CLIMATE CHANGE EFFECTS ON SEAGRASSES, MACROALGAE AND THEIR ECOSYSTEMS: ELEVATED DIC, TEMPERATURE, OA AND THEIR INTERACTIONS Marguerite S. Koch, George E. Bowes, Cliff Ross, Xing-Hai Zhang Josh Filina, Kate Peach, Brent Anderson Aquatic Plant Ecology Laboratory, Biological Sciences Department, Florida Atlantic University Department of Biology, University of Florida Department of Biology, University of North Florida Why are Marine Macroalgae & Seagrasses Important? • • • • • • • • Habitat - Foundation Base Foodwebs Sediment Stabilization Sediment Generation Tropics Settlement Sites Corals Nutrient Cycling Competitors (Nuisance spp) Substrates - Epiphytes Outline Talk I. REVIEW i. ii. iii. iv. INORGANIC C SPECIATION CARBON LIMITATION ISSUES MECHANISMS C-ACQUISITION CASCADING EFFECTS OA CLIMATE CHANGE II. EXPERIMENTAL RESEARCH CO2 X TEMP INTERACTION Inorganic Carbon Speciation – Carbonate Equilibria (modified from Fabry et al . 2008) Review Marine Macroautotroph’s Inorganic-C Pathways, Bicarb Use and Ci Saturation • Primarily C3 species (>85%) • All use HCO3- (>99%) • External Carbonic Anhydrase (CAext) • Not saturated present [Ci] Review Climate Change and OA Effects on Marine Macro-autotrophs Koch, Bowes, Zang, and Ross (in press Global Change Biology) Carboxylation vs Oxygenation C3 Plants (Problem CO2 Affinity and Photorespiration) Carboxylation (Calvin Cycle) Oxygenation • C lost not recycled – up to 50% loss C • No ATP produced and loss ATP and NADPH • Increase in temperature results > photorespiration Carbon Concentration Mechanisms (CCMs) C4/HCO3(Adaptation to Low CO2 – Concentrate CO2 at Rubisco) C4 or C4 Like (Single Cell) Bicarbonate Uptake (CCM?) H+ ATPase pump-CO2 pump 2 4 5 H+ ATPase CO2 Pump? 3 1 Cytoplasm Chloroplast C4 Radakovits et al. (2012) 1. 2. 3. 4. C3 pathway and depend on CO2 diffusion H+ Pump to lower pH cell surface speed up hydrolysis reaction CA at Ocean pH Potentially a CO2 pump Bicarbonate Transporter intercellular CA Seagrasses and Marine Macroalgae Utilize HCO3- and CO2 Are They Saturated with Ci? 8 Photosynthesis (mg O2 g-1 dry wt h-1) DIC Ocean ~2.4 mM pH 7.80 pH 8.20 6 pH 8.61 4 • Not DIC Saturated • Higher P elevated CO2 • Can utilize HCO3- 2 0 0 2 4 6 8 10 12 14 Dissolved inorganic carbon (mM) Durako 1993 Thalassia testudinum (Seagrass – Angiosperm) Ocean Acidification and Climate Change Effects on Tropical Macroalgae and Seagrass CO2(atm) Atmosphere Ocean + CO32- - pH - + + + CA H+ CO2(aq) HCO3- - ΩCaCO3 CCM C4 / HCO3- Use - Dissolution Calcification + + + + Nutrient Cycling 0/+ + - Temp No CCM C3 + Growth 0/ + - + C:N:P + Biomass Competition Life History Fleshy Respiration Rubisco Down-regulation Photosynthesis + Calcifiers Photorespiration Anti-herbivory Metabolites - Herbivory - Competition Competition Life History Life History Seagrass + Cellular Stress Response System + Temp Thermal Threshold Cyanobacteria Experimental Mesocosms (OA x Temp) Experimental Design Amb pCO2 x Amb Temp Amb pCO2 x High Temp Feb 2012/ July 2011 High pCO2 x Amb Temp High pCO2 x High Temp Tank Avg (SE) n=6 Ambient High Treatment Temperature (oC) 24.8 /28.1 28.1/32.5 +4 oC pH 7.99/8.03 7.73/7.68 - 0.3 pH 13/11 25/25 108% increase CO2 (mmol kg-1) Photosynthesis Measurements (P:I curves) • Oxy-Lab 3 – 11 Light levels 0, 25, 50, 75, 100, 200, 400, 600, 800, 1000 and 1,200 mmol m-2 s-1 Elevated pCO2 x Temperature Winter Experiment Halimeda incrassata Sargassum fluitans 600 200 High Temp High CO2 400 100 200 0 0 High CO2 x Temp -200 600 n mol O2 gwwt-1 min-1 Control High CO2 x Temp -100 200 400 High Temp (28 oC) Control (24 oC) 100 200 0 0 High Temp -200 600 High Temp -100 200 400 High CO2 (1000 uatm) Control (400 uatm) 100 200 0 0 High CO2 -200 0 200 400 600 800 1000 1200 1400 PAR High CO2 -100 0 200 400 600 800 1000 1200 1400 PAR 100 Summer 2011 80 Sargassum fluitans Halimeda incrassata High CO2 60 Pmax (% Change from Controls) 40 20 High Temp (34 oC) 32 High Temp High CO2 0 -20 -40 CATH CHTA CHTH 100 Winter 2012 80 60 40 High Temp (28 oC) High CO2 20 0 High Temp High CO2 -20 -40 Conclusions • Ocean acidification (OA) effects on marine macroautotrophs: • Increased CO2 for C3 spp not able to employ CCMs • Increase rate of dehydration of HCO3- by external Carbonic Anydrase (CAext) • Lower CO32- and saturation states CaCO3 • Potentially uncouple photosynthesis-calcification reactions (calcifiers) • Elevated CO2 and temperature (+4oC) stimulates photosynthesis below thermal limits • Thermal stress creates a negative synergy between elevated Temp x CO2 • Calcifying species unlikely to respond to CO2 constrained low CaCO3 saturation states • Competition with fleshy species may also reduce calcified algae Future Research Needs • Basic research on photosynthetic biochemistry and calcification mechanisms and their responses to CO2 and Temperature • The effect of OA on CCMs and facultative use of various DIC acquisition systems • The role of temperature and light on DIC limitation and acquisition systems employed • Thermal limits of tropical species under climate change • Short-term physiological responses need to be linked to longer-term growth experiments in the mesocosm and field and interactions at the community Acknowledgements • • • • We sincerely thank Chris Langdon/Frank Millero pCO2 measurements Students laboratory/field/ review assistance FAU Climate Change Initiative Everglades National Park Questions?