Seagrass meadows are highly productive, ecologically and economically valuable ecosystems. However, increased human activities along the coastal areas leading to processes such as eutrophication have resulted in the rapid loss and deterioration of seagrass ecosystems worldwide. This thesis focuses on the responses of seagrasses to increases in nutrients, subsequent increases in ephemeral algae, and changes in the physical-chemical properties of seawater induced by interaction with other marine biota. Both in situ and laboratory experiments conducted on the tropical seagrasses Cymodocea serrulata and Thalassia hemprichii revealed that increased concentrations of water column nutrients negatively affected seagrass photosynthesis by stimulating the growth of the epiphytic biomass on the seagrass leaves. Interaction between seagrasses and other marine organisms induced different responses in seagrass photosynthesis. Ulva intestinalis negatively affected the photosynthetic performance of the temperate seagrass Zostera marina both by reducing the light and by increasing the pH of the surrounding water. On the other hand, the coexistence of mussels Pinna muricata and seagrass Thalassia hemprichii enhanced the photosynthetic activity of the seagrass, but no effect on the mussels' calcification was recorded. This study demonstrates that seagrass productivity is affected by a multitude of indirect effects induced by nutrient over-enrichment, which act singly or in concert with each other. Understanding the responsive mechanisms involved is imperative to safeguard the ecosystem by providing knowledge and proposing measures to halt nutrient loading and to predict the future performance of seagrasses in response to increasing natural and human perturbations. / At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Papers 1, 3 and 4: Submitted. Paper 2: Manuscript. / Swedish Agency for Research Cooperation (Sida/SAREC) marine bilateral programme

This thesis examines a number of natural and anthropogenic disturbances within marine macrophyte habitats of the Caribbean. Understanding the effects of disturbance and the patterns associated with such dynamics is fundamental to ecological studies. Dynamics of interest included: interactions between populations; interactions between life history strategies; successional regimes; and alterations of community structure including loss of trophic heterogeneity and the possibility of "alternate" states. First I explored natural physical disturbance and succession. The dominance of macroalgae in the mid-shore, between areas of seagrass, challenged "classic" succession in such communities. I therefore proposed a model that included chronic "stress" by wave energy that could lead to a reversal in the climax state. Next, I investigated the importance of other grazers (i.e. trophic heterogeneity) in mediating the strength of trophic cascades (e.g. overgrazing). The enclosure experiments used suggested that different life history strategies respond differently to experimental conditions and that interference competition between specialist (conch) and generalist (urchins) grazers results in urchins switching to alternate resources and displaying lower condition. This dynamic may indirectly "buffer" the community against population expansions of urchins and overgrazing of diversity enhancing detritus. Under high nutrient enrichment, urchins maintained themselves, the trophic cascade and low diversity by switching to "expanded" autochthonous and "new" allochthonous resources. I continued to examine the effects of increasing nutrient enrichment, which correlated well with increasing human density, by examining eleven seagrass beds. The patterns of increasing consumer density and decreasing consumer diversity corresponded well to increasing enrichment and loss of autochthonous detritus. At high levels of enrichment, the community was dominated (> 90%) b

Includes bibliographical references (leaves 290-333). / xxiv, 333 leaves : ill. (chiefly col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Describes research into the nutritional value of aquatic plants as novel or non-conventional feedstuffs for ruminants in general and for sheep in particular, with especial reference to those which are available in high amount in southern Australia, such as the seagrass, Posidonia australis. / Thesis (Ph.D.)--University of Adelaide, Dept. of Animal Science, 1996?

Thesis (M.S.)--Mississippi State University. Department of Biological Sciences. / Bibliography: leaves 30-35. Also available on the World Wide Web.

Thesis (Ph.D.)--University of Wollongong, 2007. / Typescript. Includes bibliographical references: page 256-281.

Thesis (Ph.D.)--University of Wollongong, 2009. / Typescript. Includes bibliographical references: leaf 146-171.

