B31F-0352 INVITED
Nitrogen acquisition and the organization of marine phytoplankton communities
We use an ocean circulation and biogeochemistry model with self-assembling microbial communities to examine the role of nitrogen acquisition strategies in organizing marine phytoplankton communities on the global scale. The model is initialized with many tens of physiological variants of phytoplankton which "self- organize" according to their relative fitness. A subset of the initialized phytoplankton types persist and populate the virtual ocean with plausible biogeography. In one study, mutations were applied to pico- cyanobacteria, causing them to lose the ability to assimilate nitrate. The mutants accumulate in habitats closely reflecting those of non-nitrate using Prochlorococcus but were lost in regions where nitrate- using Synechococcus are observed to dominate. In a second study, a fraction of the initialized phytoplankton were given the ability to fix nitrogen. A variety of successful diazotrophic phenotypes persisted, mirroring those observed in the ocean. In both studies the importance of cellular scale, metabolic trade-offs is emphasized, demanding a closer connection between studies at the sub-cellular scale through to global ecology.
B31F-0353
Environmental Controls of Stromatolite Accretion, Highborne Cay, Bahamas
The well-laminated and easily accessible stromatolites at Highborne Cay, Bahamas (760 49' W, 240 43' N) are forming in seawater of normal marine salinity along the margin of Exuma Sound. These modern stromatolites form in the back-reef of a 2.5km algal-ridge fringing reef complex and provide an ideal opportunity to identify the processes controlling stromatolite growth. Wind has been identified as a major controller on the growth of Highborne Cay stromatolites because it is the driving force of sand waves, which migrate across the reef. The migration of these sand waves controls the locally episodic burial and exposure of the stromatolites for periods of days, weeks, and months. Variations in the duration and timing of these sedimentation events determine the exposure of the stromatolites to seasonal changes and influence the distribution of the microbial communities. Both prokaryotic and eukaryotic organisms form microbial mat communities on the surfaces of the stromatolites. Prokaryotic mats are dominated by gliding filamentous cyanobacteria and are found year long along the reef. Prokaryotic mats are dominant on the shallow, low-lying stromatolite ridges and are usually buried for months at a time with weeklong exposure periods. Prokaryotic mats have an average accretion rate of 1mm/year. The mixed eukaryotic-prokaryotic mat communities consist of diatoms overlying filamentous cyanobacteria. The mixed mat community has a seasonality depending on the overlying diatom morphology. Tube diatom mats are dominant in the winter and spring. Stalked diatom mats are dominant in the summer and fall. The eukaryotic-prokaryotic mats are predominantly found on the columnar head stromatolites and are buried and exposed for months at a time. The eukaryotic-prokaryotic mats accrete sediment more rapidly than the prokaryotic mats at a rate of more than 1cm/year. The differing accretion rates and exposure periods create distinct subsurface micro-fabrics in the stromatolites.
B31F-0354
Parameterization of a size-structured biogeochemical model for the California Current Ecosystem
To understand and quantify plankton community dynamics in the ocean, high-resolution models are needed to capture the temporal and spatial variations of physical, biological and biogeochemical processes. However, ecosystem models often fail to agree with observations. This can be due to inadequacies in the data, and inadequacies in the model formulation and parameterization. We parameterized a 1-D size- structured ecosystem model (modified from NEMURO) using data from Lagrangian field measurements conducted during the Long Term Ecological Research –California Current Ecosystem (LTER-CCE) program. The CCE process studies were focused on quantifying the size-resolved planktonic growth, grazing, production and export rates when following a water parcel; these data provide strong constraints for the model we employed. Our preliminary results indicate that the model can accurately reproduce some of the important biological features and dynamics observed in the CCE, such as the Chl-a/C ratios, the size- fractioned growth and grazing rates, and the phytoplankton community structure.
B31F-0355
What Regulates Spatial Gradients in Marine Phytoplankton Diversity?
