There are two focal points of this thesis: the acoustics of seagrass and the acoustical properties of encapsulated bubbles for underwater noise abatement. The acoustical properties of seagrass have applications in mine hunting, shallow water sonar, and environmental acoustic remote sensing. In order to optimize these applications, a predictive model of acoustic propagation in seagrass beds is sought. Previous laboratory research has indicated that the tissue acoustic properties of seagrass as well as the tissue physical structure and entrained air masses inside the leaves contribute to the overall acoustic behavior. The present research utilized a glass laboratory resonance tube to find the low frequency (1 kHz-4 kHz) acoustic compressibility of two species of seagrass, Thalassia testidinum and Halodule wrightii. By using a mixture of finely divided seagrass tissue suspended in seawater, the bulk moduli of the seagrass species were extracted. In the second section, encapsulated bubbles were analyzed as a method of abating underwater anthropogenic noise sources, since these sources, including marine piledriving and oil and gas exploration and production, pose potential harmful effects to marine life. Previous research, which used an array of rubber-shelled encapsulated bubbles, found the attenuation from these bubbles in be in close accordance with an existing encapsulated bubble model. Experiments were performed in a small laboratory resonance tank, a large outdoor acoustic tank, and at Lake Travis Test Station (LTTS) in order to determine the effects of varying an encapsulated bubble's wall thickness and fill material on bubble resonance frequency and damping. Results found that increasing the wall thickness tended to increase the balloon resonance frequencies measured in the small tank, which was strongly correlated to the frequency of maximum noise reduction in the large outdoor test tank and LTTS tests. The addition of polyester fibers and aluminum wool as fill materials decreased both the resonance frequency and quality factor, whereas helium-filled filled encapsulated bubbles had an increased resonance frequency but decreased quality factor as compared with air-filled bubbles. The resonance quality factor and void fraction further proved to affect the noise reduction near bubble resonance in the outdoor acoustic tank and LTTS tests. The measurements made with a single bubble in a small laboratory tank were correlated to measurements with a full-size system composed of many bubbles operating in open water. / text

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Ten species of seagrasses are recognized in Taiwan and adjacent islands. They are, namely, Halophila beccarii Aschers., Halophila decipiens Ostenf., Halophila ovalis (R. Br.) Hook. f., Thalassia hemprichii (Solms) Aschers., Cymodocea rotundata Ehrenb. & Hempr. ex Aschers., Cymodocea serrulata (R. Br.) Aschers. & Magnus, Syringodium isoetifolium (Aschers.) Dandy, Halodule pinifolia (Miki) den Hartog, Halodule uninervis (Forssk.) Aschers. and Nanozostera japonica (Ascherson & Graebner) Toml. & Posl. The detail morphological charactors of these speices are descripted for the first time, and can be the basis of further research. These species are mainly distributed in the west coast of Taiwan, Hengchun peninsula, the Green Island, the Orchid Island, Hsiaoliuchiu, the Pescadores Islands, Quemoy and the Pratas Island, the habitats can be categorized as 4 types, which are muddy to sandy tidal flat, coral platform, wave-cut platform and fine-muddy seabed. The relation between types of habitat and occurrence is also discussed.

Fluctuation of the seagrass ecosystem may be informative to the impacts of environmental changes. This study focuses on a small, inconspicuous triplefin blenny, Enneapterygius minutus, found in a specific tide pool of seagrass meadow on Gui Wan Bi, Green Island, Taiwan. Its high abundance and stable residence make this species a suitable candidate to monitor the condition of the seagrass ecosystem. Monthly collections were made during low tide from April 2007 to July 2008. The otolith microstructure was examined to study their age and growth circumstance. Developmental stages of the ovaries based on histological characteristics together with data of batch fecundity and GSI value were applied to estimate size at maturation and the spawning seasonality of the individual assemblages in the tide pool. A length-frequency analysis was made by using the monthly data. Enneapterygius minutus is a kind of short life species. It has a quite low batch fecundity and a year-long breeding ability with a seasonal high peak mainly from late winter to late spring. The recruitment of juvenile individuals began about a month after breeding had occurred. These data show that Enneapterygius minutus uses seagrass meadows as a hatching and nursing habitat. According to the close relationship between Enneapterygius minutus and seagrass meadow, it would be possible to monitor this ecosystem by using this species as an indicator when it is under environmental stress.

