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The influence of ocean acidification in deep-sea ecosystems is poorly understood but is expected to be large because of the presumed low tolerance of deep-sea taxa to environmental change. We used a newly developed deep-sea free ocean CO2 enrichment (dp-FOCE) system to evaluate the potential consequences of future ocean acidification on the feeding behavior of a deep-sea echinoid, the sea urchin, Strongylocentrotus fragilis. The dp-FOCE system simulated future ocean acidification inside an experimental enclosure where observations of feeding behavior were performed. We measured the average movement (speed) of urchins as well as the time required (foraging time) for S. fragilis to approach its preferred food (giant kelp) in the dp-FOCE chamber (-0.46 pH units) and a control chamber (ambient pH). Measurements were performed during each of 4 trials (days -2, 2, 24, 27 after CO2 injection) during the month-long period when groups of urchins were continuously exposed to low pH or control conditions. Although urchin speed did not vary significantly in relation to pH or time exposed, foraging time was significantly longer for urchins in the low-pH treatment. This first deep-sea FOCE experiment demonstrated the utility of the FOCE system approach and suggests that the chemosensory behavior of a deep-sea urchin may be impaired by ocean acidification.

Carrying assorted cargo and covered with paints of varying toxicity, lost intermodal containers may take centuries to degrade on the deep seafloor. In June 2004, scientists from Monterey Bay Aquarium Research Institute (MBARI) discovered a recently lost container during a Remotely Operated Vehicle (ROV) dive on a sediment-covered seabed at 1281 m depth in Monterey Bay National Marine Sanctuary (MBNMS). The site was revisited by ROV in March 2011. Analyses of sediment samples and high-definition video indicate that faunal assemblages on the container’s exterior and the seabed within 10 m of the container differed significantly from those up to 500 m. The container surface provides hard substratum for colonization by taxa typically found in rocky habitats. However, some key taxa that dominate rocky areas were absent or rare on the container, perhaps related to its potential toxicity or limited time for colonization and growth. Ecological effects appear to be restricted to the container surface and the benthos within ∼10 m.

Anthropogenic CO 2 is now reaching depths over 1000 m in the Eastern Pacific, overlapping the Oxygen Minimum Zone (OMZ). Deep-sea animals are suspected to be especially sensitive to environmental acidification associated with global climate change. We have investigated the effects of elevated p CO 2 and variable O 2 on the deep-sea urchin Strongylocentrotus fragilis , a species whose range of 200–1200 m depth includes the OMZ and spans a p CO 2 range of approx. 600–1200 μatm (approx. pH 7.6 to 7.8). Individuals were evaluated during two exposure experiments (1-month and 4 month) at control and three levels of elevated p CO 2 at in situ O 2 levels of approx. 10% air saturation. A treatment of control p CO 2 at 100% air saturation was also included in experiment two. During the first experiment, perivisceral coelomic fluid (PCF) acid-base balance was investigated during a one-month exposure; results show S. fragilis has limited ability to compensate for the respiratory acidosis brought on by elevated p CO 2 , due in part to low non-bicarbonate PCF buffering capacity. During the second experiment, individuals were separated into fed and fasted experimental groups, and longer-term effects of elevated p CO 2 and variable O 2 on righting time, feeding, growth, and gonadosomatic index (GSI) were investigated for both groups. Results suggest that the acidosis found during experiment one does not directly correlate with adverse effects during exposure to realistic future p CO 2 levels.

Sulfide oxidizing bacterial mats are common in regions of the continental shelves characterized by high primary production and the resultant oxygen minimum zone. These mats are made up of several species of Beggiatoa and/or Thioploca, which oxidize sulfide that is generated in the sediment. Thioploca spp. inhabit a large polysaccharide sheath that encompasses bundles of 1–20 filaments (trichomes), each ranging from 3 to 60 μm in diameter. This sheath has been shown to be a critical component of the autecology of Thioploca. Analysis of Thioploca from cold seeps in Monterey Bay using light and transmission electron microscopy identified new and diverse microbial assemblages associated with interstitial spaces between trichomes, inside the sheath. Small diameter, non-vacuolate, filamentous prokaryotes were numerous. Amoebae, euglenozoa, ciliates and other protists of unknown affiliation were observed in sheaths. Most of the protists possessed food vacuoles and some protists showed ultrastructural evidence of endosymbionts. These observations suggest that Thioploca sheaths may serve as oases on the sea floor, providing nutritional and detoxification services to previously unrecognized microbial partners.

The effects of low-pH, high-pCO2 conditions on deep-sea organisms were examined during four deep-sea CO2 release experiments simulating deep-ocean C sequestration by the direct injection of CO2 into the deep sea. We examined the survival of common deep-sea, benthic organisms (microbes; macrofauna, dominated by Polychaeta, Nematoda, Crustacea, Mollusca; megafauna, Echinodermata, Mollusca, Pisces) exposed to low-pH waters emanating as a dissolution plume from pools of liquid carbon dioxide released on the seabed during four abyssal CO2-release experiments. Microbial abundance in deep-sea sediments was unchanged in one experiment, but increased under environmental hypercapnia during another, where the microbial assemblage may have benefited indirectly from the negative impact of low-pH conditions on other taxa. Lower abyssal metazoans exhibited low survival rates near CO2 pools. No urchins or holothurians survived during 30–42 days of exposure to episodic, but severe environmental hypercapnia during one experiment (E1; pH reduced by as much as ca. 1.4 units). These large pH reductions also caused 75% mortality for the deep-sea amphipod, Haploops lodo, near CO2 pools. Survival under smaller pH reductions (ΔpHo0.4 units) in other experiments (E2, E3, E5) was higher for all taxa, including echinoderms. Gastropods, cephalopods, and fish were more tolerant than most other taxa. The gastropod Retimohnia sp. and octopus Benthoctopus sp. survived exposure to pH reductions that episodically reached −0.3 pH units. Ninety percent of abyssal zoarcids (Pachycara bulbiceps) survived exposure to pH changes reaching ca. −0.3 pH units during 30–42 day-long experiments.

