Previous research regarding aquatic acidification has examined the protonation of the carbonate and does not consider calcium to be a limiting factor. This is the first study to suggest that pH may affect the uptake of calcium in crustacean gills. This project describes ion transport mechanisms present in the cell membranes of white river shrimp Litopenaeus setiferus gill epithelium, and the effects of pH on the uptake of calcium by these means. Partially purified membrane vesicles (PPMV) of shrimp gills were prepared through a homogenization process that has been used previously to define ion transport in crab and lobster gill tissues. In the current study, shrimp gill PPMV calcium uptake at 50 µM, and 250 µM was greatest at pH 7.0 (p=0.01, p=0.0001). A valinomycin/K+ induced membrane potential (PD) at pH 7.0 significantly increased (p=0.003) calcium uptake from that observed in the absence of a PD. An induced PD at pH 8.0 significantly increased (p=0.003) calcium uptake from that observed in the absence of a PD, however, was not significantly greater than uptake at pH 7.0 in the presence of a PD (p=0.05). Amiloride (2mM) treatments, and amiloride (2mM) + verapamil (100µM) cocktail treatments showed significant decrease in calcium uptake from the control (p=0.03), however, they were not different from each other. This indicates an electrogenic carrier with two driving forces: calcium concentration, and asymmetric exchange stoichiometry.

Sharks are considered top predators in many marine ecosystems, and can play an important role in structuring those communities. As a result, it is necessary to understand the factors that influence their abundance and distribution. This is particularly important as fishery managers develop fishery management plans for sharks that identify areas that serve as essential fish habitat (EFH). This includes nursery habitat where sharks are born and juveniles spend the early part of their life. However, our understanding of shark habitat use in the northeast Florida waters is limited. The goal of this thesis was to characterize the abundance and distribution of sharks in northeast Florida estuaries, and to examine the effect of abiotic and biotic factors affecting shark habitat use. A bottom longline survey conducted from 2009 – 2011 indicated that 11 shark species use the estuarine waters of northeast Florida during summer months. Atlantic sharpnose (Rhizoprionodon terraenovae), blacktip (Carcharhinus limbatus), bonnethead (Sphyrna tiburo), and sandbar sharks (Carcharhinus plumbeus) were the most abundant species and made up 87.1% of the total catch. Month, bottom water temperature, and depth were the most important factors determining the presence and abundance of these species. This study also examined the role of prey abundance in determining the abundance of Atlantic sharpnose sharks. The probability of catching an Atlantic sharpnose shark, and the abundance of Atlantic sharpnose sharks, were most influenced by site. Neither potential prey abundance nor preferred prey abundance were not significant factors effecting Atlantic sharpnose abundance. This may be a result of prey sampling not providing an accurate measure of the true availability of prey resources. Other factors, such as predation risk, may better explain habitat use patterns of Atlantic sharpnose sharks. Continued sampling will give a better understanding of the factors influencing shark habitat use in this area.

The mechanisms of transepithelial absorption of dietary sucrose in the American lobster, Homarus americanus, were investigated in this study to determine whether sugars can be transported across an animal gut intact or as monosaccharides following hydrolysis. Lobster intestine was isolated and mounted in a perfusion chamber to characterize the mechanisms of mucosal to serosal (MS) 14C -sucrose transport across the intestine MS fluxes were measured by adding varying concentrations of 14C-sucrose to the perfusate which resulted in a hyperbolic curve following Michaelis-Menten kinetics. The kinetic constants of the proposed sucrose transporter were KM = 15.84 ± 1.81 µM and Jmax = 2.32 ± 0.07 ρmol cm-2min-1. The accumulation of 14C-sucrose in the bath in the presence of inhibitors, phloretin, phloridzin, and trehalose was observed. Inhibitory analysis showed that phloridzin, an inhibitor of Na+-dependent mucosal glucose transport, decreased MS 14C-sucrose transport suggesting that MS 14C-sucrose radioactive flux may partially involve an SGLT-1-like transporter. Phloretin, a known inhibitor of Na+-independent basolateral glucose transport, decreased MS 14C-sucrose transport, suggesting that some 14C-sucrose radioactivity may be transported to the blood by a GLUT 2-like carrier. Decreased MS 14C-sucrose transport was also observed in the presence of trehalose, a disaccharide containing D-glucose moieties. Thin-layer chromatography (TLC) was used to identify the chemical nature of radioactively labeled sugars in the bath following transport. TLC revealed 14C-sucrose was transported across the intestine largely as an intact molecule with no 14C-glucose or 14C-fructose appearing in the serosal bath or luminal perfusate. Bath samples evaporated to dryness and resuspended disclosed only 15% volatile metabolites. Results of this study strongly suggest that disaccharide sugars can be transported intact across animal intestine and provide support for the occurrence of a disaccharide membrane transporter that has not previously been functionally characterized.

