Universiẗat, Diss., 2002--Kiel.

Continuous or semi-continuous reproduction is the norm in deep-sea animals, with exceptions explained by seasonal pulses of surface-derived phytodetritus. Chemosynthesis-based ecosystems such as cold seeps have an independent nutritional supply and are often thought of as decoupled from surface productivity. This thesis explores reproductive patterns of four bathymodiolin mussel species from 14 cold seeps (320 to 3300 m depth) in the Gulf of Mexico (2014) and the northwestern Atlantic (2015). Using paraffin histology, I determined maturity stages for male and oocyte sizes for female mussels. All species at all sites reproduced periodically and synchronously, with geographic synchrony among sites. This suggests that mussels rely on a site-independent cue such as seasonal phytodetrital flux to synchronize reproduction, providing evidence for a stronger coupling between surface productivity and chemosynthesis-based fauna than previously expected. Mature oocytes were of similar size for all species at all depths, suggesting that egg size is phylogenetically constrained.

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Chemosynthetic ecosystems in the deep sea hold vast amounts of untapped energy that until recent decades have been largely unobtainable. With the growing demand for resources and constant advancements in technology, these ecosystems and the diverse communities that inhabit them now face increasing pressure from anthropogenic exploitation activities. Thus, employing effective management and conservation strategies to avoid devastating these long-lived communities is imperative. However, effective protection hinges on a thorough understanding of these ecosystems. Here, I present a number of studies conducted on methane seeps along the Pacific Costa Rican Margin (CRM), exploring various ecological dynamics and highlighting the unique biodiversity thriving there. These studies aim to address gaps in our knowledge regarding the “sphere of influence” surrounding chemosynthetic methane seeps, providing insights into the flow of energy within these ecosystems, their spatial dynamics and how they interact with background deep-sea habitats. In Chapter 2, I employ a novel seascape approach using systematic surveys of several actively seeping areas to characterize the seep communities and delineate distinct seep zones, testing for inter- and intraspecific differences in community structure. Our results reveal nuanced patterns in α and β diversity between sites and across different zones, driven largely by depth. Additionally, I identify transitional zones extending the spatial extent of the seeps by up to 300 meters, emphasizing the “sphere of influence” surrounding these ecosystems. / Biology

Understanding the formation conditions of seep carbonate is crucial to better constrain the dynamic fluid flow and chemical fluxes associate with cold seeps on the seafloor. Rare earth element (REE) in seep carbonates collected from modern cold seeps of Gulf of Mexico, Black Sea, Congo Fan, ancient seeps of Beauvoisin (Oxfordian, J3, Southeastern France) and Marmorito (Miocene, Northern Italy) were studied. Our focus has been on 5% HNO3-treated solution (authigenic carbonate minerals) of carbonates. Several crystalline forms of carbonate minerals have been selected for analysis. Total REE (ΣREE) contents in seep carbonates varies widely, from 0.068 to 43.655 ppm, but the common trend is that the ΣREE in microcrystalline phases is highest and lowest of in sparite, suggesting that the ΣREE of seep carbonates may be a function of diagenesis. The shale-normalized REE patterns of the seep carbonates show varied Ce anomalies across several seep sites and even within one site, suggesting that the formation condition of seep carbonate is variable and complex. Overall, our results show that apart from anoxic, oxic formation condition is also common at hydrocarbon seep environments.

