Stn ALOHA Research Articles

Food-web fluxes support high rates of mesozooplankton respiration and production in the equatorial Pacific

We investigated how the network of food-web flows in open-ocean systems might support high rates of mesozooplankton respiration and production by comparing predicted rates from empirical relationships to independently determined solutions from an inverse model based on tightly constrained field-measured rates for the equatorial Pacific. Model results were consistent with estimates of gross:net primary production (GPP:NPP), bacterial production:NPP, sinking particulate export, and total export for the equatorial Pacific, as well as general literature values for growth efficiencies of bacteria, protozooplankton, and metazooplankton. Mean rate estimates from the model compared favorably with the respiration predictions from Ikeda (1985; Mar Biol 85:1-11) (146 vs. 144 mg C m-2 d-1, respectively) and with production estimates from the growth rate equation of Hirst & Sheader (1997; Mar Ecol Prog Ser 154:155-165) (153 vs. 144 mg C m-2 d-1). Metazooplankton nutritional requirements are met with a mixed diet of protozooplankton (39%), phytoplankton (36%), detritus (15%), and carnivory (10%). Within the food-web network, NPP of 896 mg C m-2 d-1 supports a total heterotrophic carbon demand from bacteria, protozoa, and metazooplankton that is 2.5 times higher. Scaling our results to primary production and zooplankton biomass at Stn ALOHA suggests that zooplankton nutritional requirements for high growth might similarly be met in oligotrophic subtropical waters through a less efficient trophic structure. Metazooplankton production available to higher-level consumers is a significant contributor to the total export needed for an overall biogeochemical balance of the region and to export requirements to meet carbon demand in the mesopelagic depth range.

Bacterial carbon content and the living and detrital bacterial contributions to suspended particulate organic carbon in the North Pacific Ocean

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 62:165-176 (2011) - DOI: https://doi.org/10.3354/ame01462 Bacterial carbon content and the living and detrital bacterial contributions to suspended particulate organic carbon in the North Pacific Ocean Nobuyuki Kawasaki1,2,*, Rumi Sohrin3, Hiroshi Ogawa4, Toshi Nagata4, Ronald Benner1 1University of South Carolina, Marine Science Program, Columbia, South Carolina 29208, USA 2National Institute for Environmental Studies, 16-2 Onogawa Tsukuba, Ibaraki 305-8506, Japan 3Shizuoka University, 836 Ohya Shizuoka, Shizuoka 422-8529, Japan 4Atmosphere and Ocean Research Institute, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8564, Japan *Email: kawasaki.nobuyuki@nies.go.jp ABSTRACT: Carbon-normalized yields of amino acids in size-fractionated seawater samples and bacterial cultures were used in a novel application to estimate the carbon content of heterotrophic marine bacteria. The estimated carbon content (6.3 ± 1.6 fg C cell–1) of open ocean bacteria derived using this approach was lower than most values estimated in previous studies. Based on these values, living heterotrophic bacteria accounted for 6.8 ± 1.1% of suspended particulate organic carbon (POC) in surface waters at Stn ALOHA in the North Pacific gyre. Living cyanobacteria accounted for 13.3 ± 2.2% of suspended POC in surface waters. Carbon-normalized yields of muramic acid, D-alanine and D-glutamic acid, unique biomarkers of bacteria, were used to estimate that bacterial detritus accounted for 4.3 ± 2.9% of suspended POC in surface waters. The relative contribution of bacterial detritus to suspended POC increased dramatically with increasing depth, indicating that some components of bacterial detritus are resistant to decomposition in the deep ocean. The total living and detrital bacterial contribution to suspended POC in surface waters was ~25%. KEY WORDS: Bacterial carbon content · Bacterial detritus · Bacterial biomarkers · Suspended particulate organic carbon Full text in pdf format PreviousNextCite this article as: Kawasaki N, Sohrin R, Ogawa H, Nagata T, Benner R (2011) Bacterial carbon content and the living and detrital bacterial contributions to suspended particulate organic carbon in the North Pacific Ocean. Aquat Microb Ecol 62:165-176. https://doi.org/10.3354/ame01462 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 62, No. 2. Online publication date: January 19, 2011 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 2011 Inter-Research.

