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).

The draining of the Iraqi Marshlands is an example of the reorganization of a linked social-ecological system (SES) following a collapse. The goal of this study was to examine the utility of resilience as a water management tool through a case study of the Marshlands. Using the Four-Step Framework by Walker et al. (2002), it analyzed the Marshlands through the metaphor of the adaptive cycle, explored three possible future scenarios, created two models to characterize the system, and reviewed the implications of the analysis for water management in the Marshlands and resilience. This study found that resilience, and the Framework, could offer new perspectives for managing complex SESs. However, resilience is not useful during times of intense violent conflict, like war. It also found that there are resilient pathways to help the Marshlands reorganize. However, the Marshlands are very vulnerable and require strong institutional support to keep them from disappearing.

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

Cette thèse présente l’étude de la signature sédimentaire des submersions marines de tempête, dans le domaine rétrolittoral. Cette signature peut être extrêmement variable principalement en fonction des paramètres météo-océaniques menant à la submersion, de la morphologie de l’avant-côte et du domaine rétrolittoral et du disponible sédimentaire. Premièrement, l’étude de dépôts de washover mis en place lors de l’hiver 2013-2014, au sud de l’île d’Oléron, particulièrement énergétique en terme de climat de vagues, via une approche couplant processus hydrodynamiques et sédimentologie, a permis (1) de mettre en évidence l’importance des ondes infragravitaires, sur une côte dissipative à caractère macrotidal, dans le déclenchement de l’overwash de la barrière et la mise en place de washovers ; et de (2) proposer un nouveau modèle de faciès des dépôts de washover mis en place par des ondes infragravitaires combinées à la marée haute. Deuxièmement, la caractérisation de la signature sédimentaire des submersions marines en domaine rétrolittoral plus distal a montré que dans le contexte morphologique des marais de Charente-Maritime, les apports extrêmement faibles de sédiments en provenance du domaine continental, entre deux évènements de submersion marine, empêche la distinction des différents niveaux de submersion. Cependant cette étude a permis de valider des proxies tels que la microfaune ou l’isotopie de la matière organique pour l’identification de niveaux de submersion marine, permettant en partie de pallier aux limites inhérentes à l’anomalie granulométrique généralement utilisée. Cette étude a aussi permis la mise en évidence d’une variabilité dans la signature sédimentaire des submersions marines entre deux marais géomorphologiquement contrastés et plus ou moins exposés aux houles en provenance de l’océan. / This thesis presents the study of the sedimentary signature of marine submersions triggered by storms, in the back barrier area. This signature can be extremely variable mainly according to the meteo-oceanic parameters leading to the submersion of the back barrier area, the morphology of the nearshore, shore and back barrier area, and sediment availability. Firstly, the study of washover deposits emplaced during the winter of 2013-2014 on the southern end of the Oléron Island, characterized by an exceptional wave climate, via a coupled hydrodynamical and sedimentological approach, allowed us to (1) highlight the importance of infragravity waves, on macrotidal and dissipative coasts, in triggering the overwash and emplace washover deposits ; and (2) to suggest a new facies model of washover deposits emplaced by infragravity waves combined to high tides. Secondly, the characterization of the sedimentary signature of marine submersions in the distal part of the back barrier area showed that in the morphological context of the Charente-Maritime coastal marshes, the extremely limited amounts of sediments in provenance from the continent, between two submersion events, prevent the distinction of the different marine submersion sedimentary layers. Nevertheless, this study allowed validating new proxies as microfauna and organic matter isotopy for the identification of marine submersion sedimentary signature, allowing to work independently of the granulometric anomaly proxy and its known limits. This study also allowed evidencing the variability in the sedimentary signature of marine submersions in geomorphologically contrasted marshes and that this variability was linked to the ocean waves exposure.

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.

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. Page 216 blank. / Includes bibliographical references (pages 179-215). / Salt marshes are physically, chemically, and biologically dynamic environments found globally at temperate latitudes. Tidal creeks and marshtop ponds may expand at the expense of productive grass-covered marsh platform. It is therefore important to understand the present magnitude and drivers of production and respiration in these submerged environments in order to evaluate the future role of salt marshes as a carbon sink. This thesis describes new methods to apply the triple oxygen isotope tracer of photosynthetic production in a salt marsh. Additionally, noble gases are applied to constrain air-water exchange processes which affect metabolism tracers. These stable, natural abundance tracers complement traditional techniques for measuring metabolism. In particular, they highlight the potential importance of daytime oxygen sinks besides aerobic respiration, such as rising bubbles. In tidal creeks, increasing nutrients may increase both production and respiration, without any apparent change in the net metabolism. In ponds, daytime production and respiration are also tightly coupled, but there is high background respiration regardless of changes in daytime production. Both tidal creeks and ponds have higher respiration rates and lower production rates than the marsh platform, suggesting that expansion of these submerged environments could limit the ability of salt marshes to sequester carbon. / by Evan M. Howard. / Ph. D.

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