A global, three-dimensional self-assembling model of marine phytoplankton communities, initialized with many tens of plausible physiologies, shows a pronounced equator-to-pole decrease in the diversity of phytoplankton species. This pattern is common among many marine taxa. Regions of enhanced phytoplankton diversity also occur in association with areas of energetic flow including western boundary currents. In the three-dimensional model, the most abundant phytoplankton types in the stable, warm waters tend to have similar, low R* values, which indicate a strong ability to compete for scarce nutrients. We use a highly idealized, zero-dimensional model to interpret and illustrate mechanisms causing the broad meridional diversity gradient in terms of the variability of the environment. We demonstrate that in stable, oligotrophic conditions there are very long exclusion timescales (hundreds to thousands of years) for organisms with similar and low R* values if temporal variability in resource supply is either long (inter-annual or longer) or short (comparable to the growth period or shorter). High amplitude variability in resource supply, with seasonal timescales, leads to rapid competitive exclusion.
B31F-0356
Identification of Methane, Ethane, and Propane Oxidizing Bacteria at Marine Hydrocarbon Seeps by Stable Isotope Probing
Hydrocarbon seeps emit substantial amounts of oil and natural gas into the marine environment, where they can be oxidized by microorganisms in the sediment and water column. Here, we used stable isotope probing of DNA and lipid biomarkers to identify the microorganisms actively consuming 13C-labeled natural gas compounds in seep sediment samples. Surface sediment was collected from the Coal Oil Point seep field (offshore Santa Barbara, California, USA) and incubated under aerobic conditions with 13C labeled methane, ethane, or propane for up to 37 days, with sediment sub-samples taken at 3-4 intermediate time points. DNA was extracted from sediment and separated by CsCl density gradient centrifugation. The microbial community in each fraction was profiled using T-RFLP, and bacterial 16S rRNA gene clone libraries were constructed from un-incubated hydrocarbon seep sediment and selected isotopically 'heavy' (13C) and 'light' (12C) gradient fractions from ethane incubations. All clone libraries were dominated by sequences from members of the family Rhodobacteraceae (>25% of sequences) and a diverse group of Gammaproteobacteria, including sequences related to those of methylotrophs and to those of bacteria known to consume the longer-chain alkanes present in crude oil. After 14 days of incubation, the relative abundance of Rhodobacteraceae was higher in 'heavy' fractions from the 13C-ethane incubation than in 'light' fractions, suggesting incorporation of 13C label. The Rhodobacteraceae are very diverse metabolically, but have often been observed in abundance in oil contaminated seawater. Several members of this group have been shown to oxidize longer chain alkanes (C10 or higher), but none have been previously linked to the consumption of the gaseous alkanes ethane, propane, and butane. For the final time point, 13C content of phospholipid fatty acids (PLFA) were also analyzed, showing substantial incorporation of 13C over 37 days. In the methane incubation, approximately 75% of the 13C incorporated into PLFA was found in fatty acids 18:1(6), 16:0, 18:1(8), and 16:1(6), suggesting that both type I and type II methanotrophs were involved in methane oxidation. In the case of ethane, 18:1(6), 18:1(8), and 16:1(6) were also highly labeled (>10% 13C), but composed a much lower fraction of total PFLA than in the methane incubation. Instead, fatty acids anteiso-15:0 and 14:0 accounted for approximately 50% of 13C-ethane incorporated into PLFA, indicating that a different group of organisms was responsible for the bulk of ethane consumption. Additional results from the methane and propane incubations will also be presented.
