Viviana A. Alder

The influence of copepod and krill grazing on the species composition of phytoplankton communities from the Scotia-Weddell sea

The influence of copepods (mainly Oithona sim-ilis) and krill (Euphausia superba) grazing on the species composition of plankton communities in ship board con tainers was investigated during the spring and post spring period in the Scotia Weddell Sea in the Antarctic ocean. Numbers of grazers were experimentally manipulated in containers with natural phytoplankton assemblages. With ratural levels of copepods but no krill a high (700–950 μg C·l1, ca 30 μg chl a·.l1) phytoplankton biomass developed. In these cultures large diatoms, e.g. Corethron criophilum and chains of Thalassiosira sp., made up 80% of total phytoplankton cell carbon at the end of the experiment. In cultures with elevated numbers of copepods (5X or 10X the natural level) phytoplankton biomass was somewhat reduced (ca 23 μg chl a · l1) compared to cultures with natural copepod abundance, but still high. Phytoplankton species composition was on the other hand greatly influenced. Instead of large diatoms these cultures were dominated by Phaeocystis pouchetii (70%) together with small Nitszchia sp. and Chaetoceros neogracile (20%). In containers with krill (both juveniles and adults), but without elevated numbers of copepods, phytoplankton biomass rapidly approached zero. With 10X the in situ level of copepods, krill first preyed on these before Corethron criophilum and Thalassiosira sp. were grazed. When krill were removed a plankton community dominated by flagellates (60–90%), e.g. Pyramimonas sp. and a Cryptophycean species, grazed by an unidentified droplet-shaped heterothrophic flagellate, developed. These flagellates were the same as those which dominated the plankton community in the Weddell Sea after the ‘spring bloom’. A similar succession was observed in situ when a krill swarm grazed down a phytoplankton ‘bloom’ in a few hours. Our experiments show that copepods cannot control phytoplankton biomass in shipboard cultures even at artificially elevated numbers. Krill at concentrations similar to those in natural swarms have a great impact on both phytoplankton biomass and species composition in shipboard cultures. Both copepods and krill may have an impact on phytoplankton species composition and biomass in situ since the rates of phytoplankton cell division were probably artificially increased in shipboard cultures compared to natural conditions, where lower growth rates make phytoplankton more vulnerable to grazing. A similarity between phytoplankton successions in containers and in situ, especially with respect to krill grazing, supports the conclusion that grazing may structure phytoplankton communities in the Scotia-Weddell Sea.

Utility of Genetic Markers and Morphology for Species Discrimination within the Order Tintinnida (Ciliophora, Spirotrichea)

We evaluated the small- and large-subunit rDNA (SSU and LSU, respectively) for their ability to discriminate morphospecies of tintinnid ciliates. Multiple individuals from 29 morphospecies were identified according to microscopically-observed characteristics of the lorica, and then sequenced for both loci (21 new species for SSU and all of them new for LSU). Sequences from public databases were included in our analyses, and two hypervariable SSU regions (V4 and V9) were separately examined. Of the four regions, LSU is the most useful as a potential barcoding tool. It showed a gap in distances within and between species, and discriminated the maximum number of phylotypes (86% at 1% cut-off). SSU and V4 were less consistent, sometimes lumping together very distinctive morphospecies, even at the 1% level of sequence divergence. V9 was the least reliable marker in delimitating morphospecies. The agreement in sequences and morphology suggests that the lorica is useful for species discrimination, even in agglomerated forms. However, the observation of both genetically constant yet polymorphic groups of species, as well as similar morphospecies with divergent sequences, indicates that previous taxonomic schemes are complementary to the emerging molecular database.

Summer Weddell sea microplankton: Assemblage structure, distribution and abundance, with special emphasis on the Tintinnina

SummarySilicoflagellates, large thecate dinoflagellates and tintinnids were counted and measured in screened (26 μm pore-size) pump-samples retrieved from a depth of ca. 9 m in February-March 1987 along a two-leg north-south transect in the Weddell Sea (approx. 62°S to 78°S). Fourteen tintinnid taxa were identified and their individual abundances and biomasses were estimated. Highest biomass, in terms of organic carbon, was recorded for the Tintinnina, which averaged 4.001 mg C m-3, with mean cell-numbers of 161 ind. l-1 (maximum: 859 ind. l-1); followed by the dinoflagellates (1.018 mg C m-3, mean: 192 ind. l-1; max.: 1176 ind. l-1); and the silicoflagellates (0.391 mg C m-3, mean: 467 ind. l-1, max.: 3123 ind. l-1). Conspicuous abundance and settling volume peaks were recorded at some distance off the edge of the ice-pack (at approx. 69°S to 72°S), and in the ice-covered area south of 74–75°S. This pattern was paralleled by changes in the specific makeup of tintinnid assemblages: in the ice-covered southern area Cymatocylis drygalskii and Laackmanniella prolongata were dominant, while in ice-free waters north of 73°S Codonellopsis gaussi, Cd. glacialis and Cymatocylis affinis/convallaria were the main components of the fauna. Overall tintinnid abundances were higher than those reported for many (but not all) extrapolar areas, and the average size of the species present was considerably larger than elsewhere; tintinnid carbon figures were therefore very high, oscillating around 2 mg C m-3 in the northern ice-free area, and 20 mg C m-3 in the southern ice-covered zone.