Sequestration of carbon dioxide (CO2) in the ocean is being considered as a feasible mechanism to mitigate the alarming rate in its atmospheric rise. Little is known, however, about how the resulting hypercapnia and ocean acidification may affect marine fauna. In an effort to understand better the protistan reaction to such an environmental perturbation, the survivorship of benthic foraminifera, which is a prevalent group of protists, was studied in response to deep-sea CO2 release. The survival response of calcareous, agglutinated, and thecate foraminifera was determined in two experiments at ~3.1 and 3.3 km water depth in Monterey Bay (California, USA). Approximately five weeks after initial seafloor CO2 release, in situ incubations of the live-dead indicator CellTracker Green were executed within seafloor-emplaced pushcores. Experimental treatments included direct exposure to CO2 hydrate, two levels of lesser exposure adjacent to CO2 hydrate, and controls, which were far removed from the CO2 hydrate release. Results indicate that survivorship rates of agglutinated and thecate foraminifera were not significantly impacted by direct exposure but the survivorship of calcareous foraminifera was significantly lower in direct exposure treatments compared to controls. Observations suggest that, if large scale CO2 sequestration is enacted on the deep-sea floor, survival ofmore » two major groups of this prevalent protistan taxon will likely not be severely impacted, while calcareous foraminifera will face considerable challenges to maintain their benthic populations in areas directly exposed to CO2 hydrate.« less

A significant amount of the primary production in the Southern Ocean and other ice-covered oceans takes place in localized ice edge plankton blooms. The dynamics of these blooms appear to be closely related to seasonal melting of sea ice. Algal cells released from the ice are a possible source of ice edge planktonic assemblages, but evidence for this “seeding” has been equivocal. We compared algal assemblages in ice and water in the Weddell Sea during the austral spring of 1983 at a receding ice edge with a well-developed ice edge bloom. The high degree of similarity between ice and water column assemblages, the spatial and temporal patterns in the distribution and abundances of species, and preliminary evidence for the viability and growth of ice-associated species provide evidence for seeding from sea ice of some species in Antarctica.

Bathymodiolus platifrons, a chemosynthetic mussel from cold seeps off Japan, relies for its nutrition on the productivity of methylotrophic or methanotrophic endosymbionts. High densities of bacterial symbionts appearing to be type I methanotrophs were observed in transmission electron micrographs of gill tissues. Methanol dehydrogenase activity in gill tissue from a single individual was positive compared to non-methanotrophic control samples, indicating a high potential for methanotrophy. Stable isotopic ratios of carbon in symbiont-containing gill tissue, as well as host tissues, were extremely depleted in 13C, and similar to values reported for other methanotrophic species. TEMs of gill tissue showing symbionts in various stages of digestion support the hypothesis that carbon transfer from symbionts to B. platifrons occurs through intracellular digestion of the symbionts. Discovery of methane- or methanolbased symbioses in B. platifrons from cold seeps in Sagami Bay extends the range of such symbioses to include cold seeps and hydrothermal vents, and supports the idea that environmental methane levels control the distribution of these symbioses.

Deep-sea Bathymodiolus mussels, depending on species and location, have the capacity to host sulfur-oxidizing (thiotrophic) and methanotrophic eubacteria in gill bacteriocytes, although little is known about the mussels' mode of symbiont acquisition. Previous studies of Bathymodiolus host and symbiont relationships have been based on collections of nonoverlapping species across wide-ranging geographic settings, creating an apparent model for vertical transmission. We present genetic and cytological evidence for the environmental acquisition of thiotrophic endosymbionts by vent mussels from the Mid-Atlantic Ridge. Open pit structures in cell membranes of the gill surface revealed likely sites for endocytosis of free-living bacteria. A population genetic analysis of the thiotrophic symbionts exploited a hybrid zone where two Bathymodiolus species intergrade. Northern Bathymodiolus azoricus and southern Bathymodiolus puteoserpentis possess species-specific DNA sequences that identify both their symbiont strains (internal transcribed spacer regions) and their mitochondria (ND4). However, the northern and southern symbiont-mitochondrial pairs were decoupled in the hybrid zone. Such decoupling of symbiont-mitochondrial pairs would not occur if the two elements were transmitted strictly vertically through the germ line. Taken together, these findings are consistent with an environmental source of thiotrophic symbionts in Bathymodiolus mussels, although an environmentally “leaky” system of vertical transmission could not be excluded.

The utility of alkenone abundance and U37 0 ratios as proxies for haptophyte productivity and temperature variations, respectively, was examined in an upwelling setting by comparison of alkenones with other environmental variables including carbon concentrations, plankton populations, productivity, and temperature. Suspended particulate organic material (SPOM) was collected from surface waters (1-5 m) in Monterey Bay, California during the 1992 El Nino. Haptophyte algae comprise a small but significant fraction of the plankton assemblage (0.5-30%). In this upwelling environment either the haptophytes contain low cellular abundances of alkenones (0.4-5% Corg) and/or alkenone producers are weakly represented among their populations. The U37 0 -temperature relationship for SPOM exhibits a better correlation (r 2 =0.870; n=8) during periods of active upwelling and in the winter than throughout the entire annual cycle (r 2 =0.308; n=18). The alkenone-based temperatures also suggest, as observed elsewhere, that these compounds originated in colder waters at depth and were subsequently transferred to surface waters.

The physical, chemical and biological perturbations in central California waters associated with the strong 1997–1998 El Nino are described and explained on the basis of time series collected from ships, moorings, tide gauges and satellites. The evolution of El Nino off California closely followed the pattern observed in the tropical Pacific. In June 1997 an anomalous influx of warm southerly waters, with weak signatures on coastal sea level and thermocline depth, marked the onset of El Nino in central California. The timing was consistent with propagation from the tropics via the equatorial and coastal wave-guide. By late 1997, the classical stratified ocean condition with a deep thermocline, high sea level, and warm sea surface temperature (SST) commonly associated with El Nino dominated the coastal zone. During the first half of 1998 the core of the California Current, which is normally detected several hundred kilometers from shore as a river of low salinity, low nutrient water, was hugging the coast. High nutrient, productive waters that occur in a north–south band from the coast to approximately 200 km offshore during cool years disappeared during El Nino. The nitrate in surface waters was less than 20% of normal and new production was reduced by close to 70%. The La Nina recovery phase began in the fall of 1998 when SSTs dropped below normal, and ocean productivity rebounded to higher than normal levels. The reduction in coastal California primary productivity associated with El Nino was estimated to be 50 million metric tons of carbon (5 × 10 13 g C). This reduction certainly had deleterious effects on zooplankton, fish, and marine mammals. The 1992–1993 El Nino was more moderate than the 1997–1998 event, but because its duration was longer, its overall chemical and biological impact may have been comparable. How strongly the ecosystem responds to El Nino appears related to the longer-term background climatic state of the Pacific Ocean. The 1982–1983 and 1992–1993 El Ninos occurred during the warm phase of the Pacific Decadal Oscillation (PDO). The PDO may have changed sign during the 1997–1998 El Nino, resulting in weaker ecological effects than would otherwise have been predicted based on the strength of the temperature anomaly.

The influence of ocean acidification in deep-sea ecosystems is poorly understood but is expected to be large because of the presumed low tolerance of deep-sea taxa to environmental change. We used a newly developed deep-sea free ocean CO2 enrichment (dp-FOCE) system to evaluate the potential consequences of future ocean acidification on the feeding behavior of a deep-sea echinoid, the sea urchin, Strongylocentrotus fragilis. The dp-FOCE system simulated future ocean acidification inside an experimental enclosure where observations of feeding behavior were performed. We measured the average movement (speed) of urchins as well as the time required (foraging time) for S. fragilis to approach its preferred food (giant kelp) in the dp-FOCE chamber (-0.46 pH units) and a control chamber (ambient pH). Measurements were performed during each of 4 trials (days -2, 2, 24, 27 after CO2 injection) during the month-long period when groups of urchins were continuously exposed to low pH or control conditions. Although urchin speed did not vary significantly in relation to pH or time exposed, foraging time was significantly longer for urchins in the low-pH treatment. This first deep-sea FOCE experiment demonstrated the utility of the FOCE system approach and suggests that the chemosensory behavior of a deep-sea urchin may be impaired by ocean acidification.

