Beatrice C. Booth

Temporal variation in the structure of autotrophic and heterotrophic communities in the subarctic Pacific

Autotrophic and microheterotrophic plankton populations were monitored in the euphotic zone of the eastern subarctic Pacific during 6 one-month cruises in spring and summer, 1984, 1987 and 1988. Transmitted light, epifluorescence, and electron microscopy were used to identify, enumerate and estimate the biomass of size-populations of species. The 2–10μm size class dominated the biomass of both autotrophs and heterotrophs. The autotrophic flagellate, Phaeocystis pouchetii, was frequently observed in its non-colonial phase. Temporal variation in all the stocks was evident and could be explained only partially by the physical, chemical or biological factors investigated here. The general structure of the autotrophic community was similar to that in the North Atlantic, but major, unexplained variations between cruises occurred. Variation in mixed-layer depth and day length (but not variation in daily insolation) explained 25% of the variation in autotrophic doubling rate. Heterotrophic biomass comprised, in decreasing order of importance, non-pigmented flagellates, dinoflagellates, and ciliates. Ciliates rarely contributed more than 40% to the total. Microheterotrophic biomass rarely exceeded 30μg C 1−1 (avg 15μg C 1−1, 0–60m) whereas autotrophic biomass averaged 20μg C 1−1, 0–60m, and reached 74μg C 1−1 on one occasion, yet the grazing capacity of these microheterotrophs averaged 100% of primary production.

Microalgae on the arctic ocean section, 1994: species abundance and biomass

Algal species from the ice, the water directly below the ice (the sub-ice area), and the water column from 21 stations in the Arctic Ocean were examined using epifluorescence and inverted light microscopy. Biomass of autotrophic dinoflagellates and other miscellaneous autotrophic flagellates was determined for the first time in the central Arctic basins. Together these two groups dominated phytoplankton biomass in 74% of samples from the central Arctic, with diatom biomass predominant in the remainder. Picophytoplankton at selected stations in the Canada and Makarov Basins contributed 93% to autotroph cell numbers and 36% to autotroph biomass. Diatom species achieved high biomass in ice and sub-ice samples. The centric diatom Melosira arctica dominated the sub-ice area, while pennate diatoms were major contributors to the ice samples. Despite ample silicate concentrations in the water, diatom frustules were often lightly silicified.

Size classes and major taxonomic groups of phytoplankton at two locations in the subarctic pacific ocean in May and August, 1984

In order to assess the relative importance of the pico- and nanoplankton fractions, the composition of entire phytoplankton communities at Weathership Station P (50°N; 145°W) and at 53°N; 145°W were studied in May and August, 1984, using epifluorescence, scanning electron, and inverted light microscopy. The biomass of major taxa within five size classes was estimated from cell volume and cell concentration. For both months, approximately twothirds of the total phytoplankton carbon were contributed by cells<5 μm. In May, 16% of plant biomass was contributed by cells<2 μm, and in August 39%. (In both months 90% of plant carbon<2 μm was contributed by the bluegreen coccoid Synechococcus spp.) Cells 2 to 5 μm contributed about 39% to total plant carbon; they were mostly flagellates in May and nonmotile coccoids in August. The remaining one-third of algal carbon was composed of dinoflagellates, cryptomonads, other flagellates and diatoms, all >5 μm. Very little difference between taxa was observed with respect to vertical stratification. Small taxonomic changes were observed in the community between May and August, and within each month.

Nanoplankton species predominant in the subarctic Pacific in May and June 1978

Abstract Oceanic nanoplankton (2 to 20 μm) collected in May and June of 1978 from surface waters of the Gulf of Alaska (136 to 149°W) was examined in the scanning electron microscope. Species within the Prymnesiophyceae, Bacillariophyceae, and Cryptophyceae were numerically predominant. The most common and abundant forms were: Phaeocystis pouchetii (Hariot) Lagerth. (free-swimming stage), Minidiscus trioculatus (F.J. Taylor) Hasle, Nitzschia cylindrus (Grun.) Hasle cf., 2 Cryptomonas species, 4 choanoflagellate species, 5 new siliceous cysts, and an arcgeomonad cyst. Species within the Dinophyceae, Chrysophyceae, and Prasinophyceae were less important. Reasons are discussed for the success of the methods used for preservation and analysis of nanoplankton.

