Sayed Z. El-Sayed

Primary production and standing crop of phytoplankton along the ice-edge in the Weddell Sea

Chlorophyll a, phaepoigments, primary production, nannoplankton, inorganic nutrients, and physical measurements were made in the upper water column at 17 stations occupied in the Weddell Sea in February and March 1977. The most conspicuous feature is the marked contrast between the low standing crop and primary productivity of the northern and central regions, compared with the much more productive shelf waters at the head of the Weddell Sea. Chlorophyll a in the euphotic zone was 4.36 ± 1.75 mg m−2 for the former regions and 31.6 ± 9.5 mg m−2 for the southern stations. Production in the water columns of the southern stations (0.41 ± 0.23 g C m−2 day−1) was approximately four times that at the northern-central ones (0.104 ± 0.092 g C m−2 day−1). Based on plant carbon: chlorophyll a ratio of 30 ± 10 estimated in the present study, an average specific growth rate (μ) of 0.71 was calculated. The nutrient concentrations showed an inverse distribution compared with those of chlorophyll a and primary production; higher nutrient concentrations were recorded at the northern stations than at the southern waters. Phosphate: nitrate: silicate ratios in the water column suggested the importance of nitrate for phytoplankton production. A significant relationship (P < 0.001) between chlorophyll a concentration and day-zooplankton biomass and a significantly higher ratio (P < 0.06) of night-to-day catch of zooplankton in the northern-central regions than in the southern region were found. This suggests that zooplankton do not need to migrate vertically in the southern regions due to abundance of food supply, whereas in the northern-central regions zooplankton must migrate upwards during the night to consume available food produced through the photosynthetic process. The study demonstrates that water column stability, grazing, and proximity to land masses are the most significant factors controlling phytoplankton production in the Weddell Sea.

Phytoplankton standing crop, primary productivity, and near-surface nitrogenous nutrient fields in the Ross Sea, Antarctica

Abstract In austral summer 1978 a study was made of the phytoplankton standing crop, primary productivity, and nutrient chemistry of the waters along a north-south transect between New Zealand and the Ross Ice Shelf and along two east-west transects in the Ross Sea. The area was characterized by a high degree of spatial biological variability, with pronounced differences in phytoplankton biomass, primary productivity, and near-surface nitrate and ammonium fields between the northern, central, and southern regions of the Ross Sea. An extensive bloom of the colonial flagelate Phaeocystis pouchetiii (Prymnesiophyceae) was encountered along the barrier edge of the Ross Ice Shelf and extended to depths of 100 to 150 m at some stations. Chlorophyll a throughout the euphotic zone along the ice shelf barrier edge averaged > 1 mg m−3, and primary productivity locally reached nearly 1 g C m−2 day−1 there. In contrast, both chlorophyll a concentration and rates of 14C uptake averaged two- to four-fold less some 200 km offshore of the Ross Ice Shelf, where P. pouchetii generally was rare. Where P. pouchetii was abundant, more than 25% of the water column primary production occurred at depths below the 1% light penetration level. Near-surface nitrate concentrations were about a third lower at the stations where P. pouchetii was abundant than at those with few or no P. pouchetii. Regionally there was a strong negative correlation between NH4+ and chlorophyll a, suggesting that the biogenic uptake of NH4+ by the phytoplankton controlled the distribution of NH4+ within the euphotic zone.

The variance spectra of phytoplankton, krill and water temperature in the Antarctic Ocean south of Africa☆

Abstract The scale dependence of the variability in phytoplankton and krill ( Euphausia superba ) abundance, and in the physical environment, are examined by applying the techniques of power spectral analysis to continuous horizontal records of surface seawater temperature, surface in vivo fluorescence and acoustically derived estimates of integrated krill density. Data were collected in the area between 60–70°S and 15–30°E. Similarity in the power spectra for temperature and in vivo fluorescence suggests that over the range of 4–20 km, the variability in phytoplankton biomass is largely determined by physical processes. However, the steepness of the fluorescence variance spectrum relative to the temperature spectrum, together with consistent coherence between the phytoplankton and krill profiles, suggests that predator-prey interactions are also of importance in determining the distributional patterns of the phytoplankton. Krill distributions exhibit considerable small-scale patchiness, and over the 2–20 km length scales resolved in this study, the krill variance spectrum is similar to a white noise spectrum.

