IEG 환경지질연구정보센터

ABSTRACT

60th Anniversary of Geological Society of Korea

>> 88

Reef-building coral records surrounding environmental conditions in its skeleton. There is consensus on controlling factor of skeletal δ

O (δ

Oc), namely SST (sea surface temperature) and seawater δ

O composition.

However, that of skeletal δ

C ( δ

Cc) is still controversial because δ

Cc shows correlation with different environmental factors at different locations.

In order to better understand the controlling factor of δ

Cc, two different coral species, Porites sp. and Platygyra ryukyuensis, were collected at the exactly same site from Ishigaki Island, Japan, and analyzed for δ

Cc and δ

Oc.

Then the results were compared with observed environmental variables.

δ

Cc of Porites shows a clear seasonal fluctuation matching that of solar radiation, high in summer and low in winter. In contrast, δ

Cc of Platygyra showed an opposite pattern to that of Porites with weaker seasonality. Both were exposed to same environmental conditions during growth, so these opposed trends should be attributed to species-dependent responses against same environmental condition.

It is likely caused by different symbiotic algae associations of two species, resulting in different photosynthetic efficiency to the same light stress. For example, photosynthesis of symbiotic algae in Porties is active during summer, while that in Platygyra during winter. Photosynthesis of symbiotic algae takes up

C preferentially, leaving

13

C-enriched carbon pool for coral calcification. Thus active photosynthesis of symbiotic algae results in higher δ

Cc; during summer for Porites and during winter for Platygyra. These results agree well with spatial distribution of Platygyra found in middle latitude region, where Porites is not distributed, with colder temperature and less light

intensity. Higher photosynthetic efficiency of symbiotic algae seems providing its host more tolerance to low light intensity. Despite of the opposed responses of two species, both species δ

Cc variation can be used as a proxy for solar radiation.

Michiyo Shimamura

, Kiseong Hyeong

, Chan-Min Yoo

, Tsuyoshi Watanabe

, Tomohisa Irino

, and Woong-Seo Kim

1

Korea Ocean Research and Development Institute, Ansan, 426-744, Korea,

2

Hokkaido University, Sapporo, 060-0810, Japan E-mail: [email protected]

Opposed trend of skeletal carbon isotopic ratios to solar radiation in two different coral species:

species-dependent responses