatial Flexibility And Consistency, Rachael Orben, Rosana Paredes, Daniel Roby, David Irons, Scott A. Shaffer

Faculty Publications, Biological Sciences

Background Marine environments are inherently dynamic, yet marine predators are often long-lived and employ strategies where consistency, individual specialization, routine migrations, and spatial memory are key components to their foraging and life-history strategies. Intrinsic determinates of animal movements are linked to physiological and life-history traits (e.g. sex, colony, experience), while extrinsic influences occur as the result of an animal’s interactions with either other animals or the environment (e.g. prey availability, weather, competition). Knowledge of the factors affecting animal movements is critical to understand energetic bottlenecks and population dynamics. Here, we attempt to understand the interaction of some of these factors …

Foraging Behavior Links Climate Variability And Reproduction In North Pacific Albatrosses, Lesley Thorne, Elliott Hazen, Steven Bograd, David Foley, Melinda Conners, Michelle Kappes, Hyemi Kim, Daniel Costa, Yann Tremblay, Scott A. Shaffer

Faculty Publications, Biological Sciences

Background: Climate-driven environmental change in the North Pacific has been well documented, with marked effects on the habitat and foraging behavior of marine predators. However, the mechanistic linkages connecting climate-driven changes in behavior to predator populations are not well understood. We evaluated the effects of climate-driven environmental variability on the reproductive success and foraging behavior of Laysan and Black-footed albatrosses breeding in the Northwest Hawaiian Islands during both brooding and incubating periods. We assessed foraging trip metrics and reproductive success using data collected from 2002–2012 and 1981–2012, respectively, relative to variability in the location of the Transition Zone Chlorophyll Front …

Reproductive Constraints Influence Habitat Accessibility, Segregation, And Preference Of Sympatric Albatross Species, Michelle Kappes, Scott Shaffer, Yann Tremblay, David Foley, Daniel Palacios, Steven Bograd, Daniel Costa

Faculty Publications, Biological Sciences

The spatiotemporal distribution of animals is dependent on a suite of factors, including the distribution of resources, interactions within and between species, physiological limitations, and requirements for reproduction, dispersal, or migration. During breeding, reproductive constraints play a major role in the distribution and behavior of central place foragers, such as pelagic seabirds. We examined the foraging behavior and marine habitat selection of Laysan (Phoebastria immutabilis) and black-footed (P. nigripes) albatrosses throughout their eight month breeding cycle at Tern Island, Northwest Hawaiian Islands to evaluate how variable constraints of breeding influenced habitat availability and foraging decisions. We used satellite tracking and …

Shadowed By Scale: Subtle Behavioral Niche Partitioning In Two Sympatric, Tropical Breeding Albatross Species, Melinda Conners, Elliott Hazen, Daniel Costa, Scott A. Shaffer

Faculty Publications, Biological Sciences

Background To meet the minimum energetic requirements needed to support parents and their provisioned offspring, the timing of breeding in birds typically coincides with periods of high food abundance. Seasonality and synchrony of the reproductive cycle is especially important for marine species that breed in high latitudes with seasonal booms in ocean productivity. Laysan and black-footed albatrosses breeding in the northwestern Hawaiian Islands have a dual reliance on both seasonally productive waters of high latitudes and on nutrient-poor waters of low latitudes, because their foraging ranges contract during the short but critical brood-guard stage. Therefore, these species face an additional …

Seasonal And Interannual Oxygen Variability On The Washington And Oregon Continental Shelves, S. Siedlecki, N. Banas, K. Davis, S. Giddings, B. Hickey, P. Maccready, Thomas Connolly, S. Geier

Faculty Publications

The coastal waters of the northern portion of the California Current System experience a seasonal decline in oxygen concentrations and hypoxia over the summer upwelling season that results in negative impacts on habitat for many organisms. Using a regional model extending from 43°N to 50°N, with an oxygen component developed in this study, drivers of seasonal and regional oxygen variability are identified. The model includes two pools of detritus, which was an essential addition in order to achieve good agreement with the observations. The model was validated using an extensive array of hydrographic and moored observations. The model captures the …

A Tide Prediction And Tide Height Control System For Laboratory Mesocosms, Luke Miller, Jeremy Long

Faculty Publications, Biological Sciences

Experimental mesocosm studies of rocky shore and estuarine intertidal systems may benefit from the application of natural tide cycles to better replicate variation in immersion time, water depth, and attendant fluctuations in abiotic and edaphic conditions. Here we describe a stand-alone microcontroller tide prediction open-source software program, coupled with a mechanical tidal elevation control system, which allows continuous adjustment of aquarium water depths in synchrony with local tide cycles. We used this system to monitor the growth of Spartina foliosa marsh cordgrass and scale insect herbivores at three simulated shore elevations in laboratory mesocosms. Plant growth decreased with increasing shore …

