Effects of Ocean Acidification on Bioerosion of Burrowing Bivalves in French Polynesia Valentino, L.M. and Carpenter, R.C. California State University, Northridge
INTRODUCTION METHODS RESULTS
Rela on of borehole opening and Lithophaga Erosion of sclerac nian corals, is an integral part of reef dynamics, • Collected Porites containing Lithophaga and extracted the bivalve therefore inves ga ng the impacts of OA on bioerosion will be • Measured major and minor axis of the borehole opening and valve length and height important in predic ng poten al outcomes of our changing • Photos of opening and valves analyzed using ImageJ so ware environment. Figure 2. Correla on between the major axis of the borehole opening and the shell length. R2=0.52
Glynn 1997 Bioerosion Rates
0.25 -1 • Bioerosion: natural process of carbonate erosion by living day Figure 3. Es mated 0.20 -2 organisms bioerosion rates of
• Climate change and anthropogenic ac vi es threaten the balance Lithophaga in Porites in 0.15 elevated and ambient pCO between coral reef construc on (calcifica on) & destruc on 2 0.10 removed cm
3 (bioerosion) treatments. P=0.747 (n=28) Mesocosm experiment with Lithophaga cores 0.05 • Nega ve affects of climate change can increase coral mortality Hypothesis: Bioerosion rates of Lithophaga will increase within corals exposed to increased pCO 0.00 which also will increase area available for bioeroders to colonize 2 mg CaCO • Coral cores collected from the backreef of Mo‘orea at a depth of 1-3.0m using a pneuma c AMBIENT ELEVATED • Studies show that bioerosion rates will increase with increasing drill pCO with certain species 2 • 112 cores with and without Lithophaga were acclimated to laboratory condi ons for a week • Massive Porites is one of the most common components of pacific and sealed with epoxy reef flats • 28 day mesocosm experiment was conducted to test the effect of ambient (~400ppm) and Net Calcifica on Rates • Macroborer Lithophaga laevigata (boring bivalve) selec vely (Area Normalized) Figure 4. Area- normalized elevated (~850ppm) pCO on the bioerosion rate of Lithophaga 2 1.4 net calcifica on rates of se les on and erodes into Massive Porites in Mo‘orea °C • -1 Four replicate tanks (150 L) were used for each pCO2 treatment, held at 28 , and supplied 1.2 Porites with and without day 1 with filtered (50 µm) seawater -2 −L Lithophaga. Two-way 0.8 cm
• Treatments were maintained through bubbling of ambient air or pCO2 enriched air controlled 3 +L ANOVA results: 0.6 by a solenoid-gas regula on system CO2 P=0.007 0.4 Lithophaga P=0.011
• mg CaCO 0.2 LED lamps supplied light levels similar to what the coral is exposed to naturally 0 Lith x CO2 P=0.619 (n=28) AMBIENT ELEVATED
Average Respira on Rate (Lithophaga) Figure 5. Respira on rates of 0.3
0.3 Lithophaga in burrow -1 hr 0.2 mimics a er 28 days in -1 Acclima on tank
mg • 0.2
In Mo‘orea, Lithophaga laevigata abundance in massive Porites 2 elevated and ambient pCO2 2 O ranged in abundance from 3 to 122 ind/m 0.1 Mesocosms treatments. P=0.0439 (n=12)
3 -2 -1 umol • Bioerosion rate of Lithophaga can reach 9,000 g CaCO m yr 0.1 Seawater chemistry methods 0.0 • Temperature, flow rate, and salinity were monitored daily AMBIENT ELEVATED • Spectrophotometric determina on of pH using m-cresol purple dye • Total alkalinity (TA) was measured regularly using poten ometric tra on using Dickson et al. LOCATION (2003) reference materials • Carbonate chemistry was calculated using TA and pH was measured using R so ware • Net calcifica on and bioerosion rates were measured to test the effects of elevated pCO2 on DISCUSSION bioerosion rate of Lithophaga • Net calcifica on was determined from the change buoyant weight of Porites cores and -2 -1 • Results from the regression showed significant correla on normalized to surface area (mg CaCO3 cm day ) between the bore hole opening and size of the bivalve • Allowed for a non-destruc ve method to iden fy the size of the
infaunal bivalve • Bioerosion rates represented ~15% of net calcifica on rates • While bioerosion rates were not significant, it is important to note that my results were conserva ve considering the mescale of this natural process Respira on chambers Respira on experiment with Lithophaga in burrow mimics • Bioerosion rates of Lithophaga could poten ally elevate on carbonate accre ng under an OA regime over longer mescales Hypothesis: The respira on rates of Lithophaga will increase with increased pCO2 • Lithophaga in burrow mimics were incubated in mesocosms using methods listed above for • Nega ve impact of elevated treatment and Lithophaga on net 28 days calcifica on, showed an addi onal nega ve impact of this Figure 1. The island of Mo‘orea, French Polynesia. The Richard B. • Post incuba on, Lithophaga selected randomly from elevated and ambient treatments were ubiquitous coral associate Gump South Pacific Research Sta on (designated by star) and used in dark respira on trails in confined 160mL respirometers • Significant increase in respira on rates indicated metabolic stress, Mo‘orea Coral Reef LTER is located on the north shore of Cook’s • Oxygen deple on was recorded over me using a calibrated fiber op c oxygen sensor and could have indirect effects on erosion rates due to increased pCO inside the burrow Bay. • Flow was maintained using a s r-bar and temperature was kept constant 2
• Respira on rates were normalized to the dry so ssue weight of each individual
Acknowledgements: I would like to thank H Hillard, J Hayes, A Brown, A Briggs, S Swanson, V Moriarty. This work was supported by grants received from the US Na onal Science Founda on to the MCR-LTER (1026851 and 1236905), R. Carpenter and P. Edmunds (1041270), and funds from the Gordon and Be y Moore Founda on.