11th ICRS Abstract book - Nova Southeastern University

Oral Mini-Symposium 3: Calcification and Coral Reef - Past and Future
3-13
Dissolution of Calcium Carbonate in Coral Reefs
Hajime KAYANNE* 1 , Atsushi WATANABE 2 , Makoto TERAI 1 , Shoji YAMAMOTO 1 ,
Tatsuki TOKORO 1 , Ken NOZAKI 3 , Ken KATO 3 , Akira NEGISHI 3
1 Department of Earth and Planetary Science, University of Tokyo, Tokyo, Japan,
2 Hydroshperic Atmospheric Research Center, Nagoya University, Nagoya, Japan,
3 National Institute of Advanced Industrial Science and Technology, Tsukuba, Japan
Acidification of the ocean by anthropogenic CO2 absorption leads to decrease in the
saturation state of calcium carbonate, and thus calcification in the ocean. Dissolution of
calcium carbonate is predicted to occur in the high-latitude ocean, where aragonite
saturation state will become under-saturated during the 21st century. On the other hand,
coral reefs distributed in the tropical ocean have high saturation state, and is not thought
to be dissolved by the acidification. However, on-site continuous monitoring of alkalinity
in reef water at Shiraho Reef in the Ryukyu Islands showed that dissolution actually
occurred during nighttime as shown by increase in total alkalinity. Even during the time
of the dissolution, aragonite saturation state never decreased below one. When the
aragonite saturation state decreased below 3, net calcification becomes 0 and dissolution
occurred below this value. During nighttime, aragonite saturation state in pore water of
the reef sediment decreased below 2, which is lower than the saturation state of the water
column but still over-saturated for aragonite. We thought magnesian calcite contributed
to the dissolution, as it is generally soluble than calcite and aragonite but little
information has been obtained so far. We conducted a laboratory experiment to examine
its dissolution. Magnesian calcite started to dissolve under aragonite saturation state of
2.0. Based on the field monitoring and laboratory experiment, we hypothesided that
saturation state decreases below this threshold value in pore water of the sediment, and
magnesian calcite starts to dissolve even at present condition. The results suggest that
coral reefs are more soluble than has been thought and may act as a large buffer against
CO2 increase.
3-14
Use Of Replicated Coral Reef Mesocosm Studies To Establish The Potential Impact
Of Ocean Acidification.
Paul L. JOKIEL* 1 , Ku'ulei S. RODGERS 1 , Ilsa B. KUFFNER 2 , Andreas
ANDERSSON 3 , Fred T. MACKENZIE 4 , Evelyn F. COX 1
1 Hawaii Institute of Marine Biology, University of Hawaii, Kaneohe, HI, 2 Florida
Integrated Science Center, U. S. Geological Survey, St. Petersburg, FL, 3 Bermuda
Institute of Ocean Sciences, St. George, Bermuda, 4 Department of Oceanography,
University of Hawaii, Honoloulu, HI
A mesocosm facility designed to conduct long term controlled experiments on the
consequences of ocean acidification on coral reefs has been developed at the Hawaii
Institute of Marine Biology. The facility uses replicated continuous flow coral reef
mesocosms flushed with unfiltered sea water from the adjacent reef in Kaneohe Bay,
Oahu, Hawaii. The mesocosms are located in full sunlight and experience diurnal and
annual fluctuations in temperature and sea water chemistry characteristic of the adjacent
reef. In the initial long term (10 month) experiment the treatment mesocosms were
acidified to midday pCO2 levels exceeding control mesocosms by approximately 365
µatm, which is a level expected later in this century. Under these conditions crustose
coralline algae (CCA) developed 25% cover in the control mesocosms and only 4% in the
acidified mesocosms. Free-living associations of CCA known as rhodoliths that were
held in the control mesocosms increased at the rate of 0.6 g buoyant weight yr-1 while
those in the acidified experimental treatment decreased in weight at a rate of 0.9 g
buoyant weight yr-1. CCA play an important role in the growth and stabilization of
carbonate reefs, so future changes of this magnitude could have great impact on these
systems. Coral calcification decreased by 14% to 26% under acidified conditions. Coral
rate of calcification per unit of linear extension decreased by 6% to 8% in the acidified
treatment, indicating that corals were laying down a somewhat more fragile skeleton at
higher pCO2. On the other hand, various other calcifying organisms such as barnacles
and oysters showed little or no response to the acidified treatment. No differences were
observed in coral gamete production by Montipora capitata and coral recruitment by
Pocillopora damicornis. Advantages and disadvantages of the mesocosm approach are
discussed.