Nitrogen fixation rates and controls at Stn ALOHA

Rates of dinitrogen (N 2 ) fixation were measured at Stn ALOHA in the North Pacific Subtropical Gyre (NPSG) on 9 cruises during the period April 2004 to March 2005. On each cruise, a near-surface (5 m) seawater sample was incubated with 15 N-labeled N 2 under simulated in situ conditions for 24 h prior to filtration of either whole water or <10 μm filtrate on microfine (0.7 μm nominal porosity) glass fiber filters; on 3 cruises, surface to 125 m depth profiles of size-fractionated N 2 fixation rates were also obtained. Nearly all (on average 95 %) of the net N 2 fixation in the euphotic zone occurred in the upper 75 m, and was mostly (64 ± 5 [SE]%) contained in the <10 μm size fraction following a 24 h incubation period. Highest surface diazotroph activity at this site was observed in July to August (1.63 to 1.68 μmol N m -3 d -1 ) and lowest N 2 fixation rates occurred in September to November (0.38 to 0.68 μmol N m -3 d -1 ). Vertically integrated rates of whole community N 2 fixation (measured in November, February and March) varied 5-fold (20.2 to 109 μmol N m -2 d -1 ). The short-term response of the microbial community to the addition of iron (Fe) and/or phosphorus (P) was variable, suggesting that contemporaneous N 2 fixation at Stn ALOHA may be controlled by the population dynamics of the various diazotroph species rather than by instantaneous resource limitation.

Evidence for tropical endemicity in the Deltaproteobacteria Marine Group B/SAR324 bacterioplankton clade

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 46:107-115 (2007) - doi:10.3354/ame046107 Evidence for tropical endemicity in the Deltaproteobacteria Marine Group B/SAR324 bacterioplankton clade Mark V. Brown1,2,*, Stuart P. Donachie2 1NASA Astrobiology Institute, PSB211, 2565 McCarthy Mall, and 2Department of Microbiology, Snyder Hall, 2538 McCarthy Mall, University of Hawaii, Honolulu, Hawaii 96822, USA *Email: mbrown@ifa.hawaii.edu ABSTRACT: The fine-scale phylogeny of the deeply branching Deltaproteobacteria Marine Group B/SAR324 (MGB/SAR324) bacterioplankton clade was analyzed using partial 16S rRNA gene sequence and internal transcribed spacer (ITS) sequences. Both sets of analyses revealed considerable sequence variation, which, along with bootstrap calculations, strongly support the discrimination of 3 ‘species’ level clusters (i.e. displaying <98% within-cluster and >97% between-cluster 16S rRNA gene sequence identity) within this clade, which are here designated as MGB/SAR324 clade groups I and II and the MGB/SAR276 clade. The biogeographical ranges of these 3 clades were analyzed using newly acquired 16S and ITS sequences from Stn ALOHA (22.45°N, 158°W), along with sequences available in the public domain. MGB/SAR324 clade group I and the MBG/SAR276 clade display a clearly restricted distribution, occurring only in tropical and subtropical waters at depths <250 m. These groups represent the first reported species- and genus-level phylotypes displaying a ‘tropical-only’ global distribution. MGB/SAR324 clade group II, which has been previously described as ubiquitous, occurs across the latitudinal gradient, but is generally restricted to deep, colder waters in the lower latitudes. Enzyme sequences associated at least with MGB/SAR324 clade group II appear to indicate a role for this group in dissolved organic phosphate cycling. KEY WORDS: Marine Group B · SAR324 · Biogeography · Internal transcribed spacer · ITS Full text in pdf format NextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 46, No. 2. Online publication date: February 02, 2007 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 2007 Inter-Research.

Temporal and vertical dynamics in picoplankton photoheterotrophic production in the subtropical North Pacific Ocean

Heterotrophic microbial production is a fundamental determinant in the flow of bio-elements and energy within the pelagic ecosystems of the open ocean. To characterize the temporal dynamics in rates of heterotrophic picoplankton production (HPP), we examined vertical profiles of 3 H-leucine ( 3 H-leu) and [methyl- 3 H]-thymidine ( 3 H-TdR) incorporation at Stn ALOHA (22°45'N, 158° W) in the oligotrophic North Pacific Ocean. Euphotic zone rates of 3 H-leu and 3 H-TdR incorporation were measured in situ under light and dark conditions on cruises to Stn ALOHA between April 2000 and August 2005. Rates of 3 H-leu and 3 H-TdR incorporation were elevated in the well-lit upper euphotic zone ( 0.05). Both 3 H-leu and 3 H-TdR displayed similar temporal variability, but neither proxy for HPP was correlated to measured rates of primary production. These observations provide the first examination of the temporal dynamics in HPP at Stn ALOHA, and lend insight into the potential importance of photoheterotrophic growth by Prochlorococcus spp. Although organic matter utilization by Prochlorococcus spp. has been documented previously, this is the first study to evaluate their potential role in secondary production of the oceanic ecosystem.

