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Microalgal communities that colonize the hulls of at-risk vessels - those which have the highest port residency times, lowest speeds, and most stationary time in water - are expected to change as a function of environmental factors during... more
Microalgal communities that colonize the hulls of at-risk vessels - those which have the highest port residency times, lowest speeds, and most stationary time in water - are expected to change as a function of environmental factors during ocean voyages, but are rarely studied. The microalgal communities on the hull of an atypically operated ship, the T.S. Golden Bear, were quantified during the course of a voyage from San Francisco Bay to the South Pacific and back. Here we clearly demonstrate that microalgal communities can be highly resilient, and can survive physiologically strenuous journeys through extreme variation in salinity and temperature. A 42% reduction in microalgal biomass and a 62% reduction in algal cellular abundance indicated a community-wide negative reaction to an increase in both salinity and temperature after the ship left San Francisco Bay, CA and cruised southward to Long Beach, although in vivo cellular fluorescence capacity increased. Further reductions in ...
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Many efforts to improve science teaching in higher education focus on a few faculty members at an institution at a time, with limited published evidence on attempts to engage faculty across entire departments. We created a long-term,... more
Many efforts to improve science teaching in higher education focus on a few faculty members at an institution at a time, with limited published evidence on attempts to engage faculty across entire departments. We created a long-term, department-wide collaborative professional development program, Biology Faculty Explorations in Scientific Teaching (Biology FEST). Across 3 years of Biology FEST, 89% of the department's faculty completed a weeklong scientific teaching institute, and 83% of eligible instructors participated in additional semester-long follow-up programs. A semester after institute completion, the majority of Biology FEST alumni reported adding active learning to their courses. These instructor self-reports were corroborated by audio analysis of classroom noise and surveys of students in biology courses on the frequency of active-learning techniques used in classes taught by Biology FEST alumni and nonalumni. Three years after Biology FEST launched, faculty particip...
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A laboratory study using the fish-killing raphidophyte Heterosigma akashiwo was conducted to examine its capability to grow at salinities below oceanic, and to test the perceived relationship between reduced salinities and increased... more
A laboratory study using the fish-killing raphidophyte Heterosigma akashiwo was conducted to examine its capability to grow at salinities below oceanic, and to test the perceived relationship between reduced salinities and increased cytotoxicity. A non-axenic strain of H. akashiwo isolated from the U.S. Pacific Northwest was exposed to a combination of three salinity (32, 20 and 10) and five temperature (14.7, 18.4, 21.4, 24.4 and 27.8°C) conditions. Our results demonstrate that cell permeability and cytotoxicity are strongly correlated in unialgal cultures of H. akashiwo, which both increased as salinity decreased from 32 to 10. Furthermore, over a broad median range of salinities (10 and 20), neither temperature nor specific growth rate were correlated with cytotoxicity. However, in cultures grown at the salinity of 32, both temperature and specific growth rate were inversely proportional to toxicity; this relationship was likely due to the effect of contamination by an unidentifi...
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Research Interests: Carbon, MARINE POLLUTION, Carbon Sequestration, Marine biodiversity, Multidisciplinary, and 14 moreFossil Fuels, Ecological Risk Assessment, Urea, Economic Impact, Nitrogen, Greenhouse Effect, Carbon credit, Ecosystem, Algal Bloom, Fertilizers, Large Scale, Deep Sea, Oceans and Seas, and Ecological Risk
The nitrogen uptake dynamics by natural phytoplankton assemblages were measured during two progressive iron enrichment experiments conducted in High Nitrate, Low Chlorophyll (HNLC) regions of the Southern Ocean during austral summer 2002.... more
The nitrogen uptake dynamics by natural phytoplankton assemblages were measured during two progressive iron enrichment experiments conducted in High Nitrate, Low Chlorophyll (HNLC) regions of the Southern Ocean during austral summer 2002. The experiments were designed to determine if iron enrichment enhances new production in the low silicate waters north (ca. 55°S) and high silicate waters south (ca. 65°S) of the Antarctic Polar Front Zone, along the 170°W meridian of longitude. Absolute uptake rates of nitrate (determined using the N-15 tracer technique) increased ca. ten-fold in the northern patch and ca. 25-fold in the southern patch, but remained relatively constant in the un-enriched (control) waters. Biomass (particulate nitrogen) specific uptake rates of nitrate increased ca. four-fold and up to ten-fold in the northern and southern patches respectively, whereas specific uptake rates of ammonium and urea did not increase as a result of Fe enrichment. Based on progressive sampling of the 47% and 16% light depths, and the results of surface transects conducted across the southern Fe-infused region at the beginning, middle, and end of the southern patch monitoring period (>3 weeks), a clear change in the relative utilization of new and regenerated nitrogen due to Fe enrichment was evident; the daily f-ratio (f-ratio = nitrate uptake/total nitrogen uptake) increased from ca. 0.2-0.3 to 0.5-0.6 (ratio uncorrected for isotopic dilution and DON effects). However, unlike previous mesoscale enrichment experiments conducted here (SOIREE) and in the subarctic (SEEDS and SERIES) and equatorial Pacific (IronEx II), the size-structure of the phytoplankton community did not change in the southern patch following Fe enrichment; it only changed in the northern patch, where larger cells (> 5 μm) dominated the assemblage following Fe enrichment. Ambient concentrations of ammonium in the surface waters of the northern SOFeX patch declined by 0.1-0.2 μM as a consequence of Fe enrichment, but ammonium concentrations increased both inside and outside of the southern patch as a function of time; the potential inhibitory effects of ammonium on nitrate uptake will be discussed in the context of alleviation of Fe limitation in HNLC regions of the Southern Ocean.