B31F-0357
Development of Ecogenomic Sensors for Remote Detection of Marine Microbes, Their Genes and Gene Products
An internet search using the phrase "ecogenomic sensor" will return numerous references that speak broadly
to the idea of detecting molecular markers indicative of specific organisms, genes or other biomarkers within
an environmental context. However, a strict and unified definition of "ecogenomic sensor" is lacking and the
phrase may be used for laboratory-based tools and techniques as well as semi or fully autonomous systems
that can be deployed outside of laboratory. We are exploring development of an ecogenomic sensor from
the perspective of a field-portable device applied towards oceanographic research and water quality
monitoring. The device is known as the Environmental Sample Processor, or ESP. The ESP employs wet
chemistry molecular analytical techniques to autonomously assess the presence and abundance of specific
organisms, their genes and/or metabolites in near real-time. Current detection chemistries rely on low-
density DNA probe and protein arrays. This presentation will emphasize results from 2007-8 field trials when
the ESP was moored in Monterey Bay, CA, as well as current engineering activities for improving analytical
capacity of the instrument. Changes in microbial community structure at the rRNA level were observed
remotely in accordance with changing chemical and physical oceanographic conditions. Current
developments include incorporation of a reusable solid phase extraction column for purifying nucleic acids
and a 4-channel real-time PCR module. Users can configure this system to support a variety of PCR master
mixes, primer/probe combinations and control templates. An update on progress towards fielding a PCR-
enabled ESP will be given along with an outline of plans for its use in coastal and oligotrophic oceanic
regimes.
http://www.mbari.org/esp
B31F-0358
Proteomic Analysis of the Marine Cyanobacterium Synechococcus WH8102 and Implications for Estimates of the Cellular Iron Content
The proteome of the marine cyanobacterium Synechococcus WH8102 was analyzed by nanospray liquid chromatography mass spectrometry (nLC-MS) with two major goals: to provide a first examination of the relative abundance of the most abundant proteins in this important microbe and to provide the necessary mass spectra for future quantification of biogeochemically significant proteins. Analyses of 37 nLC-MS runs of whole cell tryptic digestions and SDS-PAGE gel separated tryptic digestions resulted in a total of 636 proteins identified, 376 identified with two or more tryptic peptides. The identifications used the Sequest algorithm with stringent data filters on 54003 observed peptides, 3066 of which were unique, with a false positive rate of 2.2%. These measured proteins represent ~ 25.2% (14.8% with >= 2 peptides) of the open reading frames (ORFs) in the genome, similar to or higher than the percentage found in other cyanobacterial proteome studies thus far. The relative abundance of the more abundant proteins in the proteome was examined using the exponentially modified protein abundance index from a single nLC-MS run that identified 372 proteins (14.7% of the ORFs) from 7743 observed peptides (1224 unique peptides). Estimates of the relative abundance showed the photosynthesis and respiration category contributing approximately 32% of the total detected protein, hypothetical proteins contributing about 16%, and translation about 12%. Of biogeochemical interest, multiple types of nitrogen assimilation systems were observed to be simultaneously expressed as proteins, only 5 of the 21 B12 biosynthesis proteins were identified likely due to low abundance, and the metalloproteins metallothionein and nickel superoxide dismutase were relatively abundant. In contrast to previous predictions of a high photosystem I: photosystem II ratio of approximately 3 in the cyanobacteria and a resultant high cellular iron content, the ratio of the average relative abundances of all detected proteins in each photosystem was only 1.2, and the median was only 0.72 based on the median. These results contradict the earlier predication of a biochemical basis for a high cellular iron in Synechococcus and may extend to the marine cyanobacteria in general.
B31F-0359
The Ocean Metaproteome: Where the Rubber Meets the Road
Mass spectrometry can identify proteins extracted from complex microbial communities, revealing the endpoint of transcription and translation – the proteomes of cells. To study the mechanisms of microbial survival in oligotrophic oceans, we used capillary LC-tandem mass spectrometry to detect microbial proteins in summer mixed layer samples collected from the northwestern Sargasso Sea. The biological productivity of this region is reduced during stratified periods as a result of low concentrations of phosphorus and nitrogen in the euphotic zone. A total of 2279 peptides that mapped to 236 SAR11 proteins, 1918 peptides that mapped to 402 Prochlorococcus proteins, and 3208 peptides that mapped to 404 Synechococcus proteins, were detected. Mass spectra from SAR11 periplasmic substrate-binding proteins accounted for a disproportionately large fraction of the peptides detected, consistent with models that predict streamlining selection and high surface to volume ratios in oligotrophic bacterioplankton. Abundances were highest for periplasmic substrate-binding proteins for phosphate, amino acids, phosphonate, sugars, and spermidine. Proteins implicated in the prevention of oxidative damage and protein refolding were also abundant. Our findings support the view that competition for multiple nutrients in oligotrophic systems is extreme but nutrient flux is sufficient to sustain microbial community activity.
