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Bermuda 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.

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.

Determining the relative roles of top-down vs. bottom-up forces in controlling the structure of ecological communities is of primary importance because anthropogenic nutrient loading, overharvesting of consumers, and potential interactions of these forces are pervasively changing ecosystems throughout the world. Here I use both field experimentation and meta-analyses to investigate the role of predators in controlling community composition, the relative roles of herbivores vs. nutrient enrichment in controlling the abundance of benthic primary producers, and the influence of herbivore diversity on the community structure of coral reefs. On a coral reef in the Florida Keys, I showed that release from predation by large fishes and invertebrates via exclusion cages allowed population increases in the gorgonian-eating gastropod Cyphoma gibbosum which increased predation rates on gorgonian corals. To directly address the relative roles of top-down and bottom-up forces in controlling primary producers in benthic marine habitats, I used factorial meta-analysis of 54 field experiments that orthogonally manipulated herbivore pressure and nutrient loading to quantify the effects of consumers and nutrient enrichment on community structure. The relative effects of herbivores vs. nutrient enrichment were context dependant, varying with latitude, the type of primary producer, and the nutrient status of the system. To address the influence of herbivore diversity on the community structure of Caribbean coral reefs, I used manipulative field experiments over two years to show that a Caribbean reef changes dramatically as a function of herbivorous fish diversity. The effects of herbivore diversity on community structure were strong in both years of the experiment due to different diet preferences among herbivores. Higher herbivore diversity suppressed macroalgal abundance, increased abundance of crustose coralline algae, reduced coral mortality, and increased coral growth when compared to treatments with lower herbivore diversity. Complementary feeding by different fishes drove these patterns because macroalgae were unable to effectively deter feeding by fishes with different attack strategies. Thus, herbivore diversity appears to play an important role in the healthy function of coral reef ecosystems via complementary feeding of different herbivore species.

Coastal communities will be most affected by global climate change and are important to study to understand current and future ecological processes. The current model for global climate change predicts a change in rainfall, which will alter the salinity of coastal systems. Given the presence of eutrophication in many coastal waters, it is important to understand the effects that this increase in nutrients, coupled with changes in salinity, will have on these communities. This study was conducted to understand the effect of salinity increase on the growth and herbivory of the black mangrove, Avicennia germinans, in the presence of increased nutrients. Explicitly, the effects of changing salinity (high, medium, and low) were coupled with fertilizer additions of nitrogen, phosphorus, both, or no fertilizer. Nutrient enrichment differentially affected the growth and herbivory of the plants between salinity zones. The medium salinity zone consistently produced the greatest increases in growth and herbivory. Added nutrients did not have an effect on growth in the low salinity zone. However, added nitrogen increased some growth variables in the medium salinity zone and added phosphorus increased some growth variables in the high salinity zone. Phosphorus also increased herbivory. The results point to diverse processes acting along the salinity gradient. There appears to be differential N- and P-limitation along the gradient. Additionally, the growth differences indicate abiotic and biotic limitations across the salinity gradient, with debilitating salinity acting in the high salinity zone and competition acting in the low salinity zone.

Twentieth century human settlement within the Tampa Bay watershed was linked to a dramatic mid-century decline in bay water quality and loss of seagrass acreage. Decades of direct and indirect nutrient discharges to the bay from phosphorus mining, fertilizer manufacturing, and wastewater treatment, as examples, impaired the estuary. In the past twenty years, regional stakeholders have worked to improve the bay water quality by reducing point and non-point source nutrient loading to the bay. Lakes within the Tampa Bay watershed may play an important role in attenuating the flow of nutrients into the bay. This study hypothesized that between 1990 and 2007 lake water concentrations of total phosphorus (TP) and chlorophyll-a, as well as the ratio of total nitrogen to total phosphorus (TN:TP), have changed for selected lakes in the Tampa Bay watershed. During this period, the watershed underwent a rapid shift in land use as groves and farms became shopping malls and new homes. A two-way analysis of variance (ANOVA) revealed that for 10 lakes clustered in the northern portion of the Tampa Bay watershed and classified as oligotrophic or mesotrophic, observed increases in water concentrations of TP and chlorophyll-a were statistically significant. For 6 lakes classified as hypereutrophic and scattered across the watershed, observed decreases in water TP concentrations were statistically significant, while chlorophyll-a concentrations did not change. For both groups of lakes, the TN:TP ratio declined significantly; however, oligotrophic and mesotrophic lakes were phosphorus-limited but hypereutrophic lakes were nitrogen-limited, based on this ratio. A second hypothesis of this study was that lake water concentrations of TP, total nitrogen (TN) and chlorophyll-a were lower in lakes that had more coverage of submerged aquatic vegetation, as vegetation suppresses re-suspension of sediments and is a reservoir for nitrogen and phosphorus and a surface for biofilms. The results of a one-way ANOVA showed that for 34 lakes within the Tampa Bay watershed, lakes with a greater than 20 percent volume infested by macrophytes (PVI), water concentrations of TP and chlorophyll-a but not TN were statistically lower than for lakes with a less than 20 PVI.