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ABSTRACT
Virus production was estimated in samples from diverse marine environments by incorporation of 32P-orthophosphate (32Pi) into viral DNA. Rates of virus production in the field were found to vary over three orders of magnitude (from <... more
Virus production was estimated in samples from diverse marine environments by incorporation of 32P-orthophosphate (32Pi) into viral DNA. Rates of virus production in the field were found to vary over three orders of magnitude (from < 1x10^8 to 2.3 x 10^11 viruses l-1 d-1). Due to the possibility of intracellular isotope dilution and filtration losses, these rates should be considered minimum estimates. Virus production displayed a strong onshore-offshore gradient which covaried with bacteria abundance and chlorophyll a. Minimum estimates of mortality in two coastal samples (12 and 25% of bacteria production) suggest that viruses were a significant source of bacteria mortality in these environments. The apparent dependence of virus production on host density suggests that significant phage attack is spatially and temporally episodic in the open ocean (e.g., during phytoplankton blooms), but more persistent in the highly productive coastal waters.
... NOTE The contribution of phytoplankton to ocean density gradients JAMES GMITCHELL,*t AIORA OKUBO,* JED A. FtmRMAN*~t and WILLIAM ... that are usually denser than seawater and thus sink (EPPLEY et al., 1967; VAN IERLAND and PEPERZAK,... more
... NOTE The contribution of phytoplankton to ocean density gradients JAMES GMITCHELL,*t AIORA OKUBO,* JED A. FtmRMAN*~t and WILLIAM ... that are usually denser than seawater and thus sink (EPPLEY et al., 1967; VAN IERLAND and PEPERZAK, 1984; VILLAREAL, 1986). ...
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ABSTRACT Emiliania huxleyi has been the most abundant coccolithophore in the world&#39;s ocean for the last 70,000 yr, forming extensive blooms in vast oceanic areas. Although coccolithophores in general and E. huxleyi in particular... more
ABSTRACT Emiliania huxleyi has been the most abundant coccolithophore in the world&#39;s ocean for the last 70,000 yr, forming extensive blooms in vast oceanic areas. Although coccolithophores in general and E. huxleyi in particular have been extensively studied, the selective advantage furnished by coccoliths is yet to be pinpointed. This study utilizes two substrains of E. huxleyi 1516, the original calcifying strain, and its isogenic twin which lost the capacity to calcify, in an attempt to determine the ecological advantages of producing coccoliths. Under standard laboratory conditions, the noncalcifyers outcompeted the calcifyers in growth. However, exposure of the two substrains to a combination of environmental stressors revealed that coccoliths mitigated stress imposed by a mechanical perturbation, reducing cell lysis and supporting greater cell concentrations in the presence of moderate turbulence. Noncalcifyers appeared to be susceptible to growth media with a high P : N ratio, with their nitrate acquisition capacity hampered under mechanical perturbation. We suggest that the stabilized microenvironment provided by coccoliths is essential for high-affinity nitrate transport and its regulation. Our results demonstrate that introduction of more natural stressors is instrumental in and sometimes essential to unveil the ecological advantages of coccolithophore calcification.
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The nitrogen uptake dynamics by natural phytoplankton assemblages were measured during two progressive iron enrichment experiments conducted in High Nitrate, Low Chlorophyll (HNLC) regions of the Southern Ocean during austral summer 2002.... more
The nitrogen uptake dynamics by natural phytoplankton assemblages were measured during two progressive iron enrichment experiments conducted in High Nitrate, Low Chlorophyll (HNLC) regions of the Southern Ocean during austral summer 2002. The experiments were designed to determine if iron enrichment enhances new production in the low silicate waters north (ca. 55°S) and high silicate waters south (ca. 65°S) of the Antarctic Polar Front Zone, along the 170°W meridian of longitude. Absolute uptake rates of nitrate (determined using the N-15 tracer technique) increased ca. ten-fold in the northern patch and ca. 25-fold in the southern patch, but remained relatively constant in the un-enriched (control) waters. Biomass (particulate nitrogen) specific uptake rates of nitrate increased ca. four-fold and up to ten-fold in the northern and southern patches respectively, whereas specific uptake rates of ammonium and urea did not increase as a result of Fe enrichment. Based on progressive sam...