Although herbivory and other types of plant damage typically are viewed as detrimental to plant survival and performance, vigorous regrowth, greater seed set, and fitness benefits may be possible when damage to the apical meristem, or actively growing stem terminal, is involved. Such damage releases apical dominance, or the hormonal suppression of lateral buds, activates dormant lateral buds, and enables lateral shoots to grow. Since in plants with terminal flowers, each stem may bear a flower, removal of the apical meristem may result in stem bifurcation and ultimately increase the number of flowers and seeds, thereby increasing potential fitness. In the current study, possible overcompensation in response to apical meristem damage caused by simulated herbivory (clipping) and the gall midge Asphondylia borrichiae Rossi and Strong (Diptera: Cecidomyiidae) (galling) was investigated in the native coastal halophyte, sea oxeye daisy Borrichia frutescens (L.) DC. (Asteraceae), in relation to nutrient supplementation. Results suggest a strong correlation between stem count and gall count at the study site; moreover, apical dominance was relatively weak early in the growing season and stronger in short plants that were shaded by taller neighbors later in the season. Results also indicate that overcompensation or even full compensation is an unlikely response to apical meristem damage in B. frutescens. Stem count was similar across all stem treatments, but increased significantly with nutrient supplementation, which all supports weak apical dominance in sea oxeye daisy. Nearly all measures of fitness also were either slightly or significantly lower when clipped and galled compared to plants with stems intact, while seed count responded positively to nutrient supplementation.

Previous nutritional physiology research using L-histidine and zinc in American lobster intestine (Homarus americanus) has suggested that these solutes can be co-transported as complexes (Histidine-Zinc-Histidine) across the intestine using a peptide transporter. Furthermore, transport of L-leucine was shown to be inhibited by high calcium concentrations. Dipeptide and bis-complex transport and the role of calcium were investigated in the perfused intestines of lobster and Atlantic white shrimp (Litopenaeus setiferus). Following trans-intestinal transport, serosal medium was analyzed for amino acid composition by gas chromatography. In lobster, the transport of glycylsarcosine (Gly-Sar) from mucosa to serosa was stimulated two-fold with luminal pH 8.5, compared to the pH 5.5 control. Mucosa to serosa and serosa to mucosa fluxes of Gly-Sar were measured; the dipeptide was transported intact in both directions, but the net flux was from mucosa to serosa. The use of 0.5mM calcium chloride stimulated Gly-Sar transport two-fold, compared to 25 mM. In shrimp, the addition of 50 µM zinc chloride increased the rate of L-histidine transport, while Gly-Sar inhibited histidine transport in the presence of zinc. The rate of histidine transport was significantly higher with 1mM calcium chloride than with 25mM. These results suggest that shrimp transport bis-complexes in a manner similar to lobster. High calcium concentration had an inhibitory effect on both amino acid and dipeptide transport. Proposed mechanisms accounting for the effects of metals and calcium on trans-intestinal transports of both amino acids and dipeptides by lobster and shrimp digestive tracts are discussed.

Terrestrial ecosystems in the southeastern United States have evolved with fire as a common disturbance and as a result many natural communities require the presence of fire to persist over time. Human development precludes natural fires from occurring within these communities; however, prescribed fire is considered to be a critical tool in the effort to restore fire-dependent ecosystems after decades of fire exclusion. Direct effects of fire on individual floral and faunal species as well as benefits to biodiversity at the landscape (gamma diversity) level have largely been supported in previous research. However, information on the effects of natural and prescribed fire on plant diversity at the local level (alpha diversity) is limited, particularly for southeastern forests. The applicability of the Intermediate Disturbance Hypothesis (IDH), which suggests that the highest levels of biodiversity are found at intermediate levels of disturbance, is also untested for North Florida upland plant communities. This study compared the effects of fire on local scale mean plant species diversity by examining burned and unburned portions of three fire-dependent communities to determine if there is an effect of prescribed fire on in alpha biodiversity. Alpha biodiversity was not significantly different (p=0.433) between burned and unburned fire-dependent plant communities in northern Florida, suggesting that prescribed fire does not affect plant species diversity in these communities and/or the IDH for plant communities is not supported at the time scale tested. However, the application of prescribed fire did result in changes in abundance of species, particularly with species such as Dicanthelium acuminatum, Quercus myrtifolia, and Vaccinium myrsinites, that respond positively to fire, which may have implications for associated faunal diversity.