Kurt R. Buck

Phytoplankton variability in the central and eastern tropical Pacific

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.

Phytoplankton taxa in relation to primary production in the equatorial Pacific

Abstract 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.

Raman spectroscopic and laser scanning confocal microscopic analysis of sulfur in living sulfur-precipitating marine bacteria

Abstract 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.

Winter plankton assemblage in the ice edge zone of the Weddell and scotia seas: composition, biomass and spatial distributions

Abstract 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.

Nanoplankton of the equatorial Pacific with emphasis on the heterotrophic protists

Abstract 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.

Monterey Bay Cold Seep Biota: Euglenozoa with Chemoautotrophic Bacterial Epibionts

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.

Nanoflagellates of the central California waters: taxonomy, biogeography and abundance of primitive, green flagellates (Pedinophyceae, Prasinophyceae)

Abstract Examination of whole mounts of cells prepared from samples collected off central California, September 1989, has led to the identification of 14 taxa of primitive green nanoflagellates from the Pedinophyceae (1 species) and the Prasinophyceae (13 species). Three of the prasinophyte taxa are new to science. The finding of these new taxa, provisionally identified as Prasinophyte “Point Sur” sp. 1, 2, 3, is important because it emphasizes the persistent, overall lack of knowledge of prasinophyte biodiversity, and also because these forms combine prasinophycean features in a unique way that ultimately may question the currently accepted taxonomic system. The abundance estimates suggest that prasinophytes are most numerous in coastal waters and are relatively absent from oceanic regimes.

Plankton assemblages in the ice edge zone of the Weddell Sea during the austral winter

Abstract 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 of the Central California waters: Taxonomy, Morphology and species assemblages

Abstract 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 ...

Use of a Free Ocean CO2 Enrichment (FOCE) System to Evaluate the Effects of Ocean Acidification on the Foraging Behavior of a Deep-Sea Urchin

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.