The interacting effects of nutrient enrichment and ocean acidification on the growth and physiology of the macroalgae Ulva sp.
Leah B Reidenbach1, Catriona L Hurd2, Janet Kubler1, Pamela A Fernandez2, Pablo P Leal2, Fanny Noisette2, Andrew T Revill3 and Christina M McGraw4, (1)California State University, Northridge, Biology, Northridge, CA, United States, (2)Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, Australia, (3)Commonwealth Scientific and Industrial Research Organisation (CSIRO), Hobart, TAS, Australia, (4)University of New England, School of Science and Technology, Armidale, Australia
Abstract:
Ocean acidification, caused by the increased absorption of carbon dioxide in the ocean, changes the carbon chemistry in the seawater, decreases pH, and alters the chemical speciation of some nitrogenous compounds, such as ammonium. The green macroalgae
Ulva spp. are intertidal species that occur worldwide. Ocean acidification may alter the growth response of
Ulva sp. to increased nutrients by altering the photosynthetic and nutrient physiology of the algae as well as the bioavailability of nutrients. To determine if there is an interactive effect between ocean acidification and nutrient enrichment
Ulva sp. were grown in the lab in a cross of three
pCO
2 levels under ambient and enriched ammonium concentrations.
We predicted that the growth rates of Ulva sp. in ammonium enriched treatments would be enhanced by increased pCO2 relative to those in ambient ammonium concentrations. While growth rate, relative electron transport rates, and chlorophyll content were enhanced by enriched ammonium, there was no interactive effect of high pCO2 and ammonium enrichment. Ammonium uptake rates and ammonium pools were not affected by the pH and ammonium interaction, but nitrate reductase activity increased in the high pCO2, high ammonium treatments. Increased pCO2 has been found to increase Ulva sp. growth rates under some conditions, but this was not the case in this set of experiments. To make realistic predictions of Ulva sp. abundances into the future, based on better understanding of their physiology, ocean acidification experiments should include additional environmental variables such as light intensity and macronutrient supplies that may simultaneously be affected by climate change.
