Anthony S. Overton

Chemical dispersant potentiates crude oil impacts on growth, reproduction, and gene expression in Caenorhabditis elegans

The economic, environmental, and human health impacts of the deepwater horizon (DWH) oil spill have been of significant concern in the general public and among scientists. This study employs parallel experiments to test the effects of crude oil from the DWH oil well, chemical dispersant Corexit 9500A, and dispersant-oil mixture on growth and reproduction in the model organism Caenorhabditis elegans. Both the crude oil and the dispersant significantly inhibited the reproduction of C. elegans. Dose-dependent inhibitions of hatched larvae production were observed in worms exposed to both crude oil and dispersant. Importantly, the chemical dispersant Corexit 9500A potentiated crude oil effects; dispersant-oil mixture induced more significant effects than oil or dispersant-alone exposures. While oil-alone exposure and dispersant-alone exposure have none to moderate inhibitory effects on hatched larvae production, respectively, the mixture of dispersant and oil induced much more significant inhibition of offspring production. The production of hatched larvae was almost completely inhibited by several high concentrations of the dispersant-oil mixture. This suggests a sensitive bioassay for future investigation of oil/dispersant impacts on organisms. We also investigated the effects of crude oil/dispersant exposure at the molecular level by measuring the expressions of 31 functional genes. Results showed that the dispersant and the dispersant-oil mixture induced aberrant expressions of 12 protein-coding genes (cat-4, trxr-2, sdhb-1, lev-8, lin-39, unc-115, prdx-3, sod-1, acr-16, ric-3, unc-68, and acr-8). These 12 genes are associated with a variety of biological processes, including egg-laying, oxidative stress, muscle contraction, and neurological functions. In summary, the toxicity potentiating effect of chemical dispersant must be taken into consideration in future crude oil cleanup applications.

Variability of Atlantic Coast Striped Bass Egg Characteristics

Abstract Eggs of striped bass Morone saxatilis were collected from broodfish at seven hatcheries and one wild population representing nine watersheds from Georgia to Canada to determine the relationship between watershed type and egg characteristics, including density, diameter, oil globule size, surface : volume ratio, and lipid content. These populations represented an inland freshwater lake (Lake Lanier), upland-dominated (high-physical-energy) freshwater rivers (Dan and upper Roanoke (Staunton) rivers), estuarine-influenced (low-physical-energy) coastal rivers (Savannah, Pamunkey, Choptank, and Nanticoke rivers), an upland tidal-bore river (Shubenacadie River), and an upland tidal river (Miramichi River). Water quality parameters varied among hatchery locations. Water hardening of eggs occurred within 2.5 h of fertilization. Egg diameter and relative oil globule size did not differ significantly under ambient hatchery and controlled water quality conditions. However, eggs from different watersheds dif...

Spatial and Temporal Variability in Instantaneous Growth, Mortality, and Recruitment of Larval River Herring in Tar—Pamlico River, North Carolina

Abstract We estimated the variation in the instantaneous rates of growth and mortality between cohorts of larval alewife Alosa pseudoharengus and blueback herring A. aestivalis in the Tar-Pamlico River, Pamlico Sound, North Carolina. The age of larvae captured by push net was estimated by counting the daily rings on sagittal otoliths. Weight-at-age and abundance-at-age data were used to generate instantaneous daily growth (G) and mortality rates (M) for 7-d cohorts. The instantaneous daily growth rate was relatively constant between cohorts, ranging from 0.103 to 0.277 for alewives and from 0.105 to 0.200 for blueback herring. The instantaneous daily mortality rate was more variable between cohorts, ranging from 0.064 to 0.270 for alewives and from 0.100 to 0.251 for blueback herring. All but one blueback herring cohort had an M/G value exceeding 1.0, indicating that these cohorts were losing biomass during the early larval stage. For alewives, M/G values were more variable, with 50% of the cohorts having values less than 1.0. The effect of habitat was consistent between species, with M/G values being higher and closer to 1.0 at sites in tributary creeks and backwater areas of Tar River. The overall M/G values were 0.57 for alewives and 1.60 for blueback herring from both backwater and main-channel sites, indicating that the environmental conditions in the Tar—Pamlico River are more favorable for alewives.

