Browsing by Author "Daniel Kamykowski, Committee Member"

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Biophysical Dispersal Dynamics of the Blue Crab in Pamlico Sound, North Carolina
(2004-11-29) Reyns, Nathalie Brigitte; Lian Xie, Committee Member; Thomas S. Hopkins, Committee Member; Daniel Kamykowski, Committee Member; Richard B. Forward, Jr., Committee Member; David B. Eggleston, Committee Chair
For many species such as the blue crab, Callinectes sapidus, successful estuarine recruitment to juvenile nursery habitats is dependent on the biophysical processes experienced during dispersal of the early life stages. The goal of this study was to determine how blue crab primary (postlarval) and secondary (early juvenile) dispersal occurs within a predominately wind-driven estuary, Pamlico Sound, North Carolina, USA. We (1) characterized circulation patterns in Pamlico Sound during the fall blue crab recruitment months over two consecutive years using current meters (2) sampled during multiple 24 h periods to relate spatiotemporal water column distributions of postlarval and early juveniles blue crabs with circulation patterns, and used a hydrodynamic model to recreate dispersal trajectories from eastern (inlet) to western sound nursery habitats and (3) examined the environmental (wind, diel cycle, tidal phase) and biological (ontogenetic, density-dependent) factors that contribute to early juvenile blue crab secondary dispersal from near-inlet nursery habitats. During our study, surface currents responded synchronously to wind-forcing by generally flowing in the same direction as the wind. Particle-tracking simulations suggested that dispersal from Oregon and Hatteras Inlets to across-sound nursery habitats resulted from the combined use of tidal and wind-driven currents. Simulation results and observed crab distributions further indicated that Oregon Inlet was the primary supplier of postlarval blue crabs (dispersing in surface waters at night) throughout Pamlico Sound, as postlarvae ingressing through Hatteras Inlet were not retained within our study area. Furthermore, Oregon Inlet supplied early juvenile blue crabs (dispersing in bottom waters at night) to northwestern sound habitats, while crabs from Hatteras Inlet dispersed to mid- and eastern-sound regions. Results from our study in near-inlet settlement habitats confirmed the importance of tides to mediating dispersal partway into Pamlico Sound, as early juvenile blue crabs responded to increasing conspecific density in settlement habitats by using flood-tide transport near the inlets to rapidly leave these habitats. Based on our findings, we make recommendations regarding the prioritization of nursery habitats for conservation and fisheries management.
Marine Organic Aerosols and Their Implication to Air Quality
(2009-04-27) Gantt, Brett; Nicholas Meskhidze, Committee Chair; Yang Zhang, Committee Member; Daniel Kamykowski, Committee Member
The global marine sources of organic carbon (OC) are estimated here using a physically-based parameterization for the emission of marine isoprene and primary organic matter. The emission model developed in this study allowed us, for the first time, to explore the relative contributions of sub- and super-micron organic matter and phytoplankton-produced secondary organic aerosol (SOA) to the total OC fraction of marine aerosol. New laboratory measurements of isoprene production by several abundant phytoplankton species under a range of environmental conditions were scaled up, with the help of satellite products, to infer the total annual mean ocean isoprene emissions of 0.92 Tg C yr-1. The sensitivity studies using different schemes for the euphotic zone depth and ocean phytoplankton speciation produced the upper and the lower range of marine-isoprene emissions of 0.31 to 1.09 Tg C yr-1, respectively. Empirical relationships between emissions of water soluble (WSOM) and water insoluble (WIOM) organic matter (OM) and chlorophyll a concentration were used to estimate the total primary sources of oceanic sub- and super-micron OC of 1.26 and 19.01 Tg C yr-1, respectively. Using a fixed 3% mass yield for the conversion of isoprene to SOA, our emission simulations show minor (less than 0.2%) contribution of ocean produced isoprene to the total marine source of OC. However, our model calculations also indicate that over the tropical waters, marine isoprene-derived SOA could contribute over 40% of the total monthly-averaged sub-micron OC fraction of marine aerosol. The estimated contribution of ocean-isoprene SOA to hourly averaged sub-micron marine OC fluxes is even higher, reaching 100% over the vast regions of the oceans during the midday hours. As it is widely believed that sub-micron OC has the potential to influence the cloud droplet activation of marine aerosols, our findings suggest that marine sources of SOA could play critical role in modulating properties of shallow marine clouds