Use of annual density banding to estimate longevity of infauna of massive corals

Growth bands of the colonies of the scleractinian coral Porites collected a t Okinawan coral reefs were counted on Soft-X Ray micrographs, and age and growth rates of infaunal non-boring organisms were estimated indirectly fro m the annual coral-growth rings of the host coral. The organisms include a calcareous-tube polychaete Spirobranchus corniculatus (Grube), a sand-tube sabellariid polychaete, Idanthyrsus sp., a vermetid gastropod Dendropoma ma xima Sowerby, a pecten bivalve Pedum spondyloideum Gmelin, and a coral barn acle Cantellius sp. The three tubicolous former species showed growth in va rious directions, and 15 to 20 years (S. corniculatus), 8 years (Idanthyrsu s sp.), and 15 years (D. maxima) longevity were reliable estimates in this study. In contrast, the pecten bivalve and the coral barnacle showed lesser longevities, usually less than 7 years, and they grew vertically in almost the same direction as the host coral; thus, their growth rates can be esti mated roughly by shell or slit-like hole length in relation to average host coral growth. We present here a new and practical method to estimate age a nd longevity of non-boring coral infauna, and we discuss marine organism gr owth and longevity with emphasis on polychaetes.