Microplanktonic distributional patterns west of the Antarctic Peninsula, with special emphasis on the Tintinnids

SummaryMicroplankton was sampled with a centrifugal suction pump in the surface layer (approx. 9 m) of the Bellingshausen Sea and the Bransfield Strait in March 1987, and concentrated with a 26μm-mesh net. Bulk microplanktonic settling volumes were assessed, silicoflagellates and large thecate dinoflagellates were counted, and tintinnids were counted and identified to species. Average (and maximum) values for the entire area surveyed were as follows, settling volume: 6.7 (43.3) ml/m3; silicoflagellates: 674 (7777) ind./l, 0.57 (6.54) mg C/m3; dinoflagellates: 109 (1321) ind./l, 1.40 (16.98) mg C/m3; tintinnids: 52 (589) ind./l, 1.15 (9.87) mg C/m3. The three geographic zones defined objectively on the basis of tintinnid specific assemblages also differed sharply in their surface salinity, overall microplanktonic abundance and bulk settling volume. The Bransfield Strait, with lowest settling volume values (2.1 ml/m3) and cell concentrations, was characterized by the dominance of Cymatocylis affinis/convallaria. In waters around the tip of the Antarctic Peninsula microplanktonic settling volumes averaged 4.6 ml/m3, cell concentrations were intermediate, and 79% of the tintinnids were represented by Codonellopsis balechi. The Bellingshausen Sea was characterized by the lowest salinities and the highest settling volumes (8.7 ml/m3) and cell counts; Laackmanniella spp. and Cymatocylis drygalskii, f. typica dominated this area. Almost all biological variables were significantly intercorrelated, and showed strong and mostly significant negative correlations with surface salinity, yet relationships between enhanced standing stock and ice meltwater were not obvious; rather, highest microplanktonic concentrations seemed to be due to ice-associated growth. Extremely high spatial correlations were found between the tintinnids and the dinoflagellates (r2: 0.941), suggesting the existence of close links between these two groups. Tintinnid species-specific assemblages show a coherent distributional pattern and well defined environment-related trends; most clearly differentiated preferences are exhibited by Laackmanniella prolongata (closely associated with ice-covered areas), Cymatocylis affinis/convallaria (oligotrophic open-ocean waters), and Codonellopsis balechi (coastal regions).

Radiolarian sedimentary imprint in Atlantic equatorial sediments: Comparison with the yearly flux at 853 m

Abstract Radiolarian specific compositions in a series of 20 sediment trap samples covering an entire year (1.3.1989 to 16.3.1990, collected at 853 m) were compared with bottom (0–1 cm) materials from the same site (eastern equatorial Atlantic: 01°47.5′N, 11°07.6′W). Data on mean sediment accumulation rates at the site of the mooring (1.59 g/cm2/kyr), mean radiolarian flux at 853 m (28,446 shells/m2/day), and abundance in the 0–1 cm bottom layer (48,258 shells/g) suggest that approximately 95% of the radiolarians produced are lost to the fossil record. Sediment trap sample-to-sample correlations (based on relative abundances of 40 radiolarian species present at levels≥ 1% in at least one sample, mean value, r=0.886) did not differ significantly from correlations between each water column sample and surface sediments (meanr=0.878). Similarities between the flux and the sediments were not associated with time of year and with periods of enhanced radiolarian output. Two taxa had lower, and nine taxa had higher percentage contributions in the sediments than in any one sediment trap sample, and a few of the abundant species had averages up to 7 times higher in either the water column or the sediments. These dissimilar percentage loadings are attributed to selective dissolution, lateral subsurface and deep advection of shells from higher-latitude areas, and identification biases. As opposed to species-level inventories, family-level databases (including shells identified to family only) differed significantly between the water column and the sediments. Spumellaria (especially Spongodiscidae) were more abundant in the sediments (35%) than in the water column (19%), while Nassellaria showed the opposite trend (64% and 80%, respectively). It is suggested that ease of identification of spongodiscid fragments and fragility of juvenile nassellarians are responsible for these differences.