Laser Raman microprobe spectroscopy and laser scanning confocal microscopy were used to determine the presence and speciation of sulfur in sulfur-oxidizing, marine bacteria from Monterey Bay, CA. The bacteria studied include: large, filamentous Thioploca and Beggiatoa , endosymbionts in the vesicomyid clam Calyptogena kilmeri , and a filamentous bacterium of undetermined species. All of these bacteria were shown spectroscopically to store elemental sulfur in submicrometer to several micrometer diameter vesicles. More detailed Raman spectroscopic study of the vesicles in Thioploca and Beggiatoa provided further chemical and structural characterization of the elemental sulfur. The sulfur is bonded in the common, stable S 8 ring configuration and is of an extremely fine-grained microcrystalline form. No additional (organo) sulfur compounds were detected spectroscopically in the vesicles under the low laser powers required to preserve the molecular structure of the sulfur. The present spectroscopic and optical data stand in contrast to reports and inferences of liquid-like elemental sulfur or homogeneous, complex sulfur compounds in other sulfur-oxidizing bacteria. The findings of this study are compatible with a model of sulfur vesicles as dominated by microcrystalline solid elemental sulfur, perhaps embedded in a matrix and/or confining membrane of organic material. The high reactivity and solubility observed in these vesicles is attributed to the extremely fine grain size of the solid elemental sulfur.

Although there is a growing body of evidence indicating benthic foraminifera inhabit hydrocarbon and cold seep environments, biochemical and ultrastructural data on seep foraminiferal communities are not available. Therefore, sediments collected from cold seeps in Monterey Bay, CA (900–1000 m), were examined for the presence of live benthic foraminifera. Results from three independent methods (ATP assay, ultrastructural analysis, rose Bengal staining) indicate that certain species inhabit the Clam Flat and Clam Field seeps. Abundances in our seep samples were lower than in comparable non-seep sites, although not atypical for these bathyal depths. Of 38 species represented at these two seep sites by cytoplasm-containing specimens, only Spiroplectammina biformis was restricted to the seep environment. However, because S . biformis is also known from non-seep sites in other areas, it should not be considered as endemic to seeps. Ultrastructural studies show abundant peroxisomes in seep specimens, which may allow inhabitation of such environments. One specimen of Uvigerina peregrina had prokaryotes nestled in test pores, suggesting that bacteria may play a role in the survival of foraminifera in this seep environment.

Iron has been measured for 16 months with ∼21 day resolution at three stations in the upwelling ecosystem of central California, providing the first detailed assessment of the annual iron cycle in the coastal zone. A large pulse of iron occurs during the first spring upwelling event of the year. Iron concentrations then decay up to 100-fold over several months, although upwelling continues. Excess surface nitrate and low iron are the result during the summer and fall at the two stations furthest offshore (20 and 45 km), while nitrate is depleted and iron high nearshore (5 km). Phytoplankton biomass, primary production and community structure appear to be controlled by iron concentrations in offshore waters during this period.

Summary Deep-sea cold seeps in Monterey Bay, California, are prominent sites of chemosynthetic production, mediated through bacterial oxidation of sulfur. Bacterial mats and vesicomyid clams rely upon hydrogen-sulfide oxidation. Euglenozoa comprise a large and diverse component of the protistan assemblage associated with the dense chemoautotrophic bacterial mats found in the top 1 cm of sediment at some of these seeps. A high percentage of these euglenozoans have conspicuous coats of rod-shaped bacteria that cover virtually their entire surface. In at least one of the three morphotypes identified that possess these epibionts, the epibiotic bacteria contain membrane bound translucent sulfur vesicles. Total sulfide concentration in the top 1 cm of the sediment ranged from undetectable at the sediment-water interface to a maximum of 350 uM. The presence of other hydrogen sulfide oxidizing bacteria (bacterial mats and endosymbiotic bacteria of the clams), the measurable levels of hydrogen sulfide and the distinct membrane surrounding the sulfur inclusion suggests that the epibiotic bacteria on at least some of the euglenozoans are sulfur oxidizers. This is the first report of flagellates possessing sulfur oxidizing epibiotic bacteria. No evidence has been found that the euglenozoans ingest their epibiotic bacteria, however, and the degree and mode of any nutritional contribution the bacteria might make to the host is unknown.

It is generally agreed that the origin and initial diversification of Eucarya occurred in the late Archaean or Proterozoic Eons when atmospheric oxygen levels were low and the risk of DNA damage due to ultraviolet radiation was high. Because deep water provides refuge against ultraviolet radiation and early eukaryotes may have been aerotolerant anaerobes, deep-water dysoxic environments are likely settings for primeval eukaryotic diversification. Fossil evidence shows that deep-sea microbial mats, possibly of sulphur bacteria similar to Beggiatoa, existed during that time. Here we report on the eukaryotic community of a modern analogue, the Santa Barbara Basin (California, USA). The Beggiatoa mats of these severely dysoxic and sulphidic sediments support a surprisingly abundant protistan and metazoan meiofaunal community, most members of which harbour prokaryotic symbionts. Many of these taxa are new to science, and both microaerophilic and anaerobic taxa appear to be represented. Compared with nearby aerated sites, the Santa Barbara Basin is a 'symbiosis oasis' offering a new source of organisms for testing symbiosis hypotheses of eukaryogenesis.

During the spring of 1996 we occupied a station on annual sea ice located several kilometers from Disko Island, West Greenland in water depths greater than 200 m. The goal of this 3-week field season was to characterize sea-ice communities and the underlying water column prior to, and during, ice break-up. A heavier than usual snow load depressed the sea ice below sea level and the snow-ice interface became flooded. Some of this flooded region subsequently refroze and the whole process repeated itself when additional snow accumulated. The infiltration phytoplankton and protozooplankton assemblages that developed in this region were abundant and diverse. Algal biomass in the infiltration layer was approximately an order of magnitude greater than in the underlying water column but an order of magnitude less than in the well-developed bottom ice community. The infiltration autotrophic assemblage resembled the bottom-ice assemblage while the protozooplankton assemblage was more similar to the water column assemblage.