Concentration, production and turnover of viruses and dissolved DNA pools at Stn ALOHA, North Pacific Subtropical Gyre

The concentrations, production rates and turnover times of the components of the dissolved DNA (D-DNA) pool, including viruses, were investigated in a depth profile at Stn ALOHA in the North Pacific Subtropical Gyre. A recently developed centrifugal concentration method was used to quantify the 3 major components of the D-DNA pool: free or enzymatically-hydrolyzable D-DNA (ehD-DNA), D-DNA within viruses and uncharacterized bound D-DNA. The production rates of each of these components of the D-DNA pool were estimated using a dilution technique and the turnover times of each component were calculated. Concentrations of total D-DNA and ehD-DNA were approximately 1.2 and 0.6 ng ml -1 , respectively, throughout the mixed layer (upper 100 m), and decreased with increasing depth to 0.2 and 0.06 ng ml -1 at 500 m, resulting in ehD-DNA constituting 27 to 51 % of the total D-DNA pool. Concentrations of viruses ranged from 0.9 to 1.0 x 10 7 ml -1 within the mixed layer and also decreased with increasing depth to 0.2 x 10 7 ml -1 at 500 m. The average mass of DNA per viral genome was estimated at each depth with viral genome fingerprinting, and ranged from 62.5 to 69.8 ag DNA per virus. Multiplying the concentration of viruses by the average mass of DNA per virus at each depth revealed the concentration of D-DNA within viruses, which ranged from 0.13 to 0.68 ng ml -1 and constituted 49 to 63 % of the total D-DNA pool. There was no measurable concentration of uncharacterized bound D-DNA in the depth profile. The production rates of ehD-DNA and D-DNA within viruses ranged from 0.10 to 0.41 and 0.03 to 0.07 ng ml -1 h -1 , respectively, within the mixed layer, but no production of D-DNA could be measured below the mixed layer. The calculated turnover times of ehD-DNA ranged from 0.97 to 6.2 h within the mixed layer and were 3 to 10 times shorter than the turnover times of D-DNA within viruses, which ranged from 9.6 to 24 h. In addition, the amount of phosphorus that was calculated to be produced within the ehD-DNA was able to support the biologically available phosphorus (BAP) demand, based on previously reported measurements of BAP uptake at Stn ALOHA. Using the measured virus production rates, viruses were estimated to lyse 3.2 to 16.5% of the standing stock of bacteria at Stn ALOHA h -1 , resulting in the release of ehD-DNA, which was estimated as 11 to 35 % of the total ehD-DNA production. This research supports the hypothesis that individual components of the D-DNA pool are cycled at different rates and shows that viruses in open-ocean gyre systems may have large impacts on the microbial community there, including viral-induced mortality and subsequent release of cellular contents to the dissolved organic matter pool.

Vertical distributions of nitrogen-fixing phylotypes at Stn Aloha in the oligotrophic North Pacific Ocean

In large areas of the world's oceans, biological dinitrogen (N 2 ) fixation supports a significant fraction of ecosystem productivity; to date, however, there is little information on the abundances of specific diazotrophs in the ocean. In this study, the vertical distributions of several different groups of N 2 -fixing bacteria were examined using quantitative polymerase chain reaction (QPCR) amplification of group-specific dinitrogenase reductase (nifH) genes from Stn ALOHA in the subtropical North Pacific Ocean. Depth distributions ( 700 μmol quanta m -2 s -1 ), nitrate-depleted ( 100 m). These results revealed differences in the depth distributions of N 2 -fixing plankton at Stn ALOHA, and suggest that unicellular diazotrophs comprise a significant component of plankton biomass in this oligotrophic marine ecosystem.

Presence of dissolved nucleotides in the North Pacific Subtropical Gyre and their role in cycling of dissolved organic phosphorus