Eutrophication, particularly due to nitrogen (N) and phosphorus (P) input, has been massively altered by anthropogenic activities. Thus it is important to understand the impact on salt marsh plants; however studies on salt marsh plants within Galveston Bay, Texas are limited. In this study, the effects of repeated nutrient additions in monospecific plots of Spartina alterniflora, Batis maritima¸ and Salicornia virginica as well as mixed plots of B. maritima and S. virginica were studied over 15 months. Results showed that nutrient loading led to an increase in height, biomass, growth rate and percent nitrogen (N) within all three species studied, but were species specific more than dose dependent. Nitrogen content in leaves had a positive correlation with P content in leaves but a negative correlation with carbon (C) content. Nutrient loading lead to a significant increase in total chlorophyll in the fertilized plots of S. alterniflora and S. virginica one month into the study. Nutrient addition to two succulent species, B. maritima and S. virginica in mixed plots did not reveal a distinct superior competitor within the 15 month study in terms of growth and nutrient use efficiencies; however using the maximum growth rates of the monospecific plots, the Monod model was used to determine which species would dominate at high nutrient loads. Based on height data S. alterniflora would dominate, while B. maritima would dominate according to the Monod model based on biomass.

The current study developed a paleolimnological approach to assess changes in diatom assemblages (class Bacillariophyceae) from present-day lake sediments in comparison to those deposited before significant human impact (ca. pre-1850) from 51 Halifax (Nova Scotia, Canada) region lakes in conjunction with a regional diatom-based transfer functions for pH and total phosphorus. All 51 lakes showed changes in diatom assemblages between the present-day and pre-industrial assemblages that was greater than would be expected (i.e. similarity between ‘top’ and ‘bottom’ samples was much less than the similarities within triplicate ‘top’ and ‘bottom’ samples). To help identify the most important environmental stressors impacting diatom assemblages in these lakes, diatom-based reconstructions of inferred changes in pH (DI-pH) and total phosphorus (DI-TP) that were greater than the Root Mean Squared Error (RMSE) of the respective inference models were reconstructed for each of the 51 lakes. For example, a decrease in DI-pH greater than the RMSE of the pH model would be a strong indication of recent acidification, whereas an increase in DI-TP greater than the RMSE of the model indicates nutrient enrichment. Based on this approach, 4% of the lakes are showing acidification-related trends occurring in lakes with low pre-industrial pH values and relatively undisturbed watersheds. Almost 14% of the study lakes have been impacted by nutrients and characterized by watershed development and high concentrations of TP. Approximately 4% of lakes showed oligotrophication and acidification. Diatom assemblages from almost 20% of the study lakes that were relatively unimpacted by the afore-listed environmental stressors show trends consistent with climate warming. These lakes show an increase in DI-pH greater than the RMSE of the inference model, and floristic changes typically showed a decrease in the relative abundance of Aulacoseira distans paralleled with increase in Cyclotella stelligera and other planktonic diatoms in the modern sediments. In addition, Diatoma tenue and Diploneis parma, diatoms tolerant of high conductivity, increased in 45% of the study lakes suggesting road salt as an additional stressor. This thesis provides a rapid paleolimnological-based technique to assess regional water-quality changes, and further demonstrates the complexity of ecological changes within freshwater resources. / Thesis (Master, Biology) -- Queen's University, 2009-09-10 15:18:07.01

Interactions between multiple anthropogenic stressors can have unexpected synergistic or antagonistic effects, making it difficult to predict their combined effect using single stressor studies. The interaction between invasive consumers and nutrient enrichment is particularly important as both of these stressors frequently co-occur and their respective bottom-up and top-down effects have the potential to interact across multiple trophic levels. We conducted a mesocosm experiment that crossed an increasing nutrient addition gradient against an increasing zebra mussel invasion gradient. Native zooplankton communities were added to the mesocosms, and after three months we examined how the single stressor effects on available resources and the zooplankton community were altered by their multiple stressor interaction. Added nutrients had no effect on primary producer abundance, but increased the abundance and dominance of the top consumer, which likely increased predation pressure on the producers and so prevented their response to increased nutrients. Zebra mussels reduced total phytoplankton abundance by ~75%, rotifer abundance by ~80%, and shifted communities towards dominance of cladocerans and adult/juvenile copepods. When combined, the top-down control exerted by the mussels interacted antagonistically to prevent any bottom-up influence of nutrient enrichment on the zooplankton community. These results provide insight into the potential outcomes of nutrient and invasive consumer stressor interactions, and illustrate the need for researchers to consider single stressor problems in a multiple stressor context. / Thesis (Master, Biology) -- Queen's University, 2014-01-31 15:20:15.387