Release Mortality of Undersized Fish from the Snapper–Grouper Complex off the North Carolina Coast

Abstract Red porgy Pagrus pagrus, scamps Mycteroperca phenax, and gags M. microlepis support valuable recreational and commercial fisheries in North Carolina. Fish in the snapper–grouper complex are managed to prevent overfishing and maintain a stable spawning stock. We investigated postrelease mortality of 263 undersized red porgy, scamps, and gags that were captured by angling and subjected to short-term (2 h) and long-term (48 h) holding experiments. Fish were caught at depths ranging from 15 to 45 m using traditional bottom-fishing hook-and-line gear. Catch per unit effort ranged from 0.11 to 1.80 fish/rod-hour (FRH) for sublegal-sized fish and from 0.06 to 0.50 FRH for legal-sized fish. Nontarget species predominated in the catch (N = 1,135), but the red porgy was the most frequently caught individual species (N = 196). The effects of short-term (2-h) holding within species were similar between fish held in different locations (oxygenated live well or cage anchored to the seafloor); mortality did not...

Expanded Range and New Host Species of Mycobacterium shottsii and M. pseudoshottsii

Mycobacterium shottsii and M. pseudoshottsii are recently described mycobacteria commonly isolated from Chesapeake Bay striped bass Morone saxatilis. However, their distribution in striped bass outside of the Chesapeake region and their ability to infect alternative hosts have not been described. Mycobacteria identified as M. shottsii (based on fatty acid methyl ester analysis and multigene sequencing) were isolated from striped bass collected in Albemarle Sound, North Carolina, and white perch Morone americana in the Rhode River, Maryland, and detected in striped bass from the New York Bight off Long Island, New York. Mycobacterium pseudoshottsii were isolated from white perch in the Rhode and Corsica rivers, Maryland, and detected in striped bass in the New York Bight. This work demonstrates that these mycobacteria can be found outside of the Chesapeake Bay as well as in hosts other than striped bass.

Evaluating the Efficiency of Flushed Stomach-tube Lavage for Collecting Stomach Contents from Dogfish Sharks

Abstract Concern over the use of lethal techniques to collect basic biological data from sharks has necessitated the development of nonlethal methods of data collection. We evaluated the nonlethal method of removing stomach contents using acrylic tubes. Stomach contents of Spiny Dogfish (Squalus acanthias) captured with bottom trawls and longlines were collected using acrylic tubes flushed with seawater. The largest tube used during the trawl survey was 30 mm in diameter, while a larger tube (37 mm in diameter) was used during longline sampling due to catches of larger dogfish. The average efficiency of stomach content removal was 79.5% overall, and improved to 93% with the addition of the larger tube. Selection of a tube with a diameter 10–20 mm less than mouth width can be reasonably expected to recover over 90% of stomach contents. Stomachtube lavage is a useful and efficient method for nonlethal sampling of stomach contents from Spiny Dogfish, and perhaps other small sharks.

