Anita Jacobsen

ISOLATION AND CHARACTERIZATION OF A VIRUS INFECTING PHAEOCYSTIS POUCHETII (PRYMNESIOPHYCEAE)1

A virus infecting the haptophyte Phaeocystis pouchetii (Hariot) Lagerheim was isolated from Norwegian coastal waters in May 1995 at the end of a bloom of this phytoplankter. The virus was specific for P. pouchetii because it did not lyse 10 strains of P. globosa Scherffel, Phaeocystis sp., and P. antarctica Karsten. It was a double‐stranded DNA virus, and the viral particle was a polyhedron with a diameter of 130–160 nm. The virus had a main polypeptide of about 59 kDa and at least five minor polypeptides between 30 and 50 kDa. The latent period of the virus when propagated in cultures of P. pouchetii was 12–18 h, and the time required for complete lysis of the cultures was about 48 h. The burst size was estimated to be 350–600 viral particles per lysed cell.

Effects of increased concentration of nitrate and phosphate during a springbloom experiment in mesocosm

A mesocosm experiment was carried out in the early spring of 1991 (19 February to 20 March) in Raunefjorden, Norway. The experiment consisted of four enclosures of which two were initially supplied with nitrate and phosphate corresponding to an increase in concentration of 6 and 0.2 μM, respectively. Effects of an increased concentration of nitrate and phosphate on the development of the annual phytoplankton springbloom was investigated. Measurement of light, temperature, salinity, nutrients, chlorophyll (chl) a, primary production, phytoplankton enumeration and identification were performed daily or every other day. Average daily irradiance during the experiment was low (4.8 mol · m−2 · d−1). Maximum concentrations of biomass (chl a) and primary production were 11.5 μg chl a · 1−1 and 109 μg C ·1−1 · d−1. The initial phytoplankton community in all enclosures were dominated by diatoms, mainly Skeletonema costatum (Grev.) Cleve, and maximum cell number of this species was 11.2 · 106 1−1. After 1 wk, the diatoms were replaced by flagellates, due to silicate deficiency (< 2 μM). The fertilized enclosures were dominated by the haptophyte Phaeocystis cf. pouchetii (18 · 106 cells 1−1), and the non-fertilized enclosures were dominated by unidentified flagellates, together with cryptophytes and prasinophytes. High abundance of choanoflagellates and microzooplankton were also registered in the fertilized enclosures (3.3 · 106 1−1 and 11 · 106 1−1, respectively). This indicates that the microzooplankton may have controlled the growth of flagellates by grazing in the fertilized enclosures. The effect of an increased concentration of nitrate and phosphate was not an increase in biomass (chl a) or primary production, but a change in the species composition. The species composition changed from a diatom community dominated by S. costatum to a flagellate community dominated by P. cf. pouchetii. These results also suggest that major limiting factors for the biomass and primary production have been silicate deficiency, low irradiance and temperature.

Copepod grazing during a mesocosm study of an Emiliania huxleyi (Prymnesiophyceae) bloom

Abstract Five bottle incubation experiments were done to investigate the grazing and food selection by the copepod Calanus finmarchicus (Gunnerus) during a phytoplankton bloom in aN and P fertilized mesocosm. The phytoplankton biomass was dominated by diatoms and lager dinoflagellates ( 35 µm), and selective copepod predation may have controled the development of these protists in the mesocosm. However, diatoms made up the largest part of the copepod carbon ingestion due to their dominance in the plankton. The haptophytes E. huxleyi and Phaeocystis cf. pouchetii were not prefeITe...

Morphology, Relative DNA Content and Hypothetical Life Cycle of Phaeocystis Pouchetii (Prymnesiophyceae); with Special Emphasis on the Flagellated Cell Type

The flagellated stage in the genus Phaeocystis has only been described in a few studies and its significance in nature is poorly understood. A flagellated cell type of P. pouchetii was isolated from Raunefjorden (western Norway) and described for the first time by transmission electron microscopy and light microscopy studies. The present study shows that the flagellated cell type of P. pouchetii is morphologically different from other Phaeocystis species. Two types of body scales were found, which were different from those described for other species within the genus. The flagellated cells observed in this study produce pentagonal stars, implying only one type of flagellated cell. The ultrastructure of the flagellated cell type is also presented. Flow cytometric analysis of the relative DNA content of the flagellated and the non-motile coccoid colony cell types revealed similar amounts of DNA in the different cell types. No ploidy differences in the two cell types of P. pouchetii were thus shown under the current investigation. Based on the results obtained and literature information, a hypothetical life cycle for P. pouchetii is presented.

Does a large-scale continuous algal production system provide a stable supply of fatty acids to bivalve hatcheries?

The variation of fatty acid (FA) content and composition of the microalgal production (Isochrysis sp., Pavlova lutheri and Chaetoceros muelleri) in a continuous large-scale production system (500-L bags) used in hatcheries were analysed. The variation of the FAs was analysed in replicate bags over time for the different species. Total FA content (pg cell−1) increased significantly (p < 0.05) in the P. lutheri and C. muelleri bags over time. The content of the essential FAs (arachidonic acid (ARA), eicosapentaenoic acid (EPA), n-6 docosapentaenoic acid (n-6 DPA) and docosahexaenoic acid (DHA)) increased over time in all of the species, except for DHA in Isochrysis sp. The content of EPA and ARA were highest in C. muelleri, whilst n-6 DPA and DHA were highest in Isochrysis sp. The FA composition in the C. muelleri bags showed large variability between bags at the beginning of the experiment, but decreased over time. In contrast, the FA composition of Isochrysis sp. and P. lutheri did not vary much over time, but larger variability was observed between the replicate bags. The results indicate that, even though the essential polyunsaturated FAs (PUFAs) varied between the different species, the total microalgal production secured a stable and increased supply of all the essential PUFAs to the scallop larvae and spat.

Effect of different filter methods on seawater quality at a marine scallop hatchery.

The effect of using two different filtering methods in the main seawater inlet to a scallop (Pecten maximus) hatchery in Norway was tested. Seawater was filtered through active filter media (AFM) and a protein skimmer, or through a drum filter and a protein skimmer. Seawater quality was characterized and tested on algal growth rate, egg development and larval activity. Tests were performed under winter and spring conditions (March, April and May 2009). Both seawater treatments reduced the dissolved organic carbon concentrations in the inlet seawater. The total bacterial number was stable in both seawater treatments, except for an increase in the drum filter in March. The bacterial community showed seasonal development: Actinobacteria and Alphaproteobacteria dominated in March, while Gammaproteobacteria dominated in April and May. In a cluster analysis, samples from both seawater treatments showed high similarity on similar sampling dates. Vibrio spp. occurred, but was never observed in seawater coming from the skimmer after the drum filter. This sampling point was often clustered as most similar to the incoming seawater. The fraction of scallop eggs that developed into veliger larvae increased from 10% to 50% during the sampling period, and no significant differences were found between the two seawater treatments. The fraction of 8 day old active larvae was lowest in March, in experiments with both undiluted and diluted (1:10, 1:100) seawater from both treatments. No significant difference in activity was found between the treatments, except for undiluted (April) and 100-fold dilution (April and May) from the drum filter, when the larval activity was significantly higher. The effect of both seawater treatments was tested by growing the diatom Chaetoceros muelleri in small volumes for 4-5 days. Daily growth rates (μ) varied between 0.75 and 1.15, and were highest in May. No significant difference in cell concentration was found between the treatments. The results showed that the skimmer attached to the drum filter had the best performance overall in reducing dissolved organic carbon and potentially lethal bacteria. These findings have important implications for hatchery seawater management protocols.