Herbivores and pathogens pose a consistent threat to plant productivity. In response, plants invest in structural and/or chemical defenses that minimize damage caused by these biotic stressors. In salt marshes along the Atlantic coast of the United States, a facultative mutualism between snails (Littoraria irrorata) and multiple species of fungi exert intense top-down control of the foundation grass species Spartina alterniflora. Since exposure to herbivores and pathogens are tightly coupled in this system, I investigated whether S. alterniflora utilizes chemical and/or structural defenses to deter both snails and fungi, and examined how plant defenses varied among S. alterniflora individuals and populations. I also assessed how other marsh plants prevent snails from establishing farms, and considered whether interspecific variation in plant chemical defenses influences marsh community structure. Initial experiments revealed that S. alterniflora chemical defenses inhibited L. irrorata and two fungi that snails commonly farm. A caging experiment determined that production of chemical defenses could not be induced in the presence of snails and fungi, nor relaxed in their absence. Through separations chemistry guided by ecological assays, I isolated two distinct classes of chemical defenses from short form S. alterniflora, one of which inhibited fungal growth and the other decreased plant palatability. In a community context, the chemical defenses produced by S. alterniflora were relatively weak compared to those of four other salt marsh plant species, which produced compounds that completely inhibited L. irrorata grazing and strongly hindered fungal growth in lab assays. Nutritional and structural differences among marsh plants did not influence feeding preferences, suggesting that plant secondary chemistry was the primary driver for food selection by snails. It appears that S. alterniflora produces weak chemical defenses that slow down or limit fungal growth and snail herbivory, and may compensate for tissue losses by producing new growth. In contrast, less abundant marsh plants express chemical defenses that completely inhibit fungal farming and deter snail grazing, but doing so may come at a cost to growth or competitive ability. As marsh dieback continues with rising herbivore densities and compounding abiotic stressors, the ecosystem services that salt marshes provide may be lost. Therefore, understanding how and under what conditions salt marsh plants resist losses to herbivores and pathogens will help predict which marsh communities are most likely to be threatened in the future. Initial experiments revealed that S. alterniflora chemical defenses inhibited L. irrorata and two fungi that snails commonly farm. A caging experiment determined that production of chemical defenses could not be induced in the presence of snails and fungi, nor relaxed in their absence. Through separations chemistry guided by ecological assays, I isolated two distinct classes of chemical defenses from short form S. alterniflora, one of which inhibited fungal growth and the other decreased plant palatability. In a community context, the chemical defenses produced by S. alterniflora were relatively weak compared to those of four other salt marsh plant species, which produced compounds that completely inhibited L. irrorata grazing and strongly hindered fungal growth in lab assays. Nutritional and structural differences among marsh plants did not influence feeding preferences, suggesting that differences in plant chemistry were the primary driver for food selection by snails. It appears that S. alterniflora produces weak chemical defenses that slow down or limit fungal growth and snail herbivory, and may compensate for tissue losses by producing new growth. In contrast, less abundant marsh plants express chemical defenses that completely inhibit fungal farming and deter snail grazing, but doing so may come at a cost to growth or competitive ability against S. alterniflora. As marsh dieback continues with rising herbivore densities and compounding abiotic stressors, the ecosystem services that salt marshes provide may be lost. Therefore, understanding how and under what conditions salt marsh plants resist losses to herbivores and pathogens will help predict which marsh communities are most likely to be threatened in the future.

Saltwater marshes in the Bay of Fundy act as greenhouse gases sinks and reservoirs by fixing atmospheric carbon dioxide and storing it in carbon rich deposits. There are approximately 3,131.5 hectares of saltwater marsh in the Bay of Fundy, of which 958 ha are currently owned by the government or conservation organizations and 2,173.5 ha are owned by private landowners. A multiple bounded discrete choice contingent valuation survey was conducted to estimate landowners' willingness to accept compensation for selling their saltwater marshes to a conservation program. A multiple bounded model developed by Gregory Poe and Michael Welsh (1995) was used to analyze the responses. Mean willingness to accept compensation for one hectare of saltwater marsh was estimated to be $1,004.22, and aggregate willingness to accept compensation for the total of 2,173.5 ha of saltwater marsh owned by private landowners was approximately $2,180,000. Using these estimates and the rate of carbon dioxide-equivalent absorption of saltwater marshes, the opportunity cost of one tonne of carbon dioxide-equivalent sequestered by saltwater marshes in the Bay of Fundy was calculated to range between $16.70 and $19.95. Decision-makers can use this result for policy purposes concerning the achievement by Canada of its greenhouse gases emission reduction commitment under the Kyoto Protocol (1997).