Estimating the Food Requirements and Prey Size Spectra of Larval American Shad

Abstract Widespread declines in American shad Alosa sapidissima along the Atlantic coast have been attributed to overfishing, a decrease in water quality, and loss of habitat. Recent surveys along the Roanoke River and Albemarle Sound, North Carolina, suggest that stocks are continuing to decline despite extensive management and stock enhancement efforts. Laboratory experiments were conducted to evaluate the effect of prey density on the growth and survival of American shad and to determine whether larvae can survive and grow in a riverine environment with a limited forage base. Larvae were reared from 11 to 20 d posthatch in one of five treatments: (1) no food; (2) low food (1 prey/L), which simulated the prey densities in the Roanoke River; (3) medium food (50 prey/L), which simulated the prey densities typical of coastal watersheds; (4) high food (500 prey/L); and (5) Artemia spp. (500/L). Larval survival was 35 ± 7% (mean ± SE) and was not significantly different among treatments. Treatments with starved fish had the lowest survival (22 ± 12%), while the highest survival was observed in treatments with high densities of wild Zooplankton (46 ± 18%) and Artemia (40 ± 16%). Length-specific growth rates were 0.017 mm/d for the starved treatments and 0.024, 0.029, 0.034, and 0.039 mm/d for the low-prey, medium-prey, high-prey, and Artemia treatments, respectively. Larval growth as a function of length was not significantly different between the Artemia and high-prey treatments; however, growth in these treatments was significantly higher than in those with lower prey densities. Weight-specific growth rates (Gw ) were significantly higher for the Artemia treatment (Gw = 0.129) than for all the other treatments (Gw = 0.081). Analysis of stomach contents indicated that American shad were selectively feeding on the smallest Zooplankton (80–250 µm) and that larvae exhibited a strong preference for copepod nauplii and rotifers. These results suggest that spatial and temporal overlap between larvae and Zooplankton is important for larval growth and survival.

Foraging Potential of Larval Alosines in the Lower Roanoke River and Albemarle Sound, North Carolina

Abstract Zooplankton composition and abundances were quantified in the lower Roanoke River and Albemarle Sound, North Carolina. The spatial and temporal overlap between larval alosines, including American shad Alosa sapidissima, river herring (alewife A. pseudoharengus and blueback herring A. aestivalis), hickory shad A. mediocris, and Zooplankton were examined to determine whether larval alosines in this system are food limited. Samples were collected weekly at 19 stations from March through June 2008–2009 in three habitats: River, Delta, and Sound. Spatial differences in Zooplankton were observed, with the abundance in the Sound (16,546 ± 14,678 [number/m3 ± SD]) being significantly higher than those in the River (4,934 ± 3,806) and Delta areas (4,647 ± 2,846). Zooplankton composition was dominated by Daphniidae, Bosminidae, calanoid and cyclopoid copepods, copepod nauplii, and rotifers. The spatial patterns in alosine abundance were the opposite of those for Zooplankton, being highest in the River (21.0 ± 127.6) and lower in the Delta (7.5 ± 35.5) and Sound (4.6 ± 24.8). Mouth gape models for each alosine species showed that copepod nauplii and rotifers are the most suitable-sized prey for the first feeding after yolk sac absorption. There was a high degree of spatial and temporal overlap between larval alosines and size-appropriate prey items, suggesting that the larval alosines are not food limited in Albemarle Sound.

Low prevalence of splenic mycobacteriosis in migratory striped bass Morone saxatilis from North Carolina and Chesapeake Bay, USA

Mycobacteriosis is a chronic bacterial disease causing an ongoing epizootic in striped bass Morone saxatilis in Chesapeake Bay, U.S.A. Prevalence of disease is high in pre-migratory fish, and multiple species of Mycobacterium spp. have been isolated. However, prevalence of mycobacteriosis in the coastal migratory population is unknown and is of concern to multiple coastal states, as disease-related mortality may impact the long-term health of the population. Histological examinations of spleens collected from fish caught by recreational anglers during the winter fishery in coastal North Carolina (2005-2006, n=249) and during the spring fishery in Chesapeake Bay (2006, n=120) indicated a low prevalence of mycobacteriosis (6.8% of all fish examined) in comparison to smaller, pre-migratory Chesapeake Bay fish. Genus-level PCR and subsequent sequencing of the 16-23S intergenic transcribed spacer (ITS) region revealed that all bacteria were phylogenetically related, but species is unknown. Location of survey, gender of fish, and total length of fish had no significant effect on prevalence of mycobacteriosis, parasitic granulomas, or the density of splenic granulomas (p > 0.05). These results may indicate that either granulomas resolve after Chesapeake Bay fish enter the coastal migratory population, or that there is disease-related mortality among pre-migratory Chesapeake Bay fish.