On population dynamics in multi-species cultures of diatoms and dinoflagellates

Abstract

In order to assess the phenomena possibly underlying population dynamics and species succession in the sea, the following phytoplankton culture experiments were made. In uni-algal and in multi-algal batch cultures, generation times and cell yields gained during logarithmic growth were determined for the diatomsBiddulphia regia andCoscinodiscus concinnus, as well as for the dinoflagellates,Ceratium horridum andProrocentrum micans. In multi-species cultures, none of the tested organisms showed any influence on generation time, compared with uni-algal cultures. In contrast, the cell yield of different species showed considerable changes depending on the species concerned and the species-combination used. The dinoflagellatesC. horridum reached, if cultivated together withB. regia orB. regia andC. concinnus, only 10% of the cell number of uni-algal cultures. In the combinations tested,B. regia produced always more than half of the cell number attained in uni-algal cultures. In multi-species cultures,C. concinnus cell production was not affected. Addition of nitrate and phosphate to stationary-phase multi-species cultures induced further growth. Thus it is concluded that growth is limited by nutrient competition in the multi-species experiments conducted. Possible mechanisms of nutrient competition are discussed.