Recently developed techniques for estimating bacterial biomass and productivity indicate that bacterial biomass in the sea is related to phytoplankton concentration and that bacteria utilise 10 to 50 % of carbon fixed by photosynthesis. Evidence is presented to suggest that numbers of free bacteria are controlled by nanoplankton~c heterotrophic flagellates which are ubiquitous in the marine water column. The flagellates in turn are preyed upon by microzooplankton. Heterotrophic flagellates and microzooplankton cover the same size range as the phytoplankton, thus providing the means for returning some energy from the 'microbial loop' to the conventional planktonic food chain.

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The Ecological Role of Water-Column Microbes in the Sea*

This book is written as a reference on organic substances in natural waters and as a supplementary text for graduate students in water chemistry. The chapters address five topics: amount, origin, nature, geochemistry, and characterization of organic carbon. Of these topics, the main themes are the amount and nature of dissolved organic carbon in natural waters (mainly fresh water, although seawater is briefly discussed). It is hoped that the reader is familiar with organic chemistry, but it is not necessary. The first part of the book is a general overview of the amount and general nature of dissolved organic carbon. Over the past 10 years there has been an exponential increase in knowledge on organic substances in water, which is the result of money directed toward the research of organic compounds, of new methods of analysis (such as gas chromatography and mass spectrometry), and most importantly, the result of more people working in this field. Because of this exponential increase in knowledge, there is a need to pull together and summarize the data that has accumulated from many disciplines over the last decade.

Organic geochemistry of natural waters

The principal objective of this study was to quantify the rate of heterotrophic bacterioplankton production. Production was estimated by two approaches: (i) measurement of increasing bacterial abundance with time in filtered (3-μm pore size) seawater and (ii) estimation of bacterial deoxyribonucleic acid synthesis by tritiated thymidine incorporation in unfractionated seawater. The two approaches yielded comparable results when used at the Controlled Ecosystem Population Experiment (Saanich Inlet, British Columbia, Canada), at McMurdo Sound (Antarctica), and off Scripps Pier (La Jolla, Calif.). Estimated bacterioplankton production was lower in Antarctic samples (ranging from ∼0 to 2.9 μg of C liter−1 day−1) than in those from the other two sites (ranging from 0.7 to 71 μg of C liter−1 day−1). In all three regions studied, it appeared that a significant fraction of the total primary production was utilized by the bacterioplankton and that substantial growth could occur in the absence of large particles. These results support the conclusion that bacterioplankton are a quantitatively important component of coastal marine food webs.

Bacterioplankton secondary production estimates for coastal waters of british columbia, antarctica, and california.

Dissolved organic matter (DOM) is the largest reservoir of reduced carbon in the oceans. The nature of DOM is poorly understood, in part, because it has been difficult to isolate sufficient amounts of representative material for analysis. Tangential-flow ultrafiltration was shown to recover milligram amounts of >1000 daltons of DOM from seawater collected at three depths in the North Pacific Ocean. These isolates represented 22 to 33 percent of the total DOM and included essentially all colloidal material. The elemental, carbohydrate, and carbon-type (by 13C nuclear magnetic resonance) compositions of the isolates indicated that the relative abundance of polysaccharides was high (∼50 percent) in surface water and decreased to ∼25 percent in deeper samples. Polysaccharides thus appear to be more abundant and reactive components of seawater DOM than has been recognized.

https://science.sciencemag.org/content/sci/255/5051/1561.full.pdf

Bulk chemical characteristics of dissolved organic matter in the ocean

The concentration, composition, and flux of dissolved organic carbon (DOC) were measured in the Hubbard Brook Valley, New Hampshire. Data on precipitation, throughfall, soil solution, streamside seeps, stream water, and lake water are presented for 1976-1980. Characterization of DOC included analysis of phenolics, monomeric and poly- meric carbohydrates, carboxylic acids, primary amines, and aldehydes. DOC concentrations increased with passage of water through the forest canopy and forest floor, decreased due to abiotic sorption in the mineral soil, and remained relatively low in most "downstream" ecosystems (streamside seeps, streams, and Mirror Lake). Average flux of DOC is estimated as 16, 47, 263, 54, 23, and 20 kg-ha-' yr-i in precip- itation, throughfall, soil solution (E, upper B, and B horizons), and streamflow, respectively. The composition of DOC, in particular the relative proportions of carbohydrates, appears to be related to the degree of biological activity at a given site in the landscape. Carbo- hydrates are particularly high in both absolute and relative terms in throughfall and lake water, which are the areas of highest photosynthetic activity within the terrestrial and aquatic ecosystems, respectively.

