No description available.

Studies were undertaken to examine the roles of iron and carbon in modulating prokaryotic growth in the ocean. The context of the first study was an open-open iron fertilization experiment in the high nutrient, low chlorophyll (HNLC) regime in the Southern Ocean. The context of the second study was the oligotrophic, iron-replete, and organic carbon-limited northwest Sargasso Sea. Experimental sea water cultures were amended with an iron chelator, desferrioxamine B (DFOB), and other nutrients to examine the effects of iron and carbon limitation on growth. In the first study prokaryotic abundance, carbon production, and growth rate increased in response to iron in two experimental locations north and south of the Antarctic Polar Front Zone (North Patch and South Patch, respectively). However, prokaryotes responded indirectly to iron-induced phytoplankton production. Prokaryotic production was highly correlated to particulate primary production (r2 = 0.80). Prokaryotes comprised a larger percentage of particulate organic carbon (POC) in the North versus the South Patch relative to non-fertilized waters. Analysis of prokaryotic community structure was also examined. Results showed unique prokaryotic communities existed in the North and South Patch for both iron-fertilized and non-fertilized waters. Additionally, community composition shifted over time in the South Patch and was distinct from non-fertilized waters. Measures of community diversity indicated an increase in taxonomic richness and diversity in iron-fertilized waters over time. Specific taxonomic groups monitored over time in the South Patch exhibited a differential response to the iron-induced phytoplankton bloom. at the domain level, the biomass response was greater for Eubacteria compared to Archaea. at the clade level, Cytophaga-Flavobacteria net biomass yields outpaced SAR11, although both exhibited significant increases (p < 0.05) in net growth rate over time in the South Patch. In the second study DFOB did not limit utilization of organic carbon (glucose). Conversely, DFOB stimulated prokaryotic growth in a dose-dependent manner. The trend of the response to DFOB was similar to glucose; however, the magnitude of the response (i.e. growth rate and biomass yield) at higher equivalent carbon doses was greater than that of glucose. Additionally, DFOB and glucose elicited a differential taxonomic response.

No description available.

No description available.

No description available.

Copepods are the dominant mesozooplankton in the Southern Ocean, but long- term change in their abundance and distribution along the Western Antarctic Peninsula (WAP), a region experiencing rapid climate warming, is unknown. Copepods are also potentially important grazers of phytoplankton in the WAP and contributors to carbon export through production of sinking fecal pellets. I examined summer (January- February) copepod community structure and abundance along the WAP over two decades (1993-2013) and investigated long-term trends in copepod abundance and their relationship with environmental parameters (sea ice, phytoplankton biomass and productivity, climate indices, and sea surface temperature). Copepods comprised on average 81% of total mesozooplankton abundance in the WAP; the copepod community was dominated by a few species that included Metridia gerlachei, Oithonaspp., and Calanoides acutus. There was a significant long-term increase in total copepod abundance over time, with higher abundances in years with earlier sea ice retreat and higher phytoplankton biomass and productivity. Trends for individual species reflected feeding and life cycle strategies, but generally followed those of total copepods. to examine the impact of copepod grazing on phytoplankton and contribution to carbon export, I conducted grazing and fecal pellet production experiments with the large dominant copepods (Calanus propinquus,Rhincalanus gigas, and C. acutus) in the WAP each January from 2012 to 2014. Copepods have a lowoverall impact on grazing of phytoplankton biomass (<1%) and productivity (1%, up to 11%). Copepods were likely feeding on other sources of carbon (i.e., protozoans and metazoans) besides phytoplankton to meet metabolic demands, especially in the offshore, slope region and in low chlorophyll a conditions. Fecal pellet production (egestion) rates were high, ranging from 0.82 (R. gigas)to 37.3μC ind. day -1 (Paraeuchaeta antarctica), and did not exhibit regional trends. My results suggest mechanisms leading to interannual variability of summer copepod abundance and grazing in the WAP can be used to predict how copepods will respond to future environmental changes and may affect the flow of carbon through the food web and the export of carbon to depth.