Florida Bay is a shallow, subtropical lagoon located south of the Florida mainland. Bordered by the Florida Keys to the east and south, and shallow mud banks to the west, the Bay is protected from wave action and is considered a low energy environment. Utilizing a 100 year bathymetric dataset the geomorphology of Florida Bay was examined to see if significant changes were occurring despite the lack of strong wave action and water circulation. Changes in bathymetry were investigated from using a high-resolution bathymetric dataset from 1890 and 1990. Analysis was concentrated on the three main ecological habitats of Florida Bay: seagrass beds, mud banks and basins. This study of changes in geomorphology revealed that percent coverage of seagrass beds was positively correlated to amount of shallowing, basins larger than 27 km2 have gotten deeper and the mud banks of Florida Bay have been migrating southward at approximately 1 m/y. The significant changes to bathymetry within Florida Bay reveal that the environment is quite dynamic despite being sheltered from open waters. Most importantly, the presence of the 1890 bathymetric dataset allows for remote sensing techniques to be used to follow geological processes.

Plant roots host a wide spectrum of endophytic fungi ranging from parasites through neutralistic fungi to mutualistic mycorrhizal fungi. In most of terrestrial ecosystems, these groups of symbiotic fungi are well documented. However, much less is known about fungal endophytes of aquatic plants, especially the only group of submerged marine plants, seagrasses. We focused on roots of the seagrass species Posidonia oceanica which is a Mediterranean endemite. Its roots hosted an abundant presence of endophytic fungi. We examined the roots using optical and electron microscopy in order to study its morphology. We isolated the mycobionts and determined their taxonomic classification. A specific symbiosis of P. oceanica roots and dark coloured septate fungus has been recorded all over a vast area of the Mediterranean spreading from southern Spain to south Turkey. The fungus forms distinctive and typical structures: superficial hyphae occasionally forming hyphal sheaths or dense hyphal nets, intraradical hyphae colonizing extracellular space and, occasionally, primary cortex cells, and finally intracellular microsclerotia. The colonization pattern of the fungi resembles dark septate endophytes (DSE), group of fungi commonly found in roots of both terrestrial and freshwater plants. In our following studies, we...

No description available.

Aquatic plants and submerged aquatic vegetation (SAV) are some of the most wide-ranging species and create important habitat for fish and wildlife in many ecosystems, including highly variable coastal ecotones. Mechanistically understanding factors controlling current distributions of these species is critical to project future distribution and abundance under increasing variability and climate change. I used a population-based approach to quantify the effects of spatial and temporal variability on life history transitions of the SAV Ruppia maritima L. (widgeongrass) in the highly dynamic Everglades-Florida Bay ecotone as a model to (1) examine which life history stages were most constrained by these conditions and (2) determine how management can promote life history development to enhance its distribution, an Everglades restoration target. Ruppia maritima life history transitions were quantified in a series of laboratory and field experiments encompassing a ra nge of abiotic and biotic factors known to affect seagrass and SAV (salinity, salinity variability, temperature, light and nutrients and seed bank recruitment and competition). These studies revealed that R. maritima life history varied east to west across the Everglades ecotone, driven by multiple gradients in abiotic factors that constrained different life history transitions in distinct ways. Based on this examination, persistence of SAV populations from dynamic coastal environments is highly dependent on large reproductive events that produce high propagule densities for recruitment. Large productive meadows of SAV also depend on high rates of clonal reproduction where vegetation completely regenerates in a short amount of time. Therefore, in hydrologically variable systems, maintenance or increases in SAV reproduction is required for population persistence through recruitment. However, SAV communities that do not experience high rates of sexual reproduction are dependent on successful seed germination, seedling and adult survival and clonal reproduction for biomass production and maintenance. Seedling survival and to a lesser extent, adult survival, are bottlenecks that can limit life history transitions under highly variable hydrological conditions. To ensure long-term survival in these communities, management activities that increase survival and successful life history development through these critical stages will be beneficial. If not, SAV populations may become highly reduced and ephemeral, providing less productive habitat. / Includes bibliography. / Dissertation (Ph.D.)--Florida Atlantic University, 2015. / FAU Electronic Theses and Dissertations Collection