Darnell Lab

Marine Invertebrate Ecophysiology and Behavior at Nicholls State University

My research focuses on the environmental constraints imposed on marine and estuarine species. More specifically, this encompasses (1) physiological, behavioral, and ecological responses to environmental change and environmental stress, (2) environmental effects on life histories, distributions, and population dynamics, and (3) anthropogenic impacts on organism-environment interactions. My research lies at the intersection of several disciplines and combines field and laboratory experimentation with quantitative and spatial analyses of long-term datasets to better understand the interactions between marine organisms and their environments. This research also has a strong applied focus, using ecophysiological approaches to address fisheries management and conservation questions. Please look through the information on my research and teaching, and contact me if you have any questions or are interested in joining my lab.

News

6/16/15: Our manuscript "Temperature-dependent growth and molting in early juvenile blue crabs, Callinectes sapidus has been accepted for publication in the Journal of Shellfish Research. Please contact us for a pre-print.

6/11/15: Our manuscript "Thermal ecology of the fiddler crab Uca panacea: Thermal constraints and organismal responses" has been accepted for publication in the Journal of Thermal Biology. Please contact us for a pre-print.

5/26/2015: Adam Kemberling and Abby Kuhn will be joining the lab in August as they enter the M.S. program in Marine and Environmental Biology!

Recent publications:

Lab Members

Samantha Humphrey: Samantha is an M.S. student in the Marine and Environmental Biology program. She began in Fall 2014 and her research is investigating maternal care behaviors in blue crabs.

Andrew Cumberland: Andrew is an undergraduate Biology major (Marine Biology concentration) who has been working in the lab since Fall 2014, first as a volunteer and now for course credit. Andrew's research project involves refining rearing protocols for juvenile blue crabs in a recirculating, artificial seawater system.

Erika Nuss: Erika is an undergraduate Biology major (Marine Biology concentration) who is currently working as a lab technician. Erika will primarily be responsible for testing a system for monitoring body temperature and heart rate in fiddler crabs, blue crabs, and crawfish.

Contact

Zack Darnell
Department of Biological Sciences
Nicholls State University
P.O. Box 2021
Thibodaux, LA 70310
Phone: (985) 448-4709
zachary.darnell@nicholls.edu

Current and Recent Areas of Research


   Population-level consequences of phenotypic plasticity in crustacean reproduction
Phenotypic plasticity in maternal investment and reproductive traits can be driven by environmental fluctuations or changes in population density and demography, and can have important consequences for performance and fitness of offspring. These effects can scale up to affect abundance, distribution, and population dynamics. Crustaceans in particular exhibit an astounding diversity of reproductive strategies and degrees of maternal investment, and often show remarkable plasticity in response to environmental conditions. My dissertation research examined blue crab reproductive biology including spawning behavior, reproductive timing, temperature-dependent reproductive output, and pheromonal stimulation of maternal care behaviors. The wide latitudinal range and intensive fisheries in many areas make blue crabs (Callinectes sapidus) an ideal species with which to study phenotypic plasticity in traits such as reproductive timing, degree of maternal investment, and clutch size. My research in this area is focused on phenotypic plasticity in reproductive traits in response to exploitation, environmental stochasticity, climate change, and range shifts (including both anthropogenic and climate-triggered invasions of novel habitats) and also considers the impacts of reproductive plasticity and maternal investment on performance and survival of early life history stages, stages that typically experience high mortality.

   Ecology, physiology, and behavior of migration
Marine organisms often have migratory life cycles, with migratory ability optimized by complex interactions between physiological changes, orientation mechanisms, and movement behaviors. My long-term research interests in migratory ecology are focused on the mechanisms that optimize migratory ability of both adults and larvae under a variety of biotic and abiotic conditions and the implications of these mechanisms for the abundance and distribution of the species. I am especially interested in species that use selective tidal-stream transport to increase migratory ability or decrease the energetic costs of migration. This works involves a combination of laboratory behavioral experiments to examine migratory mechanisms and decision rules and multiple telemetry techniques to monitor migratory behavior, routes, and timing in the field.

   Innovative approaches to crustacean fisheries management
Crustaceans support valuable commercial fisheries which face many of the same challenges as finfish fisheries. Yet crustacean fisheries also present unique challenges for management such as non-continuous growth and limited availability of techniques for aging. Adding to these challenges, most crustacean fisheries are considered “data-poor.” I am interested in developing management strategies for these valuable fisheries based on the life history of the species and potential life-history responses to fishing and climate change, and involving collaboration between managers, researchers, and fishers. Recent research in this area has focused on assessing the potential for blue crab aquaculture and stock assessment in the Gulf of Mexico, examining the regional stock structure and offshore spawning potential of blue crabs, and evaluating species-specific life history responses to climate change.