xviii, 160 p. : ill. (some col.) / Salt marshes are intertidal communities dominated by halophytic vascular plants that are subjected periodically to tidal inundation. These species have developed various adaptations to this stress, including tolerances of fluctuating salinity, extended periods of inundation and intervals of anoxic conditions. The marshes are divided into zones of different plant communities based on species' tolerances of ambient estuarine conditions. Abiotic stresses change along the estuarine salinity gradient (marine to riverine), potentially altering development and composition of plant communities. Abiotic gradients associated with tides are not the only factors that contribute to development of plant community composition in salt marshes. Both negative (competition) and positive (facilitation) biological interactions are also important. Factors that influence community structure in salt marshes, particularly on the eastern North American seaboard, have been well studied. In contrast, salt marshes along the Oregon coast are smaller and more discrete and have received comparatively little attention. The community structure and seed bank composition of six marshes along an estuarine salinity gradient were evaluated. Four major community types dominated marshes that varied in the salinity of inundating tidal waters. Community types were relatively consistent throughout the estuary despite the distances between the marshes. Unlike the emergent plant communities, marsh seed bank composition was more similar within a marsh than within a community type. The low and high marsh community types were separated by a distinct boundary in the marine marshes. Although abiotic factors influence the physical separation of communities, competitive interactions commonly determine the upper limit of a species. In Metcalf marsh, however, the upper boundary for two dominant low marsh species was not determined by competition with the high marsh dominant species. Positive biotic interactions between seedlings and existing vegetation in a community are important factors in determining species distributions, particularly in stressful estuarine environments. In salt marshes, where abiotic stress can be harsh, presence of existing vegetation can ameliorate these conditions and enhance germination and seedling establishment. However, interaction between seedlings and the emergent marsh community was highly competitive, though germination of one species was enhanced in the presence of existing vegetation. This dissertation includes un-published co-authored material. / Committee in charge: Dr. Scott Bridgham, Chairperson; Dr. Richard Emlet, Advisor; Dr. Steven Rumrill, Member; Dr. Alan Shanks, Member; Dr. Gregory Retallack Outside Member

