Phytoplankton pigment specific growth and losses due to microzooplankton grazing in a northern Gulf of Mexico estuary during winter/fall

Microzooplankton dilution grazing experiments were carried out on 6 dates, over a 3 month period at 2 locations in the Bay of St. Louis, MS (BSL) to determine phytoplankton pigment specific growth rates under natural (µ0) and replete (µn) nutrient conditions and microzooplankton grazing. We hypothesized that diatoms would be the largest portion of the phytoplankton composition due to the winter/fall season and that these organisms would have the highest growth/grazing rates. We suspected that river flow from the Jourdan River would adversely affect growth and grazing rates of all phytoplankton classes. Growth rates of 5 phytoplankton accessory pigments (peridinin, fucoxanthin, alloxanthin, zeaxanthin, chlorophyll b) were identified. Intrinsic growth rates (µ0) were often zero or negative (range: -0.46–0.56/d) at the location nearest the Jourdan River, particularly for alloxanthin (e.g. cryptophytes) and peridinin (e.g. dinoflagellates). Significant grazing of chlorophyll a was observed on 3 of 6 dates while grazing on marker pigments was variable. The phytoplankton community appeared nutrient limited during all but one experiment (µ0\u3cµn). Intrinsic growth and grazing rates were correlated (p \u3c 0.05, Spearman Rank Order correlation). Peridinin- and alloxanthin-based growth and grazing rates were correlated positively with salinity suggesting a river influence on these 2 phytoplankton pigment classes. We conclude that in the BSL microzooplankton preferentially grazed on the phytoplankton class which had the highest intrinsic growth rate. We show that this is greatly affected by riverine input into the estuary and nutrient limitation

Marine Microalgae: Climate, Energy, and Food Security From the Sea

Climate, energy, and food security are three of the greatest challenges society faces this century. Solutions for mitigating the effects of climate change often conflict with solutions for ensuring society’s future energy and food requirements. For example, BioEnergy with Carbon Capture and Storage (BECCS) has been proposed as an important method for achieving negative CO2 emissions later this century while simultaneously producing renewable energy on a global scale. However, BECCS has many negative environmental consequences for land, nutrient, and water use as well as biodiversity and food production. In contrast, large-scale industrial cultivation of marine microalgae can provide society with a more environmentally favorable approach for meeting the climate goals agreed to at the 2015 Paris Climate Conference, producing the liquid hydrocarbon fuels required by the global transportation sector, and supplying much of the protein necessary to feed a global population approaching 10 billion people

Effect of Sewage Enrichment on the Phytoplankton Population of a Subtropical Estuary

Phytoplankton primary production; concentrations of chlorophyll a, particulate carbon and nitrogen, adenosine triphosphate, inorganic nitrogen and phosphorus; and secchi depths were measured at four stations in Kaneohe Bay, Oahu, on a biweekly basis for 20 months prior to diversion of sewage discharges from the bay. Nutrient enrichment experiments designed to determine biomass limitation indicated that phytoplankton biomass, as measured by chlorophyll a, was nitrogen-limited in all parts of the bay, and that phosphorus was simultaneously limiting in the sector of the bay furthest from the sewer outfalls. Mean light-saturated productivity indices in all parts of the bay were about 11-12 mg C mg -1 chl a . hr -1, values close to the maximum reported for phytoplankton in eutrophic marine environments. Based on the results of dawn-to-dusk C-14 incubations and an estimated phytoplankton C: chi a ratio of 50 by weight, phytoplankton growth rates were estimated to fall in the range of 4-6 percent per hour in all parts of the bay. Such growth rates are close to the maximum growth rates reported for marine phytoplankton grown on light-dark cycles in continuous culture, suggesting that phytoplankton growth rates (as opposed to biomass) were limited primarily by suboptimal or supraoptimal light intensities rather than by nutrients. Based on these growth rates and an assumed phytoplankton C : N ratio of 5.68 by weight, nitrogen recycling was estimated to account for 80 percent of phytoplankton nitrogen uptake in the part of the bay receiving direct sewage inputs, and for over 90 percent of phytoplankton nitrogen uptake in the other sectors of the bay. Estimates of living and detrital particulate carbon were made based on an assumed C: ATP ratio in living organisms of 285 by weight. From this partitioning, living carbon was found to vary by a factor of 3-4 between the sewage-enriched and unenriched sectors of the bay. However, estimated detrital carbon concentrations were uniform throughout the bay, as were the measured concentrations of inorganic nitrogen. These results are consistent with the interpretation that the population of microorganisms, both bacteria and phytoplankton, are substrate-limited in all sectors of the bay

