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Kenneth H. Dunton, Ph.D.
(return to Dunton home page) Current Projects
Past Projects
Benthic Community Structure and Biomass in the Western Arctic: National Science Foundation
K.H. Dunton (The University of Texas at Austin, Marine Science Institute)
Spatial and temporal patterns in the flux of sinking matter are critical to the development and productivity of the benthos, particularly at high latitudes where environmental controls are extreme. The input of this energy, in the form of highly reduced organic matter, ultimately links production in the water column with the abundance and diversity of the benthos. The goal of our proposed research is to utilize the benthos as a spatial and temporal integrator of oceanographic processes that could provide a valuable indicator of potential global change impacts. Within the Western Arctic Shelf-Basin Interactions (SBI) program, Phase I was designed to undertake retrospective studies of data sets in the Chukchi and Beaufort Seas that would help focus future research efforts on the impacts of global change on arctic ecosystems. There exist large and potentially invaluable historical databases from the Arctic region that have not been synthesized, including thousands of records on the biomass, density, and composition of benthic organisms from the Chukchi and Beaufort, mostly unpublished. A wide variety of information on physical and geochemical parameters, including the seasonal extent of ice cover, circulation patterns, water column characteristics and sediment parameters, are also available from both published and unpublished sources. Together, these sources of information represent a substantial collection of baseline data, most of which was collected 20-30 years ago. The purpose of the work proposed here is to retrieve benthic biological data from NODC and other published and unpublished data sets from western and Russian sources and use Geographic Information Systems (GIS) software to examine and graphically display relationships between predominant physical forcing processes (e.g. freshwater inflows, ice cover, circulation) and ecosystem productivity. Preliminary development of coupled biological and physical models based on historical data would provide an opportunity to identify specific research needs and refine hypotheses with respect to the processes regulating
Stable Nitrogen Isotope Signatures as
Indicators of Riverine Inputs of
NOAA National Undersea Research Program The stable nitrogen isotopic signatures (del15N) of benthic algae and fauna collected in the Flower Gardens Marine Sanctuary and Stetson Bank reef systems, located only 60 km apart in the northern Gulf of Mexico, suggest that the nitrogen sources for these two reef habitats are distinctly different. Algae from the Flower Gardens, for example, have (del15N) values averaging 2‰ compared to nearly 5‰ for the same species from Stetson Bank. Furthermore, values for the Flower Gardens match the (del15N) signatures of benthic algae from the outer shelf reef of Australia’s Great Barrier Reef, while the values for Stetson Bank are indistinguishable from aquatic plants and algae of Texas estuarine systems. These preliminary data suggest that the primary nitrogen source in the Flower Gardens is autogenously produced by nitrogen-fixing cyanobacteria (e.g. benthic blue-green algal mats and /or pelagic Trichodesmium). In contrast, the primary nitrogen source at Stetson bank appears to be allochthonous, perhaps from coastal riverine inputs. The major focus of
this proposal is to investigate the use of (del15N)
tracers as indicators of riverine inputs of anthropogenic-N to the mid- and
outer shelf regions of the northern Gulf of Mexico, with particular emphasis on
the area surrounding and within the Flower Gardens Marine Sanctuary. The
proposed research coincides with continued concern over the westward expansion
of the hypoxic “dead-zone” associated with increased loadings of nitrogen and
phosphorus from Mississippi River Plume, and the known relationship between
nutrient excess and coral reef demise. Can (del15N)
signatures be used as early-warning indicators of anthropogenically introduced
nitrogen that could threaten the Flower Gardens community? To
address this question we propose an intensive sampling program that employs
divers to collect selected species of benthic biota that represent major trophic
groups. Essential elements of this effort include:
A Quantitative Assessment of Scarring in Seagrass Beds in
Texas National Resource Commission and the Texas Parks and Wildlife Department K.H. Dunton (The University of
Texas at Austin, Marine Science Institute)
The distribution and intensity of scarring in seagrass beds were quantified using high resolution (1:2,400) aerial photography taken in January 1997 in the Corpus Christi Bay National Estuary Program (CCBNEP) study area. Scarring levels were defined as light (<5%), moderate (5-20%), or heavy (>20%) based on percentage of scarred seagrasses within each of eight distinct regions. Ground-truthing surveys by boat and aircraft were used to verify aerial photography and to collect DGPS coordinates for rectification and registration procedures. Distribution and levels of seagrass scarring were digitally transferred onto USGS topographical charts and analyzed using Geographic Information System (GIS) techniques. A total area of approximately 6,000 ha of seagrass habitat was surveyed. Of this total, 2,200 ha were identified as either moderately or severely scarred. Scarring of grassbeds was greatest in Estes Flats, where over 97% of grassbed was scarred, with 75% rated as severe. Moderate and severe scarring were also prevalent in the East Flats (49%), Shamrock Island (35%) and Redfish Bay (23%) regions. Total scarring in all other areas was less than 20% with moderate/severe scarring accounting for 15% or less.
