Changes in coastal phytoplankton community structure under future climate conditions: A mesocosm study

Abstract

The coastal phytoplankton community under predicted ocean acidification and sea surface warming conditions was studied using an outdoor mesocosm approach. Nine mesocosm bags were filled with coastal waters from Jangmok bay in the South Sea of Korea. Control and two different treatments for the level of CO2 and temperature were set up in triplicates (control: 380 ppm, treatment I: 980 ppm, treatment II: 980 ppm and +3°C). Nutrients (nitrate, phosphate and silicate) were amended at the start of the experiment to facilitate phytoplankton growth. During the first 12 days of incubation when nutrients were replete, the highest phytoplankton biomass was observed in treatment I where diatoms were predominant (>95% of total phytoplankton biomass). As diatoms decreased, dinoflagellates increased for all conditions during the subsequent nutrient depleted period. The response of different phytoplankton species to the CO2 and temperature perturbations differed significantly. The diatom Skeletonema spp. showed positive growth in treatment I and II during the nutrient replete period, but no significant growth was observed during the nutrient deplete period. Chaetoceros socialis showed positive growth in treatment I, but in treatment II, negative growth was observed during the nutrient deplete period. Cerataulina dentata showed negative growth in both treatment I and II during the nutrient deplete period. The different responses ofof Korea. Control and two different treatments for the level of CO2 and temperature were set up in triplicates (control: 380 ppm, treatment I: 980 ppm, treatment II: 980 ppm and +3°C). Nutrients (nitrate, phosphate and silicate) were amended at the start of the experiment to facilitate phytoplankton growth. During the first 12 days of incubation when nutrients were replete, the highest phytoplankton biomass was observed in treatment I where diatoms were predominant (>95% of total phytoplankton biomass). As diatoms decreased, dinoflagellates increased for all conditions during the subsequent nutrient depleted period. The response of different phytoplankton species to the CO2 and temperature perturbations differed significantly. The diatom Skeletonema spp. showed positive growth in treatment I and II during the nutrient replete period, but no significant growth was observed during the nutrient deplete period. Chaetoceros socialis showed positive growth in treatment I, but in treatment II, negative growth was observed during the nutrient deplete period. Cerataulina dentata showed negative growth in both treatment I and II during the nutrient deplete period. The different responses of