B31F-0360 [WITHDRAWN]
Nutrient Limitation of Phytoplankton Growth in the Tropical South Pacific Ocean
The South Pacific Ocean is thought to be one of the most oligotrophic ocean regions. Environmental factors that limit phytoplankton growth and taxonomic composition in areas such as these are linked to regulation of the oceanic carbon sink. We conducted nutrient enrichment experiments in the South Pacific Ocean in March-April, 2007, along a transect from the coastal waters of Australia to north of Fiji. Six nutrient enrichment experiments were performed using nitrogen (N), phosphorus (P), iron+EDTA (Fe), glucose+mannitol (GM), and combinations of these. The experiments were not carried out under strictly trace element clean conditions; therefore the data indicate phytoplankton responses relative to control. In five of the six experiments, the addition of N alone enhanced phytoplankton biomass up to 5-fold of that in the control during a 72-h incubation period. In one of the experiments, the combined addition of N and Fe enhanced chlorophyll a more than N alone. In all of the experiments, the combined addition of all nutrients produced the greatest concentration of chlorophyll a, with up to a 22-fold increase in biomass. The addition of P, glucose and mannitol, or Fe, individually, did not enhance phytoplankton biomass over the control. Even if background Fe affected initial growth responses and N in fact was the secondary limiting nutrient, the data show that the impact of N was several-fold greater than the potential impact of Fe. Flow cytometric and microscopic cell counts showed that Synechococcus-like cells and small pennate diatoms were among the groups that responded favorably to nutrient additions. Bacterial abundances increased over controls only if all nutrients were added, suggesting the addition of a carbon source was necessary. Cell abundances of the nitrogen-fixing cyanobacterium Crocosphaera watsonii were reduced if N was added alone or when N was combined with P or Fe, but their abundances were not affected by additions of other nutrients. Overall the data suggest nitrogen is a major phytoplankton growth-limiting nutrient in the western South Pacific Ocean.
B31F-0361
Assessing Photosynthetic Energy Fluxes Within Microbial Communities Using Continuous Ship-Based Fast Repetition Rate (FRR) Fluorescence Measurements.
Microbial life in the ocean is sustained by photosynthetically-derived energy at a power level of about 5*1014 W. Assuming photosynthetic efficiency of about 20%, this mechanism consumes less than 10% of photosynthetically-available radiation (PAR) incident on the ocean surface. Life in the ocean operates under condition of excess energy, where factors such as nutrients/trace metals availability or prevalence of nitrogen fixation limit photosynthetic light utilization. To investigate these factors we have performed fast repetition rate (FRR) fluorescence measurements, continuously, over a period of one year, along the cruise track of R/V Kilo Moana. We have identified photosynthetic signatures of Trichodesmium blooms during two cruises in 2007 and 2008, and we have used these signatures to infer the presence of Trichodesmium along the cruise track. Most surface enhancements in photosynthetic rates and the chlorophyll biomass were observed in peripheral areas between cyclonic and anticyclonic eddies. It appears that local shear zones in these areas induce small-scale vertical mixing capable of supporting near-surface blooms. Our data indicate that the gradients in the sea surface height, rather than local minima/maxima, determine the occurrence of small-scale surface blooms in the North Pacific Subtropical Gyre.