https://www.jstor.org/stable/pdfplus/2937024.pdf

Origin, composition, and flux of dissolved organic carbon in the hubbard

Dissolved carbohydrates in seawater. II, A spectrophotometric procedure for total carbohydrate analysis and polysaccharide estimation

Dissolved organic carbon, carbohydrates, and adenosine triphosphate in the size fractions 0.2 to 3 micrometers and 3 to 1000 micrometers are significantly enriched in the upper 150-micrometer surface layer compared to subsurface water, mean enrichment factors being 1.6, 2.0, 2.5, and 3.1, respectively. When calculated as a 0.1-micrometer microlayer of wet surfactants, the mean concentration of organic matter was 2.9 grams per liter, of which carbohydrates accounted for 28 percent. The data for plant pigments and particulate adenosine triphosphate indicated that bacterioneuston was enriched at seven of nine stations while phagotrophic protists were enriched at five stations. Instances of enrichment and inhibition were verified by cultural data for bacteria and amoebas. The observations indicate that the surface microlayers are largely heterotrophic microcosms, which can be as rich as laboratory cultures, and that an appreciable part of the dissolved organic carbon is carbohydrate of phytoplankton origin, released and brought to the surface by migrating and excreting phagotrophic protists.

Dissolved organic matter and heterotrophic microneuston in the surface microlayers of the north atlantic.

Dissolved total carbohydrate (TCHO), polysaccharide (PCHO), monosaccharide (MCHO) and organic carbon (DOC) were determined at 3-h intervals over 5 diel cycles in the mixed layer of the northwestern Caribbean Sea while following a drogued buoy. These data have been compared to populations of phototrophic (PNAN) and heterotrophic (HNAN) nanoplankton (2–20 μm diameter) and heterotrophic bacteria (HBAC) (0.2–2.0 μm diameter) estimated by epifluorescence counts, as well as to ΣCO2, phosphate, chlorophyll a and phaeopigment data determined simultaneously. Two different types of apparent diel dissolved carbohydrate (CHO) patterns were found. On 3 d when no sustained net ΣCO2 uptake was evident, TCHO and PCHO generally declined during the afternoon and early evening while MCHO tended to increase. On two other days when apparent sustained ΣCO2 uptake occurred during the day, there were large evening TCHO and PCHO peaks with constant or declining MCHO levels. These accumulations probably resulted from the release of recently produced PCHO from phototrophs. As was found earlier in the Sargasso Sea, PNAN populations were inversely related to PCHO concentrations. The sample to sample fluctuations of PNAN also were inversely related to the apparent rates of change of TCHO and PCHO, possibly due to an inverse relation between the rates of PNAN cell division and CHO excretion. Fluctuations in HBAC populations were inversely correlated with PCHO dynamics and directly related to MCHO variations, possibly due to extracellular hydrolysis of PCHO to MCHO during periods of rapid bacterial growth as well as to net heterotrophic PCHO uptake. A direct relationship between HNAN and TCHO fluctuations suggests the importance of HNAN excretion in the release of dissolved organics. The combined PNAN and HBAC fluctuations accounted for a more significant fraction of the variance in the apparent rates of change of PCHO than did any single population parameter indicating that intimate interactions between the microbial plankton groups are important in the in-situ regulation of CHO dynamics. Total system net TCHO release and uptake rates for 5 d averaged 56 and 53 μg C l-1 d-1 respectively, assuming that the observed fluctuations resulted from temporal planktonic processes in homogeneous water masses. While the data contain indications that this was the case, this assumption is not definitive.

