Introduction

Chrysophytes are known to be characteristic of slightly acid, soft waters with low alkalinity and conductivity, and with moderate or low productivity (Sandgren 1988; Siver & Hamer 1989). These characteristics are typical for Finnish lakes. In addition to the diatoms and cryptophytes, the chrysophytes are important phytoplankton groups in Finnish lakes (e.g. Heinonen 1980; Eloranta 1986a). Most of the studies concerning chrysophytes in Finnish lakes are general phytoplankton surveys, but there are also some floristic studies that concern only chrysophytes (Kristiansen 1964; Eloranta 1985, 1989a, Asmund & Kristiansen 1986; Hällfors & Hällfors 1988). Eloranta (1989b) also studied the ecology of the genus Dinobryon in Finnish lakes. Some chrysophytes have siliceous scales which remain in lake sediments, and have been used since the late 1960s for paleolimnological purposes (Fott 1966; Munch 1980; Smol 1980; Smol, this volume). Some records of scales in sediments of Finnish lakes have also been reported (Battarbee et al. 1980; Tolonen et al. 1986; Christie et al 1988).

This study investigates chrysophyte ecology and seasonality in different areas of Finland, and explores some of the relationships of chrysophyte distribution with environmental factors.

Materials and methods

Phytoplankton collections from 329 lakes located in different parts of Finland are included in this survey. Information for a total of 55 lakes, mostly from coastal areas and northern Finland, was obtained from literature records (Lepistö et al. 1981).