Made available in DSpace on 2016-08-17T15:00:40Z (GMT). No. of bitstreams: 1 Dissertacao - PamellaSilvaBrito.pdf: 2572284 bytes, checksum: 775b92e1aa430b94c10075867a76b869 (MD5) Previous issue date: 2014-08-29 / FUNDAÇÃO DE AMPARO À PESQUISA E AO DESENVOLVIMENTO CIENTIFICO E TECNOLÓGICO DO MARANHÃO / The marine phanerogams meadows are important because they are nursery areas for many species of fish. In order to describe the community structure, temporal and spatial patterns of fish using Spartina alterniflora meadows of Maranhão Island present in tide macro region were held six samples of nine points in the period between July 2012 and June 2013, using a trawl net. A total of 11,660 individuals captured, representing 80 species, in which 13 are new record for the state of Maranhao. The sampled points are represented by a few abundant species (Rhinosardinia bahiensis, Atherinella brasiliensis, Lycengraulis grossidens, Lycengraulis batesii, incilis Mugil and Centegraulis edentulus) that demonstrated use the space according to interspecific preferences and presenting distribution patterns with the occurrence of distributed Juveniles throughout the year, suggesting that the studied environments are used by many species such as nursery areas and these have food preferences for zooplankton and mostly characterized as marine fish that frequent the estuary at some period of their life cycle. The species A. brasiliensis was constant in the spatial and temporal distribution, L. batesii was more abundant in the dry and the species L. grossidens, M. incilis, R. bahiensis, C. edentulus were dominant in the rainy season. The abiotic factors did not change much numerically, being only significant for dissolved oxygen between stations and different salinity for locations. We can see the meadows shown to be constant in the temporal variation and differed between sites, which showed no significant differences between the evaluation variables. Thus we can infer that the studied phytal environment is considered a nursery, it is frequented by several species of mostly juvenile fish that use this area as a place of recruitment, food and shelter; the dynamics of patches of seagrass were stable during the dry and rainy seasons and the composition and abundance of fish community is more explained by the spatial dynamics, but still have temporal distribution patterns, these features are typical of tropical environments that are inserted in mosaic adjacent environments. / Os prados de fanerógamas marinhas são importantes por serem áreas de berçário de muitas espécies de peixes. A fim de descrever a estrutura da comunidade, padrões temporais e espaciais de peixes que utilizam prados de Spartina alterniflora da Ilha do Maranhão, presentes em região de macromarés foram realizadas seis amostragens de nove pontos no período entre Julho de 2012 e junho de 2013, utilizando uma rede de arrasto. Um total de 11.660 indivíduos capturados, correspondendo a 80 espécies, na qual 13 são nova ocorrência para o estado do Maranhão. Os pontos amostrados são representados por algumas espécies abundantes (Rhinosardinia bahiensis, Atherinella brasiliensis, Lycengraulis grossidens, Lycengraulis batesii, Mugil incilis e Centegraulis edentulus) que demonstraram utilizar o espaço de acordo com preferências interespecíficas e apresentando padrões de distribuição com a ocorrência dos indivíduos juvenis distribuída durante todo o ano, sugerindo que os ambientes estudados são utilizados por várias espécies como áreas de berçário e estas apresentam preferências alimentar por zooplancton em sua maioria e caracterizadas como peixes marinhos que frequentam o estuário em algum período do seu ciclo de vida. A espécie A. brasiliensis mostrou-se constante na distribuição espacial e temporal, L. batesii foi mais abundante na seca e as espécies L. grossidens, M. incilis, R. bahiensis, C. edentulus foram dominantes no período chuvoso. Os fatores abióticos não variaram muito numericamente, apenas sendo significante para oxigênio dissolvido entre as estações e salinidade diferente para locais. Podemos observar os prados mostraram-se constantes na variação temporal e diferiu entre os locais, os quais não apresentaram variações significativas entre as variáveis de avaliação. Dessa maneira podemos inferir que o ambiente fital estudado é considerado um berçário, pois é frequentado por várias espécies de peixes principalmente juvenis que utilizam essa área como local de recrutamento, alimentação e refúgio; a dinâmica dos prados de fanerógamas se mantiveram estáveis durante os períodos seco e chuvoso e que a composição e abundância da comunidade de peixes é mais explicada pela dinâmica espacial, mas ainda assim possuem padrões de distribuição temporal, essas características são típicas de ambientes tropicais que estão inseridos em mosaico de ambientes adjacentes.

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No description available.

Vegetative health was measured both before and after Hurricane Harvey using remotely sensed vegetation indices on the coastal marshland surrounding Galveston Island's West Bay. Data were recorded on a monthly basis following the hurricane from September of 2005 until September of 2019 in order to document the vegetation response to this significant disturbance event. Both initial impact and recovery were found to be dependent on a variety of factors, including elevation zone, spatial proximity to the bay, the season during which recovery took place, as well as the amount of time since the hurricane. Slope was also tested as a potential variable using a LiDAR-derived slope raster, and while unable to significantly explain variations in vegetative health immediately following the hurricane, it was able to explain some degree of variability among spatially close data points. Among environmental factors, elevation zone appeared to be the most key in determining the degree of vegetation impact, suggesting that the different plant assemblages that make up different portions of the marsh react differently to the severe flooding that took place during Harvey.

