Thermal biology and climate change vulnerability of freshwater fishes

     Freshwater fishes occupy a variety of thermal habitats and experience a range of thermal conditions throughout the year. My research uses laboratory experiments and species comparative approaches to characterize how and why species differ in the temperature sensitivity of physiological processes.

     Another aspect of this research is monitoring, modelling, and mapping seasonal temperature regimes in streams and rivers. Linking water temperature to landscape characteristics and air temperatures provides key information on the exposure of fish populations to climate change.

     Via the integration of these lab-based sensitivity assessments and field-based exposure assessments, it is my goal to develop mechanistic and spatially-explicit predictions of climate change vulnerability.

     Beginning with my postdoc at the University of Tennessee, collaborators and I aim to understand temperature regimes in southern Appalachia and characterize thermal sensitivity of the mega-diverse minnow and darter fauna in this region.

Greenfin darters (Etheostoma chlorobranchium) thermally acclimating in the laboratory prior to thermal tolerance assays. Photo credit: Allison Veach

Thermal reaction norms showing the relationship between temperature and growth for larval longfin dace (Agosia chrysogaster), a minnow endemic to the Colorado River system. Open and filled symbols represent tributary and mainstem populations, respectively. Figure from Troia et al. (2014), Env. Biol. Fish.

Stream temperature monitoring network in the southern Appalachian region. We have over 150 monitoring stations distributed among nine sub-basins (numbered 1-9). These stations span elevation, land use, and physiographic gradients. Inset photo shows a submerged water temperature logger. Map and photo by: Matt Troia

Community ecology and species distributions

     A fundamental goal of ecology is to understand why species occur where they do. My research uses null modeling and trait-based approaches to understand the process of community assembly in stream fish communities.

     I also use species comparative approaches and ecological niche modeling to gain understanding of why congeneric species often occupy different positions along the river continuum and along elevation gradients. My postdoc research at the University of Tennessee aims to understand such distributional diversity in the mega-diverse assemblages of minnows and darters in southern Appalachia.

     A related interest is the development and assessment of large open-access datasets. For example, Oak Ridge National Laboratory collaborators and I have developed a morphological trait database for >600 species of North American freshwater fishes. We have also completed assessments of environmental and temporal bias in nationwide fish community datasets, with the goal of guiding future efforts to share data in the public domain and plan future surveys.

Species distribution models showing high-elevation affinity of greenfin darter (Etheostoma chlorobranchium; top panel) versus low-elevation affinity of redline darter (E. rufilineatum; bottom panel) in the upper Tennessee River basin. Map by: Matt Troia

University of Tennessee students sampling the fish community in the French Broad River near Newport, Tennessee. Photo credit: Matt Troia

In-stream enclosures in the Kansas River near Manhattan, Kansas---these were part of a field experiment examining the physiological performance of minnows of the genus Pimephales in large river (above photo) versus small tributary (not shown) habitats. Photo credit: Matt Troia

Human dimensions of biodiversity conservation

     Biodiversity conservation in the Anthropocene requires strategies that maximize habitat quantity and quality in human-dominated systems such as urban centers and river systems regulated for flood control and hydroelectricity. Oak Ridge National Laboratory collaborators and I have completed nationwide assessments of freshwater habitats and the impacts of hydropower operation and development.

     Increasing public awareness and appreciation for freshwater biodiversity is also essential. I am interested in characterizing the vehicles by which people can be introduced to the biodiverse freshwaters of North America, particularly those in the southeastern United States.

Which freshwater fishes are the ideal symbols of each US state based on the overlap of the species' geographic range? The above map shows the results of a GIS analysis which showcases thirteen endemic fishes of the United States that represent ideal candidates for Washington, California, Nevada, Utah, Arizona, Nebraska, Oklahoma, Texas, Florida, Tennessee, West Virginia, Virginia, and Maine  Map from Troia (2016), Fisheries