Over a four-year period the δ15N values of particulate nitrogen, PN, suspended in surface waters at several sites in Monterey Bay were observed to vary between 1.3 and 7.6‰, a significant portion of the known oceanic δ15NPN range. δ15NPN generally increased as [NO3-] declined, in keeping with the hypothesis that δ15NPN rises with increased NO3- utilization. Previously reported measurements conducted elsewhere in the Pacific and Indian oceans generally match this trend. The distinctly non-linear relationship between δ15NPN and ln[NO3-] is consistent with a closed-system, Rayleigh fractionation model where: NO3- is the reactant, PN is the accumulating end product, initial [NO3-]=30 μM, initial δ 15 N NO 3 - =7‰ , and biological fractionation, e=9‰ . There is, however, considerable scatter in the data about this trend (r2=0.37), with the uncertainty (±1 standard deviation) of empirically estimating nitrate utilization from δ15NPN of ±4.3 μM. Also, the e required to fit the model to observed δ15NPN variations produces δ15NNO3- at intermediate and low [NO3-] that is much higher than has thus far been observed in the ocean. One way to rectify this discrepancy would be if e declined as [NO3-] decreased. Lack of significant linear correlation between δ15NPN and phytoplankton growth rate, cell size, and 1/[NO3-] argues against δ being influenced by limitations imposed by diffusive NO3- transport. However, logarithmic functions of these factors can explain up to 50% of the observed δ15NPN variability, suggesting that active NO3- transport or species-specific effects may be influencing e and hence δ15NPN in Monterey Bay.

Pseudo-nitzschia australis Frenguelli is a marine pennate diatom associated with the production of domoic acid— a neuroexcitatory amino acid linked to illness and mortality of humans and wildlife. Distinguishing P. australis from its co-occurring congeners is labor intensive and time consuming because of a requirement for scanning electron microscopy. Here, we apply large-subunit ribosomal RNA (LSU rRNA)-targeted oligonucleotides in whole-cell and sandwich hybridization formats to identify and enumerate this species collected from pure cultures and natural populations. Whole-cell hybridization employed fluorescently labeled probes, filter-based sample processing, and epifluorescence microscopy to enumerate labeled cells. In contrast, sandwich hybridization was accomplished by homogenizing cells in a chaotropic solution and performing two hybridization reactions: capture of LSU rRNA using an oligonucieotide coupled to a macroscopic solid support and binding of signal probe to a region of LSU rRNA near that of the capture site. Sandwich hybrids were detected colorimetrically; color intensity was proportional to the abundance of target species in the original sample. The sandwich hybridization assay was semiautomated with a robotic processor. Both whole-cell and sandwich hybridization are useful techniques for identifying P. australis as it occurs in nature. Sandwich hybridization potentially offers the most rapid and simple means to accomplish this task when screening large numbers of environmental samples.

Anthropogenic CO2 is now reaching depths over 1000 m in the Eastern Pacific, overlapping the Oxygen Minimum Zone (OMZ). Deep-sea animals – particularly, calcifiers – are suspected to be especially sensitive to environmental acidification associated with global climate change. We have investigated the effects of hypercapnia and hypoxia on the deep-sea urchin Strongylocentrotus fragilis, during two long-term exposure experiments (1 month and 4 month) at three levels of reduced pH at in situ O2 levels of approx. 10% saturation, and also to control pH at 100% O2 saturation. During the first experiment, internal acid-base balance was investigated during a one-month exposure; results show S. fragilis has limited ability to compensate for the respiratory acidosis brought on by reduced pH, due in part to low non-bicarbonate extracellular fluid buffering capacity. During the second experiment, longer-term effects of hypercapnia and variable O2 on locomotion, feeding, growth, and gonadosomatic index (GSI) were investigated; results show significant mortality and correlation of all measured parameters with environmental acidification at pH 6.6. Transient adverse effects on locomotion and feeding were seen at pH 7.2, without compromise of growth or GSI. Based on the expected changes in ocean pH and oxygen, results suggest extinction of S. fragilis in the eastern North Pacific is unlikely. Rather, we expect a shoaling and contraction of its bathymetric range.

Large-subunit ribosomal RNA (LSU rRNA)-targeted oligonucleotides specific for Pseudo-nitzschia australis Frenguelli were used to discriminate that species from cultured isolates of P. pungens (Grunow) Hasle, P. multiseries (Hasle) Hasle, P. delicatissima (P.T. Cleve) Heiden, P. pseudodelicatissima (Hasle) Hasle, P. fraudulenta (P.T.Cleve) Heiden, P. heimii Manguin, and P. americana (Hasle) Fryxell using whole cell (in situ) and sandwich hybridization. Whole cell hybridization involved application of fluorescently labelled probes to chemically preserved (intact) cells. Cells that retained the probe were visualized using epifluorescence microscopy. In contrast, sandwich hybridization was initiated by homogenizing live cells to liberate their contents. Detection of P. australis was accomplished by capturing LSU rRNA from unpurified cell lysates using a species-specific oligonucleotide attached to a solid support. Captured molecules were washed free of other lysate and hybridized to a biotinylated si...

An extensive set of measurements of phytoplankton production, biomass and composition, and microzooplankton grazing from the coast of Peru to 170°W during 1992, together with similar data collected over the previous decade, has allowed recalculation of the primary production supported by equatorial upwelling and improved description of the variability in phytoplankton properties. Equatorial region surface chlorophyll and phytoplankton biomass were low, averaging 0.2 μg 1−1 and 20 μg C 1−1, respectively, and showed low variance. Phytoplankton in the open ocean of the tropical Pacific were dominated by small < 5 μm) solitary organisms, primarily prochlorophytes, Synechococcus, eukaryotic picoplankton, haptophytes and dinoflagellates, while coastal populations were dominated by larger organisms or colonies (primarily diatoms). At a few open ocean locations high numbers of diatoms were found. The chlorophyll maximum observed in the equatorial Pacific was a function of increased chlorophyll per cell rather than an increase in cell numbers. Surface phytoplankton carbon to chlorophyll was highly variable and a function of available irradiance and upwelling strength. On the order of 40% of the particulate nitrogen retained by GF/F filters was estimated to be phytoplankton nitrogen. Phytoplankton growth rate estimates using daily carbon uptake and phytoplankton carbon estimated from microscopic enumeration ranged from 0.55 to 0.70 day−1. Estimates of growth rates from dilution experiments gave estimates of the order of 1 day−1 and microzooplankton grazing rates that were significantly lower, 0.4 day−1. The mean mass specific grazing rate for microzooplankton was estimated to range from 1.6 to 1.8 day−1. The mean productivity for the equatorial Pacific from 90° to 180°W, 5°N−5°S, was estimated to be 900 mg C m−2 day−1 for the period from 1990 to the present, twice that estimated previously. The maximum f-ratio (new to total production) was estimated to be 0.36. Assuming that between 25 and 50% of the upwelled nitrate is never taken up by phytoplankton between 5°N and 5°S, new production would be 162–244 mg C m−2 day−1 and f would range from 0.18 to 0.27.

