Phytoplankton are crucial to maintaining the stability of marine ecosystems. Understanding the mechanisms controlling phytoplankton growth and biomass and accurately predicting changes in marine primary production is essential for evaluating the pace and impact of global climate change. To investigate the interactive effects of environmental factors such as temperature and nutrients on phytoplankton growth, we conducted a series of temperature- and nutrient-manipulated dilution experiments at two subtropical coastal sites in Dongshan Bay. We assessed the thermal traits of phytoplankton growth, including the temperature sensitivity (in terms of activation energy E_a) and optimal temperature (T_opt) under varying nutrient conditions and the nutrient utilisation capacity of phytoplankton (regarding the half-saturation constant K_n) at different temperatures. The experiments were conducted every month. Our preliminary results (six months of experiments) indicated that the T_opt of phytoplankton significantly decreased under low nutrient conditions, and the E_a of phytoplankton growth decreased when nutrient concentration may limit their growth. However, the effect of temperature on nutrient utilisation by phytoplankton (i.e., K_n) remains unclear and needs further investigation. Our findings highlight the interactive effects of temperature and nutrients on phytoplankton growth and underscore the necessity of considering multiple environmental factors when evaluating the response of marine primary production to global warming.

phytoplankton, growth rate, warming, nutrient, dilution technique