3-15
Nutrient Loading Affects the Relationship Between Coral Calcification and Aragonite
Saturation State
Pascale CUET* 1 , Marlin ATKINSON 2 , Aline TRIBOLLET 3 , James FLEMING 2 , Daniel
SCHAR 2 , James FALTER 2
1 ECOMAR, Universite de la Reunion, Saint-Denis, France, 2 Hawaii Institute of Marine
Biology, Kaneohe, HI, 3 IRD, Marseille, France
Coral calcification (G) is proportional to the ambient sea water saturation state of aragonite
(ΩA). It has also been established that G is reduced by high nutrients, but it is not apparent how
nutrient loading and ΩA interact. Experiments were conducted to determine the effect of
nutrient loading on the ″G - ΩA relationship″. Coral communities comprised of Montipora
capitata, Porites compressa and Pocillopora damicornis were placed in a wave flume in which
temperature, light, water motion, nutrient loading and initial ΩA were controlled. The flume
was closed over 4 to 5 day periods, resulting in a decrease in ΩA from 4 to 1. Gross primary
production and community respiration were respectively 320 ± 37 and 406 ± 55 mmolC m-2 d-
1. Independent of the nutrient loading, we observed a decrease in the calcification rate with a
decrease in ΩA, with no net 24H - calcification occurring at ΩA ≈ 1 - 1.5. Calcification rate of
the high nutrient loading (1 mmolP m-2 d-1 and 24 mmolN m-2 d-1), however, was 2 times
higher than the low one (0.06 mmolP m-2 d-1 and 0.3 mmolN m-2 d-1) at ΩA = 3 (respectively
186 and 100 mmolCaCO3 m-2 d-1). The range in calcification was similar to that in the field,
and the high nutrient loading was near the upper limit of nutrient uptake. Our results are
contrary to the established view that nutrients reduce calcification, and indicate that there is an
optimal nutrient loading that enhances calcification. It is likely that constant nutrient uptake is
required to offset nutrient release from basic metabolism. The high nutrient corals showed a
relatively high calcification at ΩA between 2 and 4. Therefore, further experiments should
simulate nutrient loading of the field to improve our understanding of the G - ΩA relationship.
3-16
Aragonite Saturation State And Seawater Ph Do Not Predict Calcification Rates Of The
Reef-Building Coral Madracis Mirabilis.
Christopher JURY* 1 , Robert WHITEHEAD 2 , Alina SZMANT 3
1 Biology and Marine Biology, University of North Carolina Wilmington, Wilmginton, NC,
2 Center for Marine Science, University of North Carolina Wilmington, Wilmington, NC,
3 Biology and Marine Biology, University of North Carolina Wilmington, Wilmington, NC
The calcification rate of corals has been found to decrease under experimental conditions with
reduced seawater aragonite saturation state (Ωarag), but it is unclear how this relates to changes
in seawater chemistry due to anthropogenic CO2 enrichment. The reduction of carbonate
concentration ([CO32-]) has been suggested to drive this response, but physiological data
suggest that bicarbonate ion (HCO3-) and not CO32- serves as the carbon source for coral
calcification. Reduced pH has also been suggested as the cause of reduced coral calcification
but no study to date has adequately separated the effects of these two parameters. This study
tested whether seawater pH, [CO32-], or both affect rates of calcification in corals. Madracis
mirabilis nubbins were incubated in one of four treatment chemistries (produced by
manipulation of pCO2 and total alkalinity): 1) pHT = 8.06, [CO32-] = 260 μmol kg-1 (control),
2) pHT = 7.77, [CO32-] = 150 μmol kg-1 (low pH, low [CO3 2- ]; 3x pre-industrial pCO2
conditions), 3) pHT = 7.77, [CO32-] = 260 μmol kg-1(low pH, normal [CO3 2- ]), and 4) pHT =
8.06, [CO32-] = 150 μmol kg-1(normal pH, low[CO3 2- ]). Relative to the controls, Treatment 2
resulted in a ca. 10 % increase in calcification; Treatment 3 in a ca. 21 % increase in
calcification; and Treatment 4 in ca. 43 % reduction in calcification. The results indicate that
rates of calcification in the coral Madracis mirabilis are not correlated to either seawater pH or
[CO32-]. Instead, calcification is better correlated with [HCO3-] in all experimental treatments.
These results imply that projected changes in Ωarag or pH may not offer appropriate models of
coral responses to ocean acidification and that not all corals may be negatively affected by
acidification.
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