During a spring bloom primarily composed of the centric diatom Thalassiosira paczfca in Dabob Bay, Washington, an unarmored dinoflagellate, Gyrodinium sp., phagocytized chains of Thalassiosira. The diatoms were egested in peritrophic membrane-bound fecal pellets that were collected in sediment traps. The dinoflagellate pellets accounted for an average of 29% (SD = 16%) of the volume of fecal pellet flux at 50 m. The diatoms in the pellets were intact but void of plasma content, thus reducing the flux of both POC and pigments per volume of fecal pellets, as was apparent in the sediment trap measurements. Grazing by these dinoflagellates on the large diatoms and the export of relatively carbon- and pigment-deplete pellets have much different implications for organic material cycling than if the diatoms were consumed by mesozooplankton or if they sank.

Extensive comparisons of the retention properties of glass-fiber GF/F and 0.2-μm membrane filters show that these two filter types retain equivalent amounts of Chl a. The experiments conducted were in the open ocean waters of the Pacific Ocean, from 46°N to 28°S, including waters from the equatorial divergence, the low latitude subtropical gyres, and higher latitudes. These results contradict a recent report that suggests that in some cases GF/F filters underestimate chlorophyll concentration by 4-fold when compared with 0.2-μm membrane filters. The data set also allowed examination of latitudinal gradients in integrated chlorophyll. Previously observed latitudinal gradients in the North Pacific were present but were much weaker than those found in the South Pacific.

In the equatorial Pacific during the boreal spring of 1992, nanoplankton, represented by chrysophytes, dinoflagellates, amoebae, choanoflagellates, naked flagellates and ciliates, dominated the heterotrophic protistan biomass. This component contributed 11–60% of the combined phytoplankton and heterotrophic protistan biomass. The heterotrophs, other than the dinoflagellates and ciliates, were represented by amoebae and flagellates at a mean (±SD) density and biomass of 5.85 ± 2.53 x 105 cells I −1 and 1.76 ± 1.37 μgC l −1 . Fifty-two species of lobose amoebae, apusomonads, bicosoecids, cercomonads, choanoflagellates, chrysomonads, euglenids, jakobids, kathablepharids, kinetoplastids, pedinellids and a number of taxa of uncertain position (incertaesedis taxa) were identified. The heterotrophs represent five different trophic types of organisms, defined by habitat and prey. Fifty per cent of the species identified in this study are principally associated with detritus (marine snow). The majority of free-living suspension feeders we identify in this study are choanoflagellates. Other suspension feeding planktonic taxa may not be detected using the protocols we employ. Only 42% of the species identified are obligately bacterivorous and 12% are not bacterivores at all but graze principally on algae. The remainder of heterotrophic species prey on an array of DOM, bacteria, other protists and detritus.

The idea that iron might limit phytoplankton growth in large regions of the ocean has been tested by enriching an area of 64 km2 in the open equatorial Pacific Ocean with iron. This resulted in a doubling of plant biomass, a threefold increase in chlorophyll and a fourfold increase in plant production. Similar increases were found in a chlorophyll-rich plume down-stream of the Galapagos Islands, which was naturally enriched in iron. These findings indicate that iron limitation can control rates of phytoplankton productivity and biomass in the ocean.

“Dead zones” are man-made hypoxic zones (oxygen concentrations of less than 2 mg l−1) that include the seafloor and the water column immediately above it. Such low oxygen concentrations result from the aerobic decay of organic debris from locally elevated primary production that is fueled by anthropogenic nutrient inputs to the coastal ocean (e.g., fertilizer runoff). Other benthic environments with persistent hypoxia unrelated to human activities have been known for decades. Silled basins and cold seeps are examples of natural hypoxic regions. Using microscopy, we have documented disparate, diverse, symbioses-dominated assemblages of protists as well as nematodes from all three of these hypoxic environments. The “dead zone” off the Mississippi River is dominated by flagellates and ciliates. In contrast, Monterey Bay cold seeps, while hosting biomass roughly equivalent to that from the Mississippi “dead zone,” had assemblages dominated by nematodes. The assemblage from Santa Barbara Basin was approximately an order of magnitude higher in biomass and was dominated by foraminifera. In all three hypoxic environments, symbioses were a prominent component of the assemblage and are likely the factor that allows these assemblages to thrive.

A planktonic and solitary diatom species superficially reminiscent of Nitzschia (subg. Nitzschiella) spp. has been found in marine samples from South America, central California waters, West Greenland and Denmark. Lennoxia faveolata gen. et sp. nov. is spindle-shaped with thin, extended and sometimes curved cell ends. The valve face pattern consists of a honeycomb mesh superimposed on a basal thin layer of material. A marginal structure reminiscent of a tubular process is present on at least one valve of each cell.

As part of the Antarctic Marine Ecosystem Research in the Ice Edge Zone (AMERIEZ) program, we examined the biomass and distribution of phytoplankton and protozooplankton at an advancing ice edge in the Weddell and Scotia Seas during the early austral winter. The advance of ice cover, local melting of sea ice and advection of water masses, possibly from lower latitude regions, were the main sources of variability in the physical regime of the ice-edge zone. Analysis of the plankton assemblage showed phytoplankton biomass (PPC) in the upper 100 m ranging from 100 to 272 mg C m −2 and protozooplankton biomass (PZC) ranging from 177 to 410 mg C m −2 . Autotrophic dinoflagellates dominated phytoplankton stocks, followed by other autotrophic nanoflagellates and diatoms in decreasing biomass. Heterotrophic flagellates dominated protozooplankton biomass followed by ciliates and sarcodines. The biomass of major groups comprising the planktonic assemblage was similar at most stations with the exception of one station where diatoms predominated. Integrated PPC and PZC showed no relationship to water column stability. Integrated autotrophic flagellate biomass was higher at open water stations than at ice-covered stations, but none of the other integrated group biomasses showed variations that could be related to ice cover or water mass characteristics. Analysis of discrete-depth samples indicated that all groups (except the sarcodines) showed near surface maxima, that total PPC, diatoms and autotrophic flagellates showed higher biomasses at ice-edge and open water stations than at ice-covered stations and that none of the heterotrophs showed variations related to ice cover. Some groups, however, showed differences that could be related to water mass characteristics, but this was less evident than was the effect of depth or ice cover. Comparison of species assemblages of diatoms and choanoflagellates among water column stations indicated variations that could be related to the differing cruise legs and water mass characteristics. Similar diatom assemblages were found in both ice and water, but higher concentrations occured in the ice assemblages. A few diatom species were found to be indicator species for ice versus water assemblages and to distinguish among the varying hydrographic regimes. Although phytoplankton stocks were higher at non ice-covered than at ice-covered stations, we were not able to see distinct differences between ice-edge stations and those north of the furthest ice extent. We hypothesize that advection of sea ice into water above the freezing point and subsequent melting of ice probably affected much of our study area, so that any effects of “enhanced production” in the ice-edge zone would have been difficult to resolve. Moreover, absolute primary production was very low, and based on the trophic composition of the planktonic assemblage and production estimates from our AMERIEZ colleagues, we concluded that neither algal nor bacterial production was sufficient to produce an enrichment of protozooplankton stocks in the ice-edge zone. Calculations of a carbon budget suggested bacterial production was a significant proportion of total production and that the nano- and microheterotrophs must predominate in the utilization of both phyto- and bacterioplankton production at the winter ice edge. An analysis of species assemblages suggested little advection of populations from lower latitude regions and supports the contention that material was apparently released from sea ice during localized melting events. This input of carbon biomass and detritus from ice may supply the carbon needed to support the high concentrations of heterotrophs observed in our study, but this interpretation is confounded because ice-edge heterotrophic plankton populations also may be enriched by seeding from sea ice.

