Browsing by Author "Van Dover, Cindy L"

Genetic diversity, population structure, and connectivity influence interactions among communities and populations. At hydrothermal vents in the western pacific, population structure in vent-associated species could occur at spatial scales ranging from vent sites separated by a few hundred meters to oceanic basins separated by more than 3000 kilometers. The spatial scale of population structure has important conservation implications; species that are well-connected across large geographic regions are more resilient to natural and anthropogenic disturbance. This dissertation examines the genetic diversity, population structure, and connectivity of 3 vent-associated species in the western Pacific. It first presents results from the development of microsatellite primers for Ifremeria nautilei, a deep-sea vent associated snail, then uses mitochondrial COI sequences and a suite of microsatellite markers to examine the broader connectivity of three vent-associated species, Ifremeria nautilei, Chorocaris sp. 2, and Olgasolaris tollmanni, across three back-arc basins in the western Pacific.

Within Manus Basin, no significant genetic differentiation was detected in populations of Ifremeria nautilei (based on COI and microsatellite), Chorocaris sp. 2 (based on COI and microsatellite), or Olgasolaris tollmanni (based on COI). A previously documented low-abundance cryptic species, Chorocaris sp. 1, was detected from a single site, South Su (based on COI). The population of I. nautilei in Manus Basin was found to be significantly differentiated from a second population that appeared to be panmictic across North Fiji and Lau Basin (based on COI and microsatellites). Chorocaris sp. 2 was also found to be significantly differentiated between Manus and North Fiji Basin (based on COI). Both I. nautilei and Chorocaris sp. 2 showed signs of potential low-level migration between Manus and other southwestern Pacific basins. O. tollmanni was undifferentiated between Manus and Lau Basin (based on COI). It is likely that a variable impedance filter exists that limits the realized dispersal of some, but not all species between Manus Basin and other western Pacific back-arc basins. The presence of a variable filter has implications for the conservation and management of hydrothermal vents in Manus Basin, as it is unclear what effects sustained anthropogenic disturbance will have on isolated populations of I. nautilei and Chorocaris sp. 2.

Ice shelf coverage in Antarctica is declining due to recent global warming. The northern part of Larsen Ice Shelf, the Larsen A in the Weddell Sea, has been decreasing since the 19th century and in 2000 finally disappeared. Ice shelf coverage decrease should dramatically enhance biological productivity in surface water and organic matter flux to the seafloor. This dissertation examines sources of organic matter to sediments, indicators of labile organic matter flux increase due to the ice-shelf collapse, and potential subsequent impacts of changing ocean productivity on the sedimentary microbial community in the sediment cores taken across a 170-year chronoseries of ice-shelf loss, five-transect stations. Characterizing lipid biomarkers, phytoplankton (rather than terrestrially derived organic material) was identified as the major source of organic matter in the sediments, as previously found in other nearshore Antarctic regions. The predominance of C16, C18, and C20 fatty acids, 24-methylenecholesterol, sitosterol, and 13C-enriched sea-ice diatom biomarker (C25:2 HBIs) indicate the importance of organic matter inputs from sea-ice diatom communities that become more dominant as the prevalence of sea ice coverage once the ice shelf disappears. Bacterial and Archaeal lipids were second and third largest lipid sources. These lipids could be sourced from the water column and in situ production as well as former ice shelf and ice-rafted debris. Using the vertical lipid distributions, diagenetic models were applied to estimate the pelagic lipid flux before and after the ice shelf collapse. The results suggest that the rapid increase in flux due to the ice shelf disintegration, but further characterization of degradation rates need to be undertaken to increase confidence in the magnitude of this increased flux. Lipid flux increase may induce a shift in the microbial community structure in the sediments. Multivariate analyses identified that the organic matter content and δ13CTOC values, relative abundances of labile and recalcitrant lipid biomarkers, and concentrations of nitrogen species are important factors that correlate with downcore and cross-shelf microbial community composition. Enriched organic matter content (electron donor) may influence the microbial community through the decreased availability of electron acceptors in the sediments. The quality of the organic matter may also influence the microbial community: microbes that use recalcitrant organic matter shift to phytodetritus degraders as more-labile organic matter is delivered to the seabed following ice-shelf collapse. These results will offer a new perspective on the potential impacts of the ice-shelf disintegration to the subseafloor environment. Further investigations are needed to quantify the flux increase and microbial degradation rates of organic matter to expand the knowledge on influences of glacier melt on biogeochemical cycle.

As demand for deep-sea resources increases, understanding the non-extractive use values and ecosystem services associated with the deep sea is crucial. A broader understanding of the benefits provided by deep-sea ecosystems will demonstrate why humanity should have a vested interest in the health of the deep sea, and encourage decision makers to enact sustainable environmental management plans. This dissertation contributes to the literature connecting deep-sea ecosystem structures, functions and services, with a focus on hydrothermal vents and methane seeps.

Part 1 uses a repetitive survey technique to explore the views of deep-sea stakeholders on the importance of rare-species research and the ecological importance of rare species. Overall, participants called for research that addresses deep-sea biodiversity as a whole (i.e., both rare and abundant species) but opposing opinions existed regarding the ecological importance of rare species. Opinion ranged from the acknowledgment that rare species may play important roles now or in the future to the viewpoint that, by definition, rare species play minor roles in the ecosystem. The opposing opinions likely correspond to a lack of knowledge concerning the role of rare deep-sea species in ecosystem functioning.

Part 2 uses functional trait analysis to assess the contribution of rare and common species to hydrothermal vent food-web dynamics. Some rare and common species were found to possess individually unique trait combinations and to contribute to hydrothermal vent functional diversity. In addition, trait combinations were found to vary among vent sites within the same biogeographic region, highlighting the ecological heterogeneity of hydrothermal vent systems. Part 2 suggests that both rare and common species should be incorporated into environmental management planning and that, given the uncertainty regarding species distributions and population connectivity, ensuring the persistence of functionally distinct rare species may require all active hydrothermal vents to be protected from deep-sea mining impacts.

Part 3 uses phototransects to characterize the epibenthic megafauna at seeps on the US Atlantic margin. Epibenthic megafauna were found to follow depth-related patterns in taxon-abundance, suggesting a faunal boundary exists between shallow (~400m) and deep (~1500m) seeps. Part 3 also uses stable isotope analysis, plankton samples and observational data to explore the importance of seeps to the life history of the commercially valuable deep-sea red crab (Chaceon quinquedens). Chemosynthetically derived carbon was found to contribute up to ~50% of nutrition to individual crabs, although the proportion was variable among individuals and seeps. At Chincoteague seep, dense aggregations (~15 individuals 10m-2) of red crab were observed, alongside fifteen mating pairs, three ovigerous females and numerous zoeal larvae; suggesting some seeps may act as a reproductive hotspot as well as food resource for red crab populations.

Part 4 highlights a cultural connection to the deep sea, whereby the Atlantic seabed is considered the final resting place for ~1.8 million enslaved Africans who died during slaving voyages from Africa to the Americas. Part 4 asks that the International Seabed Authority, ahead of mineral extraction from hydrothermal vent deposits on the Mid-Atlantic Ridge, to consider ways to commemorate the Middle Passage in the Area Beyond National Jurisdiction and recognize that cultural artifacts relating to the transatlantic slave trade may be found during mining-related activities.