   Behavioral thermoregulation and thermal acclimation ability as a driver of organismal performance and species distributions under climate change
Ocean temperatures and coastal climates are rising, and organisms will face challenges such as changes in heat and desiccation stress and synchronization of mating and gamete cycles. At any location, climate shifts create new microhabitats and can shift the species composition. The degree to which species are impacted by a changing climate, however, will depend on the species’ adaptability, acclimation ability, and capacity for behavioral thermoregulation, all of which can buffer effects of climate change. My research in this area has focused on fiddler crabs, a group of over 95 intertidal species with vastly differing latitudinal ranges. Fiddler crabs use a complex set of behavioral mechanisms to manage the thermal heterogeneity of their habitats. I have examined thermoregulatory mechanisms and acclimation ability, in the context of their potential implications for species distributions and performance along latitudinal gradients. Future research will focus on the role of thermal acclimation, adaptation, and behavioral thermoregulation in driving changes in performance, fitness, and species distributions under changing climatic regimes.

   Ecological consequences of sexual selection and sexual dimorphism
Sexually selected traits evolve in a complex ecological context, with interactions between multiple selective pressures driving the evolution of these traits. Such traits, including elaborate ornaments and armaments, can have substantial effects on heat exchange between the organism and the environment and thus affect thermal stress, performance, and fitness. Much of my recent research has focused on the ecological implications of sexual dimorphism in fiddler crabs. Fiddler crabs exhibit extreme sexual dimorphism and have mating behaviors that are often constrained by thermal stress during the peak activity season. This research resulted in the first direct evidence of a thermoregulatory function of the enlarged male claw. I have also recently examined sex-specific color change responses to thermal stress, and thermal constraints on sexual selection via endurance rivalry. I am interested in understanding how the need to maintain body temperature and thermoregulatory ability constrains sexual dimorphism and mating behavior, and the implications of these constraints for mating success and the evolution of sexual dimorphism under climate change.
-BBC Nature , ScienceDaily, and Science News coverage of Darnell and Munguia (2011).

   Responses of estuarine organisms to altered freshwater inflows
Under climate change, increasing variability in precipitation and increasing frequency of droughts and floods will alter patterns of freshwater inflow into estuaries. Coupled with increasing global temperatures, this variability will have substantial impacts on many organisms, including those that support valuable commercial and recreational fisheries. These effects may be exacerbated by increasing human development and diversion of freshwater. I am interested in the effects of altered freshwater inflows and environmental stochasticity on estuarine-dependent organisms, especially effects on recruitment, dispersal and migration, and interspecific interactions. I am currently examining responses of estuarine dependent crustaceans to variation in freshwater inflows, focusing on blue crabs, white shrimp, and brown shrimp. This research relies on a combination of field and lab experimentation, surveys, and GIS-based analyses of fishery-dependent and fishery-independent datasets, with the goal of developing predictive tools for assessing potential responses of these species to future alterations in freshwater inflow patterns.

Publications

* indicates undergraduate co-author
Please email me if you are unable to access a PDF of any of these papers.

(19) Cunningham, S.R.*, M.Z. Darnell. In press. Temperature-dependent growth and molting in early juvenile blue crabs, Callinectes sapidus. Journal of Shellfish Research.

(18) Darnell, M.Z., H.S. Nicholson*, P. Munguia. In press. Thermal ecology of the fiddler crab Uca panacea: Thermal constraints and organismal responses. Journal of Thermal Biology.

(17) Darnell, M.Z., K.K. Fowler*, P. Munguia. 2013. Sex-specific thermal constraints on fiddler crab behavior. Behavioral Ecology 24: 991-1003. Link

(16) Kronstadt, S.M.*, M.Z. Darnell, P. Munguia. 2013. Background and temperature effects on Uca panacea color change. Marine Biology 160: 1373-1381. Link

(15) Darnell, M.Z. 2012. Ecological physiology of the circadian pigmentation rhythm in the fiddler crab Uca panacea. Journal of Experimental Marine Biology and Ecology 426-427: 39-47. Link

(14) Darnell, M.Z., T.G. Wolcott, D. Rittschof. 2012. Environmental and endogenous control of selective tidal-stream transport behavior during blue crab Callinectes sapidus spawning migrations. Marine Biology 159: 621-631. Link

(13) Darnell, M.Z., P. Munguia. 2011. Thermoregulation as an alternate function of the sexually dimorphic fiddler crab claw. The American Naturalist 178: 419-428. PDF

(12) Hines, A.H., E.G. Johnson, M.Z. Darnell, D. Rittschof, T.J. Miller, L.J. Bauer, P. Rodgers, R. Aguilar. 2010. Predicting effects of climate change on blue crabs in Chesapeake Bay. In: Kruse, G.H., G.L. Eckert, R.J. For, R.N. Lipcius, B. Sainte-Marie, D.L. Stram, D. Woodby (eds) Biology and Management of Exploited Crab Populations Under Climate Change. Alaska Sea Grant College Program, Fairbanks. PDF

(11) Rittschof, D., M.Z. Darnell, K.M. Darnell, M. Goldman, M.B. Ogburn, R.E. McDowell. 2010. Estimating relative abundance of the female blue crab spawning stock in North Carolina. In: Kruse, G.H., G.L. Eckert, R.J. For, R.N. Lipcius, B. Sainte-Marie, D.L. Stram, D. Woodby (eds) Biology and Management of Exploited Crab Populations Under Climate Change. Alaska Sea Grant College Program, Fairbanks. PDF