and influencing the climate. The impact of marine isoprene emissions on summertime surface concentrations of isoprene, secondary organic aerosols (SOA), and ozone (O3) in the coastal areas of the continental United States is studied using the U.S. Environmental Protection Agency regional-scale Community Multiscale Air Quality (CMAQ) modeling system. Marine isoprene emission rates are based on the following five parameters: laboratory measurements of isoprene production from different phytoplankton species under a range of light conditions, remotely-sensed chlorophyll-a concentration ([Chl-a]), incoming solar radiation, surface wind speed, and sea-water optical properties. Model simulations show that marine isoprene emissions are sensitive to meteorology and ocean ecosystem productivity, with the highest rates simulated over the Gulf of Mexico. With the isoprene reactions included in this study, the average contribution of marine isoprene to SOA and O3 concentrations is predicted to be small, up to 0.004 Ã‚Âµg m-3 for SOA and 0.2 ppb for O3 in coastal urban areas. The light-sensitivity of isoprene production from phytoplankton results in a midday maximum for marine isoprene emissions and a corresponding daytime increase in isoprene and O3 concentrations in coastal locations. While SOA concentrations are consistently higher (up to 0.005 Ã‚Âµg m-3) in coastal areas due to marine isoprene emissions, the diurnal trends are dependent on the local micrometeorology. Interannual variability of [Chl-a] concentration is examined in a sensitivity study with values increased and decreased by a factor of five. Our results indicate that marine emissions of isoprene cause minor changes (< 0.5%) to coastal SOA and O3 concentrations, likely due to limitations in current model treatments of isoprene chemistry and a coarse horizontal resolution used in model simulations.
Quantifying Marine Emissions of Biogenic Volatile Organic Compounds Using Laboratory Measurements, Field Measurements and Remote Sensing Data.
(2010-11-02) Sabolis, Alyssa; Nicholas Meskhidze, Committee Chair; Daniel Kamykowski, Committee Member; Robert Reed, Committee Member
Simulation of Ocean Circulation around the Galápagos Archipelago Using a Hybrid Coordinate Ocean Model (HYCOM).
(2010-05-17) Liu, Yanyun; John Morrison, Committee Chair; Lian Xie, Committee Chair; Fredrick Semazzi, Committee Member; Daniel Kamykowski, Committee Member
Spatial Dynamics in an Estuarine System: Modeling Biophysical Components and Interactions to Advance Blue Crab Fishery Management
(2009-11-23) Durham, Christina Louise; David B. Eggleston, Committee Chair; Daniel Kamykowski, Committee Member; Amy Nail, Committee Member; Joseph E. Hightower, Committee Member
Estuaries are dynamic ecosystems with abiotic environments that exhibit extreme space-time variability. Cyclic variation is somewhat predictable, but hurricanes and large-scale atmospheric disturbances can rapidly and drastically alter anticipated conditions. These disturbances can induce rapid biological responses across large spatial scales and frequently shift distribution patterns of mobile species. Physical conditions recover relatively quickly from climactically driven perturbations, and most physically-induced animal migrations are also temporary and reversible. Nevertheless, in the case of a commercially valuable fish species, even short-term alterations can change their vulnerability (i.e., catchability) to fishery-independent surveys, which provide valuable data used in population assessment. We examined the effects of salinity and other physical forcing mechanisms on the spatial distribution of ecologically and economically important blue crabs (Callinectes sapidus) in Pamlico Sound, NC. Pamlico Sound is the second largest estuary in the U.S. and is prone to hurricane activity. The blue crab fishery, North CarolinaÃ¢â‚¬Ëœs most important, is managed using indices of spawning stock biomass (SSB) and catch-per-unit effort generated from a fishery-independent trawl survey that does not sample shallow (< 2 m deep) regions. If environmental conditions affect the proportion of the population located within the survey region at a given time, then these indices are susceptible to bias resulting from variations in crab catchability. When the majority of the population is distributed in the Pamlico Sound survey area, a relatively high catchability would inflate estimates of relative population size. Likewise, when the population is less aggregated in mainstem Pamlico Sound and distributed further up in shallow water tributaries, relative population size would be underestimated by a relatively low catchability. Our objectives, to investigate the potential existence of aggregations and their environmental causes and to develop ways to account for environmental variability to obtain unbiased estimates of relative population abundance, were accomplished in two parts using three different statistical