Bog turtles (Glyptemys muhlenbergii) are a small freshwater turtle ranging east of the Appalachian Mountains from New York to Georgia, in small, patchily distributed (<10ha) groundwater fed wetlands. Despite their name, these wetlands are more appropriately identified as seep meadows or fens owing to their reliance on groundwater, with bogs being typified by precipitation as the major hydrologic input. Groundwater inputs are not only important in taxonomically classifying wetland type, but also contribute in important ways to bog turtle natural history. Bog turtles ectothermically regulate body temperature by utilizing thermally buffered groundwater inputs during seasonal extremes. Perennially saturated wetland areas disrupt the establishment of facultative wetland vegetation or woody vegetation that may induce wetland succession, maintaining adequate bog turtle habitat. Further, groundwater input mechanistically contributes to microtopographic variation, providing viable nesting locations. Hydrologic studies pertaining to these wetland habitats has been limited in scope, and often attempts to define hydrologic regimes by use of a centrally placed monitoring well. Several studies that have comprehensively monitored these seep meadow wetlands show hydrologic regime variability at intrasite scales. In this thesis, I sought to confirm the spatially variable nature of hydrologic regimes in bog turtle wetlands. Finding that hydrologic conditions were location-dependent, I then tested whether a seep to non-seep hydrologic gradient, or the defining physical components therein, explained variation in bog turtle population density across a wetland. In Chapter II, I observed wetland conditions in summer extremes to categorize wetland areas based on surface saturation into seep, always wet, and sometimes wet locations. I placed multiple water level monitoring wells within these categories at six bog turtle wetlands and used observed water level data to test for spatial hydrologic variability at within- and across-site scales, finding that hydrologic regime can vary at short distances (<10m), and that alike categorized wells differed in groundwater inputs across-sites. I then used observed water level monitoring data during the growing season to test initial observer-based classifications. These classifications were then reorganized using the amount of time water remained near the soil surface, the degree of fluctuation that water level experienced, and differences in thermal exchange with ambient air temperature and thermally buffered groundwater input. I created a method to delineate spatially variable hydrologic regimes based on groundwater discharge by using several seep-associated features. Soil water temperature, depth to resistive soil layer, and specific conductivity were tested for sampling applicability across seasonal extremes, and for co-occurrence in constrained ordination with spatially explanatory covariates. I found that spatial gradients for relative measures of each seep-associated feature were largely consistent across seasons and that all seep-associated features were more often correlated than any other spatial arrangement. Constrained ordination model results were visualized to depict the seep to non-seep hydrologic gradients found within these wetlands. These gradients were then tested against observed water level data for their predictive capability, finding mixed results across seasons and that hydrologic gradients as modeled could likely be improved with additional explanatory information. Depending on where groundwater is entering a wetland, habitat conditions might vary for bog turtles. Seep areas create perennially saturated or mucky soil conditions, with locations further from groundwater discharge experiencing total or some degree of drying out in the growing season. Bog turtle habitat associations recorded in literature suggest that bog turtles are typically found in or near these soft mud or open water areas. Constant groundwater input near these seeps also leads to rivulet formation. Cool, gently flowing water weaves between hummocks of vegetation near these locations, creating pathways for easy movement, elevated platforms for turtles to bask, and muddy substrates to which turtles can retreat to. Because of the habit conditions afforded by these seep areas, I hypothesized that turtle density might be higher with seep occurrence as influenced by the underlying wetland hydrologic gradient. In Chapter III, I tested whether bog turtle population density was a function of hydrologic features across seep to non-seep gradients, relative soil water temperatures, the depth of substrate above a consolidated soil layer, and relative soil moisture conditions. In the summer of 2022, I trapped at six bog turtle wetlands and tracked 24 bog turtles with radiotelemetry. I used a spatially explicit capture mark recapture framework to estimate density and used data developed for hydrologic datasets in Chapter II to examine density associations. Bog turtle density relationships to hydrologic covariates varied across wetlands and supports the view that bog turtles in their active season are not particularly sensitive to specific hydrologic regime conditions, but rather utilize the entirety of wetland conditions. / Master of Science / Bog turtles (Glyptemys muhlenbergii) are a small freshwater turtle ranging east of the Appalachian Mountains from New York to Georgia, in small, patchily distributed (<10ha) groundwater-fed seep meadows and fens. Groundwater inputs create these wetlands and conditions necessary for bog turtle survival. Hydrologic studies in these wetland types are limited but hint towards a reliance on groundwater input as contributing to hydrologic regimes that are locationally dependent. In this thesis, I sought to confirm the spatially variable nature of hydrologic conditions in these wetlands by focusing on ground water entry points and testing whether seeps, or associated seep characteristics, influenced bog turtle population density across a wetland. In Chapter II, I used water level monitoring wells to establish that hydrologic regimes in bog turtle wetlands are spatially variable and characterized these regimes by the resulting saturated to dry surface conditions. I then selected wetland features hypothesized to be associated with groundwater discharge locations and provided evidence that these features occur together and are seasonally constant. These features were then used to delineate hydrologic gradients and tested for whether they could predict conditions observed in water level monitoring. Hydrologic gradients drawn from seep to non-seep locations had limited ability to predict observed hydrologic regimes. Ground water seeps are considered to contain necessary habitat conditions for bog turtles as thermal and predatory refugia, a mechanistic disturbance favoring herbaceous vegetation over woody vegetation, and provide processes that establish microtopographic variation favorable to bog turtle nesting behavior. In Chapter III, I used delineated gradients from the preceding chapter to assess underlying hydrologic conditions that explain where turtles are more likely to be found within their habitat, and whether these associations were shared across bog turtle populations. Bog turtle density across wetlands differed by hydrologic-associated features, and findings suggest that site-wide variability in conditions is the more important aspect of bog turtle wetlands than a specific hydrologic regime.

