Seasonal variation in chlorophyll-specific phytoplankton growth and zooplankton grazing in an artificial pond of Kuwabukuro biotope park

We investigated the seasonal variation of specific growth and grazing rate, zooplankton and phytoplankton species and chlorophyll α concentration, and examined the relationship between the phytoplankton biomass and species, and specific grazing rate and zooplankton species in a pond of the Kuwabukuro biotope park in April-December 2012. The chlorophyll α concentration ranged from 10 to 161 μg L-1 and was the maximum value in August. The specific growth rate showed in the range of 0.05 to 1.46 d-1 and the maximum value in June. The specific grazing rate was in the range of 0.05 to 0.71 d-1, and the maximum value in June. The value of the specific grazing rate reduced to 0.28 d-1 in July and increased to 0.61 d-1 in August. The values were lower than the specific growth rate throughout the study period. A significant positive relationship was found for the specific grazing and growth rate（ p < 0.05, n = 9）. It is thought that the specific grazing rate increased due to the fact that the specific growth rate increased with water temperature and the amount of solar radiation. Cell number of diatom negatively correlated with individual number of nauplius from April to July （p < 0.05, n = 4）. Consequently, it is possible that the nauplius top-down controlled the cell number of diatom. As blue-green algae were dominated in July, one factor the specific grazing rate was greatly reduced in July might be due to an increase in blue-green algae, Microcystis novacekii . In the biotope pond, a bloom of phytoplankton, particularly green algae, occurred in August, because the specific grazing rate of zooplankton was reduced by blue-green algae in July, and the higher water temperature and the amount of solar radiation and the lower N/P ratio in August.departmental bulletin pape