RSS 1.0Whitney, Emily J.
Recent Submissions
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Seasonality and hydroclimatic variability shape the functional and taxonomic diversity of nearshore fish communities in glacierized estuaries of AlaskaNearshore fish communities in glacierized estuaries contend with environmental changes brought on by seasons and a shifting climate, which include alterations in freshwater runoff and environmental conditions shaped by the interplay of warming temperatures and receding glaciers. Spatial and temporal changes in environmental parameters can directly impact fish behavior and community structure, thereby affecting the dynamics of the entire ecosystem. Taxonomic diversity is commonly used to measure changes in communities, and while it offers important insights into community structure, considering the functional roles of organisms is necessary for understanding community dynamics through expressed traits and trophic interactions. Here, we evaluate the influence of environmental drivers on both taxonomic and functional diversity of fish communities at multiple sites in two glacially-influenced, high-latitude regions in the Gulf of Alaska (GoA): oceanic-influenced Kachemak Bay and the more typical estuarine Lynn Canal. Sites were analyzed monthly (April–September) for three years (2019, 2021, 2022) to address two questions: (1) Do taxonomic and functional diversity of nearshore fish communities show similar patterns of interannual and regional variation in glacially-influenced GoA estuaries? and (2) Do similar seasonal (i.e., monthly) and environmental (i.e., temperature, salinity, turbidity, freshwater discharge) drivers shape taxonomic and functional fish communities within these regions? Taxonomic and functional diversity were both significantly different between the two glacially-influenced GoA regions in all years. Environmental drivers of these patterns differed, but were weak across regional comparisons. Regional taxonomic composition was correlated to temperature, salinity, and turbidity while regional functional composition was not related to any environmental variables. Within regions, seasonality played a much stronger role in structuring Lynn Canal taxonomic and functional composition compared to Kachemak Bay where a stronger interannual signature was present. Taxonomic composition in Kachemak Bay was correlated with similar environmental variables to the regional comparison while Lynn Canal taxonomic composition was correlated to salinity and discharge. Both regions exhibited weak or non-existent relationships of functional composition to environmental drivers. In the more freshwater-influenced Lynn Canal, strong taxonomic and functional coupling across months indicates that seasonality structures communities, while in the more oceanic Kachemak Bay, weak seasonal differences and strong interannual differences indicate a system more influenced by oceanographic processes, as opposed to local changes.
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Glacier runoff impacts the stoichiometry of riverine nutrient export from coastal Alaskan catchmentsUnderstanding the impacts of glacier change on riverine ecosystems is limited by a lack of multi-year studies in glacierized mountain catchments quantifying the magnitude and stoichiometry of riverine biogeochemical yields. Here we evaluate riverine concentration-discharge relationships using the power function between daily runoff and element yields and stoichiometry across 10 catchments of varying glacial coverage within two climatically distinct regions in the Gulf of Alaska. Our multi-year study showed that biogeochemical stoichiometry and concentration-discharge relationships for dissolved carbon, nitrogen, and phosphorus varied significantly with catchment glacier coverage across both regions. This stoichiometric variability could drive regional differences in proglacial riverine food webs given that high trophic levels in low productivity rivers are generally driven by bottom-up controls. The coherence of our findings across the Gulf of Alaska suggests that observed patterns in concentration-discharge relationships are likely globally generalizable to catchments in which discharge is dominated by glacier ice and/or snowmelt.
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Seasonal patterns in riverine carbon form and export from a temperate forested watershed in Southeast AlaskaRiverine export of carbon (C) is an important part of the global C cycle; however, most riverine C budgets focus on individual forms of C and fail to comprehensively measure both organic and inorganic C species in concert. To address this knowledge gap, we conducted high frequency sampling of multiple C forms, including dissolved organic C (DOC), inorganic carbon (as alkalinity), particulate organic C (POC), coarse particulate organic C (CPOC), and invertebrate biomass C across the main run-off season in a predominantly rain-fed watershed in Southeast Alaska. Streamwater concentrations were used to model daily watershed C export from May through October. Concentration and modeled yield data indicated that DOC was the primary form of riverine C export (8708 kg C/km2), except during low flow periods when alkalinity (3125 kg C/km2) was the dominant form of C export. Relative to DOC and alkalinity, export of particulate organic C (POC: 992 kg C/km2; CPOC: 313 kg C/km2) and invertebrates (40 kg C/km2) was small, but these forms of organic matter could disproportionately impact downstream food webs because of their higher quality, assessed via C to nitrogen ratios. These seasonal and flow driven changes to C form and export likely provide subsidies to downstream and nearshore ecosystems such that predicted shifts in regional hydroclimate could substantially impact C transfer and incorporation into aquatic food webs.
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Seasonal and interannual variation in high‑latitude estuarine fsh community structure along a glacial to non‑glacial watershed gradient in Southeast AlaskaAlong the Gulf of Alaska, rapid glacier retreat has driven changes in transport of freshwater, sediments, and nutrients to estuary habitats. Over the coming decades, deglaciation will lead to a temporary increase, followed by a long-term decline of glacial influence on estuaries. Therefore, quantifying the current variability in estuarine fish community structure in regions predicted to be most affected by glacier loss is necessary to anticipate future impacts. We analyzed fish community data collected monthly (April through September) over 7 years (2013–2019) from glacially influenced estuaries along the southeastern Gulf of Alaska. River delta sites within estuaries were sampled along a natural gradient of glacial to non-glacial watersheds to characterize variation in fish communities exposed to varying degrees of glacial influence. Differences in seasonal patterns of taxa richness and abundance between the most and least glacially influenced sites suggest that hydrological drivers influence the structure of delta fish communities. The most glacially influenced sites had lower richness but higher abundance overall compared to those with least glacial influence; however, differences among sites were small compared to differences across months. Two dominant species—Pacific staghorn sculpin and starry flounder—contributed most to spatial and temporal variation in community composition; however, given only small interannual differences in richness and abundance over the period of the study, we conclude that year-to-year variation at these sites is relatively low at present. Our study provides an important benchmark against which to compare shifts in fish communities as watersheds and downstream estuaries continue to transform in the coming decades.
