Tessa B. Francis

Pacific salmon and the ecology of coastal ecosystems

One of the most spectacular phenomena in nature is the annual return of millions of salmon to spawn in their natal streams and lakes along the Pacific coast of North America. The salmon die after spawning, and the nutrients and energy in their bodies, derived almost entirely from marine sources, are deposited in the freshwater ecosystems. This represents a vital input to the ecosystems used as spawning grounds. Salmon-derived nutrients make up a substantial fraction of the plants and animals in aquatic and terrestrial habitats associated with healthy salmon populations. The decline of salmon numbers throughout much of their southern range in North America has prompted concern that the elimination of this “conveyor belt” of nutrients and energy may fundamentally change the productivity of these coastal freshwater and terrestrial ecosystems, and consequently their ability to support wildlife, including salmon. If progress is to be made towards understanding and conserving the connection between migratory sa...

Habitat structure determines resource use by zooplankton in temperate lakes

While the importance of terrestrial linkages to aquatic ecosystems is well appreciated, the degree of terrestrial support of aquatic consumers remains debated. Estimates of terrestrial contributions to lake zooplankton have omitted a key food source, phytoplankton produced below the mixed layer. We used carbon and nitrogen stable isotope data from 25 Pacific Northwest lakes to assess the relative importance of particulate organic matter (POM) from the mixed layer, below the mixed layer and terrestrial detritus to zooplankton. Zooplankton and deep POM were depleted in ¹³C relative to mixed layer POM in lakes that can support deep primary production. A Bayesian stable isotope mixing model estimated that terrestrial detritus contributed <5% to zooplankton production, and confirms the role of lake optical and thermal properties; deep POM accounted for up to 80% of zooplankton production in the clearest lakes. These results suggest terrestrial support of lake zooplankton production is trivial.

Degradation of Littoral Habitats by Residential Development: Woody Debris in Lakes of the Pacific Northwest and Midwest, United States

Abstract One of the least understood aspects of aquatic ecology is the role of riparian zones of lakes, and how these habitats and their functions are impacted by human development of lakeshores. We investigated the effects of residential lakeshore development on littoral coarse woody debris (CWD) distribution and on riparian forest characteristics by comparing 18 lakes in the U.S. Pacific Northwest with 16 previously surveyed lakes in the U.S. Upper Midwest. Residential development had a strong negative effect on CWD and riparian forest characteristics at both local and whole-lake scales. There was a strong positive correlation between riparian forest density and littoral CWD abundance in both regions. We found regional variation in CWD and riparian forest characteristics, mostly owing to differences in native forests. Our results suggest the role of local processes in determining CWD distribution and point to potential regional differences in littoral habitat structure associated with forest composition and lakeshore development that may have consequences for littoral-pelagic coupling in lakes.

Effects of Urbanization on the Dynamics of Organic Sediments in Temperate Lakes

Residential development of lakeshores affects the structure and function of riparian and littoral habitats. Organic detritus in sediments is a critical component of littoral food webs, but the effects of urbanization on sediment characteristics are unexplored. We characterized the quantity of organic sediments in Pacific Northwest lakes along a development gradient and found a 10-fold decline in the proportion of detritus in littoral sediments associated with density of lakeshore dwellings. In a comparison between two fully developed lakes and two undeveloped reference lakes, we examined several possible controls on sedimentary organic content, including terrestrial inputs, decomposition rates and associated macroinvertebrate communities, and physical retention by coarse wood. The littoral sediments of undeveloped lakes ranged from 34 to 77% organic by mass, whereas the range on urban lakes was an order of magnitude less, ranging from 1 to 3% organic. We found no significant differences in terrestrial litter inputs between the two sets of lakes. Leaf litter decomposition rates did not vary significantly between the two sets of lakes, and we found higher densities of shredder macroinvertebrate taxa in the littoral zones of undeveloped lakes. Sedimentary organic matter on undeveloped lakes accumulated in shallow waters and declined with distance from shore, whereas the opposite pattern existed on urban lakes. Our results suggest that coarse wood physically retains organic matter in littoral zones where it can enter the detrital energy pathway, and the loss of this feature on urban lakes alters littoral sediment characteristics, with potentially far-reaching consequences for lake food webs.

Shifting regimes and changing interactions in the Lake Washington, U.S.A., plankton community from 1962-1994.

Understanding how changing climate, nutrient regimes, and invasive species shift food web structure is critically important in ecology. Most analytical approaches, however, assume static species interactions and environmental effects across time. Therefore, we applied multivariate autoregressive (MAR) models in a moving window context to test for shifting plankton community interactions and effects of environmental variables on plankton abundance in Lake Washington, U.S.A. from 1962–1994, following reduced nutrient loading in the 1960s and the rise of Daphnia in the 1970s. The moving-window MAR (mwMAR) approach showed shifts in the strengths of interactions between Daphnia, a dominant grazer, and other plankton taxa between a high nutrient, Oscillatoria-dominated regime and a low nutrient, Daphnia-dominated regime. The approach also highlighted the inhibiting influence of the cyanobacterium Oscillatoria on other plankton taxa in the community. Overall community stability was lowest during the period of elevated nutrient loading and Oscillatoria dominance. Despite recent warming of the lake, we found no evidence that anomalous temperatures impacted plankton abundance. Our results suggest mwMAR modeling is a useful approach that can be applied across diverse ecosystems, when questions involve shifting relationships within food webs, and among species and abiotic drivers.