The land-fast sea-ice brine contains a diverse phagotrophic protist assemblage consisting of

Cuvelier, Marie L. ... et al.-- 6 pages, 4 figures, 1 table, this article contains supporting information online at https://www.pnas.org/content/pnas/suppl/2010/07/27/1001665107.DCSupplemental/pnas.201001665SI.pdf.-- Data deposition: The sequences reported in this paper have been deposited in the Gen-Bank database (accession nos. HM581528–HM581638 and HM565909–HM565914). Other scaffolds with predicted genes from this Whole Genome Shotgun/454 project have been deposited at DNA Data Bank of Japan/European Molecular Biology Laboratory/GenBank under the accession no. AEAR00000000. The version described in this paper is the first version, AEAR01000000, Among eukaryotes, four major phytoplankton lineages are responsible for marine photosynthesis; prymnesiophytes, alveolates, stramenopiles, and prasinophytes. Contributions by individual taxa, however, are not well known, and genomes have been analyzed fromonly the latter two lineages. Tiny >picoplanktonic> members of the prymnesiophyte lineage have long been inferred to be ecologically important but remain poorly characterized. Here, we examine pico-prymnesiophyte evolutionary history and ecology using cultivation-independent methods. 18S rRNA gene analysis showed picoprymnesiophytes belonged to broadly distributed uncultivated taxa. Therefore, we used targeted metagenomics to analyze uncultured pico-prymnesiophytes sorted by flow cytometry from subtropical North Atlantic waters. The data reveal a composite nuclear-encoded gene repertoire with strong green-lineage affiliations, which contrasts with the evolutionary history indicated by the plastid genome. Measured pico-prymnesiophyte growth rates were rapid in this region, resulting in primary production contributions similar to the cyanobacterium Prochlorococcus. On average, pico-prymnesiophytes formed 25% of global picophytoplankton biomass, with differing contributions in five biogeographical provinces spanning tropical to subpolar systems. Elements likely contributing to success include high gene density and genes potentially involved in defense and nutrient uptake. Our findings have implications reaching beyond pico-prymnesiophytes, to the prasinophytes and stramenopiles. For example, prevalence of putative Ni-containing superoxide dismutases (SODs), instead of Fe-containing SODs, seems to be a common adaptation among eukaryotic phytoplankton for reducing Fe quotas in low-Fe modern oceans. Moreover, highly mosaic gene repertoires, although compositionally distinct for each major eukaryotic lineage, now seem to be an underlying facet of successful marine phytoplankton, Sequencing was under DE-AC02- 05CH11231, by a Department of Energy Community Sequencing Program award to A.Z.W. and J. Eisen. Support was in part by DE-FC02-02ER63453, NSF OCE-0722374, and NSF-MCB-0732448 (to A.E.A.); a National Human Genomic Research Institute, National Institutes of Health grant (to R.S.L.); National Oceanic and Atmospheric Administration and David and Lucile Packard Foundation (DLPF) grants (F.P.C.); NSF-OCE-0241740 (to B.J.B.); and major funding by NSF-OCE-0836721, the DLPF, and a Moore Foundation Young Investigator Award as well as Moore 1668 (to A.Z.W.). Author contribution details are given in SI Materials and Methods, Section 12

Tintinnid ciliates were present throughout the upper (100m) water column of the ice-edge zone when sampled in autumn 1986 in the Weddell Sea. Biomass ranged from 0.02 μgC1−1 under the sea-ice to 1.3 μgC1−1 in the ice-free water column. Cymatocylis, Codonellopsis, Laackmaniella and a small Salpingella were the most abundant and/or largest biomass contributors. The under ice assemblage was characterized by low biomass and dominated by small species (Salpingella and Codonellopsis); the ice edge stations were dominated by these same taxa but in higher abundances while the open water assemblage was characterized by high biomass and dominated by Cymatocylis, the largest taxa. All taxa exhibited maximum concentrations in the upper 50m of the water column. Both krill and salps grazed upon the Cymatocylis and Codonellopsis without preference in both the ice covered and open water regimes.

The small (< 15 μm) hypnozygote of an autotrophic athecate dinofiagellate found in association with Antarctic sea ice had an external covering composed of approximately 60 plates, each of which was bounded by sutural ridging and possessed an intratabular process. A cingulum and sulcus were also evident. The ultrastructure of the cyst was increasingly dominated by storage bodies as the cyst matured, and the cell wall thickened from 0.2 to 0.8 μm over 2 months. This cyst has been encountered often but usually at low abundances (103−104 cells·L−1); however, the maximum abundances observed (106 cells·L−1) indicate that the formation of this cyst may play an important part in the ecology of sea ice communities.

Concentrations of phytoplankton and NO{sub 3} are consistently low and high in surface waters of the oceanic eastern and central equatorial Pacific, and phytoplankton populations are dominated by small solitary phytoplankton. Growth rates of natural phytoplankton populations, needed to assess the relative importance of many of the processes considered in the equatorial Pacific, were estimated by several methods. The growth rates of natural phytoplankton populations were found to be {approximately}0.7 d{sup {minus}1} or 1 biomass doubling d{sup {minus}1} and were similar for all methods. To keep this system in its observed balance requires that loss rates approximate observed growth rates. Grazing rates, measured with a dilution grazing experiment, were high, accounting for a large fraction of the daily production. Additions of various forms of Fe to 5-7-d incubations utilizing ultraclean techniques resulted in significant shifts in autotrophic and heterotrophic assemblages between initial samples, controls, and Fe enrichments, which were presumably due to Fe, grazing by both protistan and metazoan components, and incubation artifacts. Estimated growth rates of small pennate diatoms showed increases in Fe enrichments with respect to controls. The growth rates of the pennate diatoms were similar to those estimated for the larger size fraction of the natural populations.

