BBG21-P01

Room:Convention Hall

Time:May 27 18:15-19:30

Diversity index of coral distributions and its relation to physical variables in Amitori Bay,Iriomote Island, Japan.
SHIMOKAWA, Shinya1∗ ; MUKARAMI, Tomokazu1 ; UKAI, Akiyuki2 ; KOHNO, Hiroyoshi3 ; MIZUTANI, Akira3 ;NAKASE, Kouta2
1NIED, 2 Penta-Ocean Construction. Co. Ltd., 3 Tokai Univerisity

The relationship between coral distributions and physical variables was investigated in Amitori Bay, Iriomote Island, Japan.
Amitori Bay is located in the northwest region of Iriomote Island, Japan. Broad areas of coral have developed in the bay, and theirlife forms, coverages, sizes, and species vary depending on their locations. In addition, Amitori Bay has no access roads, and thebay perimeter is uninhabited. Thus, this small bay, with its variety of environments and lack of human impact, is considered to
be one of the most suitable areas for studying the relationship between coral distribution and physical variables.
Field observations were conducted to obtain data on coral distributions, sea temperature, sea salinity, wind speed, and river flowrate [Shimokawa et al., 2014]. Ocean and wave model numerical simulations and soil particle tracking analysis were conductedto obtain the spatial and temporal distributions of wave height and the numbers of soil particles with the observed physical data.
Our results showed that the life forms and sizes of corals significantly varied depending on their locations in the bay, because thephysical variables differed significantly among these locations.
From the results of the above observations and simulations, we calculated diversity index of coral distributions and its relation
to physical variables. The diversity index, DI [Shannon, 1948; MacArthur and MacArthur, 1961, Clark & Warwick, 2001, McCune and Grace, 2002] is defined asDI=-∑ ci log2 ci,
where ci is the ratio of i-th type coverage to total coverage. DI is a quantitative measure for the degree in which a dataset
includes different types and is related closely to entropy concept in Thermodynamics. The value of DI increases when both thenumber of types and the evenness increase. For a given number of types, the value of DI is maximized when all types are equallyabundant.
The results show that Averages of diversity index of the coral types at the mouth and inner parts of the bay are lower than
average of the whole region, but average of diversity index at the intermediate part of the bay with the intermediate physicaldisturbances is higher than it. This seems to support the intermediate disturbance hypothesis demonstrated by Connell [1978]
which states species diversity in local area is maximized when environmental disturbances is neither too weak not too strong.
References:
Clarke, K. R. and R. M. Warwick (2001), Changes in marine communities: an approach to statistical analysis and interpretation, 2nd ed., PRIMER-E, Plymouth, pp. 176.
Connell, J. H. (1978), Diversity in Tropical Rain Forests and Coral Reefs, Science, 199, 1302-1310.
MacArthur, R. H. and J. W. MacArthur (1961), On bird species diversity, Ecology, 42, 594-598.
McCune, B. and J. B. Grace. (2002), Analysis of Ecological Communities, MjM Software Design, Oregon, pp.300.
Shannon, C. E. (1948), A mathematical theory of communication. The Bell System Technical Journal, 27, 379-423 and 623656.
Shimokawa S., T. Murakami, A. Ukai, H. Kohno, A. Mizutani and K. Nakase, 2014, Relationship between coral distributions and physical variables in Amitori Bay, Iriomote Island, Japan, J. Geophys. Res.: Oceans, 119, 8336-8356 (doi:10.1002/2014JC010307).

Keywords: Coral, Diveristy index, Wave height, Soil particle, Intermediate disturbance hypothesis

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BBG21-P02

Room:Convention Hall

Time:May 27 18:15-19:30

Variation in the oxygen isotope ratio of dissolved orthophosphate induced by uptake process by hermatypic corals
FERRERA, Charissa M.1 ; WATANABE, Atsushi1 ; NADAOKA, Kazuo1 ; UMEZAWA, Yu3 ; MORIMOTO, Naoko2 ;NAKAMURA, Takashi1 ; MIYAJIMA, Toshihiro2∗
1Tokyo Institute of Technology, 2 AORI, University of Tokyo, 3 Faculty of Fisheries, Nagasaki Univ.

