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1

Diversity and biogeography of picoplankton communities from the Straits of Malacca to the South China Sea

Jiang Zhao-Yu, Sun Fu-Lin

Oceanological and Hydrobiological Studies

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2020

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Vol. 49, No. 1

23--33

EN

Marine picoplankton, including prokaryotic and eukaryotic picoplankton, drive many biogeochemical processes, such as carbon, nitrogen and sulfur cycles, making them crucial to the marine ecosystem. Despite the fact that picoplankton is prevalent, its diversity and spatial distribution from the Straits of Malacca (SM) to the South China Sea (SCS) remain poorly investigated. This work explores the phylogenetic diversity and community structure of picoplankton in relation to environmental factors from the SM to the SCS. To this end, the Illumina MiSeq sequencing technique was applied to 16S and 18S rRNA genes. The results showed significant differences in the dynamics of picoplankton between the open sea and the strait region. Proteobacteria and Cyanobacteria constituted a larger part of the prokaryotic group. Within Cyanobacteria, the abundance of Prochlorococcus in the open sea was significantly higher than that of Synechococcus, while the opposite trend was observed in the strait. Dinoflagellata, Cnidaria, Retaria, Tunicata, and Arthropoda dominated among the eukaryotic taxa. High-throughput sequencing data indicated that salinity, temperature and NO2-N were the key factors determining the prokaryotic community structure, while temperature and dissolved oxygen determined the eukaryotic community structure in the studied region. The network analysis demonstrated that the cooperation and competition were also important factors affecting the picoplankton community.

2

Spatio-temporal variability of the size-fractionated primary production and chlorophyll in the Levantine Basin (northeastern Mediterranean)

Yucel N.

Oceanologia

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2018

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No. 60 (3)

288--304

EN

Spatial and temporal variations in size-fractionated primary production (PP) and chl a, in relation to ambient physicochemical parameters, were studied in the three distinct ecosystems of northeastern Levantine Basin namely eutrophic Mersin Bay, mesotrophic Rhodes Gyre, and oligotrophic offshore waters. These ecosystems were visited in July and September 2012 and March and May 2013. Total primary production (TPP) rates ranged between 0.22 and 17.8 mg C m−3 h−1 within the euphotic zone, whereas depth-integrated TPP rates were in the range 21.5-348.8 mg C m−2 h−1 (mean: 105.5 ± 88 mg C m−2 h−1), with the lowest rates recorded for offshore waters. Similar spatio-temporal variations were observed in chl a concentrations, ranging from 2.3 to 117.9 mg m−2 (mean: 28.9 ± 24.9 mg m−2) in the study area. The Mersin Bay TPP rates have exceeded almost 8-12 times those measured in the offshore waters and the Rhodes Gyre; however, the chl a concentrations measured in coastal waters (0.343 mg m−3) and the Rhodes Gyre (0.308 mg m−3) were only threefold larger than the offshore values. PP and chl a were dominated by picoplankton in the study area whereas small nanoplankton, being the most active, displayed the highest assimilation ratio in offshore waters (6.8) and the Rhodes Gyre (2.8). In the upper-layer waters depleted of P (0.02-0.03 μM) of the northeastern Mediterranean, a positive correlation was observed between NO3 + NO2 and PP (and thus, chl a), which strongly suggests that reactive P and inorganic nitrogen are co-limiting factors in the production and biomass distribution of the phytoplankton community in both shelf and offshore waters.

3

Possible means of overcoming sedimentation by motile sea-picoplankton cells

Pundyak O.

Oceanologia

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2017

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No. 59 (2)

108--112

EN

A model for overcoming the gravity by sea-picoplankton cells is proposed here. It is based on different means of escaping from potential predators used by cells of co-existing picoplankton species. These different means cause friction anisotropy of motile cells with strong antipredator behavior (AB). According to equations of stochastic movement used in this model for picoplankton cells with strong AB, collocated with high concentration of cells with weak or absent AB, the sedimentation can be considerably overcome.

4

Seasonal changes in phytoplankton on the north-eastern shelf of Kangaroo Island (South Australia) in 2012 and 2013

Balzano S., Ellis A. V., Le Lan C., Leterme S. C.

Oceanologia

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2015

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No. 57 (3)

251--262

EN

This work investigates for the first time the seasonal changes in phytoplankton, bacteria, and photosynthetic picoplankton as well as nutrient concentrations on the North-western shelf of Kangaroo Island, South Australia. Seawater samples were collected off Penneshaw desalination plant, where waters from the Investigator Straight, Gulf Saint Vincent and Backstairs Passage meet. Low nutrient values were measured throughout the period of study (July 2012–July 2013) suggesting the occurrence of oligotrophic conditions on the region. The phytoplankton community was dominated by Bacillariophyceae, Dinoflagellata and Cryptophyta. Prochlorococcus Cyanobacteria prevailed among picophytoplankton during most of the period of study (July 2012–July 2013). Previous studies indicate that oligotrophic environments are indeed typically dominated by Prochlorococcus. The dominant species found here seem either adapted to grow under low nutrient concentrations, possessing high surface/volume ratios, or have a mixotrophic behaviour allowing them to complement photosynthesis with predation. This study provides base knowledge on the microbial communities north of Kangaroo Island that is needed to sustain the ecosystem and associated economic activities in the future.

5

Composition and abundance of picoplankton in the coastal zone of the Gulf of Gdańsk

Gławdel M., Mackiewicz T., Witek Z.

Oceanological Studies

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1999

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Vol. 28, No. 1-2

17-30

EN

With the aid of epifluorescence microscopy, picoplankton (0.2-2mum) in the coastal zone of the Gulf of Gdansk (southern Baltic) was studied from March to December 1997. The main portion of the picoplankton biovolume was comprised of bacteria, making up on average 70% of picoplankton. Autotrophic picoplankton (APP) prevailed over the bacterioplankton only in late August and early September. The main components of APP were cyanobacteria. The APP proportion in the total phytoplankton biomass was highest in summer. The assessment of this share in terms of quantity varied depending on the picoplankton separation method. In the microscopic analysis of unfiltered samples, all cells 2mum were counted as picoplankton, including colony-forming types. Based on the analysis of unfiltered samples, the amount of APP in the overall phytoplankton biomass was assessed at 16-22% in summer, and 0.5-6% in the remaining period. Initial filtration of samples through a 2mum filter caused great losses in APP, resulting mainly in the elimination of colony-forming cyanobacteria cells from samples. Prefiltered samples were also contaminated by cells 2mum. In prefiltered samples the APP proportion in the total phytoplankton biomass was 1-7% in summer and 0.2-3% in the remaining period.