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 39:193-203 (2005) - doi:10.3354/ame039193 Presence of dissolved nucleotides in the North Pacific Subtropical Gyre and their role in cycling of dissolved organic phosphorus Karin M. Björkman*, David M. Karl Department of Oceanography, SOEST, University of Hawaii, Honolulu, Hawaii 96 822, USA *Email: bjorkman@hawaii.edu ABSTRACT: Dissolved and particulate nucleotide triphosphate (NTP) concentrations were measured in the upper 1000 m of the water column during 3 summer and 3 winter months at Stn ALOHA (22.75°N, 158°W) in the oligotrophic North Pacific Subtropical Gyre. In the euphotic zone (0 to 175 m) particulate adenosine-5’-triphosphate (P-ATP) and dissolved ATP (D-ATP) concentrations were positively correlated in summer (0 to 175 m; r2 = 0.61, p < 0.001, n = 24), but not in winter (r2 =0.02, n = 24). D-ATP comprised >65% of the total ATP (T-ATP) pool in the summer, and ~50% in winter. Dissolved guanosine-5’-triphosphate (D-GTP) inventories were 5- to 6-fold greater in July and August than those observed in mid-June (1.1 ± 0.1 vs. 8.0 ± 0.6 and 6.5 ± 0.3 µmol D-GTP m–2, respectively) and winter concentrations were on average lower than the mean summer concentrations. The particulate GTP (P-GTP) inventories were almost twice those measured in winter (mean 1.1 ± 0.4 in summer vs. 0.6 ± 0.1 µmol P-GTP m–2 in winter, n = 3). These results are consistent with higher microbial growth rates in summer. Uptake of D-ATP showed multi-phasic kinetic patterns. The halfsaturation constants (Kt) ranged from 1 to 26 nM at D-ATP concentrations of 0.2 to 30 nM, and Vmax ranged from 0.3 to 1.4 nM d–1. At concentrations >30 nM, Kt exceeded 100 nM and Vmax was 10.4 nM d–1. The calculated net production rates of D-ATP ranged from 40 to 150 pM d–1, and the turnover time of the ambient D-ATP pool was estimated to be 1 to 2 d. The P flux through the D-ATP pool could potentially be 5 times faster than that of the bulk DOP pool, implying that P derived from nucleotides may be an important pathway in the P cycle of oligotrophic oceans. KEY WORDS: North Pacific · ATP · GTP · Nucleotides · DOM · Microbial ecology Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 39, No. 2. Online publication date: May 30, 2005 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 2005 Inter-Research.

Bacteria-flagellate interactions in the microbial food web of the oligotrophic subtropical North Pacific

The number and relative strengths of trophic linkages in the microbial community of the oligotrophic subtropical North Pacific were studied in 12 experiments from August 1998 to April 1999 at Stn ALOHA (100 km north of Oahu, Hawaii). Collected seawater was manipulated by sequential size-fractionation to truncate the food web at different organism sizes (1, 2, 5, 10 and 20 µm), and the response variable, net bacterial growth rate, was assessed from flow cytometric analyses of the changes in cell abundance (combined heterotrophic bacteria and Prochlorococcus) after 24 h incuba- tions. The corresponding size structure of the protistan grazer assemblage was measured microscop- ically. With a coefficient of variability of 7% and a 2-fold range overall, total bacterial abundance dis- played relatively low temporal variability. Despite the relative constancy of standing stock, however, microbial community interactions varied markedly among the experiments. For experiments con- ducted at higher levels of bacterial biomass, the bacteria showed little growth response to the removal of predators and may have been resource limited. In contrast, the growth response was high- est when conditions were defined by relatively low bacterial biomass and high heterotrophic flagel- late biomass. Trophic cascades were evident only at intermediate to high levels of bacterial biomass, and may appear in transitions between high and low levels of bacterial biomass. These results sug- gest that resources and predators oscillate in importance in regulating open-ocean microbial popula- tions. In such oscillations, the indirect influences of a protistan predatory chain may determine the balance between resource limitation and strong predatory control.

Role of Trichodesmium spp. in the productivity of the subtropical North Pacific Ocean

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 133:263-273 (1996) - doi:10.3354/meps133263 Role of Trichodesmium spp. in the productivity of the subtropical North Pacific Ocean Letelier RM, Karl DM The concentrations of filamentous diazotroph Trichodesmium spp., present as free trichomes and in colonial assemblages, were measured at approximately monthly intervals at Stn ALOHA (22*45'N, 158*00'W) between October 1989 and December 1992. The average abundance of filaments in the upper 45 m of the water column was highly variable ranging from 1.1 to 7.4 x 104 trichomes m-3 and from 0.02 to 1.4 x 102 colonies m-3. Colonies were composed, on average, of 182 filaments accounting for 12% of total (free filament plus colonies) Trichodesmium biomass. Low densities of single trichomes were associated with, but not restricted to, deep mixing events and winter periods. During 1991 and 1992 the concentration of Trichodesmium spp. present in the water column increased relative to the pre 1991 observations. This increase coincided with increases in photosynthetic carbon assimilation and in the molar ratio of N:P of suspended particulate matter in the upper 45 m of the water column. However, the change in Trichodesmium biomass alone does not account for the change observed in autotrophic carbon assimilation and elemental biomass composition. Trichodesmium spp. comprised, on average, 18% of the chlorophyll a, 4% of the photosynthetic carbon assimilation, 10% of the particulate nitrogen and 5% of the particulate phosphorus. We also estimate that Trichodesmium dinitrogen fixation accounted for, on average, at least 27% of the new production at this study site. These observations, combined with primary production experiments conducted on isolated colonies, suggest that phytoplankton production is enhanced due to the release of NH4+ and dissolved organic nitrogen by Trichodesmium spp. during episodes of nitrogen fixation. Trichodesmium . Nitrogen fixation . Nutrients . Productivity . Time-series Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 133. Publication date: March 28, 1996 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1996 Inter-Research.