Ultrahigh bacterial production in a eutrophic subtropical Australian river : does viral lysis short-circuit the microbial loop?

Author Posting. © American Society of Limnology and Oceanography, 2011. This article is posted here by permission of American Society of Limnology and Oceanography for personal use, not for redistribution. The definitive version was published in Limnology and Oceanography 56 (2011): 1115-1129, doi:10.4319/lo.2011.56.3.1115.We studied trophic dynamics in a warm eutrophic subtropical river (Bremer River, Australia) to determine potential sources of dissolved organic carbon (DOC) and the fate of heterotrophic bacterial production. Sustained high rates of bacterial production suggested that the exogenous DOC was accessible (labile). Bacterial specific growth rates (0.2 h−1 to 1.8 h−1) were some of the highest measured for natural aquatic ecosystems, which is consistent with high respiration rates. Bacteria consumed 10 times more organic carbon than that supplied by the daily algal production, a result that implies that terrestrial sources of organic carbon were driving the high rates of bacterial production. Viruses (1011 L−1) were 10 times more abundant than bacteria; the viral to bacterial ratio ranged from 3.5 to 12 in the wet summer and 11 to 35 in the dry spring weather typical of eutrophic environments. Through a combination of high bacterial respiration and phage lysis, a continuous supply of terrestrial DOC was lost from the aquatic ecosystem in a CO2-vented bacterial–viral loop. Bacterial processing of DOC in subtropical rivers may be contributing disproportionately large amounts of CO2 to the global carbon cycle compared to temperate freshwater ecosystems.Thanks go to the Coastal Cooperative Research Centre and the Healthy Waterways Partnership for their funding

Concentrations and uptake of neutral monosaccharides along 14°W in the equatorial Pacific: Contribution of glucose to heterotrophic bacterial activity and the DOM flux

We examined concentrations and uptake of dissolved neutral monosaccharides (DNMS) in order to determine the contribution of DNMS to heterotrophic bacterial production and to the flux of dissolved organic matler (DOM) in the equatorial Pacific. DNMS concentrations were greater during El Niño‐affected months of February–April 1992 than during August–October 1992; in contrast, glucose turnover was the opposite— turnover was faster in August–October than in February–April. The variation in sugar concentrations and turnover probably resulted from El Niño‐induced changes in primary production; as El Niño waned primary production increased, which appeared to stimulate bacterial activity, especially glucose turnover, that in turn forced down DNMS concentrations. In all months, however, DNMS concentrations were low, especially compared with total dissolved organic carbon concentrations (\u3c1%). Glucose was the dominant neutral monosaccharide and alone supported 15–47% of bacterial production. Other monosaccharides apparently did not support much bacterial growth; concentrations of other sugars were low, as probably was turnover. Respiration of glucose (30–60% of uptake) and mannose (60–90%) was relatively high, suggesting that DNMS supported a large fraction of bacterial respiration as well as biomass production. These results point to the importance of DNMS and glucose in particular in supporting bacterial growth and in contributing to the flux of labile DOM

The microbial loop concept: A history, 1930–1974

The microbial loop as a leading concept in marine microbiology gained wide recognition in the 1980s, but it has roots extending back to the 1930s when microbiologists first began to take a more dynamic approach to investigating the roles of bacteria in ocean food webs and biogeochemical cycles. Here we present a history of the microbial loop concept with emphasis on the period starting in 1930, when marine bacteriologists in Russia and the West began to study explicitly the roles of marine bacteria in the sea. Selman Waksman at Woods Hole and Claude ZoBell at La Jolla relied on colony counts on agar plates as the basis of their work. We suggest that failure to accept direct microscopic evidence of high numbers of bacteria in seawater retarded conceptual development in the West well into the 1970s. Easterners pioneered direct count and radioisotopic techniques and created a dynamic marine microbiology integrating bacteria as important components of marine food webs by the 1960s. Yurii Sorokin and colleagues carried out extensive experimental studies of bacteria as food for marine grazers and provided data for Mikhail Vinogradov and his group to write the first numerical simulation models of ocean ecosystems incorporating microbial components. It had little impact on the Western modeling community, as other Russian work of the times. In spite of continuing technical shortcomings in the field, Lawrence Pomeroy constructed a new conceptual model, providing a synthesis pointing the way toward a modern view of marine microbial ecology that finally matured technically and conceptually in the West in the early 1980s