Cold seeps are areas of high biomass in the deep-sea, the impacts of these food-rich environments upon the sediment community is unknown in the Gulf of Mexico. The structure and function of benthic communities was investigated at food-rich and food-limited sites on the northern Gulf of Mexico continental slope. Cold seeps were richer in macrofauna densities and total sediment respiration, but were poorer in biomass and taxa diversity than normal slope communities. Decreased diversity is seen at most chemosynthetic communities and suggests a competition for resources. The spatial extent of these results at seeps is unknown and may be a localized, bioenhancement effect caused by seeping fluids.

A deep-sea time-lapse camera and several temperature probes were deployed on the Gulf of Mexico continental shelf at a biological community associated with a gas hydrate outcropping to study topographic and hydrologic changes over time. The deployment site, Bush Hill (GC 185), is located at 27°47.5' N and 91°15.0' W at depths of ~540m. The digital camera recorded one still image every six hours for three months in 2001, every two hours for the month of June 2002 and every six hours for the month of July 2002. Temperature probes were in place at the site for the entire experimental period. The data recovered provide a record of processes that occur at gas hydrate mounds. Biological activity was documented by identifying the fauna observed in the time-lapse record and recording the number of individuals and species in each image. 1,381 individual organisms representing 16 species were observed. Sediment resuspension and redistribution were regular occurrences during the deployment periods. By digitally analyzing the luminosity of the water column above the mound and plotting the results over time, the turbidity at the site was quantified. A significant diurnal pattern can be seen in both luminosity and temperature records, indicating a possible tidal or inertial component to deep-sea currents in this area. Contrary to expectations, there was no major change in shape or size of the gas hydrate outcrop at this site on the time frame of this study. This indicates that this particular mound was more stable than suggested by laboratory studies and prior in situ observations. The stable topography of the gas hydrate mound combined with high bacterial activity and sediment turnover appears to focus benthic predatory activity in the mound area. The frequency and recurrence of sediment resuspension indicates that short-term change in the depth and distribution of surface sediments is a feature of the benthos at the site. Because the sediment interface is a critical environment for hydrocarbon oxidation and chemosynthesis, short-term variability and heterogeneity may be important characteristics of these settings.

A deep-sea time-lapse camera and several temperature probes were deployed on the Gulf of Mexico continental shelf at a biological community associated with a gas hydrate outcropping to study topographic and hydrologic changes over time. The deployment site, Bush Hill (GC 185), is located at 27°47.5' N and 91°15.0' W at depths of ~540m. The digital camera recorded one still image every six hours for three months in 2001, every two hours for the month of June 2002 and every six hours for the month of July 2002. Temperature probes were in place at the site for the entire experimental period. The data recovered provide a record of processes that occur at gas hydrate mounds. Biological activity was documented by identifying the fauna observed in the time-lapse record and recording the number of individuals and species in each image. 1,381 individual organisms representing 16 species were observed. Sediment resuspension and redistribution were regular occurrences during the deployment periods. By digitally analyzing the luminosity of the water column above the mound and plotting the results over time, the turbidity at the site was quantified. A significant diurnal pattern can be seen in both luminosity and temperature records, indicating a possible tidal or inertial component to deep-sea currents in this area. Contrary to expectations, there was no major change in shape or size of the gas hydrate outcrop at this site on the time frame of this study. This indicates that this particular mound was more stable than suggested by laboratory studies and prior in situ observations. The stable topography of the gas hydrate mound combined with high bacterial activity and sediment turnover appears to focus benthic predatory activity in the mound area. The frequency and recurrence of sediment resuspension indicates that short-term change in the depth and distribution of surface sediments is a feature of the benthos at the site. Because the sediment interface is a critical environment for hydrocarbon oxidation and chemosynthesis, short-term variability and heterogeneity may be important characteristics of these settings.

Cold seeps are areas of high biomass in the deep-sea, the impacts of these food-rich environments upon the sediment community is unknown in the Gulf of Mexico. The structure and function of benthic communities was investigated at food-rich and food-limited sites on the northern Gulf of Mexico continental slope. Cold seeps were richer in macrofauna densities and total sediment respiration, but were poorer in biomass and taxa diversity than normal slope communities. Decreased diversity is seen at most chemosynthetic communities and suggests a competition for resources. The spatial extent of these results at seeps is unknown and may be a localized, bioenhancement effect caused by seeping fluids.