Phytoplankton biovolume can be measured or calculated through the calculation of similar geometric models. A set of geometric models is suggested for calculating cell biovolume and surface area for 284 phytoplankton genera in China Sea waters. Thirty-one geometric shapes have been assigned to estimate the biovolume and surface area of phytoplankton cells. Reductions of error and microscopic effort are also discussed. The model has been verified by its application in the China Seas regions. The software to make these calculations is available at http://www.ouc.edu.cn/csmxy/sunjun/biovolume.htm

We examined the effects of increased temperature, pCO₂, and irradiance on a calcifying strain of the marine coccolithophore Emiliania huxleyi in semi-continuous laboratory cultures. Emiliania huxleyi CCMP 371 was cultured in four temperature and pCO₂ treatments at both low and high irradiance (50 and 400 µmol photons m⁻² s⁻¹): (i) 20°C and 375 ppm CO₂ (ambient control); (ii) 20°C and 750 ppm CO₂ (high pCO₂); (iii) 24°C and 375 ppm CO₂ (high temperature); and (iv) 24°C and 750 ppm CO₂ (‘greenhouse’). The growth of E. huxleyi was greatly accelerated by elevated temperature at low irradiance. Photosynthesis was significantly promoted by increases in both pCO₂ and temperature at both irradiances. Higher cellular C/P ratios were found in the higher CO₂ treatments at high irradiance, indicating a reduced requirement for P. The PIC/POC (particulate inorganic to organic carbon) ratio remained constant at low light, regardless of CO₂ or temperature conditions. However, both the cellular PIC content and PIC/POC ratio were greatly decreased by elevated irradiance, and were further decreased by increased pCO₂ only at high light, indicating a combined effect of CO₂ and light on calcification. These results suggest that future trends of CO₂ enrichment, sea-surface warming and exposure to higher mean irradiances from intensified stratification will have a large influence on the growth of Emiliania huxleyi, and potentially on the PIC/POC ‘rain ratio’. Our study demonstrates that it is possible to obtain a more complete picture of global change impacts on marine phytoplankton by designing experiments that consider multiple global change variables and their mutual interactions.

International audienceThe North Atlantic spring bloom is one of the largest annual biological events in the ocean, and is characterized by dominance transitions from siliceous (diatoms) to calcareous (coccolithophores) algal groups. To study the effects of future global change on these phytoplankton and the biogeochemical cycles they mediate, a shipboard continuous culture experiment (Ecostat) was conducted in June 2005 during this transition period. Four treatments were examined: (1) 12°C and 390 ppm CO2 (ambient control), (2) 12°C and 690 ppm CO2 (high pCO2), (3) 16°C and 390 ppm CO2 (high temperature), and (4) 16°C and 690 ppm CO2 ('greenhouse'). Nutrient availability in all treatments was designed to reproduce the low silicate conditions typical of this late stage of the bloom. Both elevated pCO2 and temperature resulted in changes in phytoplankton community structure. Increased temperature promoted whole community photosynthesis and particulate organic carbon (POC) production rates per unit chlorophyll a. Despite much higher coccolithophore abundance in the greenhouse treatment, particulate inorganic carbon production (calcification) was significantly decreased by the combination of increased pCO2 and temperature. Our experiments suggest that future trends during the bloom could include greatly reduced export of calcium carbonate relative to POC, thus providing a potential negative feedback to atmospheric CO2 concentration. Other trends with potential climate feedback effects include decreased community biogenic silica to POC ratios at higher temperature. These shipboard experiments suggest the need to examine whether future pCO2 and temperature increases on longer decadal timescales will similarly alter the biological and biogeochemical dynamics of the North Atlantic spring bloom