Assessment of primary production and optical variability in shelf and slope waters near Cape Hatteras, North Carolina. Final project report

In this project we determined primary production and optical variability in the shelf and slope waters off of Cape Hatteras, N.C. These processes were addressed in conjunction with other Ocean Margins Program investigators, during the Spring Transition period and during Summer. We found that there were significant differences in measured parameters between Spring and Summer, enabling us to develop seasonally specific carbon production and ecosystem models as well as seasonal and regional algorithm improvements for use in remote sensing applications

Has the Importance of Photoautotrophic Picoplankton Been Overestimated

Postincubation differential filtration (PIDF), preincubation differential filtration (Pre-IDF), and track autoradiography (TA) were compared for estimating cell-specific and total photo-autotrophic picoplankton production. Experiments were performed in Lakes Michigan and Huron and in the Ful of Mexico. When Synechococcus dominated the photoautotrophic picoplankton community (\u3e70% of total picoplankton abundance), PIDF estimates of cell-specific and total picoplankton production were ~3.0 x (range, 2.0--3.8 x) higher than TA estimates. PreIDF estimates of cell-specific and total picoplankton production, however, were only slightly higher than TA estimates (mean, 1.4 x; range, 1.4--1.5 x). The higher PIDF estimates were attributable to breakage and damage of larger photoautotrophs during postincubation filtration and to retention of this labeled material on the smaller (0.2 µm) pore-size filter. Results from PIDF experiments must be viewed with caution and previous estimates of picoplankto production, cell-specific or total, based solely on PIDF may need to be re-evaluated

Phytoplankton Dynamics within a Discrete Water Mass off Cape Hatteras, North Carolina: the Lagrangian Experiment

As part of the Department of Energy Ocean Margins Program, we examined the spatial and temporal variability in primary production and phytoplankton pigments during two cruises to the shelf waters between the Chesapeake Bay and Cape Hatteras. The first cruise was conducted in March 1996, reflecting well-mixed conditions just prior to the spring transition, while the second cruise was conducted during July 1996 when the water column was more stratified. During each cruise, primary production and high performance liquid chromatography (HPLC) pigments for the whole community and \u3c8-mum size fraction were determined for several successive days within a discrete water mass by following a near-surface tracking drogue. In March, production ranged from 0.50 to 0.65 g C m(-2) d(-1), with 52-62% of the production attributed to the smaller size fraction. About 50% of the total chlorophyll a (chl a) was found in the \u3e 8-mum size fraction. Pigment composition was dominated by chlorophylls a, c(1) and c(2), and fucoxanthin, indicating the importance of diatoms. In July, production was more variable, ranging from 0.38 to 2.09 g C m(-2) d(-1), with 41-83% of production attributed to the \u3c8-mum size fraction. Rates increased over the 4-day study. Most of the chi a was found in the \u3c8-mum size fraction. The phytoplankton pigments were dominated by chi a and fucoxanthin with chlorophylls c(1) and c(2), again indicating the importance of diatoms during this cruise.CHEMTAX (Mackey et al. CHEMTAX User\u27s Manual: a program for estimating class abundances from chemical markers-application to HPLC measurements of phytoplankton pigments. CSIRO Marine Laboratories, Report 229, Hobart, 42 pp.), a factor analysis computer program, was used to examine phytoplankton community structure using marker pigments from our HPLC analyses to determine the relative importance of various taxa. In March, diatoms dominated whole water samples, with consistent contributions from dinoflagellates and cryptophytes. The \u3c8-mum fraction was dominated by small diatoms, chrysophytes, cryptophytes and dinoflagellates. In July, diatoms were still present and important, but prymnesiophytes, cryptophytes and cyanobacteria contributed in both size classes. Correlation analyses indicated that primary production was positively correlated with light and temperature. Chl a biomass was positively correlated with the concentrations of NO2 + NO3 and negatively correlated with temperature. These correlations support the observation that temperature played a major role in the phytoplankton dynamics in this shelf ecosystem. (C) 2002 Elsevier Science Ltd. All rights reserved

