| dc.description.abstract |
<p>Understanding to what extent a particular ecosystem can influence the larger environment
is the driving question behind my research. To begin examining this topic, several
factors should be considered including 1) the community composition within a certain
ecosystem 2) what factors drive community assembly, to predict the composition and
organization of other related communities, and 3) the extent of influence of the ecosystem
on the surrounding environments.</p><p>Chemosynthetic ecosystems are systems that
are dependent on chemicals as the base of the food chain, rather than light as in
photosynthesis. These systems are frequently biological hotspots within the ocean,
where benthic communities can research a higher density than surrounding regions.
Methane seeps, where methane and other hydrocarbons migrate through sediments to the
seafloor, are one of the major forms of chemosynthetic ecosystems. The known environmental
influence of seeps grows stronger as the number of discovered seeps increases, making
understanding their breath of impact increasingly relevant.</p><p>Data collected in
this study utilized two types of underwater research tools, an autonomous underwater
vehicle (AUV) and a remotely operated vehicle (ROV). The study begins by examining
seep fields about 200 nm off the South Carolina coast, at the Blake Ridge (~2150 m
depth) and Cape Fear (~2580 m depth) Diapirs. Geophysical and photographic data were
collected during surveys were used to examine the relationship between biomass-dominant
invertebrates (mussels, Bathymodiolus heckerae, and clams, Vesicomya cf. venusta)
and seafloor physiography. Concentric zonation of mussels and clams at each of the
four sites within the seep field suggests the influence of chemical gradients on megafaunal
distribution. Distributions of dominant seep features (bivalves, carbonates, bacterial
mats) were used to define the active seep site. The relationship between seeps and
nearby non-endemic fauna is examined in this study, with a focus on trophic guilds.
Geospatial mapping indicated that non-seep-endemic taxa (those not hosting chemoautotrophic
endosymbionts) either show positive association (e.g., squat lobsters, cake urchins),
negative association (e.g., sea urchins, certain sea cucumbers), or no distributional
bias (e.g., sea stars, certain fish) to the presence of a seep. </p><p>Further investigation
into these faunal relationships may improve understanding of predictive community
assembly rules, as well as clarifying the services that seeps provide to the larger
ocean ecosystem. Data collection and analytical techniques used here yielded high-resolution
habitat maps that can serve as baselines to constrain temporal evolution of seafloor
seeps, and to inform ecological niche modeling and resource management. </p><p>Another
aspect of the study is how seep communities differ when in an extremely low oxygen
environment. Methane seeps are typically biological hotspots on the seafloor, with
dense faunal communities relative to background (non-chemosynthetic) areas (Carney,
1994). However, some areas of the ocean are extremely low in oxygen, leading to decreases
in overall fauna diversity, which can sometimes also affect seep communities. The
eastern Pacific contains extensive oxygen minimum zones (OMZs), areas where the dissolved
oxygen concentration falls below 22 μM, or 0.5 mg/L (Helly and Levin, 2004; Karstensen
et al., 2008), as opposed to averages of 180-270 μM (4-6 mg/L) typically found in
the ocean. These zones can intersect the continental slope, affecting benthic organisms,
including those found at methane seeps in the region.</p><p>The Redondo Knoll Seep
(~900 m depth), located just ~30 km off the California coast, shares features of both
a seep and an oxygen minimum zone. High-resolution imaging providing a highly detailed
photo mosaic and 1 cm resolution bathymetric maps, allowed for a comprehensive site
view to further the geologic and microbial examinations. Particularly notable were
the extensive microbial mats and, due to its location near the core of a local OMZ
(averaging <1 μM oxygen), the lack of endemic seep megafauna or other non-endemic
fauna. </p><p>While both seeps and OMZs are common by themselves, only a small number
of studies have examined them together, such as off the coast of Chile (Sellanes et
al., 2010), Pakistan (Fischer et al., 2012; Himmler et al., 2015), and Oregon (Levin
et al., 2010). Consequently, there is still much to learn about the ecosystem and
organisms at these combination sites. </p><p>Overall, this study considers the sphere
of influence methane seeps provide the surrounding area through examination of the
relationship between endemic fauna, their geologic habitat, and non-endemic fauna,
with the intention to use these interactions to better inform seep roles in the environment
in the face of anthropogenic disruptions, such as deep-sea mining and climate change,
and as well as sites to consider for astrobiological studies.</p>
|
|