Updating Biodiversity Studies in Loricate Protists: The Case of the Tintinnids (Alveolata, Ciliophora, Spirotrichea)

Species determination is crucial in biodiversity research. In tintinnids, identification is based almost exclusively on the lorica, despite its frequent intraspecific variability and interspecific similarity. We suggest updated procedures for identification and, depending on the aim of the study, further steps to obtain morphological, molecular, and ecological data. Our goal is to help improving the collection of information (e.g. species re‐/descriptions and DNA barcodes) that is essential for generating a natural tintinnid classification and a reliable reference for environmental surveys. These suggestions are broadly useful for protistologists because they exemplify data integration, quality/effort compromise, and the need for scientific collaborations.

The ecology and biogeography of tintinnid ciliates in the Atlantic sector of the Southern Ocean

Abstract Qualitative and quantitative analyses of the tintinnids retrieved in surface and vertical (down to 1150 m ) samples in the Scotia, Weddell, Bransfield and Bellingshausen areas allow us to define three distinct zones: (A) the Scotia Sea, Bransfield Strait and oceanic waters of the northern-central Weddell Sea, dominated by Codonelopsis gaussi and Cymatocylis affinis/conmllaria ; (B) shelf and mostly ice-covered areas of the southernmost Weddell Sea and the Bellingshausen Sea, characterized by Laackmanniella prolongata and Cymatocylis drygalskii ; (C) Bransfield-Weddell waters around the tip of the Antarctic Peninsula, where Codonellopsis balechi accounts for 80% of the tintinnids. These areas have (often significantly) different ice regimes, water-column depths, surface salinities, bulk planktonic settling volumes and microplanktonic concentrations. On the other hand, the composition of tintinnid assemblages is very similar on both sides of the Antarctic Peninsula. Causal interpretations for these heterogeneous distribution patterns and probable specific adaptations to the dissimilar environmental settings involved are analyzed.

Phylogeny of the order Tintinnida (Ciliophora, Spirotrichea) inferred from small- and large-subunit rRNA genes.

Concatenated sequences of small‐ and large‐subunit rRNA genes were used to infer the phylogeny of 29 species in six genera of Tintinnida. We confirmed previous results on the positions of major clusters and the grouping of various genera, including Stenosemella, the paraphyletic Tintinnopsis, the newly investigated Helicostomella, and some species of the polyphyletic Favella. Tintinnidium and Eutintinnus were found to be monophyletic. This study contributes to tintinnid phylogenetic reconstruction by increasing both the number of species and the range of genetic markers analyzed.

Copepod distribution in surface waters of the Drake Passage using Continuous Plankton Recorder and a Pump-Net onboard system

There is no single instrument that can sample quantitatively the complete spectrum of pelagic organisms, or even all the components of zooplankton. Mesh size is the main factor affecting species selectivity in the Continuous Plankton Recorder (CPR), implying a need to use multiple net systems to fully characterize a community. The spatial distribution of copepod communities in the water masses of the western and eastern sectors of Drake Passage were studied using, respectively, a CPR and a Pump Net onboard system. For this purpose, and assuming that copepod community size structures of each of the three water masses were similar in both the sectors studied, the possibility of complementing CPR results using a Pump-Net onboard system was evaluated. The latter system allows the estimation of absolute abundances and has the advantage of solving two problems associated with CPR, namely mesh clogging and low catching efficiency. The contribution of the nauplius forms and species accurately identified with both samplers was analyzed. Although Oithona similis dominated both communities, in the western sector small species made a greater contribution than Calanus simillimus, the opposite being true for the eastern sector. Nauplii and early copepodite stages of O. similis were missing from the CPR samples and represented between 69 and 79% of total copepod communities, whereas small calanoid copepods, C. simillimus copepodites and later stages of O. similis were inaccurately sampled by the CPR and represented between 14 and 18% of the copepod community. Hence, the Pump Net sampler is useful for complementing the semi-quantitative information of the CPR and for its calibration.

Incorporación de nitrato por fitoplancton en dos ambientes marinos diferentes de la provincia de Chubut (42°-46°S, Argentina)

Resumen es: La distribucion espacio-temporal de los nutrientes y procesos de produccion primaria son fundamentales para la comprension del funcionamiento de ecosiste...