Coupling Between Primary Production and Pelagic Consumption in Temperate Ocean Margin Pelagic Ecosystems

Three fates potentially consume primary production occurring on ocean margins: portions can be oxidized within the water column, portions can sediment to shelf/slope depots, and portions can be exported to the interior ocean. Zooplankton mediate all three of these processes and thus can alter the pathway and residence time of particulate organic carbon. As part of both US DOE- and NSF-sponsored studies on the Cape Hatteras and South Atlantic Bight (SAB) shelves, the role of microzooplankton in these processes was determined by measuring phytoplankton production and its consumption by microzooplankton. Grazing and growth rates were measured during 46 dilution incubation experiments using chlorophyll a (chl a) as a proxy for phytoplankton (prey) biomass. Chl a production and grazing were determined for the \u3c 200 gm phytoplankton community and also the \u3c 8 gm size class. Primary production at Cape Hatteras was determined using (HCO3-)-C-14 incubations during two Lagrangian drifter studies lasting several days in March and July 1996. From similar measurements during cross-shelf transects over larger spatial scales, primary production was also calculated for the Hatteras study area using a wavelength-resolved bio-optical model. Primary production during the Lagrangian studies was generally 0.5-1.0gC/m(2)/d in March and 0.5-2.0 gC/m(2)/d in July. Modeled estimates of primary production for the larger Hatteras study region in March and July averaged 1.8 gC/m(2)/d . Typically, \u3c 8 mum cells contributed one-half or more of primary production. Positive linear regressions described relationships between phytoplankton production measured as changes in chl a and its grazing by microzooplankton. In the dilution experiments conducted throughout the SAB and Hatteras shelves, microzooplankton grazed 65% of \u3c200 mum chl a production, and 81% of \u3c 8 mum chl a production. These relationships were temperature-dependent: losses of chl a production in both size fractions to microzooplankton herbivory increased with increasing temperature. Higher grazing rates were found in the \u3c 8 mum compared to the \u3c 200 mum size class. Model regressions were used to estimate the impact of microzooplankton grazing on (HCO3-)-C-14-derived estimates of primary production in Cape Hatteras shelf waters. Integrated water column grazing removed 40% and 58% of \u3c200 mum and \u3c8 mum primary production, respectively, during the Lagrangian experiment in March, and 61 % and 74% in July. Averaged over larger spatial scales using a bio-optical model, microzooplankton ingested 42% and 61 % of primary production in March and July, respectively, with an overall mean of 52%. These data generally support the notion that, contrary to traditional paradigms about shelf ecosystems, small autotrophs contributed significantly to production, and that this carbon was actively incorporated into the microbial food web. (C) 2002 Elsevier Science Ltd. All rights reserved

Primary Production in the Gulf of Mexico Coastal Waters Using Remotely Sensed Trophic Category Approach

Attempts to derive ocean-color based estimates of pigment and primary production in coastal waters have been complicated by the contributions of signals from non-pigment materials to the water leaving radiance. An ocean-color model to estimate primary production was evaluated for coastal waters of the northern Gulf of Mexico. The model utilizes C-sat, (mg m(-3)) (a variable that accounts for the pigment sensed by the satellite sensor), photosynthetically available radiation (PAR, J m(-2) day(-1)) and a parameter. psi* m(2) (g Chl)(-1), the water column chlorophyll specific cross-section for photosynthesis. C-sat and PAR were treated as variables while psi*; was a site-specific parameter in the model. The model uses the approach outlined in Morel and Berthon (1989) Limnology and Oceanography, 34, 1545-1562, but with site-specific statistical relationships to estimate the integrated pigment in the water column from C-sat and site-specific trophic categories (oligotrophic to eutrophic) based on pigment concentration in the water column. The statistical relationships perform extremely well within the ranges of C-sat and integral chlorophyll normally encountered in the coastal waters of the northern Gulf of Mexico. psi* varies between 0.054 and 0.063 m(2) (g Chi)(-1) and are comparable to values observed in other regions. The ability of the model to predict production using psi* within each of the trophic categories was demonstrated. The overall performance of the model has been encouraging for two reasons: (a) the possibility of estimating production from future ocean-color sensors, and (b) the fact that the model performs well in a dynamic coastal area