Browsing by Subject "nutrient enrichment"
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Item Evaluation of Natural Markers to Assess Cross-Shelf Connectivity of MesoAmerican Reef Fish Populations in Belize(2014-05-06) Wetmore, Lynne S.Quantitative evaluations of early-life connectivity in reef fish populations are critical to the effective identification and management of productive nearshore nurseries. The present study evaluates the use of natural markers in assessing both trophic and population connectivity for three species of snappers (Lutjanidae) utilizing back-reef nurseries in southern Belize: dog snapper (Lutjanus jocu), gray snapper (L. griseus), and schoolmaster (L. apodus). Juvenile snappers were collected from inner- and outer-shelf nurseries across two latitudinal regions in the Belize coastal lagoon in order to: (a) utilize tissue stable isotopes (?^(13)C and ?^(15)N) as dietary tracers to characterize organic matter production across the continental shelf, and (b) evaluate the utility of otolith stable isotopes (?^(13)C and ?^(18)O) as a marker of nursery origin. Isosource models (based on tissue ?^(13)C and ?^(15)N) revealed distinct differences in food web dynamics between pristine nurseries and those influenced by heavily impacted watersheds. Juvenile snappers at pristine sites were supported by organic matter derived from both benthic sources (seagrass/benthic diatoms) and the water column (phytoplankton), while sites impacted by anthropogenic runoff displayed significant decreases in water column-based production during the rainy season, accompanied by significantly decreased juvenile snapper condition (muscle lipid content) for all three species. These results emphasize the high land-sea connectivity in this system and indicate that runoff from impacted watersheds has the potential to disrupt trophic production in nurseries across the continental shelf. Otolith stable isotopes (?^(13)C and ?^(18)O) appeared to be strongly related to salinity gradients within the Belize coastal lagoon and, consequently, showed considerable promise in identifying juvenile snappers to shelf position. Both isotopes were both consistently enriched in snappers from outer-shelf nurseries, where freshwater influence was minimal, and ?^(18)O was enriched in the northern sampling region, which receives lower amounts of freshwater input compared to the south. Although individuals of each species were classified to specific study sites with varying success (58-81%), discrimination to shelf position was consistently high for all species (74-92%), indicating that otolith ?^(13)C and ?^(18)O may be useful in determining relative contribution rates of juvenile snappers produced at inner- and outer-shelf nurseries within tropical back-reef systems.Item Factors Affecting Carbohydrate Production and Loss in Salt Marsh Sediments of Galveston Bay(2010-10-12) Wilson, Carolyn E.Benthic microalgae (BMA) living within the surface sediment of salt marshes are highly productive organisms that provide a significant proportion of organic carbon inputs into estuarine systems. BMA secrete extracellular carbohydrates in the form of low molecular weight carbohydrates and extracellular polymeric substances (EPS) as they migrate within the sediment. EPS plays an important role in the structure and function of BMA biofilms in shallow-water systems as EPS affects habitat structure, stabilizes the sediment, reduces sediment erosion, and is a carbon source for organisms. This study looked at the effect of nutrients and carbohydrate additions on BMA biomass, bacterial biomass, carbohydrate production, and glycosidase activity in the surface 5 mm of intertidal sediment in a subtropical salt marsh (Galveston Bay, Texas). Nitrogen and phosphorus were added to cores collected from the salt marsh and incubated in the lab over four days. Very little change was seen in the biomass of the benthic microalgae or in the different carbohydrate fractions with the added nutrients. The mean chlorophyll a concentration was 13 +/- 5 ug g-1 sediment, the mean saline extractable carbohydrate concentration was 237 +/- 113 ug g-1 sediment, and the mean EPS concentration was 48 +/- 25 ug g-1 sediment. The chlorophyll a and saline extractable carbohydrate concentrations initially decreased over the first 24 hours, but then increased over the rest of the experiment, indicating a possible species compositional shift in the BMA. With no major response with nutrient additions, it is likely that a different environmental factor is limiting for the growth of the benthic microalgae, and therefore the production of sEPS, in this salt marsh. A series of experiments was conducted in situ by adding glucose, alginic acid, and phosphorus to sediment within experimental plots. Samples were taken periodically over three to seven days to determine the biomass of the microbial community, enzyme activities and kinetics, and changes in the concentrations of several sediment carbohydrate pools. u-glucosidase activities (15 +/- 3 nmol g-1 h-1) were significantly higher than u-xylosidase (6 +/- 2 nmol g-1 h-1) and u-galactosidase (8 +/- 2 nmol g-1 h-1) activities within the sediment, and there was no suppression of u-glucosidase activity measured with the glucose addition. These data represent the first measurement of u- xylosidase and u-galactosidase activity in intertidal sediment dominated by BMA. Although preliminary experiments suggested a possible phosphorus limitation within the sediment, there was little change in the bacteria abundance or the benthic microalgae biomass when phosphorus was added in situ. This study begins to illustrate the dynamics of carbohydrate production and loss in this salt marsh, and the ability for the microbial community in the salt marshes of Galveston Bay to adjust to the nutrient and carbohydrate treatments.Item The role of macroalgal species as bio-indicators of water quality in bermudian karstic cave pools(2009-05-15) Maloney, Bridget MarieBermuda has one of the highest concentrations of cave systems of any country in the world, but as the resident human population and tourism expand, this unique habitat is becoming increasingly threatened by development and water pollution. A water quality assessment was performed in six of Bermuda?s anchialine cave pools during summer 2007. Vertical water profiles were collected at each site to determine temperature, salinity, dissolved oxygen, and pH levels throughout the water column. Each cave pool had its own unique hydrological patterns. Additionally, water samples were collected at the surface and at the maximum depth to determine the concentration of nitrate, nitrite, ammonium, phosphate, and urea in the water. Further samples were collected to establish the fecal bacteria content in the surface waters. High nitrate levels were measured in two of the cave pools, while unsafe bacterial levels were measured in three pools. In situ nutrient addition experiments were used to examine effects of nutrient enrichment on algae naturally occurring in the six cave pool. Initial assessments of the pools determined distribution of foliose species. Six algal species (Ulva sp., Caulerpa mexicana, C. racemosa, C. sertularioides, Halymenia floresii, and Cryptonemia sp.) inhabited multiple sites, but not all species occurred at all sites. Changes in the biomass of individual plants were recorded for 6 to 12 days in response to N (nitrate), P (phosphate), and NP additions. The effect of nutrient addition on increase in biomass was significant over a 6 day period for Ulva sp. and H. floresii. Intermediate to no growth was seen in C. mexicana and Cryptonemia sp. C. mexicana exhibited both increases and in biomass depending on the site. Cryptonemia sp. had low but positive growth. A significant decrease in biomass occurred with C. racemosa and C. sertularioides. Primary productivity was measured using the traditional light dark bottle method. Differences in net productivity and respiration may explain why some plants responded positively and other negatively to nutrient additions. Ulva sp. and H. floresii showed potential as bioindicators for groundwater quality.