Several explanations account for propeller scarring of seagrasses by boating
activity. These include accidental events such as misjudgement of water depth or
channel location, taking shortcuts to access an area, maintaining a channel
through a grassbed by placement of illegal navigational aids, and ignorance with
respect to the damage caused by propellers. Initial management priorities should
focus on education and the marking of secondary channels to minimize damage to
adjacent grassbeds. Future research efforts should be directed toward an
understanding of the long-term effects of seagrass scarring, to justify the
variety of management options that are available to state resource agencies to
minimize continued damage to this valuable resource. Click on an
area chart below for a full screen view of the distribution and intensity of
seagrass scars.
Thermal Adaptation in Polar Macroalgae National Science Foundation K.H. Dunton (The University of
Texas at Austin, Marine Science Institute)
The genetic adaptations that enable certain plants species to survive and grow in polar environments where temperatures are near or below 0 degree Celsius year-round are poorly understood. Low-temperature adaptation is complicated in terrestrial plants by freezing, desiccation and stomatal conductance, and in marine phytoplankton by a variable and unpredictable physical environment. Polar macroalgae provide an experimental system that is not subject to these complications and that is well-suited to the study of cold-adaptation in plants. Cold-adaptation is particularly well developed in Antarctic macroalgae, in which rates of photosynthesis and growth at 0 degree Celsius are comparable to rates achieved at 10-15 degrees Celsius by temperate species. The proposed research uses endemic Arctic and Antarctic seaweeds to answer the question, "What adaptations do polar algae possess that enable them to assimilate carbon and grow rapidly at very low temperatures?" This question will be addressed in a collaborative effort between Dr. Ian Davison (University of Maine), Dr. Ken Dunton (University of Texas), and Dr. Val Gerard (State University of New York at Stony Brook) at Palmer Station and in their respective laboratories. The research focusses on carbon-metabolism characteristics of three closely related polar-temperate pairs of brown algae: Arctic Laminaria solidungula and temperate Laminaria saccharina; Antarctic Desmarestia anceps and temperate Desmarestia aculeata, and Antarctic Himantothallus grandifolius, that is related to Desmarestia aculeata and D. aceps, but is morphologically similar to Laminaria saccharina. Carbon-metabolism processes (photosynthesis, respiration and light-independent carbon fixation) that are important in cold-adaptation will be identified in sporophytes of each species pair acclimated to the same temperature. Specific mechanisms of adaptation will be determined by comparing components of the photosynthetic apparatus (PSI and PSII reaction centers and electron transport, cytochrome-f and plastoquinone, proteins of the chlorophyll a/c light-harvesting complex, etc.) as well as contents, activities and thermal properties of key enzymes involved in photosynthesis, respiration and light-independent carbonfixation (Ribulose-1, 5-bisphosphate carboxylase oxygenase (Rubisco), fructose-bisphosphatase, malate dehydrogenase, phosphoenolpyruvate carboxykinase, etc.). We will test specific hypotheses, such as, "The ability of polar seaweeds to achieve high rates of photosynthesis at low temperatures is related to changes in the content and characteristics of Rubisco". By examining most key aspects of photosynthetic metabolism we will avoid prejudicing our results by relying on hypotheses developed from the very limited physiological data currently available for polar seaweeds. Comparisons of multiple species pairs and a broad suite of C-assimilation parameters will provide a comprehensive analysis of the mechanisms of low-temperature adaptation in algal species endemic to both the Arctic and Antarctic Oceans and increase our overall understanding of low temperature adaptation in all plants.
Ozone Depletion and UV Inhibition of Photosynthesis in National Science Foundation K.H. Dunton (The University of Texas at Austin, Marine
Science Institute)
Depletion of stratospheric ozone, particularly in the polar regions, is causing increased concern over the effects of harmful UV radiation (mainly UVB, 280-320 nm). UVB is damaging to many biological processes, and in plants, specifically targets photosynthesis. Large increases in the penetration of solar UVB in the Southern Ocean during the austral spring from ozone depletion is known to have significant effects on phytoplankton productivity. The phenomenon is less severe in the Arctic, but ozone related increases in incident UVB have accelerated over the last three years. This proposal addresses the question of the effects of increased UVB on large benthic marine macroalgae (kelp) and the levels of UVB that penetrate into the coastal waters of the Arctic. Throughout the coastal regions of the circumpolar arctic, primary productivity by kelp beds often meets or exceeds that of the local phytoplankton, resulting in the development of rich and diverse benthic communities. However, little is known about the sensitivity of kelp photosynthesis to UVB. Assessment of UV effects (280-400 nm) in an environmental context can be made by weighting the spectrum of UV irradiance with a biological weighting function (BWF; similar to an action spectrum). The methods for determining the BWF for inhibition of photosynthesis have been developed in studies of marine phytoplankton. a preliminary application of a similar approach using cultured Laminaria sporophytes from the Arctic suggests that kelp photosynthesis is, in general, more sensitive to inhibition by UV than phytoplankton, and, in particular, has a higher specific sensitivity of UVB. Our preliminary measurements show that detailed kinetics of decreased photosynthesis during UV exposure can be obtained using Pulse Amplitude Modulated (PAM) fluorometry. These kinetics indicate that recovery processes rectifying UVB damage are slow in kelp. We