Daily Activity Budgets Reveal A Quasi-Flightless Stage During Non-Breeding In Hawaiian Albatrosses, Sarah Gutowsky, Lee Gutowsky, Ian Jonsen, Marty Leonard, Maura Naughton, Marc Romano, Scott A. Shaffer

Faculty Publications, Biological Sciences

Background Animals adjust activity budgets as competing demands for limited time and energy shift across life history phases. For far-ranging migrants and especially pelagic seabirds, activity during breeding and migration are generally well studied but the “overwinter” phase of non-breeding has received less attention. Yet this is a critical time for recovery from breeding, plumage replacement and gaining energy stores for return migration and the next breeding attempt. We aimed to identify patterns in daily activity budgets (i.e. time in flight, floating on the water’s surface and active foraging) and associated spatial distributions during overwinter for the laysan Phoebastria immutabilis …

Interannual Variability Of Wintertime Temperature On The Inner Continental Shelf Of The Middle Atlantic Bight, Thomas Connolly, Steven Lentz

Faculty Publications

The shallow depth of the inner continental shelf allows for rapid adjustment of the ocean to air-sea exchange of heat and momentum compared with offshore locations. Observations during 2001–2013 are used to evaluate the contributions of air-sea heat flux and oceanic advection to interannual variability of inner-shelf temperature in the Middle Atlantic Bight. Wintertime processes are important for interpreting regional interannual variability at nearshore locations since winter anomalies account for 69–77% of the variance of the annual anomalies and are correlated over broad along-shelf scales, from New England to North Carolina. At the Martha's Vineyard Coastal Observatory on the 12 …

Hindcasts Of Potential Harmful Algal Bloom Transport Pathways On The Pacific Northwest Coast, S. Giddings, P. Maccready, B. Hickey, N. Banas, K. Davis, S. Siedlecki, V. Trainer, R. Kudela, N. Pelland, Thomas Connolly

Faculty Publications

Harmful algal blooms (HABs) pose a significant threat to human and marine organism health, and negatively impact coastal economies around the world. An improved understanding of HAB formation and transport is required to improve forecasting skill. A realistic numerical simulation of the US Pacific Northwest region is used to investigate transport pathways from known HAB formation hot spots, specifically for Pseudo-nitzschia (Pn), to the coast. We show that transport pathways are seasonal, with transport to the Washington (WA) coast from a northern source (the Juan de Fuca Eddy) during the summer/fall upwelling season and from a southern source (Heceta Bank) …

Regional Impact Of Submarine Canyons During Seasonal Upwelling, Thomas Connolly, Barbara Hickey

Faculty Publications

A numerical model of the northern California Current System along the coasts of Washington and British Columbia is used to quantify the impact of submarine canyons on upwelling from the continental slope onto the shelf. Comparisons with an extensive set of observations show that the model adequately represents the seasonal development of near-bottom density, as well as along-shelf currents that are critical in governing shelf-slope exchange. Additional model runs with simplified coastlines and bathymetry are used to isolate the effects of submarine canyons. Near submarine canyons, equatorward flow over the outer shelf is correlated with dense water at canyon heads …

Coastal Trapped Waves, Alongshore Pressure Gradients, And The California Undercurrent, Thomas Connolly, Barbara Hickey, Igor Shulman, Richard Thomson

Faculty Publications

The California Undercurrent (CUC), a poleward-flowing feature over the continental slope, is a key transport pathway along the west coast of North America and an important component of regional upwelling dynamics. This study examines the poleward undercurrent and alongshore pressure gradients in the northern California Current System (CCS), where local wind stress forcing is relatively weak. The dynamics of the undercurrent are compared in the primitive equation Navy Coastal Ocean Model and a linear coastal trapped wave model. Both models are validated using hydrographic data and current-meter observations in the core of the undercurrent in the northern CCS. In the …

High Predation On Small Populations: Avian Predation On Imperiled Salmonids, Ann-Marie Osterback, Danielle Frechette, Andrew Shelton, Sean Hayes, Morgan Bond, Scott A. Shaffer, Jonathan Moore

Faculty Publications, Biological Sciences

Generalist predators can contribute to extinction risk of imperiled prey populations even through incidental predation. Quantifying predation on small populations is important to manage their recovery, however predation is often challenging to observe directly. Recovery of prey tags at predator colonies can indirectly provide minimum estimates of predation, however overall predation rates often remain unquantifiable because an unknown proportion of tags are deposited off‐colony. Here, we estimated overall predation rates on threatened wild juvenile steelhead Oncorhynchus mykiss by generalist adult Western Gulls Larus occidentalis in six central California (USA) watersheds. We estimated predation rates by gulls from the recapture of …

University Scholar Series: Scott Shaffer, Scott Shaffer

University Scholar Series

A New Form Of Biotechnology: Novel Data Logging Devices Reveal Secrets About The Lives Of Marine Animals

