Combined effects of CO₂, temperature, irradiance and time on the physiological performance of Chondrus crispus (Rhodophyta)

Abstract

In natural environments, marine biotas are exposed to a variety of simultaneously acting abiotic factors. Among these, temperature, irradiance and CO₂ availability are major factors influencing the physiological performance of marine macroalgae. To test whether elevated levels of CO₂ may remediate the otherwise reduced performance of uncalcified seaweeds under the influence of other stressful abiotic factors, we performed multi-factorial experiments with the red alga Chondrus crispus from Helgoland (North Sea) with two levels of CO₂, temperature and irradiance: low and high pCO₂ levels were tested in combination with either (1) optimal and low irradiances or (2) optimal and sub-lethal high temperatures for growth. Performance of C. crispus was evaluated as biomass increase and relative growth rates (RGR), gross photosynthesis and pigment content. Acclimations of growth and photosynthesis were measured after 4 and 8 days. Acclimation time was crucial for elucidating single or combined CO₂ effects on growth and photosynthesis. Significant CO₂ effects became evident only in combination with either elevated temperature or reduced irradiance. Growth and photosynthesis had divergent patterns: RGR and biomass significantly increased only under a combination of high pCO₂ and elevated temperature; gross photosynthesis was significantly reduced under high pCO₂ conditions at low irradiance. Pigment content varied in response to irradiance and temperature, but was independent of pCO₂.