Showing papers in "Journal of Plankton Research in 1992"
448 citations
TL;DR: The present work indicates that the most effective measure to prevent the spreading of toxic dinoflagellate cysts via ships' ballast water would be to avoid taking on ballast water during din oflageLLate blooms in the water column of the world's ports.
Abstract: Diatom and dinoflagellate species that are not endemic to a region can be inadvertently
introduced when their resistant resting stages are discharged with the ballast-tank waters and
sediments of bulk cargo vessels. A survey of 343 cargo vessels entering 18 Australian ports showed
that 65% of ships were carrying significant amounts of sediment on the bottom of their ballast tanks.
All of these samples contained diatoms, including species that are not endemic to Australian waters.
Diatom resting spores, especially of Chaetoceros , were also detected. Dinoflagellate resting spores
(cysts) were present in 50% of the sediment samples. Of the 53 cyst species identified, 20 (including
Diplopelta, Diplopsalopsis, Gonyaulax, Polykrikos, Protoperidinium, Scrippsiella and
Zygabikodinium spp.) were successfully germinated to produce viable cultures. Such diversity of
diatom and dinoflagellate species in ships' ballast water suggests that the apparent 'cosmopolitanism'
of many coastal phytoplankton species may be due partly to the global transport of seawater ballast.
Of considerable concern was the detection in 16 ships of cysts of the toxic dinoflagellates
Alexandrium catenella, Alexandrium tamarense and Gymnodinium catenatum . One single ballast
tank was estimated to contain >300 million viable A. tamarense cysts, some of which were
successfully germinated in the laboratory to produce toxic cultures. These toxic dinoflagellate
species, which can contaminate shellfish with paralytic shellfish poisons, pose a serious threat to
human health and the aquaculture industry. Ballast-water quarantine measures recently introduced
in Australia are discussed. Mid-ocean exchange of ballast water is only partially effective in removing
dinoflagellate cysts which have settled to the bottom of ballast tanks. The present work indicates that
the most effective measure to prevent the spreading of toxic dinoflagellate cysts via ships' ballast
water would be to avoid taking on ballast water during dinoflagellate blooms in the water column of
the world's ports.
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108 citations
TL;DR: Cladoceran grazing on bacteria was important in both lakes contrary to the initial expectation and emphasize the significance of cladocerans and attached tlagellates as consumers of bactena in freshwater ecosvstems.
Abstract: We tested the hypothesis that grazing on bacteria would vary between lakcs with differing plankton community structures. Paul and Tuesday lakes (Gogebic County. MI) are respectively dominatcd by piscivorous and planktivorous fish. Consequcntly, zooplankton in Paul are primarily large daphnids, while zooplankton in Tuesday are primarily small cladocerans and copepods. Wc measured flagellate grazing on bacteria using a fluorescent minicqll method, while cladoceran grazing was estimated from the relationship between body length and filtering rate. We predicted that cladoceran grazing on bacteria would bc higher in Paul, and f'lagellate grazing would be highcr in Tuesday. Cladoceran grazing on bacteria was important in both lakes contrary to our initial expectation. Large populations ofthe small cladoceran, Bosmina longirostris, in Tuesday exertcd a grazing pressure (0.18-35 x 106 bacteria I ' h ') approximately equal to that of thc large cladoceran, Daphnia pulex, in Paul (0.34-30 x 106 bacteria I ' h ').Flagellate grazingwas higher in Tuesdayaspredict ed(range: Paul,0.l 6 x l06bacterial rh rlTuesday.0.2-20 x 10('bacterial I h '). Hrrwever, there was not a simple relationship bctwcen total abundance of flagellates and total grazing rates. High community grazing by flagellates occurred when attached choanoflagellates were present. These flagellates had higher ingestion rates than free forms. We find no clear evidcnce that differences in food-web structure between the two lakes influence the process ofgrazing on bacteria. Instead, our results emphasize the significance ofcladocerans and attached tlagellates as consumers of bactena in freshwater ecosvstems.
108 citations
TL;DR: Protozoan bacterivory and production of bacteria were simultaneously measured in the mesotrophic Rimov Reservoir from April to November, 1988 and ciliates, not HNF, were the most important bacterial micrograzers through the summer-fall period.
Abstract: Protozoan bacterivory [via uptake of fluorescently labelled bacteria (FLB)] and production of bacteria ([H]thymidine assay) were simultaneously measured in the mesotrophic Rimov Reservoir (Southern Bohemia) from April to November, 1988. Heterotrophic nanoflagellates (HNF) were mostly responsible for a greater fraction of protozoan bacterivory during the spring period. From 10 to 23% of bacterial production was grazed daily with the only exception of the spring peak of ciliate abundance (up to 60%). Protozoans decreased significantly during the clearwater phase (ciliates disappeared), and thus their role in bacterivory was negligible. Through the summer-fall period ciliates, not HNF, were the most important bacterial micrograzers. Protozoan community grazing balanced or even exceeded the daily bacterial production in August and September. Alternate fates of bacterial production besides protozoan grazing during the spring period are discussed.
TL;DR: Cyanobacteria populations were much larger than those of microalgae in the 80-100 m upper layer, whereas the latter were more numerous at that depth and below the chorophyll maximum, shows how the communitv structure is related to the depth and gradient of the nitracline.
Abstract: The distribution of physical and chemical parameters and their impact on the biomass and abundance of phytoplankton in the Western Pacific Ocean were compared in two opposing situations: the El Nino Southern Oscillation (ENSO) event of 1987 and the non-ENS0 period of 1988. During El Nino conditions (September 1987), maximum cell abundance was recorded at 10"s at the boundary between the South Equatorial Current (SEC) and the South Equatorial Countercurrent (SECC). In September 1988, after the return of non-ENSO conditions, a well- established equatorial upwelling produced an increaseb the surface layer nutrient supply over 7" of latitude. This in turn caused an increase in phytoplankton populations in the upper layer, with chlorophyll concentrations >0.2 mg mb3 and cyanobacteria and microalgae populations X.0 X lo6 1-' and >1.2 X lo6 I-' respectively. Integrated over 120 m, the cyanobacteria and microalgae populations were respectively 4.7 and 3.2 times larger than the year before. On the other hand, transient nutrient inputs such as those observed at 10"s in September 1987 caused a large increase in cyanobacteria populations (4.4 times), compared with those in neighbouring zones, and a somewhat smaller increase in microalgae populations (1.3 times). Cyanobacteria populations were much larger than those of microalgae in the 80-100 m upper layer, whereas the latter were more numerous at that depth and below the chorophyll maximum. Population variations in cyanobacteria were accom- panied by changes in form, size and fluorescence of the cells. The analysis of the 52 profiles of depth distribution of cyanobacteria and microalgae shows how the communitv structure is related to the depth and gradient of the nitracline. L> .:Fot -taire