propose to measure detailed BWFs and the kinetics of UV effects on
photosynthesis of macroalgae in High Arctic, emphasizing the kelps, Laminaria
saccharina and
L. solidungula, which are distributed throughout the circumpolar Arctic.
We will use both laboratory cultured plants and sporophytes collected during two
spring and one summer field season in the Canadian High Arctic. We will also
measure surface UVB and penetration of UVB to arctic kelp beds. Plants exposed
to different natural light environments during the nine-month ice covered period
will be examined for differences in their sensitivity to UV radiation; the
importance of the nitrogen status of the plants in recovery processes that
counteract UV-induced damage will also be investigated. The results will enable
the first quantification of potential UV exposure in kelp habitats and the
biological effects of such exposure in terms of kelp productivity in arctic
coastal systems.
The Effect of
Dredge Deposits on the Distribution and Productivity
The primary goal of this project is to incorporate both above- and below-ground
seagrass tissues (shoots, rhizomes and roots) into a predictive model of
seagrass productivity. The purpose of the model is to assess the effect of
changes in both water transparency and sediment geochemistry caused by dredging
practices in the Laguna Madre. Since one of the most significant effects of
dredging is increased water column light attenuation caused by high
concentrations of suspended particles, research has focused on (1) the
physiological response of seagrasses to decreased irradiance with respect to
photosynthetic performance and, (2) the changes in sediment chemistry that occur
when the transport of photosynthetically produced oxygen to below-ground tissues
is reduced. The production of toxic substances (e.g. sulfides) in the sediments
under anaerobic conditions that result when the seagrass oxygen pump fails can
be critical to seagrass survival since over 80% of total plant biomass often
resides in below-ground tissues.
Interdisciplinary
research over the past two years by a multi-investigator team from three
institutions has resulted in the development of a highly predictive productivity
model for the shoal grass, Halodule wrightii. Models for both manatee
grass (Syringodium filiforme) and turtle grass (Thalassia testudinum)
are not yet complete. For H. wrightii, our efforts have produced an
integrative and quantitative model that predicts the response of the species to
changes in light availability, based on extensive interdisciplinary field
observations and experimental studies conducted over the past two years.
Although the full model must await the completion and integration of the
hydrodynamic and sediment transport models, our data strongly suggest that
dredging operations are very likely to have a measurable negative impact on the
health of seagrasses, particularly if dredging activities occur over extended
periods (weeks) when the plants are metabolically most active (spring through
autumn).
The Productivity
and Distribution of Vegetation in the Nueces Marsh:
U.S. Bureau of Reclamation and the City of Corpus Christi K.H. Dunton (The University of Texas at Austin, Marine Science Institute)
Periodic flooding and inundation of coastal marshes by freshwater are critical to high productivity and biotic diversity of these wetland habitats. In south Texas, diversion of the Nueces river from the deltic marsh system in combination with continuous declines in freshwater inflow since 1968 have resulted in higher salinities, erosion of the marsh, and decreased plant productivity. Net aerial primary production of the Nueces marsh is only 60 - 70% of that measured in adjacent river deltas in south Texas. The lower productivity of the Nueces marsh is attributed to the nearly complete diversion of freshwater inflow to the marsh, which has resulted in reduced nutrient input and increased salinities. Several efforts are now underway to restore, at least partially, the frequency of freshwater events into the Nueces Estuary. These include the construction (by the U.S. Bureau of Reclamation) of a 305-meter overflow channel from the Nueces river to the Rincon Bayou, a headwater of the estuary, and the diversion of up to 4 million gallons per day of treated watewater into the central portion of the delta. Our research in the Nueces delta addresses the changes in biomass, vegetative cover (leaf area index), species composition and soil chemistry in response to the restoration of freshwater inflow events and additions of treated wastewater. Large scale changes in vegetation patterns are documented using color IR photography and multispectral remote imaging in cooperation with Dr. Warren Pulich (Texas Parks and Wildlife) and Dr. Melba Crawford (Center for Space Research, UT-Austin). In addition, all data are being analyzed using GIS technology in collaboration with Dr. David Maidment (Center for Research in Water Resources) at UT-Austin. Other collaborators at UTMSI on this long-term project include Drs. Paul Montagna (benthos) and Ed Buskey (zooplankton). Preliminary results indicate that the vegetation responds quickly to increases in freshwater inflow as measured by increases in plant biomass, leaf area index, and overall expansion of smooth cordgrass, Spartina alterniflora.
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