Diel Relationships of Microbial Trophic Groups and In Situ Dissolved Carbohydrate Dynamics in the Caribbean Sea

A scheme has been developed for observing diurnal changes in dissolved organic matter in the photic zone and correlating the with specific microbial fractions and their rates of growth and uptake. Particulate ATP for procaryote and protist size fractions were augmented by pigment analyses to differentiate phototroph from phagotroph dominated accumulations. A temporary daytime increase in carbohydrates of some 32% above pre-dawn threshold values accounted for 41% of the labile DOC. Polysaccharide and monosaccharide maxima were mainly associated with phagotrophic protists, the monosaccharide maxima occurring during the daytime. Apparent maximum in situ heterotrophic uptake rates of this released DOC of 9.8 μg C L−1 hr−1 agree well with the growth rates of natural populations of the bacterial size fraction (picoplankton) on in situ water in diffusion culture of 5.1 μg C L−1 hr−1. This growth was associated with phototroph maxima but occurred only during the afternoon and evening hours and not during the early morning and intense daylight hours. Proposed follow-up studies are outlined.

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Estimation of in situ rates of heterotrophy using diurnal changes in dissolved organic matter and growth rates of picoplankton in diffusion culture

A selective and sensitive spectrophotometric assay for monosaccharide (MCHO) before and after a hydrolysis step has permitted the estimation of total carbohydrate (TCHO) and of polysaccharide (PCHO) by difference. The concentrations and diel variations of MCHO, TCHO, PCHO, and dissolved organic carbon (DOC) were estimated on some 90 samples obtained at 15 stations between Rhode Island and Spain. DOC ranged from 570 to 1330 μg C 1−1 with a mean of 940 μg C 1−1. MCHO, calculated as hexose, ranged from 65 to 356 μg 1−1 (mean 163 μg 1−1), accounting for 3.5 to 13.2% of the DOC. TCHO varied from 175 to 583 μg 1−1 (mean 348 μg 1−1), 8.0 to 24.5% of the DOC. PCHO ranged from 0 to 379 μg 1−1 (mean 184 μg 1−1), up to 16.0% of the DOC. MCHO, TCHO, and PCHO were positively correlated with DOC at the 0.01 level. PCHO as a % of TCHO decreased significantlyfrom 69% in coastal to 37% in mid-ocean samples.

The vertical distribution of the microbial plankton smaller and larger than 3 μm was determined at 12 of the stations by ATP assay on samples sequentially filtered through Nuclepore membranes. Living biomass for the bacterioplankton (0.2 to 3.0 μm) calculated from the ATP concentration ranged from 1 to 55 μg C 1−1 (approx 104 to 106 bacterial cells ml−1) and accounted for 3 to 80% of the total living biomass in the microbial plankton, averaging 30% in the photic and 40% in the aphotic zone. Vertical profiles of bacterial and protist ATP at six stations are compared with those for dissolved carbohydrates, DOC, chlorophyll a, phaeopigments, dissolved oxygen, and temperature. These include four diel drift stations in which a daylight sampling was followed by a predawn resampling on the following day. Carbohydrate peaks were often associated with accumulations of organisms in the > 3-μm size fraction, which were low in chlorophyll a, possibly indicative of collections of protozooplankton. During the day there was evidence of net release of carbohydrate at the depth of the chlorophyll a maxima at oceanic stations but not at neritic stations. Appreciable bacterioplankton maxima (0.2 to 3.0 μm ATP) occurred most often with carbohydrate minima.

Curtis M. Burney

Papers

Dissolved carbohydrates in seawater. II, A spectrophotometric procedure for total carbohydrate analysis and polysaccharide estimation

Dissolved organic matter and heterotrophic microneuston in the surface microlayers of the north atlantic.

Diel Relationships of Microbial Trophic Groups and In Situ Dissolved Carbohydrate Dynamics in the Caribbean Sea

Estimation of in situ rates of heterotrophy using diurnal changes in dissolved organic matter and growth rates of picoplankton in diffusion culture

Dissolved carbohydrate and microbial ATP in the North Atlantic: concentrations and interactions