Thesis (M.S.)--University of Puerto Rico, Mayagüez Campus, 2008. / Tables. Printout. Includes bibliographical references (leaves 64-70).

Seagrasses are submerged marine plants that provide essential ecosystem functions, but are declining in abundance worldwide. As angiosperms, seagrasses are capable of sexual reproduction, but also propagate asexually through clonal rhizome growth. Clonal growth was traditionally considered the primary means for seagrass propagation. Recent developments in genetic techniques and an increasing number of studies examining seagrass population genetics, however, indicate that sexual reproduction is important for bed establishment and maintenance. Few studies have investigated the reproductive biology and ecology of sub-tropical seagrass species, although this information is necessary for effective management and restoration. This work investigates the influence of pore-water nutrients on flowering, water flow on seed dispersal, consumption on seed survival, and describes the reproductive phenology in Texas for the two dominant seagrass species in the Gulf of Mexico: turtle grass (Thalassia testudinum) and shoal grass (Halodule wrightii). These species exhibit distinctive reproductive seasons that span summertime months, but reproductive output varies spatially and temporally. Results of an in situ nutrient enrichment experiment indicate that turtle grass produces fewer flowers (but more somatic tissue) when exposed to high pore-water ammonium than when exposed to low pore-water ammonium, suggesting that nutrient loading has the potential to reduce seagrass reproductive output. Seed consumption may also limit reproduction and recruitment in some areas, as laboratory feeding experiments show that several local crustaceans consume shoal grass and turtle grass seeds and seedlings, which do not survive consumption. Dispersal experiments indicate that seed movement along the substrate depends on local water flow conditions, is greater for turtle grass than shoal grass, and is related to seed morphology. Under normal water flow conditions in Texas, turtle grass secondary seedling dispersal is relatively minimal (< 2.1 m d⁻¹) compared to primary dispersal, which can be on the order of kilometers, and shoal grass secondary seed dispersal can be up to 1.1 m d⁻¹, but seeds are likely retained in the parent meadow. Results from this work can be used when developing seagrass management, conservation and restoration actions and provide necessary information concerning a life history stage whose importance was historically under-recognized. / text

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

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Seagrass is a key stone component for the Indian River Lagoon (IRL) ecosystem, and therefore it is an important topic for many studies in the lagoon. This study focuses on the effects of seagrass beds on the hydrodynamics in the IRL. A hydrodynamic model based on the Delft3D modeling system has been developed for the southern IRL including the St. Lucie estuary, Ft. Pierce and St. Lucie Inlets, and adjacent coastal waters. The model is driven by freshwater inputs from the watershed, tides, meteorological forcing, and oceanic boundary forcing. The model has been systematically calibrated through a series of numerical experiments for key parameters, particularly the bottom roughness, and configuration including heat flux formulation and bottom bathymetry. The model skills were evaluated with quantitative metrics (point-to-point correlation, root-mean-square difference, and mean bias) to gauge the agreements between model and data for key variables including temperature, salinity, and currents. A three-year (2013-2015) simulation has been performed, and the results have been validated with available data including observations at HBOI Land-Ocean Biogeochemistry Observatory (LOBO) stations and in situ measurements from various sources. The validated model is then used to investigate the effects of 1) model vertical resolution (total number of model vertical layers), 2) spatial variability of surface winds, and 3) seagrass beds on the simulated hydrodynamics. The study focuses on the vicinity of Ft. Pierce Inlet, where significant seagrass coverage can be found. A series of numerical experiments were performed with a combination of different configurations. Overall, the experiment with 2-dimensional (2-D) winds, ten vertical layers and incorporating seagrass provided the most satisfactory outcomes. Overall, both vertical resolution and spatial variability of surface winds affect significantly the model results. In particular, increasing vertical resolution improves model prediction of temperature, salinity and currents. Similarly, the model with 2-D winds yields more realistic results than the model forced by 0-D winds. The seagrass beds have significant effects on the model results, particularly the tidal and sub-tidal currents. In general, model results show that both tidal and sub-tidal currents are much weaker due to increase bottom friction from seagrass. For tidal currents, the strongest impacts lie in the main channel (inter-coastal waterway) and western part of the lagoon, where strong tidal currents can be found. Inclusion of seagrass in the model also improves the simulation of sub-tidal currents. Seagrass beds also affect model temperature and salinity including strengthening vertical stratification. In general, seagrass effects vary over time, particularly tidal cycle with stronger effects seen in flood and ebb tides, and seasonal cycle with stronger effects in the summer than in winter. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2016. / FAU Electronic Theses and Dissertations Collection