B31F-0362
Identifying Historical Occurrences of HABs Using Sedimentary Algal Pigments
Algal blooms are a common feature of many coastal areas. Under some environmental conditions, these develop into Harmful Algal Blooms (HABs) and present an environmental hazard and a health risk for humans and wildlife due to toxin production. While monitoring programs track the development of contemporary HABs, data are lacking for historical blooms. We use sedimentary algal pigments to identify the occurrence of Karenia Brevis (Florida Red Tide) in sediment cores collected from mangrove environments along the west coast of Florida. Karenia Brevis has a unique pigment, gyroxanthin-diester, that is routinely used to identify red tide in the water column. Gyroxanthin-diester and other carotenoid pigments associated with red tide taxa are analyzed using HPLC techniques. Identification of gyroxanthan-diester is based on comparison with HPLC analysis of gyroxanthin standard, a monoculture sample of K. Brevis and with published spectra of Gyroxanthin-diester in water samples. We track the timing of the K. Brevis using Pb-210 dating models which allows an examination over the last 100 years.
B31F-0363
Comparison of Methods to Determine Algal Concentrations in Freshwater Lakes
Algal populations are extremely important to the ecological health of freshwater lake systems. As lakes become eutrophic (highly productive) through nutrient loading, sediment accumulation rates increase, bottom waters become anoxic in the mid-to late summer, the opacity of the water column decreases, and significantly decreases the lake's potential as a drinking water source and places respiratory stress on aquatic animals. One indicator of eutrophication is increasing algal concentrations over annual time frames. Algal concentrations can be measured by the concentration of chlorophyll a, or less directly by fluorescence, secchi disk depth, and turbidity by backscattering and total suspended solids. Here, we present a comparison of these methods using data collected on Honeoye, Canandaigua, Keuka, Seneca, Cayuga, Owasco, Skaneateles, and Otisco, the largest Finger Lakes of western and central New York State during the 2008 field season. A total of 124 samples were collected from at least two mid-lake, deep-water sites in each lake monthly through the 2008 field season (May-Oct); Seneca Lake was sampled weekly at four sites and Cayuga Lake every two weeks at six sites. Secchi depths, CTD profiles and surface water samples were collected at each site. Chlorophyll a was measured by spectrophotometer in the lab after filtration at 0.45 um and digestion of the residue in acetone. Water samples were also filtered through pre-weighed glass-fiber filters for total suspended solids concentrations. A SBE-25 SeaLogger CTD collected profiles of turbidity and fluorescence with WetLabs ECO FL-NTU. Surface CTD values were used in the comparison. The strongest linear correlations were detected between chlorophyll-a and fluorescence (r2 = 0.65), and total suspended solids and turbidity (r2 = 0.63). Weaker correlations were detected between secchi depths and chlorophyll-a (r2 = 0.42), and secchi depths and turbidity (r2 = 0.46). The weakest correlations were detected between secchi depths and fluorescence (r2 = 0.29), total suspended solids and fluorescence (r2 = 0.29), chlorophyll-a and turbidity (r2 = 0.34) and fluorescence and turbidity (r2 = 0.25). The results suggest that water clarity in these lakes was controlled by both inorganic and organic (algal) suspended matter, and each method typically focuses on either the organic or inorganic fractions of the total suspended sediment population. Interestingly, fluorescence profiles revealed algal peaks at depth in the epilimnion and occasionally in the upper hypolimnion of these lakes. The peak in fluorescence was shallower in algal-rich lakes. Thus, lake monitoring protocols and assessments should include all of these parameters to adequately quantify the type and concentration of suspended matter, and expand from surface samples to integrate the entire water column.
B31F-0364
Mixing of groundwater and seawater changes the nutrient structure in coastal areas
Submarine groundwater discharge (SGD) extensively occurs along continental margins. The discharge of nutrient-enriched groundwater into coastal waters may result in changes of the nutrient structure. Field survey and simulation experiments indicated that the exchange rates of nutrients between groundwater and seawater are related to the hydrodynamic conditions during their mixing. The concentrations of SO42-, TN, and TP in the mixed waters fluctuate largely at different pH values, which implied that pH has an obvious effect on nutrients. Although a relative minor influence was observed for temperature, it can cause variation in pH values and thus result in form transformation among NH4-N, NO2-N and NO3-N and in variation of relative contents. Though nutrient component does not vary with the input of submarine groundwater, its flux changes the relative contents of nutrients and physical parameters in near- shore waters, which has potential implications for approach of a new marine ecological balance.