2009 Research Experience for Undergraduates
Gulf of Maine and the World Ocean
2009 REU Participants
|Alexis Gillmore||Estrella Mountain Community College|
|Amanda Graumann||University of Wisconsin, Superior|
|Amy Langdon||Swarthmore College|
|Andrew Gross||The Pennsylvania State University|
|Ashley Couture||University of Maine, Machias|
|David Brazel||Colby College|
|Hannah McDaniel||University of Maine, Orono|
|Noah Oppenheim||Reed College|
(Some abstracts have been withheld pending publication.)
Determining the interrelationship between growth rate and Silica content of diatoms and the grazing rates of mesozooplankton
Alexis Gillmore, Estrella Mountain Community College
Bigelow Mentor: Dr. David Fields
The relationship between marine phytoplankton and marine zooplankton is essential to oceanic and atmospheric carbon cycles. Among phytoplankton, diatoms contribute up to 40% of all oceanic primary production and are a main food source for zooplankton. As environmental conditions change, however, the characteristics of diatoms may be altered in ways that affect the grazing behavior of zooplankton, changing the balance of oceanic carbon sequestration. This study exposed 3 species of diatoms (Thalassiosira weissflogii, Thalassiosira pseudonana and Phaeodactylum tricornutum) to different light levels to determine if biogenic silica content within the cell was affected by growth rate. Grazing experiments were then conducted to examine if biogenic silica content affects ingestion rates by the marine copepod Acartia tonsa. Our results show that growth rate is directly proportional to light levels: as irradiance increases, the growth rate of the culture increases. The bSi content of cells, however, is inversely related to growth rate in the two Thalassiosira spp. When P. tricornutum wastested it was found that in this species there is no relationship between growth rate and silica content. When A. tonsa cultures were exposed to T. weissflogii of different bSi contents, grazing was 5x greater for food with a low bSi content than for food with a higher bSi content. This suggests that copepods may select diatoms for food based upon bSi content.
The relationship between biogenic silica (BSi), diatom concentration, and temperature in the Gulf of Maine
Amanda Graumann, University of Wisconsin, Superior
Bigelow Mentor: Dr. William Balch
The Gulf of Maine North Atlantic Time Series (GNATS) investigates phytoplankton abundance, bio-optical properties, biomass, and carbon fixation across the GoM, which are important to the biogeochemistry of this productive Shelf ecosystem. Diatoms produce BSi incorporating it into their frustules which serves as a ballast mineral. Diatoms help drive the ocean biological pump by transporting organic carbon from the ocean surface to the ocean floor. BSi, particle size spectra, particle image files and cell counts were collected and examined at nine discrete sites across the GoM between Portland, Maine and Yarmouth, Nova Scotia, on 5 July 2009. The west-most site BSi concentration was 2000 nmol/L higher than the other eight sites. High values likely resulted from heavy rainfall in the weeks prior to sampling with possible export of silica rich sediments from local rivers. Diatom biomass was highest closest to Yarmouth, N.S., where Scotia Shelf waters were nitrate and phosphorous-rich. Si:C molar ratios of diatoms, however, showed values highest at the first and fifth stations. The fifth station was in the Jordan Basin water which has had elevated Si(OH)4:NO3 ratios, despite low absolute concentrations of nitrate and phosphate. Elevated Si(OH)4:NO3 ratios may have allowed the diatoms to generate thicker frustules, increasing the Si:C ratio. Higher Si:C ratios may have resulted from high concentrations of detrital Si. Si:C molar ratios also showed a significant exponential increase with surface seawater temperature, which may have been associated with differences in diatom species growing in the water masses or temperature-dependent physiological processes.
Iron Enrichment: Natural Causes & Anthropogenic Effects
Andrew R. Gross, Pennsylvania State University
Iron is a crucial micronutrient needed from the growth of phytoplankton. One third of the world's oceans are low chlorophyll regions despite high concentrations of nutrients like nitrogen, and it is widely believed that iron is the limiting agent. The northern Pacific ocean is one of the largest high nutrient/low chlorophyll regions in the western hemisphere, while the nearby Bering sea is highly productive. To test the effects of iron enrichment on phytoplankton growth, water samples were collected from the north Pacific ocean and spiked with dissolved iron. To give a frame of reference and study the process by which non-iron limited waters gain iron, the process was repeated slightly north in waters with higher productivity.