Planctomycetes are members of a unique superphylum along with Verrucomicrobia and Chlamydia, situated in the domain Bacteria. They have distinct structural and morphological features, and discoveries made through phylogenetic analysis indicate their important role in nutrient cycling. Their known relationships with marine photosynthetic organisms led to the formation of this study's hypothesis, namely, that Planctomycetes can be isolated from the biofilm of seagrass species of the Red Sea using cultivation techniques adapted for these organisms. Preparation of solid and liquid media using M13 with both agar and gellan, and 2216 Difco Marine Broth full-­ strength, 1/10-­strength, and with antibiotics, resulted in the successful isolation of Planctomycetes as confirmed by morphological examination and transmission electron microscopy. The work performed in this study provides a solid foundation for further studies to elucidate the metabolic pathways and ecological significance of Planctomycetes.

Microplastics have been discovered ubiquitously in marine environments. While their accumulation is noted in seagrass meadows, much work is required to understand microplastic accumulation patterns and mechanisms in this ecosystem, as well as microplastic impacts on seagrass plants and their associated epiphytic and sediment communities. We pursue this effort by quantifying microplastic densities in seagrass blades, sediments, and nearby water columns across nine sites in coastal Massachusetts and exploring their relationships to morphological and anthropogenic variables. Further, we synthesize the potential impacts microplastics have on relevant seagrass plant, epiphyte, and sediment processes and functions. Microplastics were found ubiquitously at all sites regardless of proximity to anthropogenic interference, with plant epibiont density influencing their accumulation on seagrass blades, and bulk density influencing accumulation within sediments. Literature review revealed that microplastics may harm seagrass ecosystems via physical obstruction of epiphytic and plant surfaces, nutrient cycle and sediment characteristic alteration, and sediment organism ingestion, with all impacts exacerbated by seagrasses high trapping efficiency. As microplastics become a permanent and increasing member of seagrass ecosystems it will be pertinent to direct future research towards continuing to explore their impacts and patterns behind their accumulation. / 2023-09-28T00:00:00Z

This investigation characterized karstic and nearshore environments of Bermuda to describe 1) behavior and periodicity of cave springs; 2) submarine spring water quality; and 3) nearshore marine seagrass density. Caves can be conduits for groundwater pollution where terrestrial anthropogenic processes leach nutrient enriched water into marine caves springs that flow directly into coastal waters. Seagrass may serve as an environmental indicator due to its susceptibility to anthropogenic pollution. In 2007, environmental water monitoring devices were moored at the entrance of coastal cave springs throughout Bermuda to retrieve data on water quality, flow volume, velocity and direction. Nutrients (nitrate, phosphate, nitrite, and ammonium) and fecal bacteria (Enterococcus spp. and Escherichia coli) were measured in each cave. To qualify a link between terrestrial pollution and the nearshore environment, seagrass density within 100 m from cave entrances were measured. Bermuda caves were tidally influenced. Caves in Harrington Sound showed a delayed tidal flux with smaller ranges due to the restricted tidal inlet. Four caves exhibited a 1:1 in:out flow ratio. Caves with an imbalance flow ratio could be influenced by additional entrances, connection to an alternate water body, or cave geometry. Cave water was similar between caves. Environmental parameters and nutrients changed together, excluding seasonal variations in temperature (17.89 to 22.94 degrees C). Higher nutrients and fecal coliforms within caves indicated sewage may be leaching into the subsurface ground water system. Three seagrass species were evenly distributed within patchy meadows. Densities ranged from 0.91 to 4.5 (on a Braun-Blanket Scale). Higher mean densities in Harrington Sound, suggested the enclosed, protected nature of the sound allowed for reduced wave and current action. Syringodium filiforme decreased in density towards the ocean signifying a direct influence of cave water on seagrass beds. Tidal in and out-flux allowed for a constantly changing environment suitable for a mixture of seagrass species. Higher dissolved inorganic nutrient concentrations were associated with locations lacking seagrass. This study found 1) cave springs connected groundwater and nearshore seagrass ecosystems; and 2) components associated with terrestrial sewage pollution (DIN, HPO4=, and Enterococcus spp.) were higher within caves than nearshore waters.