The objectives of my research were to test the hypothesis that compensatory (density-dependent) growth of sandbar shark (Carcharhinus plumbeus) occurred after severe population reduction, to describe the juvenile sandbar shark fauna present in the Chesapeake Bay during 1980-81 and 1990-93, and to perform demographic analyses to examine potential population growth. Age and growth of sandbar sharks were investigated by counting rings in vertebral samples collected in 1980-81 and 1991-92. Age at maturity was 15-16 years for both sample periods and both sexes. For sexes combined, the von Bertalanffy growth parameters were L&\sb{lcub}\infty{rcub}& = 199 cm precaudal length (PCL), K = 0.057, t&\sb{lcub}\rm o{rcub}& = &-&4.9 years for the 1980-81 sample and L&\sb{lcub}\infty{rcub}& = 164 cm PCL, K = 0.089, t&\sb{lcub}\rm o{rcub}& = &-&3.8 years for the 1991-92 sample. Significant differences in size at age and annual incremental growth of juveniles suggest a small increase in juvenile sandbar shark growth rate between the two sampling periods. Annual catches of sharks &>&105 cm PCL declined substantially between survey periods. Males and females were present in a 1:1 ratio. During 1980-81 juveniles ranged in age from 0-7 yr, but in 1990-93 few sandbar sharks over age 4 were taken. Based on the best estimate of fishing mortality the population ranged from 10,087 to 8509 sharks from 1989-1993. Annual year-class size was variable but all estimates were within one order of magnitude. Juvenile sandbar sharks declined in abundance by approximately 15% between 1989 and 1993. The annual population growth rate was highest under a scenario of natural mortality (M) = 0.05 and maximum age of 30 yr, but was only 11.9%/yr. at higher juvenile mortality rates and adult M fixed at 0.10, the best estimate of M for sandbar sharks, population growth rate was only 2.6%/yr. Adding fishing mortality (F) at immature ages caused the population to decline unless F levels were &<&0.10 and 0.05 at maximum age = 30 and 60 yr, respectively. It is apparent that sandbar shark populations will decline under any substantial fishing mortality on immature ages, and mature fish can only be exploited at very low levels of fishing mortality.

Recent studies have demonstrated that the morphologically similar white marlin (Kajikia albida) and roundscale spearfish (Tetrapturus georgii) co-occur in the western North Atlantic, including the U.S. Mid‐Atlantic Bight. Differences in scale morphology have been proposed as one morphological character to discriminate these species, but a thorough analysis of scale morphology is lacking. Because the validity of the roundscale spearfish was not established until 2006, much of the biological information previously collected for “white marlin” may include data for both white marlin and roundscale spearfish. The objectives of this study were to obtain a better understanding of the movements and habitat utilization of positively identified white marlin that inhabit the U.S. Mid-­‐Atlantic Bight during summer months, and to describe the morphological variation of white marlin and roundscale spearfish scales. Eleven long‐term (6 or 12 month) pop-up satellite archival tags were placed on white marlin that were caught and released in the U.S. recreational fishery. Nine tags reported information on temperature, pressure (depth), and light levels for light‐based geolocation for periods of 8 days to 12 months. Most fish moved out of the Mid-Atlantic Bight in September, and overwintered in areas ranging from east of the Gulf Stream off the Carolinas to the Caribbean, and as far south as northern Brazil. of the seven fish that retained tags for more than 40 days, five spent time in known spawning grounds in waters of the Dominican Republic leading up to the spring spawning season. These data demonstrate a large degree of connectivity among white marlin in the western North Atlantic. as noted in previous studies, individuals spent a large proportion of their time in the surface waters (0-10m; 75% across all white marlin pooled), the vast majority of their time in the top 100 m of the water column (97%), and within eight degrees of sea surface temperature (98%), although definite shifts in habitat utilization were evident as fish departed coastal offshore waters of the Mid‐Atlantic Bight. Diel habitat utilization varied greatly, with white marlin spending 81% of total nighttime in the surface waters (0‐10m), and only 26% of total daytime in surface waters. Past studies have characterized the scales of white marlin and roundscale spearfish as being morphologically distinct, but little effort has been made to describe variation within an individual, among individuals, or between species. to better understand morphological variation of scales and squamation patterns of distinct body regions of these two species, individual scales were collected from 11 specific anatomical regions, and scale patches were collected from 3 specific regions of each white marlin and roundscale spearfish brought into marlin tournament weigh stations in the Mid-Atlantic Bight during 2012 and 2013. Scales were measured and described, and scale patches were cleared and stained to examine the level of imbrication of the scales, as well as the overall squamation patterns. In addition to the scales, denticular plates, ossified formations occurring on the surface layer of the dermis, were measured and described. Although considable morphological variation was observed among scales from different anatomical regions of individuals of both species, white marlin scales generally have pointed anterior ends, fewer posterior points, and are more heavily imbricated than those of roundscale spearfish, which are frequently rounded anteriorly, but often have many posterior points and are farther separated within the skin. Over all areas and individuals, roundscale spearfish scales were significantly wider and had a lower length-­‐to-­‐width aspect ratio than those of white marlin. Detailed scale descriptions allow for a more accurate characterization of the variation within and differences between these two species, and could potentially be a valuable tool for investigating istiophorid systematics.