Productivity of the southern ocean: a closer look

Abstract 1. 1. This paper reviews present knowledge of the standing crop and productivity of Antarctic phytoplankton and of the factors that govern primary production. 2. 2. Investigations have shown that (a) productivity of Antarctic waters varies by at least one to two orders of magnitude; and (b) generally, these waters display their richness mainly in the coastal regions. 3. 3. Recent studies of the autotrophic and heterotrophic pico- and nanoplankton are reviewed, and new data are presented. 4. 4. The relative abundances of these very small-sized classes of organisms are discussed, and their potentially important role in the emerging paradigm of the Antarctic food web is considered.

Phytoplankton Species Composition and Abundance in the Indian Sector of the Antarctic Ocean

SummaryWater samples collected in the southwestern Indian Ocean between Africa and Antarctica in March 1980 were analyzed quantitatively for phytoplankton. Diatoms dominate the phytoplankton in this region and their numbers generally increase southward with peaks of abundance in both the northern Antarctic Zone and south of the Antarctic Divergence. Average cell numbers (i.e., 6.1×105 diatoms l-1 in the Antarctic Zone) are comparable to maximum numbers previously reported for the Southern Ocean. Dinoflagellates, flagellates and “monads” occur in highest concentrations north of the Polar Front. Their numbers are somewhat reduced south of the Antarctic Divergence, and are lowest in the Antarctic Zone. Various diatom assemblages are characteristic of different latitudinal zones. Waters north of and in the vicinity of the Polar Front are rich in the Nitzschia, Pseudonitzschia group of species. In the Antarctic Zone, Nitzschia “nana” and Dactyliosolen tenuijunctus dominate. Nitzschia species of the Fragilariopsis group are most numerous at stations south of the Antarctic Divergence. Striking differences are noted between the species compositions of quantitative and net-haul samples. A few nanoplanktonic diatoms (e.g. Nitzschia “nana” and single cells of Chaetoceros spp.) and the weakly silicified Dactyliosolen tenuijunctus, which are dominant in the quantitative samples, are either entirely absent or present only as solitary cells in the net collections.

Grazing of Euphausia superba Dana on natural phytoplankton populations

SummarySelective feeding by Euphausia superba (krill) has been suggested from stomach content analysis (Nemoto 1971/1972) and from the comparison of krill and phytoplankton species distribution (Kawamura 1981). Laboratory experiments can help determine whether krill selectively graze certain phytoplankton species. Grazing experiments were conducted at Palmer Station, Antarctica, during the austral summer 1977/1978. krill, collected from waters surrounding the Antarctic Penninsula, were maintained in flow-thru aquaria at Palmer Station. E. superba were added to glass bottles (4.48 1), containing 220 μm mesh filtered sea water. Bottles, with and without krill, were incubated in the dark at sea surface temperature, for two to twenty-seven hours. End point determinations were made for phytoplankton cell number. The cell counts were divided into size and species categories, and the calculated filtering rates were compared through analysis of variance. These experiments led to the conclusion that krill “selectivity” for phytoplankton species is probably size dependent, with solitary cells smaller than 20 μm (maximum diameter) being filtered less rapidly than larger diatoms and chain forming species.

