Phytoplankton production and consumption rate in the warm and cold seasons in the coastal ecosystem of Matsu Island

Abstract

To elucidate the trophic link between classical and microbial food webs in the coastal ecosystem of Matsu Island during the warmer (27.5°C) and colder (16°C) months, we estimated the impact of mesozooplankton and microzooplankton grazing on > 20 μm and < 20 μm phytoplankton groups, respectively. In the warmer months, the > 20 μm fraction of Chl a accounted for more than 70% of the total Chl a; however, the Chl a > 20 μm fraction contributed little to the total phytoplankton biomass, at about 16%, in the colder months. Overall, the < 20 μm fraction represented 26 and 90% of the < 200 μm daily primary production in the warmer and colder months, respectively. Furthermore, the grazing loss of mesozooplankton on microzooplankton was 4.7 mgC m-3 d-1 in the warmer months; however, no significant loss rate was measured in the colder months. The results showed that large autotrophs (> 20 μm) were available for direct mesozooplankton ingestion, which indicated that they could be considered as an important link in the complex food web structures, particularly during the warmer season.