Plankton studies in Antarctic waters have emphasized the importance of diatoms. The species composition, abundances and contribution to biomass of the other planktonic groups are stil poorly documented. This is particularly true for the heterotrophic members of the nano- and microplankton assemblage. As part of the Antarctic Marine Ecosystem Research in the Ice age Zone (AMERIEZ) program, we sampled nano- and microplankton across the ice edge zone during the austral winter. A variety of microscopial techniques allowed us to the composition, trophic mode and biomass of the spectrum of organisms that make up the winter plankton assemblage. Total nano- and microplankton biomass in the upper 100 meters of the water column ranged from 0.3 to 0.6 gC m −2 . The biomass composition of plankton assemblages among the stations was relatively uniform throughout the ice edge zone; however, the autotrophic flagellates and dinoflagellates showed significantly higher biomass at the ice edge or in open water relative to ice covered stations. The heterotrophic biomass (protozooplankton) exceeded the biomass of phytoplankton at most stations. Among the autotrophic forms, dinoflagellates made up 38% of the biomass, followed by other autotrophic flagellates (35%) and diatoms (27%). The phytoplankton biomass was dominated by nanoplankton ( μ m). Dinoflagellates also dominated among the heterotrophs, making up as much as 73% of the total heterotrophic biomass. Most of the heterotrophic dinoflagellates were μ m. The ciliates present were mostly non-sheathed oligotrichs. Tintinnids were present but in densities of usually −1 . Many of the larger oligotrichous ciliates examined contained sequestered chloroplasts, which have been reported to retain photosynthetic activity. Larger protozoans (e.g., Radiolaria, Acantharia and Foraminifera) were a minor constituent of the plankton biomass in surface waters. This study suggests that winter plankton assemblages were dominated by nanoplankton for both algae and protozoans. The abundance of athecate dinoflagellates, both autotrophic and heterotrophic forms, was unusual and warrants further investigation of the role of these organisms in the Antarctic plankton community. Generally low production and the high abundance of heterotrophic organisms relative to the phytoplankton, suggests the protozooplankton will be important in utilizing winter primary and bacterial production and transferring this production to higher levels of the food web.

Choanoflagellates have been enumerated at between 7 and 10 stations on a transect > 300 km in length off the central California coast on 7 cruises from August 1989 to June 1990. Abundances and biomass of choanoflagellates, estimated from epifluorescence counts, ranged from 2900 to 3900 000 cells per liter and from 0.01 to 38.44 μgC per liter. Minimum abundances were associated with offshore stations during March and maximum abundances with the coastal stations during the same cruise, coincident with a Chaetoceros bloom. Choanoflagellate biomass comprised approximately 12% of the total heterotrophic biomass and was significandy correlated (r-0.54, P < 0.001) with the heterotrophic flagellates. An average of 17% of the choanoflagellates had autotrophic picoplankton in their vacuoles. Choanoflagellates were calculated to clear between < 0.1 and 180% of the water column per day

A qualitative and quantitative survey of nanoplankton communities at offshore Californian localities sampled during September 1989, has revealed a diverse choanoflagellate community consisting of more than 40 taxa, three ofwhich are described as new species (Acanthocorbis haurakiana sp. nov., Parvicorbicula zigzag sp. nov. and Stephanoeca apheles sp. nov.). A biogeographic analysis of the distributional patterns of species encountered indicate that the Californian choanoflagellate fauna consists of species with quasi-cosmopolitan distribution, on top of which is superimposed a contingent of species otherwise associated with warm water regions. A station by station clustering analysis based on the relative abundance counts showed that onshore stations formed a cluster that was significantly different from that formed by offshore stations. Clustering of the PSI values for the species by species matrix revealed two significant clusters, one formed by species found throughout the study area, and one ...

The morphology and ultrastructure of four species of Cryothecomonas gen.nov. (Protista incertae sedis) in material from the Weddell Sea, Antarctica, and the Isefjord, Denmark, are described. These heterotrophic flagellates, which were initially observed in association with sea ice, display a unique combination of morphological characteristics. At present it is impossible to assign the new genus to an existing higher taxonomic level of protistan flagellates. Cryothecomonas species are furnished with a close-fitting multilayered theca. The two naked anterior flagella emerge through narrow thecal funnels. A transitional helix is part of the flagellar transition zone. A conspicuous cytostome is located in a posterior (lateral) position. Food uptake is mediated through the extension of cytostomal pseudopodia. The nucleus is anteriorly located and contains a conspicuous nucleolus and distinct areas of chromatin. Mitochondrial cristae are tubular. Cryothecomonas species feed on cells in the size range 2–4.5 μm (e.g., algal flagellates). Data are presented on the abundance of Cryothecomonas armigera sp.nov. in Antarctic waters.

Equatorial regions, especially the equatorial Pacific, are important to the global carbon and nitrogen cycle, yet little is known about the processes regulating phytoplankton dynamics in these areas. Here we report on the abundance of planktonic groups, in the picoplankton to netplankton range, estimated using epifluorescence microscopy, in samples collected in the equatorial Pacific from 110 to 140°W, and discuss their relation to primary production, chlorophyll, chemical and physical properties. Microscopic examination supports previous reports ( Chavez , 1989, Global Biogeochemical Cycles, 3, 27–35), based on size separations of biomass and production, that the equatorial Pacific is dominated by small phytoplankton, most of them smaller then 5 μm. The phytoplankton in this region is dominated by relatively few taxa: Synechococcus spp., red fluorescing picoplankton, a small naked dinoflaellate (4 × 7 μm), small prymnesiophytes (on the order of 3–5 μm), and small single-celled pennate diatoms (2 × 15 μm). The spatial variability in phytoplankton biomass, composition and production could be clearly related to distinct physical features of the equatorial circulation, such as equatorial upwelling, Long or Legeckis waves and the Equatorial Front. During November 1988, a period of abnormally cool sea surface temperatures, changes in the abundance of pennate diatoms accounted for the largest proportion of the variability in chlorophyll and primary production even though this group was a relatively minor contributor to the total biomass of the phytoplankton community. Since primary production and particulate organic flux are well correlated in the equatorial Pacific ( Betzer et al., 1984, Deep-Sea Research, 31, 1–11), variations in the abundance of pennate diatoms also must have important consequences to variations in particulate organic flux. Before a predictive model for particulate organic flux in the equatorial Pacific can be established further understanding of the forces structuring phytoplankton communities is required.

A study of the choanoflagellate species composition of an Antarctic ice edge zone (northern Weddeil Sea, March 1986) has resulted in the finding of 16 taxa of which one, Cosmoeca takahashii Thomsen sp.n., is described here. An emended description is given of Parvicorbicula circularis. Morphological, numerical and dimensional aspects of other species have been analysed in an attempt to improve the circumscription of certain taxa, and to increase our understanding of the nature of intraspecific variability. Data on the relative abundance of choanoflagellate species along seaward transects perpendicular to the ice edge showed that seven species account for more than 95% of all choanoflagellates identified. The two most abundant species were Parvicorbicula socialis and Diaphanoeca pedicellata.