models. First, we modeled salinity observations collected in Pamlico Sound over the past 20 years as a function of recent and long-term freshwater influx from four rivers, distance to nearby inlets, and hurricane incidence. Maps of salinity predictions generated by this model illustrated changes in spatial salinity patterns during 40 survey time periods that encompassed a variety of climatic conditions. Salinity predictions were used to characterize the relationship between salinity and the presence and spatial distribution of blue crab SSB to predict historic distribution patterns. Observed survey SSB was modeled as function of space-time variable environmental factors that likely affect crab catchability in order to estimate time period-specific SSB means that were adjusted for these environmental effects. The time series of estimated means comprise an environmentally-adjusted SSB index that is more suitable for tracking relative population size over time than the index currently used to manage the fishery. This adjustment validated conclusions drawn from previous analyses and field observations that blue crab SSB has decreased over the past 20 years, most notably since 1999. A second model, including factors that did not change over time but likely affected crab spatial distribution, allowed us to predict SSB at a given space-time location. Predictions revealed consistent SSB spatial distribution patterns over successive monthly time periods and under variable environmental conditions. This information could help managers station no-take marine reserves to better conserve the blue crab spawning stock. In addition to yielding results that will better inform blue crab fishery managers, this research significantly increases the knowledge base regarding the effects of abiotic forcing events on mobile estuarine species. Furthermore, these methods provide a rigorous and robust analytical template to create future adjustment indices to manage mobile species that change their spatial distribution in response to environmental variables.
Spatiotemporal Variation in Broodstock Reserve Fecundity at Multiple Scales
(2009-05-15) Mroch, Raymond Millard III; David B. Eggleston, Committee Chair; Daniel Kamykowski, Committee Member; Kenneth Pollock, Committee Member
A major expectation of marine no-take reserves is that organisms within a reserve, over time, will export eggs and larvae to help sustain populations within and outside of reserves. Because fecundity and reproductive output can vary in space and time, the success of broodstock reserves depends on selecting the habitat or location that maximizes reproductive output to the target population. The goals of this study were to quantify spatial and temporal variation in (1) per capita fecundity (# eggs/individual) of female eastern oysters (Crassostrea virginica) within a network of marine broodstock reserves in Pamlico Sound, North Carolina; (2) fecundity per square meter (eggs/m2); (3) reserve fecundity (# eggs/reserve); and (4) the effects of endogenous and exogenous factors on spatiotemporal variation in per capita fecundity. A total of 1768 oysters were collected by scuba divers from six broodstock reserves over five sampling periods during 2006-2008 and processed in the laboratory for fecundity. Per capita fecundity ranged from 0 to 340,500 eggs, and mean per capita fecundity increased exponentially with oyster size (LVL mm) peaking in May of all years. In general, there were distinct spatial differences in fecundity depending upon the response variable, with per capita fecundity highest at more inshore reserves of moderate salinity, and fecundity m2 and reserve fecundity highest at more seaward reserves with relatively high salinity. Ranking of broodstock reserves for management purposes will likely depend upon the specific management goal. For example, if the goal is to expand broodstock reserves at locations that maximize reproductive potential per square meter of habitat created or improved, then reserves such as Ocracoke and Hatteras, that combine the joint effects of relatively high oyster density, size and per capita fecundity, would be ranked highest for expansion. If the management goal is to rank conservation of current broodstock sanctuaries, then relatively high salinity reserves such as Hatteras, that combine the joint effects of relatively high m2 fecundity and large substrate surface area, provide the greatest reproductive potential in terms of reserve fecundity. Lastly, if the management goal is to augment oyster densities via stocking with oyster spat at sites with high reproductive potential at the individual level, then more inland reserves such as Bluff Point and West Bay would be ranked highest. These results highlight the need to consider time and space when measuring reproductive potential of marine reserves, as well as the need to consider a comprehensive suite of response variables that best inform managers.