Parallel plastic tank experiments with cultures of marine diatoms

In a southern Norwegian fjord (Rosfjord) during POSER a plastic enclosure (1 m 0, 20 m depth) was filled with filtered fjord water enriched with inorganic nutrients and inoculated with a monoculture of Skeletonema costaturn. The enclosure was exposed to fjord conditions from March 18 to April 5, 1979. Pre-filtration had removed ca. 80 % of the bacterial population in the fjord water. Following a short lag phase, bacteria grew exponentially. After consumption of nitrogen-containing organic substances, dissolved carbohydrates were the main energy source; however, bacterial numbers did not increase further, probably due to grazing by nanoflagellates. In spite of sub-optimal light and temperature conditions, S. costaturn reached cell densities as high as 35. 106 dm-3 at 3 m water depth, since competing algae and grazing zooplankton were missing in the enclosure. The diatoms grew exponentially, with a division rate of p = 0.6 d-' and reached the stationary phase after 16 d, when inorganic nutrients were exhausted. During growth of S. costatum relatively high amounts of carbohydrates were released. Maximum concentrations followed the exponential phase, but highest release rates per cell -2.0 pmoles glucose equivalents cell-' d-' -were reached immediately after inoculation. Measurements at 3 h intervals at the end of the experiment showed that concentrations and therefore release activities varied abruptly within a few hours. Main release occurred from noon to midnight. Not all dissolved carbohydrates were immediately taken up by heterotrophic organisms, part of them could not be utilized, others only after adaptation or succession of bacteria. During the experiment, the proportion of the labile fraction to the total dissolved carbohydrates varied greatly.

Section: Succession Of Organotrophic Microorganismscontrasting

confidence: 53%

Section: Growth Of Skeletonema Costatummentioning

confidence: 92%

Total dissolved carbohydrates in an enclosure experiment with unialgal Skeletonema costatum culture

Eberlein¹,

Brockmann²,

Hammer³

et al. 1983

“…The inhibitory effects during POSER were comparable to those obtained by Azam et al (1977); the stronger increase of bacteria after addition of nutrients and mercury was comparable to results obtained by Azam et al (1977) and Kuiper (1980Kuiper ( , 1981. This stronger increase is probably caused by increased substrate availability from dead phytoplankton and absence of inhibitory substances, sometimes released by exponentially growing phytoplankton (Brockmann et al, 1977). In this respect, the bacterial decrease in the non-polluted, but nutrientspiked bags, between Days 7 and 11, may be interpreted as an inhibition effect by the exponentially growing phytoplankton at this time.…”

Section: Bacteriasupporting

confidence: 88%

Effects of mercury on enclosed plankton communities in the Rosfjord during POSER

Kuiper¹,

Brockmann²,

Groenewoud³

et al. 1983

During POSER 2 experiments were performed to study the effects of a single addition of mercury (11) chloride on the development of plankton communities enclosed in large plastic bags. containing 1.5 to 30 m3 water and ranging from 3 to 40 m in depth. The experiments lasted 1 and 3 wk. respectively. In one of these experiments the influence of an additional dose of nutrients was studied. During both experiments mercury concentrations in the water decreased after the addition. Part of the mercury was found in the sediment collected on the bottom of the bags during the experiment, but most of the mercury probably volatilized and was lost to the atmosphere. Addition of 1 or 5 yg Hg I-' in the first experiment resulted in lower numbers of bacteria than in the controls. The first experiment was too short to show effects on phytoplankton and zooplankton. Addition of 5 pg Hg 1-' in the second experiment inhibited bacteria and phytoplankton, and increased the mortality of copepods, which formed the principal part of the zooplankton. Our results are comparable to those obtained during other experiments with natural marine plankton communities also enclosed in large plastic bags in fairly different sea areas Addition of nutrients stimulated phytoplankton growth, but had no observable effects on bacteria or zooplankton.

“…did not tolerate confinement in the incubating chambers, and led Garcés & Massó (2001) to suggest that the difference between in situ division rates and net growth estimated from cell counts in incubation chambers could be used as an estimation of in situ cell lysis. Cell counting or other approaches applied to large (>1 m 3 ) mesocosm bags (Brockmann et al 1977) were not used, as it would not have allowed representative sampling without disturbance of the vertical structure of the water column. To avoid secondary effects of the incubation techniques it was decided to try the maximum frequency (Swift & Durbin 1972) and the mitotic index (McDuff & Chisholm 1982) approaches as modified by Vaulot (1992) and by Carpenter & Chang (1988) respectively.…”

Section: Introductionmentioning

confidence: 99%

Cell cycle patterns and estimates of in situ division rates of dinoflagellates of the genus Dinophysis by a postmitotic index

Reguera¹,

Garcés²,

Pazos³

et al. 2003

A cell cycle-analysis method based on morphological recognition of cytokinesis and sulcal list regeneration was chosen to estimate in situ division rates (µ) of 4 dinoflagellate species of the genus Dinophysis, associated with diarrhetic shellfish poisoning (DSP), following 2 different models. Sampling over 24 h was conducted on 4 mini-cruises in the Galician rías during spring and autumn proliferations of these species. Frequencies of paired and recently divided cells in integrated water samples (0 to 20 m) were measured at 30, 60, or 120 min intervals. Cellular division was phased in D. acuminata, D. acuta, D. caudata and D. tripos, but the shape of the phase fraction curves and the values of estimated division rates varied considerably between seasons and cruises for the same species. Frequencies of paired plus recently divided cells were maximal at dawn in D. acuminata, and 2 to 3 h later in the other species. The results presented here confirm that the cytokinetic (paired) phase can be very fast in Dinophysis spp. (0.3 to 2.7 h), but sulcal list regeneration was shown to be a more stable process and an unambiguous marker of cellular division. This 'postmitotic index' allowed estimates of µ at low field concentrations (10 2 to 10 3 cell l -1 ) of the target species and required a short time for sample processing (1 to 2 h per sample). Moderate (0.24) to high (0.57) values of µ were found under oceanographic conditions considered unfavourable for growth of Dinophysis spp., and the phase in the population growth season seemed to be a key factor affecting this value. A critical revision of previous results of asynchronous division obtained in cell cycle studies of Dinophysis spp. is presented. It is suggested that monitoring the content of DNA per cell through the cell cycle in Dinophysis spp. is not a reliable method until a reasonable knowledge on the nuclear behaviour during sexual processes and other nonmitotic processes is available for these species, and that even accepting that mitosis is a non-return process, cell division may be arrested in one of its phases, adding further inconsistencies to µ measurements based on quantification of DNA per cell.