The oxygen isotope ratio (δ 18 O) of dissolved orthophosphate (PO4 3− ) has been recognized as a promising tool to evaluate thecontributions of both external sources and internal recycling of phosphorus (P) to the P budget in natural aquatic ecosystems.
However, coexistence of many biological processes that can significantly alter the phosphate δ 18 O (δ 18 Op ) in a given system
often complicates quantitative interpretation of this parameter. To use the information of δ 18 Op effectively in biogeochemical
researches, we have to know both the magnitudes of oxygen isotope effect and the reaction kinetics of major biological processes
that take part in the P cycle of the concerned ecosystem. In this study, we conducted a model incubation experiment using
natural hermatypic corals to evaluate the influence of uptake process of PO4 3− by corals on the δ 18 Op . Live coral samples(Porites cylindrica , Heliopora coerulea , Acropora digitifera ) were collected from coral reefs around Ishigaki Island (Okinawa)
and Bolinao (northern Luzon), acclimatized in incubation aquaria for a few days, and then incubated for 3 to 5 days under natural light conditions with elevated concentrations of NO3 − and PO4 3− . Subsamples of seawater were regularly collected andanalyzed for the concentration and the δ 18 O of PO4 3− . PO4 3− was usually taken up by corals linearly with incubation time,and the uptake rate apparently depended on temperature. Difference in the uptake rate between coral species was not significant.
The δ 18 Op was initially approx. 3 ‰ lower than the equilibrium value with regard to oxygen-isotope exchange with ambient
seawater. In a few cases, the δ 18 Op remained unchanged during the incubation even though uptake proceeded. In the othercases, however, the δ 18 Op gradually increased with time, and in some cases became even higher than the equilibrium value
at the end of incubation. This observation suggests that kinetic isotope fractionation rather than simple equilibration operated
during the uptake of PO4 3− by corals and influenced the δ 18 Op . The magnitude of isotope effect associated with uptake seemed
to depend on coral species, being the largest with A. digitifera and the smallest with H. coerulea . In natural environments where
the concentration of PO4 3− is much lower than the incubation conditions we used, PO4 3− is presumably turned over much fasterand the δ 18 Op is easily altered by corals and other major primary producers. This fact may limit the advantage of the δ 18 Op as
an indicator of external PO4 3− sources.
Keywords: Phosphate, Isotope effect, Stable isotopes of oxygen, Hermatypic coral, Coastal marine ecosystem

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BBG21-P03

Room:Convention Hall

Time:May 27 18:15-19:30

Holocene sea-level record from a drilled core at land reclamation on reef crest in Okinawa
IslandHONGO, Chuki1∗ ; FUJITA, Kazuhiko1 ; KAWASAKI, Yuko1 ; MINEI, Shogo1 ; SASAKI, Toru1
1

Dept. Physics & Earth Sciences, University of the Ryukyus

Holocene sea level records provide the opportunity to understand reef formation history, mangrove development, and settlement by ancient people. Especially, the mid-Holocene sea-level record is important to accurate forecast coastal response tosea-level change in the near future because the amplitude of sea-level rise is similar to that of future sea-level rise. However, themagnitude and timing of Holocene sea-level records display great variability, inflecting ice sheet uploading and the redistribution of water masses in the global ocean, and glacio-isostatic and hydro-isostatic effects. Therefore, the local sea-level record
is fundamental to a geological evidence for understanding the above topics. In the present study, we analyzed a drilled coreand five radiocarbon ages at land reclamation on reef crest in Okinawa Island, Ryukyu Islands. Analyses of corals (Isoporasp. and Goniastrea reriformis ) enable the reconstruction of a sea-level curve because these species are distributed in a shallow
water depth. The Holocene sea-level curve reconstructed based on the drill core data reveals a sea-level rise until ca. 7000 cal.
years BP. A mid-Holocene highstand occurred at 6760 cal. years BP, at a level of 2.7 m above the present mean sea level. The
reconstructed mid-Holocene highstand is characterized by one of highest and oldest records in the Ryukyu Islands. The findingreflects the hydro-isostatic effect in response to size and volume of islands because Okinawa Island is the biggest island in theRyukyu Islands.

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