Guy Hällfors

Records of chrysophytes with siliceous scales (Mallomonadaceae and Paraphysomonadaceae) from Finnish inland waters

Seventy-three taxa of silica-scaled chrysophytes were found with LM and TEM in 264 samples from 141 Finnish water bodies, including the genera Mallomonas (40 taxa), Synura (9), Chrysosphaerella (3), Spiniferomonas (8) and Paraphysomonas (13). More than half of the taxa are recorded for the first time from Finland and five (Mallomonas actinoloma v. actinoloma, M. favosa, M. mangofera f. gracilis, M. scrobiculata and Spiniferomonas serrata) are new to Europe. Most taxa are illustrated with TEM micrographs and the taxonomy of some interesting species is discussed in detail. The seasonal occurrence of the commonest species is described.

A Field Manipulation of Trophic Interactions in Rock-Pool Plankton

Three rock-pools (ca. 10 Daphnia 1-1, ca. 100 Daphnia 1and > 100 Daphnia 1-1) were each bisected with a plastic curtain. One side of each pool was left intact, while planktivorous fish were introduced into the other side. The succession of the zooplankton and phytoplankton communities in the rock-pools was followed, using quantitative sampling, for one summer. In the experiment the fish eliminated large (> 0.5 mm) herbivorous cladocers from the zooplankton within 20-40 d of introduction. An increase in the numbers of small zooplankton (rotifers, cladocers) then occurred. In the control sides large Daphnia thrived well, though with fluctuating densities, throughout the summer. The response of phytoplankton to the elimination of large herbivores varied between the rock-pools. In terms of species diversity and evenness no obvious differences were observed between control and experiment in the rock-pool with low Daphnia density. In the medium-density rock-pool both species diversity and evenness were lower in the experimental part, while in the high-density rock-pool the opposite was observed. In these two pools elimination of Daphnia resulted in an increase in total numbers of cells 11 of 2-3 orders of magnitude. The difference between control and experimental parts was due to the increase in small cells (< 64 Bm diameter). The elimination of large herbivores resulted in lowered densities (low-density) or elimination (medium and high-density) of filamentous algae from the phytoplankton.

The transfer of two epipsammic diatom species to the genus Martyana

Investigation by SEM of the diatoms previously known as Fragilaria atomus Hustedt and Opephora schulzii (Brockmann) Simonsen showed that these species should be transferred to the genus Martyana Round.

The extensive bloom of alternate-stage Prymnesium polylepis (Haptophyta) in the Baltic Sea during autumn–spring 2007–2008

During autumn 2007, an unusual increase in an algal species belonging to the order Prymnesiales was observed throughout the Baltic Sea Proper during routine national monitoring. Electron microscopical examination of the blooming species showed two types of flat scales – small and large – that resembled those of the alternate stage of Prymnesium polylepis. No spine-bearing scales were found. The 18S rDNA sequence data (n = 20, c. 1500 bp) verified the species identification as P. polylepis. There was up to 0.5% (7 bp) variability in the P. polylepis partial 18 S rDNA sequences from the Baltic Sea. These environmental sequences differed by 0–0.35% (0–4 bp) from cultured P. polylepis (isolate UIO036), and by 1.0–3.7% from other available Prymnesium sequences. The number of cells assumed to be P. polylepis began to increase in October 2007 coincidently with significantly calm and dry weather, and at their maximum the cells accounted for over 80% of the total phytoplankton biovolume in December–January. During February–April 2008, 95% of the Prymnesiales cells were in the size class of P. polylepis (>6 µm). The species attained bloom concentrations (>1 × 106 cells l–1) from March to May 2008. The species was observed throughout the Baltic Sea, except the Bothnian Bay, Gulf of Riga and the Kattegat. No toxic effects of the bloom were observed.

TAXONOMY AND ECOLOGY OF CATACOMBAS OBTUSA COMB. NOV.

A taxonomic investigation of the diatom previously known as Synedra tabulata var. obtusa (Pantocsek) Hustedt shows that it differs from Tabularia fasciculata and that it should be transferred to the genus Catacombas Williams & Round. The ecology of the species is discussed.