Greta A. Fryxell

ALGAL ASSEMBLAGES IN ANTARCTIC PACK ICE AND IN ICE-EDGE PLANKTON1

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.

Austral spring microalgae across the Weddell Sea ice edge: spatial relationships found along a northward transect during AMERIEZ 83

In the northwestern Weddell Sea and eastern Scotia Sea on a transect north from ice-covered, through ice-melt, to open-ocean stations, microalgae were compared to document an enhanced biological activity expected near the ice edge. The highest numbers of cells were found in open water, with 68.7 × 109 cells m−2 north of the ice edge, although melted ice cores and brine from pore water samples averaged more than an order of magnitude more cells per liter. The dominant taxa under the ice and in the ice-melt stations were the pennate diatom genus Nitzschia and the prymeesiophyte Phaeocystis. In the open ocean, the dominants were the centric diatom Thalassiosira gravida and Phaeocystis; both grew in gelatinous colonies, a growth habit that apparently gave competitive advantage and may have inhibited grazing. Phaeocystis could have been seeded from the melting ice and from the water under the ice; it seems less likely that T. gravida came only from those sources. Although Phaeocystis cells were frequently dominant in number, the genus represented far less carbon than T gravida in open waters; Phaeocystis presents a taxonomic and ecological enigma in comparison with accounts from the northern hemisphere in that it was abundant where diatoms also fluorished. Nitzschia survived in low light under the ice and in the brine pockets in the ice and increased steadily in abundance at the ice edge in the open water, whereas Thalassiosira was most abundant to the north and west where the water had recently been uncovered by the retreating ice edge. Of the three dominant taxa, Nitzschia appears to provide the best food base for the zooplankton such as krill.

Morphology, phylogeny and taxonomy of species within the Pseudo-nitzschia americana complex (Bacillariophyceae) with descriptions of two new species, Pseudo-nitzschia brasiliana and Pseudo-nitzschia linea

Abstract Pseudo-nitzschia americana and the two closely related species P. brasiliana Lundholm, Hasle & G.A. Fryxell sp. nov. and P. linea Lundholm, Hasle & G.A. Fryxell sp. nov. are described, based on morphology. The phylogenetic positions of P. americana and P. brasiliana are inferred from partial nuclear-encoded large-subunit ribosomal DNA and their toxin production is assessed. The new species P. brasiliana and P. linea form stepped colonies, whereas P. americana is single celled. Pseudo-nitzschia americana, P. brasiliana and P. linea possess morphological features typical of Pseudo-nitzschia and Fragilariopsis, differentiating them from Nitzschia. All three species possess valve shapes similar to many Fragilariopsis species and they seem to constitute a morphological continuum between Pseudo-nitzschia and Fragilariopsis. Molecular phylogenetic analyses showed P. americana and P. brasiliana to be sister taxa within a strongly supported monophyletic clade comprising Pseudo-nitzschia and Fragilariopsis. On the basis of both the morphological and phylogenetic results, we conclude that P. americana can be assigned to Pseudo-nitzschia, following previous uncertainty as to whether it might belong to Nitzschia. Both P. americana and P. linea have been observed as epiphytes on other diatoms, which might indicate physiological differences from P. brasiliana, which has only been found free-living. In addition, P. americana and P. brasiliana differ with respect to valve width (transapical axis), the density of the transapical ribs (interstriae) and fibulae and the structure of the girdle bands (copulae). The results of the phylogenetic analyses and differences in distribution support these morphological differences. Pseudo-nitzschia linea differs with respect to valve shape, density of interstriae and structure of the girdle bands.

THALASSIOSIRA ECCENTRICA (EHRENB.) CLEVE, T. SYMMETRICA SP. NOV., AND SOME RELATED CENTRIC DIATOMS1

Examination of original material from the Ehrenberg collection plus clonal cultures from the Gulf of Mexico and net hauls from widely separated stations in the worlds oceans confirms that Coscinodiscus eccentricus is correctly placed as Thalassiosira eccentrica (Ehrenb.) Cleve. A closely related species, T. symmetrica, is described, with, the main differences being found in the value processes and distribution patterns. The former species is more abundant in inshore waters; the latter has been found in oceanic waters. Comparisons are drawn between these 2 species, T. mendiolana and Planktoniella sol.