[1] Oceanic CO2 levels are expected to rise during the next 2 centuries to levels not seen for 10–150 million years by the uptake of atmospheric CO2 in surface waters or potentially through the disposal of waste CO2 in the deep sea. Changes in ocean chemistry caused by CO2 influx may have broad impacts on ocean ecosystems. Physiological processes animals use to cope with CO2-related stress are known, but the range of sensitivities and effects of changes in ocean chemistry on most ocean life remain unclear. We evaluate the effectiveness of various designs for in situ CO2 release experiments in producing stable perturbations in seawater chemistry over experimental seafloor plots, as is desirable for evaluating the CO2 sensitivities of deep sea animals. We also discuss results from a subset of these experiments on the impacts of hypercapnia on deep sea meiofauna, in the context of experimental designs. Five experiments off central California show that pH perturbations were greatest for experiments using “point source” CO2 pools surrounded by experimental plots. CO2 enclosure experiments with experimental plots positioned within a circular arrangement of CO2 pools had more moderate pH variation. The concentration of dissolution plumes from CO2 pools were related to the speed and turbulence of near-bottom currents, which influence CO2 dissolution and advection. Survival of meiofauna (nematodes, amoebae, euglenoid flagellates) was low after episodic severe hypercapnia but lower and variable where pH changes ranged from 0 to 0.2 pH units below normal.

Sulfi de-enriched environments are not typically considered to be sites that support abundant eukaryotes, yet it is known that plentiful and relatively diverse protistan and metazoan fauna inhabit at least one modern bathyal sulfi dic site (Santa Barbara Basin, California). This contribution adds to our knowledge of eukaryotic communities inhabiting sulfi de-enriched deep-water sediments by presenting data from Soledad Basin (off the western coast of Baja California, Mexico) and Cariaco Basin (off Venezuela). Results indicate that, when considered at the appropriate scale, the density of eukaryotes in Soledad Basin was comparable to that of Santa Barbara Basin. Eukaryotic biovolume and abundance were dominated by foraminifera at all three sites. Unlike the Santa Barbara Basin assemblage, Soledad eukaryotic abundance and biovolume were not dominated by eukaryotes with associated putative symbionts. An undescribed polychaete found in Cariaco Beggiatoa-laden sediments had bacterial ectobionts. Sub-millimeter life-position analysis indicated that Soledad eukaryotes concentrated within the top 2 mm even when the bottom-water oxygen concentration was relatively high (2.7 μM). Observations suggest that the eukaryotic fauna of a Thioploca-dominated site (Soledad) varied substantially in taxonomic composition and sub-millimeter life positions from Beggiatoa-dominated sites (Cariaco and Santa Barbara).

Cultured isolates of Pseudonitzschia australis Frenguelli, P. delicatissima (Cleve) Heiden, P. americana (Hasle) Fryxell, P. pungens (Grunow) Hasle, and P. pungens f. multiseries (Hasle) Hasle from Monterey Bay, California, were compared on the basis of their large-subunit ribosomal RNA gene (LsrDNA). Pseudonitzschia australis, P. pungens f. multiseries, and P. delicatissima were previously shown to produce the neurotoxin domoic acid; the remaining isolates are considered non-toxic. For each isolate approximately 800 base pairs of LsrDNA, encompassing both evolutionarily conserved and evolutionarily variable regions of the molecule, were amplified using the polymerase chain reaction (PCR) and sequenced. Phylogenetic trees generated by parsimony analysis of aligned sequences afford a preliminary view of the organisms genetic relationships. Species defined by morphological criteria are also distinguishable by LsrDNA sequence. Organisms known or suspected to produce domoic acid cluster at different termini on the phylogenetic tree. Two genetically distinct strains of P. australis and P. pungens were identified. Development of a restriction fragment length polymorphism (RFLP) assay of the LsrDNA is described. The RFLP assay discriminates each species, including distinguished strains of P. australis and P. pungens. The restriction test provides a rapid and convenient method for screening isolates' LsrDNA, facilitating further tests of the apparent positive correlation between Pseudonitzschia species' ribosomal gene signatures, morphology, and capacity to produce domoic acid. copy; 1994 Wiley-Liss, Inc.

Oceanic dimethylsulfide (DMS) emissions to the atmosphere are potentially important to the Earth's radiative balance. Since these emissions are driven by the surface seawater concentration of DMS, it is important to understand the processes controlling the cycling of sulfur in surface seawater. During the third Pacific Sulfur/Stratus Investigation (PSI-3, April 1991) we measured the major sulfur reservoirs (total organic sulfur, total low molecular weight organic sulfur, ester sulfate, protein sulfur, dimethylsulfoniopropionate (DMSP), DMS, dimethylsulfoxide) and quantified many of the processes that cycle sulfur through the upper water column (sulfate assimilation, DMSP consumption, DMS production and consumption, air-sea exchange of DMS, loss of organic sulfur by particulate sinking). Under conditions of low plankton biomass ( 8 μM nitrate), 250 km off the Washington State coast, DMSP and DMS were 22% and 0.9%, respectively, of the total particulate organic sulfur pool. DMS production from the enzymatic cleavage of DMSP accounted for 29% of the total sulfate assimilation. However, only 0.3% of sulfate-S assimilated was released to the atmosphere. From these data it is evident that air-sea exchange is currently only a minor sink in the seawater sulfur cycle and thus there is the potential for much higher DMS emissions under different climatic conditions.

We present some of the first records and quantitative data on protists from the ice-edge region of the Weddell Sea. Major groups were diatoms (33 species), dinoflagellates (4 species), prymnesiophytes (2 species), cryptomonads (2 species), prasinophytes (1 species), chrysophytes (3 species), and choanoflagellates (11 species). The prymnesiophyte, Phaeocystis pouchetii , diatoms (predominantly Nitzschia of the Fragilariopsis group), and choanogflagellates (Acanthoecidae) were numerically dominant, although other protists sometimes contributed significantly to plankton populations. Most groups were more abundant at the ice edge than under the pack ice or in the open water. The abundance of choanoflagellates suggests that food chains based on bacterial production must be important, as well as the traditional diatom-krill-vertebrate food chain.

Protozooplankton were sampled in the iceedge zone of the Weddell Sea during the austral spring of 1983 and the austral autumn of 1986. Protozooplankton biomass was dominated by flagellates and ciliates. Other protozoa and micrometazoa contributed a relatively small fraction to the heterotrophic biomass. During both cruises protozoan biomass, chlorophyll a concentrations, phytoplankton production and bacterial biomass and production were low at ice covered stations. During the spring cruise, protozooplankton, phytoplankton, and bacterioplankton reached high concentrations in a welldeveloped ice edge bloom ∼ 100 km north of the receding ice edge. During the autumn cruise, the highest concentrations of biomass were in open water well-separated from the ice edge. Integrated protozoan biomass was 20%. Bacterial biomass exceeded protozooplankton biomass at ice covered stations but in open water stations during the fall cruise, protozooplankton biomass reached twice that of bacteria in the upper 100m of the water column. The biomass of different protozoan groups was positively correlated with primary production, chlorophyll a concentrations and bacterial production and biomass, suggesting that the protozoan abundances were largely controlled by prey availability and productivity. Population grazing rates calculated from clearance rates in the literature indicated that protozooplankton were capable of consuming significant portions of the daily phyto- and bacterioplankton production.