Introduction to the special issue on Antarctic oceanography in a changing world

Author Posting. © The Oceanography Society, 2012. This article is posted here by permission of The Oceanography Society for personal use, not for redistribution. The definitive version was published in Oceanography 25, no. 3 (2012): 14-17, doi:10.5670/oceanog.2012.68."Antarctic Oceanography in a Changing World" commemorates the twentieth anniversary of the commissioning of Research Vessel Icebreaker (RVIB) Nathaniel B. Palmer and the fifteenth anniversary of Antarctic Research and Supply Vessel (ARSV) Laurence M. Gould. The addition of these two Antarctic research vessels to the US fleet in the 1990s ushered in a new era of Antarctic oceanographic research for US scientists and their international collaborators. Although several US Coast Guard icebreakers in the Arctic and Antarctic waters conduct oceanographic research, their primary mission is icebreaking to facilitate access to land-based stations. The Palmer was, and remains to this day, the first and only purpose-built US research icebreaker in Antarctic service and has been serving sea-going scientists in all areas of Antarctica's seas for two decades. The Gould has afforded reliable year-round access to Palmer Station and has conducted oceanographic research in the Antarctic Peninsula area since 1997

Long-term studies of the marine ecosystem along the west Antarctic Peninsula

Author Posting. © The Author(s), 2008. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Deep Sea Research Part II: Topical Studies in Oceanography 55 (2008): 1945-1948, doi:10.1016/j.dsr2.2008.05.014.Articles in this volume focus on longer-term studies of the marine ecosystem of the continental shelf west of the Antarctic Peninsula, principally by the Palmer, Antarctica Long- Term Ecological Research project (Ross et al., 1996; Ducklow et al., 2007). There is a rich history of oceanographic and ecological research in the Bellingshausen Sea region and on the continental shelf dating back to the 19th and early 20th centuries (El-Sayed, 1996). The modern era of scientific research started with the British Discovery Investigations of 1925-37 (Hardy, 1967), and included classic studies of phytoplankton (Hart, 1934) and krill (Marr, 1962). Hart’s report presciently suggested primary producers could be limited by iron availability. El-Sayed (1996) dissects the subsequent history of oceanographic research up to the advent of the Southern Ocean GLOBEC (Hofmann et al., 2001; Hofmann et al., 2004) and JGOFS (Anderson and Smith Jr., 2001) programs. The period from the 1970’s to the mid-90’s was dominated by expeditionary and process-level studies of particular regions and processes extending over a few seasons to a few years at most. The Research on Antarctic Coastal Ecosystem Rates (RACER) Program (Huntley et al., 1991; Karl, 1991) is the outstanding example of this mode of research, having focused on determination of key rate processes as a new approach to understanding ecosystem dynamics (Karl et al., 1991a; Karl et al., 1991b). RACER was a direct predecessor and major influence on Palmer LTER, GLOBEC and JGOFS. What was lacking in Antarctic waters, as in most other regions and ocean provinces were sustained, long-term observations of a variety of ocean properties and rates, conducted in the context of hypothesis-driven, experimental science (Ducklow et al., 2008a). The creation of the US LTER Network in 1980 (Magnuson, 1990) made this possible.Observations reported in this volume were supported by NSF Grants OPP-90-11927 and OPP- 96-32763 to the University of California-Santa Barbara and OPP-02-17282 to the Virginia Institute of Marine Science

