<p>Cyanobacteria which can form resting cells (in this case akinetes) are common in meso-eutrophic lakes in temperate regions, often dominating the phytoplankton communities during summer. The life cycles of akinete-forming cyanobacteria has been studied with <i>Gloeotrichia echinulata</i> as a model organism. <i>Anabaena</i> and <i>Aphanizomenon</i> were also included in a migration study. The focus of this thesis has been the factors influencing the processes of germination and subsequent growth, the factors influencing migration from the sediment, and the amount of growth occurring in the water. </p><p>Germination of <i>G. echinulata</i> was strongly favoured by light, and recruitment was highest from organic-rich sediments in shallow, sheltered littoral areas, between 0-3 m. Recruitment of <i>Anabaena</i> and <i>Aphanizomenon</i> was less light dependent, yet the highest recruitment occurred from shallow sediments (0-2 m). This means that organic-rich sediments (0-3 m) in shallow areas are the most important seed-banks of akinete-forming cyanobacteria. The inocula contributed only to a minor extent to the maximum pelagic populations. 4% for <i>G. echinulata</i> in the mesotrophic Lake Erken, and 0.03% for both <i>Anabaena</i> and <i>Aphanizomenon</i> in the eutrophic Lake Limmaren. This implies that processes of growth and division in the water are important for the maximum size of the pelagic population. Prolonged recruitment from the sediment strongly promoted establishment of the species in the water, especially <i>G. echinulata</i>. </p>

Cyanobacteria which can form resting cells (in this case akinetes) are common in meso-eutrophic lakes in temperate regions, often dominating the phytoplankton communities during summer. The life cycles of akinete-forming cyanobacteria has been studied with Gloeotrichia echinulata as a model organism. Anabaena and Aphanizomenon were also included in a migration study. The focus of this thesis has been the factors influencing the processes of germination and subsequent growth, the factors influencing migration from the sediment, and the amount of growth occurring in the water. Germination of G. echinulata was strongly favoured by light, and recruitment was highest from organic-rich sediments in shallow, sheltered littoral areas, between 0-3 m. Recruitment of Anabaena and Aphanizomenon was less light dependent, yet the highest recruitment occurred from shallow sediments (0-2 m). This means that organic-rich sediments (0-3 m) in shallow areas are the most important seed-banks of akinete-forming cyanobacteria. The inocula contributed only to a minor extent to the maximum pelagic populations. 4% for G. echinulata in the mesotrophic Lake Erken, and 0.03% for both Anabaena and Aphanizomenon in the eutrophic Lake Limmaren. This implies that processes of growth and division in the water are important for the maximum size of the pelagic population. Prolonged recruitment from the sediment strongly promoted establishment of the species in the water, especially G. echinulata.

Freshwater green algae within species complex Haematococcus pluvialis are best natural producers of secondary carotenoid astaxanthin famous for its strong antioxidant activity. Despite worldwide distribution, great biotechnological potential and extensive literature dealing with different approaches to the cultivation of these organisms, there still remains surprising gaps in knowledge of their complex life cycle and behaviour. First uncertainty concerns asexual cell division of zoospores, hypothetically limited to five cell doublings (Lee & Ding 1994). No such genetic limitation was observed in this thesis, number of cell divisions is thus influenced mainly by cultivation conditions. There is still considerable uncertainty regarding to the asexual reproduction, as well. Ambiguity might be caused by scarce observation of the whole process of gametogenesis and conjugation of gametes. Published studies differed in some particular points. Unfortunately, we did not succeed in induction of gametogenesis despite broad scale of tested cultivation conditions applied to two different species within the H. pluvialis complex, namely H. pluvialis and H. rubicundus. This failure might be caused by heterothalism of the studied strains. Haematococcus pluvialis inhabits mainly ephemeral pools. Its ability to...