Large-scale movements, spawning locations, and structure of the Gulf of Mexico blue crab spawning stock
Blue crabs support the 9th most valuable commercial fishery in the U.S., with 2014 coastwide landings of over 60,000 metric tons (132 million lbs.) for a wholesale value of over $208 million. Blue crab abundance and commercial landings, however, are highly variable from year to year and many states have seen large declines in crab harvests in recent years. Management efforts for this species typically take place on a state-by-state basis and have been hindered by a lack of information on stock structure and boundaries. Difficulties in assessing stock structure and boundaries have arisen due to a lack of information on large-scale movements of adult crabs and larval dispersal patterns and unclear and often conflicting population genetic information for the species. A collaborative project with Dr. Elizabeth North
(UMCES) as well as all five Gulf states fisheries agencies, this project uses a Gulf-wide mark-recapture study of spawning female blue crabs, combined with spatial analyses of state and regional fishery-independent survey data, to better understand the structure and boundaries of the blue crab stock(s) in the Gulf of Mexico.
Linking blue crab abundance, growth, and mortality to marsh fragmentation and submerged aquatic vegetation cover
Louisiana supports the largest blue crab fishery in the Gulf of Mexico, yet is is experiencing unprecedented loss of salt marsh nursery habitats due to a combination of sea level rise, subsidence, saltwater intrusion and reduced sediment inflow. The overarching goal of this project is to assess the effects of marsh fragmentation and associated changes in submerged plant distribution on blue crab abundance, growth and mortality, and improve existing habitat suitability models to increase understanding of the consequences of landscape change, either degradation or restoration, for the blue crab fishery. This project is a collaboration with Tim Carruthers, Kelly Darnell, and Ann Hijuelos at The Water Institute of the Gulf.
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.. Research in this area is focused on phenotypic plasticity in reproductive traits and behaviors 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.
Ecological consequences of sexual selection and sexual dimorphism
The form of a secondary sexual trait is determined by the complex interplay between sexual selection and natural selection, which interact to facilitate or constrain the evolution of sexually selected traits. For example, sexual selection often favors exaggerated male traits, armaments, or ornaments that confer reproductive advantages, but these exaggerated traits may impose ecological or physiological costs on the male. Natural selection thus often limits the degree of exaggeration of the trait. Conversely, in certain cases, sexual dimorphism can arise, be maintained, or even be enhanced because of ecological differences between the sexes. Thus, the form and degree of sexual dimorphism are shaped by both sexual and natural selection and must be considered in the context of multiple, interacting selective pressures. Research in this area has focused on ecological consequences of the sexually dimorphic major claw of fiddler crabs, especially the role of the major claw in heat transfer and thermoregulation.
, and Science News
coverage of Darnell and Munguia (2011).
Behavioral, physiological, and life history responses to climate change
Ocean temperatures and coastal climates are rising, and organisms will a number of challenges, including changes in heat and desiccation stress, and synchronization of mating and gamete cycles, and shifts in phenology. 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. Research in this area has focused on understanding responses to thermal shifts and thermal stress in the context of predicting future responses to climate change, focusing on a number of crustaceans including fiddler crabs and blue crabs.
Biological timing and endogenous rhythmicity
Regardless of habitat, organisms encounter numerous environmental cycles on a variety of temporal scales, from tidal cycles of salinity and hydrostatic pressure (for marine/estuarine organisms) to seasonal cycles of photoperiod, temperature, and food availability. Endogenous biological rhythms allow an organism to alter physiology or behavior in anticipation of these cycles, rather than in response to these cycles. I have previously examined endogenous biological rhythms in blue crabs, amphipods, fiddler crabs, and terrestrial crabs. My interests in biological rhythms lie in the functional significance of these rhythms as adaptations to fluctuating environmental conditions, as well as the entrainment cues used for synchonization of rhythms in marine animals.