Spring and summer growth rates of subarctic Pacific phytoplankton assemblages determined from carbon uptake and cell volumes estimated using epifluorescence microscopy

In order to determine whether phytoplankton growth rates were normal or depressed, total plant carbon (μg l−1) and in situ production rates (μg C l−1 d−1) were measured for phytoplankton assemblages at Weathership Station P (50°N; 145°W) and at 53°N; 145°W in the subarctic Pacific in May and August 1984. Plant carbon, estimated from cell volumes determined using epifluorescence microscopy, was distributed as follow: 28% in the <2 μm fraction, 38% in the 2 to 5 μm size fraction, and the remainder in size classes >5 μm. Carbon-specific growth rates (k), as doublings d−1, were calculated for the phytoplankton assemblages as a whole at each sampling depth down to 100 m for three days in May and for four days in August. The populations in the upper part of the euphotic zone showed average doubling rates of 1 d−1 and thus appeared to be growing at rates normally expected for the prevailing conditions of light and temperature. The low chlorophyll concentrations (0.3 to 0.4 mg chl a m−3) characteristically found in this oceanic region do not seem to be due to very slow growth of algal populations.

PARMALES, A NEW ORDER OF MARINE CHRYSOPHYTES, WITH DESCRIPTIONS OF THREE NEW GENERA AND SEVEN NEW SPECIES

A new order, Parmales, in the Chrysophyceae has cells with siliceous walls made up of round, triradiate and sometimes oblong plates all fitting edge to edge. In the new family, Octolaminaceae, cell walls have eight plates. Cell walls in the new genus Tetraparma have four round plates and four triradiate plates. Cell walls in the new genus Triparma have three round plates of equal size, one larger round plate, one triradiate plate and three oblong plates. In the new family, Pentalaminaceae, cell walls have three round and two triradiate plates. A total of seven new species and four subspecies are described from subarctic Pacific and Antarctic waters.

Abundance, variability, and potential grazing impact of planktonic ciliates in the open subaratic Pacific Ocean

Abstract The abundance and variability of planktonic ciliates in the open subarctic Pacific were determined during four month-long cruises in 1987 and 1988. The ciliate community, numerically dominated by relatively small aloricate choreotrichs, was comparable in abundance to communities in a range of oceanic and neritic environments, including waters with much higher average chlorophyll concentrations. Integrated (0–80m) ciliate biomass was typically 100–200mgC m −2 , although 3- to 4-fold higher levels were observed on two occasions in spring. Ciliate community biomass, in general, was dominated by large (>20 μ m width) individuals, although in August 1988 the biomass of smaller cells was as great or greater. The estimated grazing impact of the ciliate community averaged 20% of the primary production. On one instance in May 1988, however, a large biomass of ciliates led to an estimated grazing impact equivalent to 55% of phytoplankton production. While ciliates may be major phytoplankton grazers during sporadic ciliate “blooms”, dino- and other heterotrophic flagellates, which make up the bulk of microheterotroph biomass, must normally be of equal or greater importance as herbivores in this ocean region.

Siliceous nanoplankton I. Newly discovered cysts from the Gulf of Alaska

Siliceous nanoplankton in the size range 2.5 to 5.5 μm and of a type hitherto undescribed are reported from Eastern Subarctic water samples. Nine distinct cell types were recognizable, each possessing an unusual tetrahedral symmetry, resulting from the arrangement of 8 siliceous plates. Since the cells were abundant (maximum concentration of about 7×105 cells 1-1) and were distributed over a wide oceanic area (136° to 149°W), they could well play an important role in the food web in Subarctic seas. Similar cells were found simultaneously in Antarctic waters (see following paper: Silver et al., 1980), where they were as abundant and widespread as in the Subarctic. Evidence that the siliceous forms are likely a cyst stage and that they may be part of the life cycle of species of siliceous oceanic choanoflagellates is presented.

EFFECT OF SILICATE LIMITATION ON VALVE MORPHOLOGY IN THALASSIOSIRA AND COSCINODISCUS (BACILLARIOPHYCEAE)1

Coscinodiscus radiatus Ehrenb. and Thalassiosira eccentrica (Ehrenb.) Cleve were grown in a silicate‐limited chemostat at silicate concentrations below 1 μg‐atoms · l−1. The resulting abnormal valves of C. radiatus lacked a thickened ring around the foramina; their pore membranes were thinner and their loculi shallower than those in normal cells. Abnormal valves of T. eccentrica had a fasciculate areolae pattern; they lacked a silica covering over the foramina and some tangential areolae walls. Neither abnormal valve could be termed a new species.