Organic carbon partitioning during spring phytoplankton blooms in the Ross Sea polynya and the Sargasso Sea

In this study we evaluate the partitioning of organic carbon between the particulate and dissolved pools during spring phytoplankton blooms in the Ross Sea, Antarctica, and the Sargasso Sea. As part of a multidisciplinary project in the Ross Sea polynya we investigated the dynamics of the dissolved organic carbon (DOC) pool and the role it played in the carbon cycle during the 1994 spring phytoplankton bloom. Phytoplankton biomass during the bloom was dominated by an Antarctic Phaeocystis sp. We determined primary productivity (PP; via H14CO3, incubations), particulate organic carbon (POC), bacterial productivity (BP; via [3H]thymidine incorporation), and DOC during two occupations of 76°30′S from 175°W to 168°E. Results from this bloom are compared to blooms observed in the Sargasso Sea in the vicinity of the Bermuda Atlantic Time‐Series Study station (BATS). We present data that demonstrate clear differences in the production, biolability, and accumulation of DOC between the two ocean regions. Despite four‐ to fivefold greater PP in the Ross Sea, almost an order of magnitude less DOC (mmol m−2) accumulated during the Ross Sea bloom compared to the Sargasso Sea blooms. In the Ross Sea 89% (˜1 mol C m−2) of the total organic carbon (TOC) that accumulated during the bloom was partitioned as POC, with the remaining 11% (˜0.1 mol C m−2) partitioned as DOC. In contrast, a mean of 86% (0.7.5–1.0 mol m−2) of TOC accumulated as DOC during the 1992, 1993, and 1995 blooms in the Sargasso Sea, with as little as 14% (0.08–0.29 mol C m−2) accumulating as POC. Although a relatively small portion of the fixed carbon was produced as DOC in the Ross Sea, the bacterial carbon demand indicated that a qualitatively more labile carbon was produced in the Ross Sea compared to the Sargasso Sea. There are fundamental differences in organic carbon partitioning between the two systems that may be controlled by plankton community structure and food‐web dynamics

What is the metabolic state of the oligotrophic ocean? A debate

Author Posting. © The Author(s), 2012. This is the author's version of the work. It is posted here by permission of Annual Reviews for personal use, not for redistribution. The definitive version was published in Annual Review of Marine Science 5 (2013):525-533, doi:10.1146/annurev-marine-121211-172331.For more than a decade there has been controversy in oceanography regarding the metabolic state of the oligotrophic gyres of the open sea. Here we review background on this controversy, commenting on several issues to set the context for a moderated debate between two groups of scientists. In a companion paper, Williams et al (2013) take the view that the oligotrophic subtropical gyres of the global ocean exhibit a state of net autotrophy, that is, the gross primary production (GPP) exceeds community respiration (R), when averaged over some suitably extensive region and over a long duration. Duarte et al (2013) take the opposite view, that the oligotrophic subtropical gyres are net heterotrophic, with R exceeding the GPP. This idea -- that large, remote areas of the upper ocean could be net heterotrophic raises of host of fundamental scientific questions about the metabolic processes of photosynthesis and respiration that underlie ocean ecology and global biogeochemistry. The question remains unresolved, in part, because the net state is finely balanced between large opposing fluxes and most current measurements have large uncertainties. This challenging question must be studied against the background of large, anthropogenically-driven changes in ocean ecology and biogeochemistry Current trends of anthropogenic change make it an urgent problem to solve and also greatly complicate finding that solution.The authors acknowledge support from the U.S. National Science Foundation through the Center for Microbial Oceanography Research and Education (C-MORE), an NSF Science and Technology Center (EF-0424599), and NSF award OPP 0823101 (Palmer LTER) from the Antarctic Organisms and Ecosystems Program

Seasonal succession of free-living bacterial communities in coastal waters of the Western Antarctic Peninsula