Forty years of seagrass population stability and resilience in an urbanizing estuary

Coasts and estuaries contain among the most productive and ecologically important habitats in the world and face intense pressure from current and projected human activities, including coastal development. Seagrasses are a key habitat feature in many estuaries perceived to be in widespread decline owing to human actions. We use spatio-temporal models and a 41-year time-series from 100s of km of shoreline which includes over 160,000 observations from Puget Sound, Washington, USA to examine multi-scale trends and drivers of eelgrass (Zostera spp.) change in an urbanizing estuary. At whole estuary scale (100s of km) we find a stable and resilient eelgrass population despite a more than doubling of human population density and multiple major climactic stressors (e.g. ENSO events) over the period. However, the aggregate trend is not reflected at the site scale (10s of km), where some sites persistently increase while others decline. Site trends were spatially asynchronous; adjacent sites sometimes exhibited opposite trends over the same period. Substantial change in eelgrass occurred at the sub-site (0.1 km) scale, including both complete local loss and dramatic increase of eelgrass. Metrics of local human development including shoreline armoring, upland development (imperviousness), and human density provide no explanatory power for eelgrass population change at any spatial scale. Our results suggest that the appropriate scale for understanding eelgrass change is smaller than typically assumed (approximately 1 to 3 km scale) and contrasts strongly with previous work. Synthesis. Despite ongoing conservation concern over seagrasses worldwide, eelgrass in Puget Sound has been highly resilient to both anthropogenic and environmental change over four decades. Our work provides general methods that can be applied to understand spatial and temporal scales of change and can be used to assess hypothesized drivers of change. This article is protected by copyright. All rights reserved.

Population diversity in Pacific herring of the Puget Sound, USA

Demographic, functional, or habitat diversity can confer stability on populations via portfolio effects (PEs) that integrate across multiple ecological responses and buffer against environmental impacts. The prevalence of these PEs in aquatic organisms is as yet unknown, and can be difficult to quantify; however, understanding mechanisms that stabilize populations in the face of environmental change is a key concern in ecology. Here, we examine PEs in Pacific herring (Clupea pallasii) in Puget Sound (USA) using a 40-year time series of biomass data for 19 distinct spawning population units collected using two survey types. Multivariate auto-regressive state-space models show independent dynamics among spawning subpopulations, suggesting that variation in herring production is partially driven by local effects at spawning grounds or during the earliest life history stages. This independence at the subpopulation level confers a stabilizing effect on the overall Puget Sound spawning stock, with herring being as much as three times more stable in the face of environmental perturbation than a single population unit of the same size. Herring populations within Puget Sound are highly asynchronous but share a common negative growth rate and may be influenced by the Pacific Decadal Oscillation. The biocomplexity in the herring stock shown here demonstrates that preserving spatial and demographic diversity can increase the stability of this herring population and its availability as a resource for consumers.

Thirty‐two essential questions for understanding the social–ecological system of forage fish: the case of Pacific Herring

Abstract Forage fishes are ecologically and economically important low trophic level species, and in recent years interest in their biology and management has intensified. Pacific Herring are emblematic of the management issues facing forage species—they are central components of the Northeast Pacific pelagic food web and support important commercial fisheries. In addition, the importance of Herring to indigenous peoples have made them cultural keystone species. We employed a participatory process to promote collaborative priority-setting for this critical forage species. Working with managers, the fisheries industry, indigenous peoples, and scientists, we co-constructed a conceptual model of the Pacific Herring social–ecological system () in the Northeast Pacific. We then identified a set of questions, that, if answered, would significantly increase our ability to sustainably manage the Herring . Our objective was to generate a road map for scientists who wish to conduct useful forage fish research, for resource managers who wish to develop new research efforts that could fill critical gaps, and for public agencies and private foundations seeking to prioritize funding on forage fish issues in the Pacific. With this socio-cultural centrality comes complexity for fisheries management. Our participatory process highlighted the value of conceptualizing the full SES, overcame disciplinary differences in scientific approaches, research philosophy, and language, and charted a path forward for future research and management for forage species.

Using best available science to protect critical areas in Washington state: challenges and barriers to planners

Urban development has profound impacts on ecological patterns and processes making the scientific information required for developing environmental ordinances central for mitigating these negative ecological impacts. Washington State requires that planners use the best available science (BAS) to formulate land use ordinances as part of the state’s Growth Management Act (GMA). We present empirical findings describing challenges to planners in defining “best available science” and using BAS to create local ordinances that balance development needs with natural resource protection. We interviewed city and county planners (and their consultants) in western Washington to determine what they find useful about BAS, whether or not BAS is applicable to their jurisdictions, and what constraints they experience in reviewing and using BAS to create or update their land use ordinances. Our results suggest that applying the BAS requirement is particularly difficult in urban areas. Specifically, planners had difficulty applying results from research conducted in systems dissimilar to their urban landscapes. These challenges to planners were exacerbated by (1) a lack of resources and (2) political tensions among stakeholders with competing values in urban settings. We conclude with recommendations for improving the consideration of science in statewide land-use planning.

Contributions of adult mortality to declines of Puget Sound Pacific herring

Contributions of adult mortality to declines of Puget Sound Pacific herring Margaret C. Siple,* Andrew O. Shelton, Tessa B. Francis, Dayv Lowry, Adam P. Lindquist, and Timothy E. Essington School of Aquatic and Fishery Sciences, University of Washington, P.O. Box 355020, Seattle, WA 98105, USA Northwest Fisheries Science Center, NOAA, 2725 Montlake Blvd E, Seattle, WA 98112, USA Puget Sound Institute, University of Washington Tacoma, 326 E D St, Tacoma, WA 98421, USA Washington Department of Fish and Wildlife, Marine Fish Science Unit, Olympia, WA, USA *Corresponding author: tel: þ1 (206) 661-8403; fax: +1 (206) 685-7471; e-mail: siplem@uw.edu