Episodic turbulence is a short-lived, high-intensity phenomenon in marine environments produced by both anthropogenic and natural causes, such as boat propellers, strong winds, and breaking waves. Episodic turbulence has been shown to cause mortality in zooplankton, but its effects on marine phytoplankton have rarely been investigated. This study focused on two diatoms: Thalassiosira weissflogii and Skeletonema costatum. I found that exposure for 45 s to turbulence intensities above 2.5 cm2 s-3 caused 24-32% reduction in diatom abundance and increased the amount of intact dead cells to 22%. Turbulence also caused extracellular release of optically reactive DOM. At a turbulence level of 4.0 cm2 s-3, photosynthetic efficiency (Fv/Fm) decreased from 0.51 to 0.38 and 0.55 to 0.50 in T. weissflogii and S. costatum respectively. These turbulence levels are comparable to those under breaking surface waves and are much smaller than those generated by boat propellers. Despite its relatively short duration, episodic turbulence has the potential to affect phytoplankton via lethal and sublethal effects. An improved technique using the Evans Blue stain was developed to enable visual live/dead plankton cell determinations. When used in conjunction with preservation and flow cytometry, this staining method allows the study of phytoplankton mortality due to turbulence and other environmental stresses.

Epibiosis is a common phenomenon in aquatic environments. The chitinous exoskeletons of crustaceans provide stable surfaces for attachment and growth of epibiotic microorganisms. Epibiont ciliate colonization on copepods is commonly recorded but has rarely been studied in Chesapeake Bay; also, little is known about the life cycles of epibiont ciliates in the bay. The present work focuses on the life cycle of Zoothamnium intermedium in Chesapeake Bay. A peritrich ciliate belonging to the genus Zoothamnium was found as an epibiont on the calanoid copepods Acartia tonsa and Pseudodiaptomus pelagicus during the summer in the York River, a tributary of the lower Chesapeake Bay. By using primers conservative for the genus Zoothamnium, two almost identical (99.8% similarity) 2171-bp ribosomal DNA (rDNA) sequences containing the complete small subunit (SSU) and partial internal transcribed spacer (ITS) rDNA regions were obtained from epibiont ciliates on the two hosts, indicating that they were the same ciliate species. Based on phylogenetic analysis and morphological characteristics, the epibiont was presumptively identified as Z. intermedium. In winter, Z. intermedium was only found on P. pelagicus, never on A. tonsa or A. clausi. The continuous presence of Z. intermedium on P. pelagicus during the winter suggests that it used P. pelagicus as its primary host for overwintering. PCR assays specific to Z. intermedium were designed to detect this ciliate in the environment. Positive PCR results were obtained from some sediment samples, potentially implicating the existence of a benthic cyst stage as another possible overwintering strategy. In the laboratory, formation of cyst-like cells from detached zooids was observed at 5°C. In detachment-recolonization trials, colonization of telotrochs to the same host species was higher than across host species, indicating a certain seasonal host specificity.