Marine phytoplankton at the Weddell Sea ice edge: Seasonal changes at the specific level

SummaryThe Antarctic ice edge acts as a dynamic frontal system on the phytoplankton in the water column. Austral spring and autumn cruises to the Weddell Sea ice edge provided the opportunity to compare phytoplankton at the beginning of biological spring and at the end of biological autumn. The USCGC icebreakers Westwind (1983) and Glacier (1986) went into the sea ice, and the RV Melville (1983 and 1986) completed the transects in the adjacent open ocean. Field samples were observed alive on board ship to record different lifestages near the ice edge. In both seasons cell numbers were low under the ice, and single cells or short chains were the common growth habit. In spring in the open ocean, long chains of vegetative cells with large vacuoles and gelatinous colonies of diatoms and of prymnesiophytes dominated; in autumn in the open ocean close to the accreting ice edge, short chains, single cells, and resting spores were mostly packed with storage products. Enlarged cell diameters and auxospores also occurred near the ice cover in the autumn. Species from the following genera are included: the diatoms Leptocylindrus, Stellarima, Thalassiosira, Eucampia, Corethron, and Chaetoceros, the prymnesiophyte Phaeocystis, and the chrysophyte Distephanus.

Fragilariopsis cylindrus (Grunow) Krieger: The most abundant diatom in water column assemblages of Antarctic marginal ice-edge zones

SummaryPlanktonic diatoms were sampled in the ice-edge zone of the Bellingshausen Sea during the early austral spring of 1990 and of the Weddell Sea during the late spring of 1983, the autumn of 1986, and the winter of 1988. The four cruises in the Antarctic marginal ice edge zones, combined with the summer cruise in Prydz Bay during a brief ice-free period (1988) provided us with opportunities for spatial and seasonal studies of diatom abundance and distribution in the water column. Cells from discrete water samples from 73 stations near the marginal ice-edge zones during all seasons were counted to gain quantitative information on the composition, abundance, and distribution of diatoms. Diatom abundance was dominated by the pennate diatom, usually nanoplanktonic, Fragilariopsis cylindrus (Grunow) Krieger, during all five cruises. The highest integrated numbers of F. cylindrus were found during the summer cruise with 7.9 × 1010 cells m−2 and the lowest numbers were found during the winter cruise with 1.1 × 108 cells m−2. The average integrated abundance of F. cylindrus from the five cruises was about 35% of the total diatom abundance. The overall spatial pattern of F. cylindrus near the marginal ice-edge zones during the five seasonal cruises were similar with the highest number of cells in open waters compared to ice-covered waters. When all 73 stations during the five cruises were included in the correlation analysis, the abundance of total diatoms was positively correlated with the abundance of F. cylindrus, suggesting that the ice-edge pulses of diatom assemblages in the water column largely reflected its abundance. Cluster analysis revealed that the stations in marginal ice-edge zones were not only separated by seasons and locations, but they also separated based on location of stations in relation to the ice edge (open water stations vs. ice-covered stations).

Micro-phytoplankton at the equatorial Pacific (140°W) during the JGOFS EqPac Time Series studies: March to April and October 1992