On September 25, 2013, Dr. Scott Shaffer gave a talk titled “A New Form Of Biotechnology: Novel Data Logging Devices Reveal Secrets About The Lives Of Marine Animals” as part of the University Scholar Series hosted by Provost Ellen Junn at the Dr. Martin Luther King, Jr. Library. Dr. Shaffer’s research focuses on the ecology, physiology, and conservation of marine vertebrate species. Specifically, he uses novel smart technologies to study long-range movements, distribution, and behavior of wild seabirds and marine mammals. This new …

A Springtime Source Of Toxic Pseudo-Nitzschia Cells On Razor Clam Beaches In The Pacific Northwest, Barbara Hickey, Vera Trainer, P. Kosro, Nicolaus Adams, Thomas Connolly, Nancy Kachel, Susan Geier

Faculty Publications

Concentrations of domoic acid (DA) above the regulatory limit in Washington coast razor clams are usually higher on northern beaches from summer to fall. Recent field studies have confirmed that the primary source of toxic Pseudo-nitzschia (PN) cells in those seasons is a semi-retentive topographically trapped seasonal eddy located offshore and north of the clamming beaches. Another semi-retentive coastal feature, Heceta Bank, that has been shown to support toxic PN cells in summer, is located south of Washington’s clamming beaches. In this paper we present evidence to demonstrate that Heceta Bank, although not a likely source of toxic cells to …

Contemporary And Historical Separation Of Transequatorial Migration Between Genetically Distinct Seabird Populations, M J. Rayner, M E. Hauber, T E. Steeves, H A. Lawrence, D R. Thompson, P M. Sagar, S J. Bury, R A. Phillips, T J. Landers, L Ranjard, Scott A. Shaffer

Scott A. Shaffer

Pelagic seabirds are highly mobile, reducing the likelihood of allopatric speciation where disruption of gene flow between populations is caused by physically insurmountable, extrinsic barriers. Spatial segregation during the non-breeding season appears to provide an intrinsic barrier to gene flow among seabird populations that otherwise occupy nearby or overlapping regions during breeding, but how this is achieved remains unclear. Here we show that the two genetically distinct populations of Cook's petrel (Pterodroma cookii) exhibit transequatorial separation of non-breeding ranges at contemporary (ca. 2–3 yrs) and historical (ca. 100 yrs) time scales. Segregation during the non-breeding season per se appears as …

Contemporary And Historical Separation Of Transequatorial Migration Between Genetically Distinct Seabird Populations, M J. Rayner, M E. Hauber, T E. Steeves, H A. Lawrence, D R. Thompson, P M. Sagar, S J. Bury, R A. Phillips, T J. Landers, L Ranjard, Scott A. Shaffer

Faculty Publications, Biological Sciences

Pelagic seabirds are highly mobile, reducing the likelihood of allopatric speciation where disruption of gene flow between populations is caused by physically insurmountable, extrinsic barriers. Spatial segregation during the non-breeding season appears to provide an intrinsic barrier to gene flow among seabird populations that otherwise occupy nearby or overlapping regions during breeding, but how this is achieved remains unclear. Here we show that the two genetically distinct populations of Cook's petrel (Pterodroma cookii) exhibit transequatorial separation of non-breeding ranges at contemporary (ca. 2–3 yrs) and historical (ca. 100 yrs) time scales. Segregation during the non-breeding season per se appears as …

Processes Influencing Seasonal Hypoxia In The Northern California Current System, Thomas Connolly, Barbara Hickey, S. Geier, William Cochlan

Faculty Publications

This paper delineates the role of physical and biological processes contributing to hypoxia, dissolved oxygen (DO) < 1.4 mL/L, over the continental shelf of Washington State in the northern portion of the California Current System. In the historical record (1950–1986), during the summer upwelling season, hypoxia is more prevalent and severe off Washington than further south off northern Oregon. Recent data (2003–2005) show that hypoxia over the Washington shelf occurred at levels previously observed in the historical data. The year 2006 was an exception, with hypoxia covering ∼5000 km2 of the Washington continental shelf and DO concentrations below 0.5 mL/L at the inner shelf, lower than any known previous observations at that location. In the 4 years studied, upwelling of low DO water and changes in source water contribute to interannual variability, but cannot account for seasonal decreases below hypoxic concentrations. Deficits of DO along salinity surfaces, indicating biochemical consumption of DO, vary significantly between surveys, accounting for additional decreases of 0.5–2.5 mL/L by late summer. DO consumption is associated with denitrification, an indicator of biochemical sediment processes. Mass balances of DO and nitrate show that biochemical processes in the water column and sediments each contribute ∼50% to the total consumption of DO in near-bottom water. At shorter than seasonal time scales on the inner shelf, along-shelf advection of hypoxic patches and cross-shelf advection of seasonal gradients are both shown to be important, changing DO concentrations by 1.5 mL/L or more over 5 days.