Ciliate Time Series From a Long-term Dock Study
Ashley Couture, University of Maine, Machias
Bigelow Mentor: Dr. Michael Sieracki
Data from a long term Dock Study was used to assess the composition and concentration of ciliates present in the water column over time in West Boothbay Harbor, Maine. Ciliates are single-celled organisms that are characterized by the presence of cilia, which assist in movement and feeding. They can be autotrophic, heterotrophic or mixotrophic. In addition to the weekly Dock Study data, daily samples were also collected. Samples were collected using a Niskin bottle lowered to a meter depth. Images and counts from an imaging flow cytometer (FlowCAM) assisted in classifying the different types of ciliates. Comparison of the autoimage and fluorescence modes on the FlowCAM shows that there is a positive correlation between the two modes. The fluorescent particle, Laboea, shows this well by its location in comparison with a 1:1 line. Annual results show that there is a seasonal trend in ciliate concentrations with more present during the warmer months. This could be because their prey, bacteria and plankton, are abundant too. Myrionecta rubra may be able to survive better in winter because it is a mixotroph, while the heterotrophic Strombidiid/Strobilidiid family depends on the presence of organic nutrients for survival. Daily data shows differences similar to the annual data indicating that the life cycle of ciliates could be on an even smaller time scale. For further work, smaller sampling times could be used to try to observe more gradual changes in ciliate populations.
A Time Course Study of Bacterial Community Dynamics
David Brazel, Colby College
Bigelow Mentor: Dr. Ramunas Stepanauskas
Bacteria are now acknowledged to be ubiquitous in and essential to oceanic environments. Flow cytometry has been used to estimate that 1 mL of seawater contains 105 – 106 bacteria. While bacterial communities are known to play key roles in marine ecosystems and in geochemical and climate processes, the interactions between bacterial communities and physical factors have not been well characterized. The aim of my study was to test the hypothesis that weather has a significant effect on the metabolic activity and taxonomic composition of coastal bacterioplankton. The Bigelow Laboratory for Ocean Sciences has been performing a weekly water collection for over 10 years. The weekly samples were subjected to microbiological and chemical analyses and correlated with weather data. We used preserved samples to perform a metabolic analysis and bacterial community fingerprinting. The metabolic analysis was achieved through 5-cyano-2,3-ditolyl tetrazolium chloride (CTC) staining. CTC is a non-fluorescent, soluble compound that is reduced to form a fluorescent, insoluble compound. CTC will form fluorescent deposits in cells with active electron transport chains. Environmental samples stained with CTC were then analyzed with a flow cytometer to obtain counts and concentrations of metabolically active cells. Terminal Restriction Fragment Length Polymorphism (T-RFLP) analysis is a community fingerprinting method based on restriction enzyme digestion of fluorescently labeled copies of 16S rDNA. The resulting labeled fragments are analyzed by a DNA sequencer, generating an overview of the community composition of the environmental sample. I found that the abundance of metabolically active bacterioplankton correlated positively with water temperature but not with precipitation. Further work is underway to incorporate microbial community composition and additional physical variables into these analyses.
Potential regulation of Synechococcus growth and silica content by silicic acid concentrations in sea water
Hannah C. McDaniel, University of Maine, Orono
The marine cyanobacterium Synechococcus is a small (0.6 to 1.6 µm diameter), coccoid prokaryote with a widespread geographical distribution. Synechococcus has no known silicon requirement, however in preliminary studies utilizing synchrotron x-ray fluorescence microscopy, the presence of silicon was detected in Synechococcus cells (Twining et al. unpublished). Other non-silicon dependent algae have been found to vary silica content based on silicate availability. We looked at the affect varying silicic acid concentrations in sea water had on Synechococcus growth and silica content. Axenic Synechococcus batch cultures were grown in triplicate under either low (0.1uM), medium (1uM), or high (10uM) silicic acid concentrations. Three variables; growth rate, silicate drawdown, and silica accumulation, were monitored during the culture experiment. Cell counts were taken every other day using either a Coulter Counter or Epifluorescence microscopy. Reactive silicate samples were collected every other day and were run at the end of each trail. Particulate Silica samples were collected and analyzed at the end of each trial. The silicic acid concentration of the cultures was found to increase slightly over the course of the trials. Silicic acid concentration was found to have no affect on Synechococcus growth. Silica content of Synechococcus was found to vary with silicic acid concentration. Synechococcus uptake of silicon seems to be based on availability with no clear disadvantage or benefit to the cell.
In situ monitoring of tethered lobsters reveals diel shifts in predation intensity and cannibalism
Noah Oppenheim, Reed College
Bigelow Mentor: Dr. Richard Wahle
Predation is a key ecological process regulating marine benthic communities, however, little is known of how predation rates vary over the day-night cycle. The American lobster is a conspicuous and ecologically important member of the coastal benthic community in the Gulf of Maine. As a mid-trophic level consumer, its role is both predator and prey. Lobster population densities in midcoast Maine are at an all-time high at a time when fish predators are at an all-time low from overharvesting. Previous daytime observations indicate that juvenile lobsters are vulnerable to visual predators, mostly fishes, which are active in the daytime, whereas lobsters are primarily nocturnally active, emerging from shelter to forage at night. Using infrared time-lapse video monitoring and tethering experiments, we observed significant diel differences in predation rates and predator species composition. Predation rates were unexpectedly higher at night and most of the observed predation was by larger lobsters. The results suggest that cannibalism could be a density-dependent process operating when lobster population densities are high as a consequence of reduced predatory pressure from fishes.