Abstract Micro-phytoplankton (>20 um cell size) was sampled in the upper 200 m of the water column at the Pacific equator, 140°W during two JGOFS EqPac Time Series (TS) Studies, in order to determine the changes in the micro-phytoplankton assemblage between March–April and October 1992, to find the vertical distribution of micro-phytoplankton taxa, and to relate any changes in the environmental factors to micro-phytoplankton structure. Cell abundance and carbon biomass of three major taxonomic classes: diatoms, dinoflagellates and coccolithophorids were examined. During the abnormal warmth of El Nino 1992 (SST = 28−29°C), low abundance ( −1 ) and carbon biomass ( −1 ) characterized the micro-phytoplankton structure, accompanied by low numbers of diatoms and coccolithophorids. Pennate diatoms, Pseudonitzschia delicatissima and thecate dinoflagellate, Oxytoxum variabile , were the most abundant organisms observed during March–April 1992 Time Series study. The microphytoplankton assemblage during El Nino conditions in March–April 1992 exhibited lower microphytoplankton species richness and abundance compared with October 1992. Also in contrast to the spring, in October 1992 the micro-phytoplankton assemblage showed large variability, mainly due to the passage of an instability wave through the study site. During this period, the coldest temperatures (SST = 25°C) were associated with increased abundance (range = 2 × 10 2 to 12 × 10 3 cells liter −1 ) and richness in micro-phytoplankton species assemblage, which was again dominated by a colonial pennate diatom P. delicatissima . On the average, micro-phytoplankton carbon ranged from 0.5 to 4.0 μg C liter −1 , where the diatom group consistently comprised the major part of the micro-phytoplankton autotrophic biomass in the upper 60 m. Large centric diatoms, such as Rhizosolenia species, as well as chains of P. delicatissima united in stepped colonies, and heavily silicified species of the Thalassionema/Thalassiothrix spp. complex were important groups contributing to the total micro-phytoplankton carbon biomass. At the equator, diatoms and dinoflagellates were restricted to the surface and to the upper 60 m, respectively, during both Time Series cruises, while coccolithophorid cells were concentrated at 90 m during TS I. The presence of an El Nino event and a instability wave during March–April and October 1992, respectively, may explain most of the variability in abundance and species richness found in the equatorial Pacific at 140°W during the study periods.

PSEUDO‐NITZSCHIA PUNGENS AND P. MULTISENES (BACILLARIOPHYCEAE): NUCLEAR RIBOSOMAL DNAS AND SPECIES DIFFERENCES1

The region of the nuclear ribosomal DNA (rDNA) operon containing the small subunit (SSU), internal transcribed spacer 1 (ITS1), and a portion of the 5.8s rDNA gene was sequenced in one isolate each of Pseudo‐nitzschia multiseries (Hasle) Hasle and Pseudo‐nitzschia pungens (Grunow in Cleve & Möller) Hasle. The SSUs of these two species were highly similar, differing only in 14 point mutations and one insertion/deletion in 1774 bp. The ITS1 sequences were more variable, with 57 point mutations and three insertion/deletions in 257 bp. There were no differences in 44 bp of the 5.8S sequences. Restriction fragment patterns (RFPs) for the restriction endonucleases HaeIII, Hha1, and Rsa1 for 13 isolates of P. multiseries from the Atlantic, Pacific, and Gulf coasts of the United States and 16 isolates of P. pungens from the three coasts of the United States, in addition to Japan and China, were compared. There were differences between the RFPs of P. multiseries and P. pungens that corresponded to sites mapped by the DNA sequences, but no infraspecific variation in RFPs was observed for either species. The differences in RFPs correlate with morphological, immunological, and other rDNA differences and support the recognition of these taxa as separate species.

CHAIN-FORMING DIATOMS: THREE SPECIES OF CHAETOCERACEAE1,2

Bacteriastrum furcatum Shadbolt, Chaetoceros bacteriastroides Karsten and C. pseudocurvisetum Mangin are each connected in chains by fusion of silica between setae. The first two have specialized heterovalvate end cells indicating physiological control of the length of chains, but chains of C. pseudocurvisetum have usually been seen broken. There are specialized deeply lobed connecting bands in B. furcatum and C. pseudocurvisetum, allowing the setae of sibling valves to protrude outside the diameter of the chain during their formation. C. bacteriastroides and C. pseudocurvisetum are not identical; differences include presence of small setae, fusion of large setae some distance from the valves, symmetry of apertures between cells, and straight chains of C. bacteriastroides, compared with valve mantle connections with no small setae, large setae joined by crossing over, asymmetry of windows between cells, and curved chains of C. pseudocurvisetum. The evolutionary direction is hypothesized to be from Bacteriastrum to Chaetoceros through C. bacteriastroides.

Detection of the marine toxins okadaic acid and domoic acid in shellfish and phytoplankton in the Gulf of Mexico

Liquid chromatographic analyses of extracts from shellfish and phytoplankton from the Gulf of Mexico indicated the presence of the marine toxins okadaic acid (0.162 microgram/g shellfish) and domoic acid (2.1 pg/cell phytoplankter). These toxins are causative agents of diarrhetic shellfish poisoning (DSP) and amnesic shellfish poisoning (ASP), respectively. The presence of DSP and ASP toxins in a region with no previous record of outbreaks may indicate a potential for human poisoning under conditions appropriate for accumulation of these toxins in shellfish.