Phytoplankton seasonal cycle

Winter: Low production, deep mixing and mixed out of euphotic zone. Spring: Thermocline is stronger, high biomass, diatoms stop growing. Zooplankton have longer generation times and leads to lag phase and the increase of grazers. Increase ammonia excretion. Si recycling is slow so diatoms are being replaced by microflagellates. Late summer: Increased grazing activity results in more re-generation of nutrients & there can be a late summer bloom. Dinoflagellates may sometimes dominate giving rise to ‘red tides’. Late Autumn: More heat is lost, thermocline is eroded, phyt. are mixing below the euphotic zone.