© The Author(s), 2016. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Frontiers in Microbiology 7 (2016): 1731, doi: 10.3389/fmicb.2016.01731.The marine ecosystem along the Western Antarctic Peninsula undergoes a dramatic seasonal transition every spring, from almost total darkness to almost continuous sunlight, resulting in a cascade of environmental changes, including phytoplankton blooms that support a highly productive food web. Despite having important implications for the movement of energy and materials through this ecosystem, little is known about how these changes impact bacterial succession in this region. Using 16S rRNA gene amplicon sequencing, we measured changes in free-living bacterial community composition and richness during a 9-month period that spanned winter to the end of summer. Chlorophyll a concentrations were relatively low until summer when a major phytoplankton bloom occurred, followed 3 weeks later by a high peak in bacterial production. Richness in bacterial communities varied between ~1,200 and 1,800 observed operational taxonomic units (OTUs) before the major phytoplankton bloom (out of ~43,000 sequences per sample). During peak bacterial production, OTU richness decreased to ~700 OTUs. The significant decrease in OTU richness only lasted a few weeks, after which time OTU richness increased again as bacterial production declined toward pre-bloom levels. OTU richness was negatively correlated with bacterial production and chlorophyll a concentrations. Unlike the temporal pattern in OTU richness, community composition changed from winter to spring, prior to onset of the summer phytoplankton bloom. Community composition continued to change during the phytoplankton bloom, with increased relative abundance of several taxa associated with phytoplankton blooms, particularly Polaribacter. Bacterial community composition began to revert toward pre-bloom conditions as bacterial production declined. Overall, our findings clearly demonstrate the temporal relationship between phytoplankton blooms and seasonal succession in bacterial growth and community composition. Our study highlights the importance of high-resolution time series sampling, especially during the relatively under-sampled Antarctic winter and spring, which enabled us to discover seasonal changes in bacterial community composition that preceded the summertime phytoplankton bloom.CL was partially funded by the Graduate School and the Department of Ecology and Evolutionary Biology at Brown University and the Brown University-Marine Biological Laboratory Joint Graduate Program. This material is based upon work supported by the National Science Foundation under Grant Nos. ANT-1142114 to LA-Z, OPP-0823101 and PLR-1440435 to HD, and ANT-1141993 to JR

Assessing sources and ages of organic matter supporting river and estuarine bacterial production: A multiple-isotope (D14C, d13C, and d15N) approach

We used radiocarbon (D14C) and stable isotopic (d13C, d15N) signatures of bacterial nucleic acids to estimate the sources and ages of organic matter (OM) assimilated by bacteria in the Hudson River and York River estuary. Dualisotope plots of D14C and d13C coupled with a three-source mixing model resolved the major OM sources supporting bacterial biomass production (BBP). However, overlap in the stable isotopic (d13C and d15N) values of potential source end members (i.e., terrestrial, freshwater phytoplankton, and marsh-derived) prohibited unequivocal source assignments for certain samples. In freshwater regions of the York, terrigenous material of relatively recent origin (i.e., decadal in age) accounted for the majority of OM assimilated by bacteria (49–83%). Marsh and freshwater planktonic material made up the other major source of OM, with 5–33% and 6–25% assimilated, respectively. In the mesohaline York, BBP was supported primarily by estuarine phytoplankton–derived OM during spring and summer (53–87%) and by marsh-derived OM during fall (as much as 83%). Isotopic signatures from higher salinity regions of the York suggested that BBP there was fueled predominantly by either estuarine phytoplankton-derived OM (July and November) or by material advected in from the Chesapeake Bay proper (October). In contrast to the York, BBP in the Hudson River estuary was subsidized by a greater portion (up to ;25%) of old (;24,000 yr BP) allochthonous OM, which was presumably derived from soils. These findings collectively suggest that bacterial metabolism and degradation in rivers and estuaries may profoundly alter the mean composition and age of OM during transport within these systems and before its export to the coastal ocean