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Marine chlorophytes of the genus Chlorella are unicellular algae capable of accumulating a high proportion of cellular lipids that can be used for biodiesel production. In this study, we examined the broad physiological capabilities of a... more
Marine chlorophytes of the genus Chlorella are unicellular algae capable of accumulating a high proportion of cellular lipids that can be used for biodiesel production. In this study, we examined the broad physiological capabilities of a subtropical strain (C596) of Chlorella sp. "SAG-211-18" including its heterotrophic growth and tolerance to low salt. We found that the alga replicates more slowly at diluted salt concentrations and can grow on a wide range of carbon substrates in the dark. We then sequenced the RNA of Chlorella strain C596 to elucidate key metabolic genes and investigate the transcriptomic response of the organism when transitioning from a nutrient-replete to a nutrient-deficient condition when neutral lipids accumulate. Specific transcripts encoding for enzymes involved in both starch and lipid biosynthesis, among others, were up-regulated as the cultures transitioned into a lipid-accumulating state whereas photosynthesis-related genes were down-regulate...
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ABSTRACT The toxigenic diatom Pseudo‐nitzschia cuspidata, isolated from the U.S. Pacific Northwest, was examined in unialgal batch cultures to evaluate domoic acid (DA) toxicity and growth as a function of light, N substrate, and growth... more
ABSTRACT The toxigenic diatom Pseudo‐nitzschia cuspidata, isolated from the U.S. Pacific Northwest, was examined in unialgal batch cultures to evaluate domoic acid (DA) toxicity and growth as a function of light, N substrate, and growth phase. Experiments conducted at saturating (120 μmol photons · m−2 · s−1) and subsaturating (40 μmol photons · m−2 · s−1) photosynthetic photon flux density (PPFD), demonstrate that P. cuspidata grows significantly faster at the higher PPFD on all three N substrates tested [nitrate (NO3−), ammonium (NH4+), and urea], but neither cellular toxicity nor exponential growth rates were strongly associated with one N source over the other at high PPFD. However, at the lower PPFD, the exponential growth rates were approximately halved, and the cells were significantly more toxic regardless of N substrate. Urea supported significantly faster growth rates, and cellular toxicity varied as a function of N substrate with NO3−‐supported cells being significantly more toxic than both NH4+‐ and urea‐supported cells at the low PPFD. Kinetic uptake parameters were determined for another member of the P. pseudodelicatissima complex, P. fryxelliana. After growth of these cells on NO3− they exhibited maximum specific uptake rates (V max) of 22.7, 29.9, 8.98 × 10−3 · h−1, half‐saturation constants (K s) of 1.34, 2.14, 0.28 μg‐at N · L−1, and affinity values (α) of 17.0, 14.7, 32.5 × 10−3 · h−1/(μg‐at N · L−1) for NO3−, NH4+ and urea, respectively. These labo‐ratory results demonstrate the capability of P. cuspidata to grow and produce DA on both oxidized and reduced N substrates during both exponential and stationary growth phases, and the uptake kinetic results for the pseudo‐cryptic species, P. fryxelliana suggest that reduced N sources from coastal runoff could be important for maintenance of these small pennate diatoms in U.S. west coast blooms, especially during times of low ambient N concentrations.
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ABSTRACT Marine phytoplankton have conserved elemental stoichiometry, but there can be significant deviations from this Redfield ratio. Moreover, phytoplankton allocate reduced carbon (C) to different biochemical pools based on... more
ABSTRACT Marine phytoplankton have conserved elemental stoichiometry, but there can be significant deviations from this Redfield ratio. Moreover, phytoplankton allocate reduced carbon (C) to different biochemical pools based on nutritional status and light availability, adding complexity to this relationship. This allocation influences physiology, ecology, and biogeochemistry. Here, we present results on the physiological and biochemical properties of two evolutionarily distinct model marine phytoplankton, a diatom (cf. Staurosira sp. Ehrenberg) and a chlorophyte (Chlorella sp. M. Beijerinck) grown under light and nitrogen resource gradients to characterize how carbon is allocated under different energy and substrate conditions. We found that nitrogen (N)-replete growth rate increased monotonically with light until it reached a threshold intensity (~200 μmol photons · m−2 · s−1). For Chlorella sp., the nitrogen quota (pg · μm−3) was greatest below this threshold, beyond which it was reduced by the effect of N-stress, while for Staurosira sp. there was no trend. Both species maintained constant maximum quantum yield of photosynthesis (mol C · mol photons−1) over the range of light and N-gradients studied (although each species used different photophysiological strategies). In both species, C:chl a (g · g−1) increased as a function of light and N-stress, while C:N (mol · mol−1) and relative neutral lipid:C (rel. lipid · g−1) were most strongly influenced by N-stress above the threshold light intensity. These results demonstrated that the interaction of substrate (N-availability) and energy gradients influenced C-allocation, and that general patterns of biochemical responses may be conserved among phytoplankton; they provided a framework for predicting phytoplankton biochemical composition in ecological, biogeochemical, or biotechnological applications.