(10) Darnell, M.Z., K.M. Darnell, R.E. McDowell, D. Rittschof. 2010. Postcapture survival and future reproductive potential of ovigerous blue crabs Callinectes sapidus caught in the central North Carolina pot fishery. Transactions of the American Fisheries Society 139: 1677-1687. PDF

(9) Darnell, M.Z., D. Rittschof, R.B. Forward Jr. 2010. Endogenous swimming rhythms underlying the spawning migration of the blue crab, Callinectes sapidus: ontogeny and variation with ambient tidal regime. Marine Biology 157: 2415-2425. PDF

(8) Darnell, M.Z., D. Rittschof. 2010. Role of larval release pheromones and peptide mimics in abdominal pumping and swimming behavior of ovigerous blue crabs, Callinectes sapidus. Journal of Experimental Marine Biology and Ecology 391: 112-117. PDF

(7) Darnell, M.Z., D. Rittschof, K.M. Darnell, R.E. McDowell. 2009. Lifetime repoductive potential of female blue crabs Callinectes sapidus in North Carolina, USA. Marine Ecology Progress Series 394: 153-163. PDF

(6) Forward Jr, R.B., M.H. Bourla*, M.Z. Darnell, J.H. Cohen. 2009. Entrainment of the circadian rhythm of the supratidal amphipod Talorchestia longicornis by light and temperature: mechanisms of detection and hierarchical organization. Marine and Freshwater Behaviour and Physiology 42: 233-247. PDF

(5) Ramach, S.M., M.Z. Darnell, N.G. Avissar, D. Rittschof. 2009. Habitat use and population dynamics of blue crabs, Callinectes sapidus, in a high-salinity embayment. Journal of Shellfish Research 28: 635-640. PDF

(4) Darnell, M.Z., M.B. Ogburn, H. Diaz. 2008. A novel running wheel apparatus to monitor locomotor rhythms in land crabs. Marine and Freshwater Behaviour and Physiology 41: 205-210. PDF

(3) Welch, M.E., M.Z. Darnell, D.E. McCauley. 2006. Variable populations within variable populations: quantifying mitochondrial heteroplasmy in natural populations of the gynodioecious plant Silene vulgaris. Genetics 174: 829-837. PDF

(2) Forward Jr, R.B., J.H. Cohen, M.Z. Darnell, A. Saal. 2005. The circatidal rhythm in vertical swimming of female blue crabs, Callinectes sapidus, during their spawning migration: A reconsideration. Journal of Shellfish Research 24: 587-590. PDF

(1) McCauley, D.E., M.F. Bailey, N.A. Sherman, M.Z. Darnell. 2005. Evidence for paternal transmission and heteroplasmy in the mitochondrial genome of Silene vulgaris, a gynodioecious plant. Heredity 95: 50-58. PDF

Teaching

Marine and Environmental Biology I (BIOL 551) is a core course in our M.S. program in Marine and Environmental Biology. My goals for this course are for students to to gain a thorough understanding of ecological principles from readings and discussions of foundational papers and to stimulate critical thinking about ecological theory, experimental design, and the current state of research in the field. This is a discussion-based course with discussions focusing on the primary literature, including both foundational papers as well as more current papers. The 2014 syllabus can be downloaded here.

Marine Field Ecology is offered at LUMCON during even-year summers. This course focuses on introducting students to the marine environment through a number of excursions to local habitats throughout the Louisiana Coastal Zone. Students spend the first two weeks of the course exploring the local environment and learning basic principles of marine ecology. The second two weeks of the course are devoted to original research projects conducted in groups of 2–3 students. The 2014 syllabus can be downloaded here.

Introduction to Marine Biology (BIOL 283/284) is offered during the Fall semester. This course has two primary objectives. The first is for students to gain an understanding of and appreciation for life in the the marine environment. The second goal is for students to develop a mechanistic understanding of the processes structuring marine populations, communities, and ecosystems. We will take a process-based approach to study the diversity of life in the oceans, the interactions between these organisms, and the interactions between organisms and their environment. The 2014 syllabi can be downloaded here (Biol 283, lecture) and here (Biol 284, lab).

Invertebrate Zoology (BIOL 354) is offered during the Spring semester. The primary objective of this course is for students to gain an understanding of and appreciation for the diversity of invertebrate life in marine, freshwater, and terrestrial environments. We will work our way through the invertebrate phyla from Porifera to Chordata, focusing on form, function, and phylogeny. In addition to lectures, dissections and labs will be used to explore invertebrate anatomy, morphology, and behavior, and field trips to local habitats will be used to collect invertebrate organisms and explore relationships between invertebrates and their environment. The 2015 syllabus can be downloaded here.

Prior to coming to Nicholls, I taught several courses at the University of Texas at Austin, including Marine Invertebrates, Marine Environmental Science, and Laboratory Studies in Marine Ecology.