Robert R. L. Guillard

Bio: Robert R. L. Guillard is an academic researcher. The author has an hindex of 1, co-authored 1 publications receiving 6560 citations.

Studies of marine planktonic diatoms: i. cyclotella nana hustedt, and detonula confervacea (cleve) gran.

Abstract: Bacteria-free clones of the small centric diatom Cyclotella nana Hustedt were isolated, three from estuarine localities, one from Continental Shelf waters, and one from the Sargasso Sea. Detonula confervacea was isolated from Narragansett Bay. Morphology of all clones was studied with the light and electron microscopes. Morphological differences between clones of C. nana do not at present warrant separating any as distinct species.Clones of C. nana require only vitamin B12; D. confervacea has no vitamin requirement.Growth of the estuarine clones of C. nana was unaffected by salinity down to 0.5‰ and increased with temperature to 25 °C. The Shelf clone grew more rapidly at salinities above 8‰ and at temperatures between 10° and 20 °C. The Sargasso Sea clone did not survive below 15 °C or 17.5‰, while D. confervacea did not survive at temperatures above 15° or at salinities below 8‰. The physiological differences between clones correspond roughly to the conditions obtaining in nature where each was collected.

Culture of Phytoplankton for Feeding Marine Invertebrates

Abstract: These pages describe relatively simple and reliable methods for the culture of marine phytoplankton species useful for feeding marine invertebrates. The methods suffice for the most fastidious algae now routinely cultivable, and simplifications indicated for less demanding species are easily made; for example, omission of silicate for plants other than diatoms. Certain modifications of techniques, ancillary methods, and precautions will be treated briefly because questions often arise concerning them, but documentation will be minimal and hopefully restricted to publications readily available.

Microalgae for oil: strain selection, induction of lipid synthesis and outdoor mass cultivation in a low-cost photobioreactor.

Abstract: Thirty microalgal strains were screened in the laboratory for their biomass productivity and lipid content. Four strains (two marine and two freshwater), selected because robust, highly productive and with a relatively high lipid content, were cultivated under nitrogen deprivation in 0.6-L bubbled tubes. Only the two marine microalgae accumulated lipid under such conditions. One of them, the eustigmatophyte Nannochloropsis sp. FM102: 100–112. © 2008 Wiley Periodicals, Inc.

Temperature and phytoplankton growth in the sea

Abstract: The variation in growth rate with temperature of unicellular algae suggests that an equation can be written to describe the maximum expected growth rate for temperatures less than 40°C. Measured rates of phytoplankton growth in the sea and in lakes are reviewed and compared with maximum expected rates. The assimilation number (i.e., rate of photosynthetic carbon assimilation per weight of chlorophyll a) for phytoplankton photosynthesis is related to the growth rate and the carbon/chlorophyll a ratio in the phytoplankton. Since maximum expected growth rate can be estimated from tempera­ ture, the maximum expected assimilation number can also be estimated if the carbon/ chlorophyll a ratio in the phytoplankton crop is known. Many investigations of phytoplankton photosynthesis in the ocean have included measures of the assimilation number, while fewer data are available on growth rate. Assimilation numbers for Antarctic seas are low as would be expected from the low ambient temperatures. Tropical seas and temperate waters in summer often show low assimilation numbers as a result of low ambient nutrient concentrations. However, coastal estuaries with rapid nutrient regeneration processes show seasonal variations in the assimilation number with temperature which agree well with expectation. The variation in maximum expected growth rate with temperature seems a logical starting point for modeling phytoplankton growth and photosynthesis in the sea.

Reduced calcification of marine plankton in response to increased atmospheric CO2.

Abstract: The formation of calcareous skeletons by marine planktonic organisms and their subsequent sinking to depth generates a continuous rain of calcium carbonate to the deep ocean and underlying sediments1 This is important in regulating marine carbon cycling and ocean–atmosphere CO2 exchange2 The present rise in atmospheric CO2 levels3 causes significant changes in surface ocean pH and carbonate chemistry4 Such changes have been shown to slow down calcification in corals and coralline macroalgae5,6, but the majority of marine calcification occurs in planktonic organisms Here we report reduced calcite production at increased CO2 concentrations in monospecific cultures of two dominant marine calcifying phytoplankton species, the coccolithophorids Emiliania huxleyi and Gephyrocapsa oceanica This was accompanied by an increased proportion of malformed coccoliths and incomplete coccospheres Diminished calcification led to a reduction in the ratio of calcite precipitation to organic matter production Similar results were obtained in incubations of natural plankton assemblages from the north Pacific ocean when exposed to experimentally elevated CO2 levels We suggest that the progressive increase in atmospheric CO2 concentrations may therefore slow down the production of calcium carbonate in the surface ocean As the process of calcification releases CO2 to the atmosphere, the response observed here could potentially act as a negative feedback on atmospheric CO2 levels

Prochlorococcus, a Marine Photosynthetic Prokaryote of Global Significance

Abstract: The minute photosynthetic prokaryote Prochlorococcus, which was discovered about 10 years ago, has proven exceptional from several standpoints. Its tiny size (0.5 to 0.7 μm in diameter) makes it the smallest known photosynthetic organism. Its ubiquity within the 40°S to 40°N latitudinal band of oceans and its occurrence at high density from the surface down to depths of 200 m make it presumably the most abundant photosynthetic organism on Earth. Prochlorococcus typically divides once a day in the subsurface layer of oligotrophic areas, where it dominates the photosynthetic biomass. It also possesses a remarkable pigment complement which includes divinyl derivatives of chlorophyll a (Chl a) and Chl b, the so-called Chl a2 and Chl b2, and, in some strains, small amounts of a new type of phycoerythrin. Phylogenetically, Prochlorococcus has also proven fascinating. Recent studies suggest that it evolved from an ancestral cyanobacterium by reducing its cell and genome sizes and by recruiting a protein originally synthesized under conditions of iron depletion to build a reduced antenna system as a replacement for large phycobilisomes. Environmental constraints clearly played a predominant role in Prochlorococcus evolution. Its tiny size is an advantage for its adaptation to nutrient-deprived environments. Furthermore, genetically distinct ecotypes, with different antenna systems and ecophysiological characteristics, are present at depth and in surface waters. This vertical species variation has allowed Prochlorococcus to adapt to the natural light gradient occurring in the upper layer of oceans. The present review critically assesses the basic knowledge acquired about Prochlorococcus both in the ocean and in the laboratory.