Response of eelgrass Zostera marina to CO2 enrichment: possible impacts of climate change and...

Projected increases in dissolved aqueous concentrations of carbon dioxide [CO2 (aq)] may have significant impacts on photosynthesis of CO2-limited organisms such as seagrasses. Short-term CO2 (aq) enrichment increases photosynthetic rates and reduces light requirements for growth and survival of individual eelgrass Zostera marina L. shoots growing in the laboratory under artificial light regimes for at least 45 d. This study examined the effects of long-term CO2 (aq) enrichment on the performance of eelgrass growing under natural light-replete (33 % surface irradiance) and light-limited (5 % surface irradiance) conditions for a period of 1 yr. Eelgrass shoots were grown at 4 CO2 (aq) concentrations in outdoor flow-through seawater aquaria bubbled with industrial flue gas containing approximately 11 % CO2. Enrichment with CO2 (aq) did not alter biomass-specific growth rates, leaf size, or leaf sugar content of above-ground shoots in either light treatment. CO2 (aq) enrichment, however, led to significantly higher reproductive output, below-ground biomass and vegetative proliferation of new shoots in light-replete treatments. This suggests that increasing the CO2 content of the atmosphere and ocean surface will increase the area-specific productivity of seagrass meadows. CO2 (aq) enrichment did not affect the performance of shoots grown under light limitation, suggesting that the transition from carbon- to light-limited growth followed Liebig's Law. This study also demonstrated that direct injection of industrial flue gas could significantly increase eelgrass productivity; this might prove useful for restoration efforts in degraded environments. The broader effects of CO2 (aq) enrichment on the function of natural seagrass meadows, however, require further study before deliberate CO2 injection could be considered as an engineering solution to the problem of seagrass habitat degradation.