TY - JOUR
T1 - Rhodoliths from deep fore-reef to shelf areas around Okinawa-jima, Ryukyu Islands, Japan
AU - Matsuda, Shinya
AU - Iryu, Yasufumi
N1 - Funding Information:
We are grateful to D. W. J. Bosence and K. Ishizaki for critical comments on the manuscript and improvement of the English text and to W. Ahr and L. Montaggioni for providing constructive suggestions for an earlier version of the manuscript. Thanks are also extended to M. Nohara for giving us the opportunity to examine samples and photographs around Okinawa-jima; the captain (S. Yata) and crew of the R/V Nagasaki Maru for onboard assistance; K. Arai and T. Itaki for providing rhodoliths collected during a GH08 Cruise; H. Oba and J. Hohenegger for identifying peyssonneliacean algae and A. inhaerens, respectively; K. Kigoshi for 14 C dating; J. Nemoto for taking photographs; M. Shishido for making thin sections; and S. Iryu for preparing the manuscript. This work was funded, in part, by Grant-in-Aid for Scientific Research from the Ministry of Education, Science and Culture of Japan and from the Japan Society for the Promotion of Science ( 02640613 , 11640465 , and 20300261 to S.M. and 18340163 to Y.I.). We also thank Dr. J. T. Wells for the editorial handling and two anonymous reviewers for their constructive comments and suggestions.
PY - 2011/4/15
Y1 - 2011/4/15
N2 - The distribution, abundance, composition, and growth history of rhodoliths were investigated based on 222 grab samples and 202 submarine photographs taken from 223 sites arranged at regular intervals and on 13 additional samples (5 dredge and 8 grab samples). These samples were collected at water depths ranging from 15 to 970. m around Okinawa-jima, Ryukyu Islands, Japan. The rhodoliths grow in deep fore-reef to shelf areas at water depths of 50 to 135. m. Where rhodoliths occur, they cover 45% of the sea bottom. The rhodoliths are primarily spheroidal to ellipsoidal in shape (with mean diameters usually less than 8. cm); internally they are primarily composed of nongeniculate coralline algae and an encrusting foraminifer Acervulina inhaerens. The rhodoliths have envelopes of well-preserved, concentric to irregular laminations or, much more commonly, are bored and display various degrees of bioerosion. Constructional voids (primary spaces between encrusters) and borings range from empty to completely filled with unlithified and lithified mixtures of micrites and bioclasts. The bioerosion is more extensive with increasing water depth and is progressively much more pervasive at water depths greater than 90. m. The rhodoliths are covered with nongeniculate coralline algae and A. inhaerens associated with other epilithic skeletal and nonskeletal organisms. The living biotic cover on rhodoliths is relatively great down to water depths ~. 100. m; below this, the cover decreases rapidly with increasing water depth. Rhodoliths with similar size, shape, and composing organisms to those in the Ryukyu Islands are commonly found on deep fore-reef to shelf areas or on the banks and seamounts of tropical reef regions, likely as the combined result of ecological degradation (=decreased number and coverage) of hermatypic corals and the relative predominance of nongeniculate coralline algae and encrusting foraminifers in such areas. The slow accretion rates of rhodoliths (<0.1 mm/year) indicate that their formation is commonly to frequently intermittent, probably because of their burial in the surrounding sediment.
AB - The distribution, abundance, composition, and growth history of rhodoliths were investigated based on 222 grab samples and 202 submarine photographs taken from 223 sites arranged at regular intervals and on 13 additional samples (5 dredge and 8 grab samples). These samples were collected at water depths ranging from 15 to 970. m around Okinawa-jima, Ryukyu Islands, Japan. The rhodoliths grow in deep fore-reef to shelf areas at water depths of 50 to 135. m. Where rhodoliths occur, they cover 45% of the sea bottom. The rhodoliths are primarily spheroidal to ellipsoidal in shape (with mean diameters usually less than 8. cm); internally they are primarily composed of nongeniculate coralline algae and an encrusting foraminifer Acervulina inhaerens. The rhodoliths have envelopes of well-preserved, concentric to irregular laminations or, much more commonly, are bored and display various degrees of bioerosion. Constructional voids (primary spaces between encrusters) and borings range from empty to completely filled with unlithified and lithified mixtures of micrites and bioclasts. The bioerosion is more extensive with increasing water depth and is progressively much more pervasive at water depths greater than 90. m. The rhodoliths are covered with nongeniculate coralline algae and A. inhaerens associated with other epilithic skeletal and nonskeletal organisms. The living biotic cover on rhodoliths is relatively great down to water depths ~. 100. m; below this, the cover decreases rapidly with increasing water depth. Rhodoliths with similar size, shape, and composing organisms to those in the Ryukyu Islands are commonly found on deep fore-reef to shelf areas or on the banks and seamounts of tropical reef regions, likely as the combined result of ecological degradation (=decreased number and coverage) of hermatypic corals and the relative predominance of nongeniculate coralline algae and encrusting foraminifers in such areas. The slow accretion rates of rhodoliths (<0.1 mm/year) indicate that their formation is commonly to frequently intermittent, probably because of their burial in the surrounding sediment.
KW - Encrusting foraminifer
KW - Fore-reef
KW - Nongeniculate coralline alga
KW - Rhodolith
KW - Ryukyu Islands
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U2 - 10.1016/j.margeo.2011.02.013
DO - 10.1016/j.margeo.2011.02.013
M3 - Article
AN - SCOPUS:79955144517
VL - 282
SP - 215
EP - 230
JO - Marine Geology
JF - Marine Geology
SN - 0025-3227
IS - 3-4
ER -