Mapping of marine benthic flora using remote sensing techniques has, over the past decade, been used to locate environmentally stressed areas in the South Australian marine environment. These studies used panchromatic/colour aerial photography and/or medium resolution multispectral satellite imagery to create a time series showing location and rate of seagrass loss. While successful within their project parameters, these studies were limited by conditions at time of image capture, such as sun-glare, wave action and low contrast in deeper waters due to absorption and scattering. This research thesis reports the successful use of polarisation on the capture of visible and near infra-red optical imagery as a method to minimise these limiting factors. Two experimental test flights were undertaken using commercial off-the-shelf digital cameras mounted in the camera port of a light aircraft. The first flight compared vertical polarisation using co-mounted visible and infra-red cameras. The second flight compared vertical and horizontal polarisation using co-mounted identical visible spectrum cameras. The main finding of this series of airborne polarisation experiments is that sea surface reflection is removed by using vertically polarised filters at, and around, the Brewster angle of 53 degrees off nadir, especially when viewing sunwards. The effect is the same in the visible and infra-red parts of the spectrum. This reflection includes sky reflectance, lambertian sun glare, reflection due to wave action, and turbulence, but not direct solar specular reflection. Vertical polarisation filters improve the imaging of benthic flora compared to horizontally polarised imagery and, by extension, non-polarised imagery. The successful use of polarisation to remove surface reflectance over water is limited to imagery captured at or near the Brewster angle. By using successive overlapping frames this can be achieved, as shown by the experiments. Ideally all of the image should be at the Brewster angle. A conceptual design for a conical optical scanner which builds wide-swath imagery where each pixel in each band is solely a record of the vertically polarised signal at the Brewster Angle is presented as a result of these experiments. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1374494 / Thesis (M.Sc.) - University of Adelaide, School of Earth and Environmental Sciences, 2009

Photosynthetic activity of three seagrass species, Posidonia sinuosa Cambridge et Kuo, Posidonia australis Hook. f. and Halophila ovalis (R. Br.) Hook., growing in Cockburn Sound, Western Australia, was assessed using an underwater pulse amplitude modulated fluorometer (Diving-PAM). The study aimed to determine possible causes and the extent of stress to seagrasses during transplantation, so that rehabilitation efforts can be improved by reducing stress during the transplant process. Absorptance factors for each species were determined as 0.64 ± 0.04 for P. sinuosa, 0.59 ± 0.02 for P. australis and 0.55 ± 0.02 for H. ovalis, which were substantially lower than previously reported photosynthetic absorption factors. Transmittance, reflectance and non-photosynthetic absorptance of light diverted between 35-45% of irradiance from use in photosynthesis. An investigation of potential errors during measurement of rapid light curves (RLCs) reinforced the importance of ensuring that leaves remained stationary in the Universal Sample Holder. Any movement of seagrass leaves resulted in incorrect measurements of electron transport rates (ETR). A study on seasonal photosynthetic rates of each species found that maximum ETR (ETRmax) varied seasonally and among species. The highest ETRmax for each species occurred during summer, when ambient irradiances were at a maximum, and decreased during autumn. H. ovalis had the highest overall ETRmax in summer, followed by P. australis and P. sinuosa. Effective quantum yield(ΔF/Fm′)of each species varied seasonally, changing inversely with irradiance, which agrees with previously reported studies. ETRmax for each species also showed a diurnal pattern coincident with irradiance throughout the day. The ÄF/Fm for all species demonstrated a diurnal decrease in photosynthetic efficiency coincident with the midday irradiance maximum. Large natural variation in ETR was detected in all species, indicating that the effects of external stress on ETR may be difficult to detect. Two adjacent, physically separated seagrass meadows were examined to determine if apparent visual differences between the sites were reflected by measured physical and photosynthetic characteristics. ETR, leaf area index and sediment grain size differed between sites, but ΔF/Fm, canopy height, shoot density and epiphyte biomass did not, indicating a poor connection between physical and photosynthetic characteristics at these two meadows. Therefore caution should be used when attempting to visually assess the photosynthetic activity of a site based on physical characteristics. Changes in photosynthetic activity were monitored to determine seagrass stress during transplantation, and post-transplantation recovery. Two transplantation methods, sprigs and plugs, were examined, and photosynthetic activity was compared before, during and after transplantation. ETRmax of sprigs took one to two months to increase to the same level recorded at a control meadow, primarily due to desiccation stress suffered during transport. The ΔF/Fm′ decreased below 0.2 after transplantation, but fully recovered after three months. Survival of sprigs was reduced due to strong currents and heavy epiphytic fouling. The ETRmax of transplanted plugs (5, 10 and 15 cm diameter) took up to one week to recover to the same level recorded at a control meadow. Survival of plugs was reduced due to winter swells and storms. Since the leading human-controlled cause of transplant failure was desiccation stress, future transplanting efforts should endeavour to keep seagrasses submerged at all times during the transplanting process.