Spatial and temporal variations in phytoplankton biomass and primary productivity in the Southwest Atlantic and the Scotia Sea

SummaryTwo cruises of the ARA/Islas Orcadas (late winter/early spring 1978 and late summer/early fall 1979) provided data which show that temporal variability of phytoplankton biomass and productivity in the oceanic wates of the Southwest Atlantic and Scotia Sea is insignificant when compared to the influence of geographical variability. Two bloom stations sampled during the late winter/early spring cruise had chlorophyll a concentrations and productivity values an order of magnitude higher than waters sampled from the same locations the following late summer/early fall. However, a comparison of 10 paired stations from the two cruises indicated no seasonal trend, as measured values of chlorophyll a and productivity from the first cruise were randomly larger or smaller than values measured during the second cruise. Consideration of individual stations from both seasons suggests the need to re-examine widely held notions regarding the effect of the Polar Front Zone and the “island-mass effect” on phytoplankton abundance and productivity. Higher-than-expected standing stock and productivity values at some open-ocean stations and at some stations within the Polar Front Zone indicate that looking for specific factors which promote localized enhancement or impoverishment of phytoplankton would be more useful than continuing with attempts to generalize Antarctic productivity data into broad seasonal or geographical patterns.

Vertical Distribution of Diverse Phytoplankton Communities in the Central Pacific

Southeast of Hawaii in the central Pacific, phytoplankton samples were taken on three transects. An average of over 20,500 cells/liter, including flagellates, was found for all depths counted, with diatoms, dinoflagellates, and coccolithophorids together accounting (in about equal numbers) for half that number. Coccolithophorids were dominant at some depths. The profile of cell numbers with depth showed a subsurface maximum with decreasing numbers at greater depths. The empty cell counts followed the same profile, with counts that were almost an order of magnitude smaller, probably indicating much recycling within the euphotic zone. Diversity indices revealed the complexity of the phytoplankton communities on these transects, and the Shannon Weaver index (H′) summed over all depths for each station appeared to approach an asymptote in most cases. Transect C (northeast of the other sites) showed a deeper mixed layer and greater diversity.

History and evolution of primary productivity studies of the Southern Ocean

The main objective of the article is to give an overview of the history and evolution of phytoplankton research in the Southern Ocean during the past century and a half. It traces the evolution of phytoplankton investigations as it went through several phases commencing with intensive collecting and cataloging and leading to the Discovery investigations with its extensive and detailed studies of Southern Ocean phytoplankton. Following, in the footsteps of the Discovery was the USNS Eltanin with its specialized cruises that centered around the study of the ecology of the primary producers and the dynamics of the lower trophic levels of the food chain. Spurred by the findings of the Eltanin cruises and with the growing concern over the impending exploitation of the Antarctic marine living resources, in particular krill, the BIOMASS program was initiated. The program was the first international collaborative effort to study the dynamic functioning of the Antarctic marine ecosystem. The success of the program has rekindled great international interest in the Southern Ocean which resulted in an explosion of programs such as SO-JGOFS, SO-GLOBEC, EPOS, and several others. In recent years, there has been a major shift in phytoplankton research in the Southern Ocean. This was in response to worldwide concern over the effects of global warming and stratospheric ozone depletion on species diversity, primary production and ecosystem function. This has led to process-oriented programs to study phenomena and processes of global significance in which Antarctica and its surrounding seas play key roles.

Phytoplankton Standing Crop and Primary Productivity in the Tropical Pacific

Phytoplankton standing crop and primary production were studied during the summer of 1975 and the winter of 1976, in the Deep Ocean Mining Environmental Study (DOMES) area between 5° – 20°N and 128° – 155°W. Chlorophyll a values (used as a measure of phytoplankton standing crop) averaged 0.063 mg/m3 in summer and 0.17 mg/m3 in winter. In the euphotic zone average values were 9.8 mg/m2 in the summer and 21 mg/m2 in the winter. The vertical distribution of chlorophyll a at the majority of the stations occupied was characterized by the presence of a subsurface chlorophyll maximum layer (CML). CML was found at a deeper depth (about 60 ± 24 m) in summer than in winter (about 54 ± 30 m). This layer occurred either at the middle or the bottom of the maximum density gradient (pycnocline) in summer whereas in winter it was found either at the top or the middle of the pycnocline. CML was also found to be closely associated with the distribution of the nutricline especially that of NO3-N.