Thesis: Ph. D., Joint Program in Oceanography/Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2017. / Cataloged from PDF version of thesis. / Includes bibliographical references. / The marine carbon cycle plays an important role in regulating Earth's climate. The vastness of the open ocean and the large variability in the coastal ocean provide obstacles to accurately quantify storage and transport of inorganic carbon within marine ecosystems and between marine and other earth systems. Thus far, the open ocean has been the only true net sink of anthropogenic carbon dioxide (Canthro) emissions. However, ocean storage of Canthro is not uniformly distributed. Changes in water chemistry in the Northeast Pacific were quantified to estimate the amount of Canthro stored in this region over the last decade. This additional Canthro was found to cause acidification and aragonite saturation horizon shoaling at rates towards the higher end of those found in Pacific and Atlantic Ocean basins, making the Northeast Pacific one of the most sensitive regions to the invasion of anthropogenic carbon dioxide. Due to large variability in biogeochemical signals in coastal oceans, it is challenging to accurately assess carbon fluxes across different boundaries, such as tidal exchange between coastal wetlands and coastal oceans. Coastal salt marshes have been suggested to be a large net CO₂ sink, thus designated as a type of "blue carbon." However, accurate and dynamic estimates of carbon fluxes to and from tidal marshes are still premature, particularly carbon fluxes from marshes to the coastal ocean via tidal exchange, often referred to as marsh lateral fluxes. In this thesis, lateral total alkalinity (TA) and dissolved inorganic carbon (DIC) export fluxes were realistically quantified using high frequency time-series, in situ data. High-resolution fluxes permitted a closer look at how marsh generated TA and DIC are being exported over diurnal, spring-neap, and seasonal scales. I investigated the best way to capture variability of marsh exports via traditional bottle sampling and assessed uncertainties associated with different sampling strategies. Marsh TA and DIC exports significantly modified buffering capacity of coastal waters. This work contains the first realistic estimate of TA exports from a tidal salt marsh. Accurate estimates of DIC and TA fluxes indicate the significance of salt marshes to the coastal carbon and alkalinity budgets. / by Sophie Ning-Shin Chu. / Ph. D.

The upper Bay of Fundy's Cumberland Basin contains an estimated 16,500 hectares of salt marsh, nearly all of which have been diked and converted to agricultural lands since the arrival of the Acadians in the late 17 th century. John Lusby Marsh is a 600 ha salt marsh that was diked and farmed for approximately 250 years, until dikes breached in the late 1940s and the marsh was restored to tidal conditions. A sediment core that contained the reclamation surface was extracted in John Lusby Marsh, and a trial set of eight fossil pollen spectra was compared to the modern analogues. Discriminant analysis classified the fossil samples into a plausible sequence of historic land uses which included phases when the marsh was diked and farmed. A comparison of the soil characteristics and pollen spectra from this study to those in a previously published study of a nearby salt marsh at Amherst N.S. suggest that flooding of a dikeland was misinterpreted as a sudden increase in the rate of sea level rise. Historical air photos support this conclusion by showing that the sampling location was indeed diked and farmed before the 1940s.

In 1996, four cores (∼30 cm depth) were extracted from the high marsh zone of Dipper Harbour salt marsh in the Bay of Fundy. Soil bulk densities are shown to be controlled by mineral density and are higher than those reported for salt marshes in the northeastern United States. Examination of variations in mineral content suggests that regular tidal action and ice rafting deposits the majority of the mineral sediment to the high marsh zone. Dating techniques (based upon pollen, 137Cs, 210Pb and total Pb) were applied to selected cores, suggesting accretion rates from 0.25 to 0.31 cm yr-1 which are higher than the rates of local relative sea level rise. Correlation of trace metal densities (Cu, Fe, Pb and Zn) to Al densities were used to justify Al normalization. After consideration of natural sources and adsorption factors, the normalized Pb profiles are shown to reflect historical pollution levels of leaded gasoline consumption. Carbon storage values in the upper 25 cm of sediment range from 7.3--10.5 kg C m-2 and carbon accumulation rates vary from 95 to 124 g C m-2 yr-1, representing 15--29% of the salt marsh macrophyte productivity.