Abstract:
Effects of air-sea interaction of carbon dioxide in the sea are highly speculated with
ocean acidification and alteration of seawater chemistry. This research studied the
effects of elevated carbon dioxide, pC02 towards health of scleractinian corals,
Porites cylindrica and Galaxea fascicularis by inspecting photosynthesis rate,
chlorophyll content, zooxanthellae cell density and calcification rate. Normal free
CO2 (aq) in seawater ranged from 23.34 - 38.65 μmol.kg- 1 while the elevated free CO2
(aq) was 67.32 - 109.44 μmol.kg- 1 • Daily, monthly and seasonal variation affects the
CO2 level depending on the geographic region, wind velocity and tidal range. Net
photosynthesis corresponds with high chlorophyll content resulting significant
increase in productivity for both species in elevated pC02 . High photosynthesis
activity causes high metabolism in algal cells. Zooxanthellae adjust to external stress
and facilitates uptake of elevated pC02 causing cell density in P. cylindrica and G.
fascicularis to decline 26.80% and 69.85% respectively. At high pC02, mitotic cell
division increases in G. fascicularis from 4.14% to 6.47% but decrease in P.
cylindrica from 2.31 % to 0.95%. Species-specific reactions retard zooxanthellae
reproduction in P. cylindrica while G. fascicularis shows stress-related response by
increasing mitotic division to replenish significant cell loss. Effects of elevated pC02
show species-dependant response in calcification by promoting dissolution rate in P.
cylindrica but facilitate carbonate precipitation rate in G. Jascicularis. Calcification
rate decline with time suggest the interacting effects of seawater carbonate chemistry
could affect calcification in marine calcifying organism such as planktonic pteropod,
foraminifera, echinoderm and coccolithophorid as predicted in future.