A series of laboratory experiments were conducted to determine the effect of sperm dilution, egg concentration, sperm-egg contact time, and gamete aging on fertilization success in the tropical sea urchin, Echinometra mathaei. The results demonstrated that sperm dilution, sperm age, and sperm-egg contact time were sequentially the most important factors influencing fertilization success, while egg concentration was not significant over the range tested. Sperms retained their potency for more than two hours only in relatively dense sperm suspensions (≥10^-4 dilution of ‘dry’ sperm) whereas they exhibited lower viability with increasing dilutions and age. In egg-sperm contact time experiments more than 80% fertilization was achieved at lower sperm dilutions (10^-3-10^-2) within 10 sec of mixing, while at higher sperm dilutions, longer times of contact were needed to achieve the similar fertilizations. Consequently, eggs remained in good quality for up to 3 h and there was no abnormality or adverse effects in fertilization were observed in a series of sperm dilution tested. These laboratory experiments suggest that sperm dilution and its limited longevity can play an important role in limiting the fertilization of sea urchin eggs in the field during natural spawnings. It follows, therefore, that sea urchin (E. mathaei) are under considerable selective pressures to spawn synchronously in order to generate high sperm concentrations and higher sperm-egg encounters in the water column to maximize the probability of successful fertilization.

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The Ryukyu Group, composed of Pleistocene reef-complex deposits that pass laterally into terrigenous sediments, crops out on Kume-jima and its adjacent islet, Ohajima, Ryukyu Islands, southwestern Japan. We propose a major revision of the previous stratigraphic scheme for the Ryukyu Group, based on new investigations, and provide a formal stratigraphic description. These Pleistocene deposits comprise the Nakandakari, Kumejima, and Torishima Formations, in ascending order, on Kume-jima. The lowest of these, the Nakandakari Formation, consists of pumice-bearing detrital limestone (<20m thick); its surface exposure is confined to the type locality, which is on the coast to the northwest of Nakandakari. The unconformably overlying Kumejima Formation exceeds 30m in thickness and is exposed in the northwestern part of Kume-jima at elevations less than ca. 50m. It is divisible into at least three units, each comprising coral limestone and overlying rhodolith, Cycloclypeus-Operculina, and detrital limestones. The Torishima Formation rests unconformably on the Kumejima Formation, and is characteristically thin (<15m thick) and composed of well-sorted detrital and coral limestones that are thought to have been deposited in a shallow lagoon (moat). The Oha Limestone is limited in its distribution to Oha-jima and consists of diagenetically altered, reddish to brownish, coral limestone. The stratigraphic relationship between limestones on Kume-jima and those on Oha-jima remains unknown, as does the geological age of these limestones. It is evident from the stratigraphic succession and configuration of lithofacies that the reefs grew in response to at least three repeated cycles of sea-level change with amplitudes of up to 80m during deposition of the Kume-jima Formation. Subsequently, a relatively small reef now assigned to the Torishima Formation grew to fringe the older reefs.

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多くのサンゴでは放卵・放精及びプラヌラ放出が夜間におこるが、日本及び韓国固有種のニホンアワサンゴ Alveopora japonica ではプラヌラ放出が昼間に行われることがわかった。光がこの種のプラヌラ放出にいかに影響しているかを調べるため室内実験を行った。自然光下ではニホンアワサンゴは午前7時から12時までの間にプラヌラを放出した。サンゴ群体に光を照射する時間帯を変更したところ、本来の時刻に関係なく、光を照射した時間に一致してプラヌラを放出した。また、午前と夕方の2回、光を与えた場合では、すべての群体が本来の時間帯である午前中にプラヌラを放出した。直接観察によりプラヌラ放出に先立ちポリプの伸長がおこることが確認されたが、伸長は光が与えられたときにのみおこった。これらのことから、ニホンアワサンゴにおいて、光はポリプの伸長を介してプラヌラ放出を制御する直接の要因であると考察された。

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In order to restore disturbed coral reefs, transplantation of coral fragments or coral heads has been conducted in many parts of the world. We reviewed methods and results of the transplantation experiments described in numerous previous reports in order to determine recommendable methodologies. Problems that should be solved by future studies are discussed. For transplantation, generally, small pieces of coral are taken from the donor colony using hammer, chisel and the like. If the collection site is far from the transplantation site, fragments should be placed in bucket full of seawater. There are various methods to fix the coral fragment onto substrate, e. g. by means of epoxy cement, plastic coated wire and nails. They should be chosen according to size and shape of coral fragments, but we found fixation with nails and cable ties is easy and reliable for staghorn corals. The cost of transplantation with a density of 245, 000 fragments per hectare secured by means of nails and cable ties has been estimated at about 36, 000, 000 JPN Yen. So far, species of the genera Acropora, Porites, Pavona and Galaxea were most frequently used for transplantation as they have relatively high survival rates.

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塊状の造礁サンゴ Favites sp. と Porites sp. の生育するメソコズム (隔離水界) で1998年の白化現象の初期段階と後期段階における有機炭素生産量 (光合成-呼吸量) と無機炭素生産量 (石灰化-溶解量) を測定した。海水面では大気-海水間のCO₂フラックスを直接測定し、メソコズムでの炭素収支を算出した。
純有機炭素生産量は白化初期段階の15.8mmol m^-2 d^-1から白化後期段階の9.5mmol m^-2 d^-1に減少した。純無機炭素生産量は白化初期段階の11.2mmol m^-2 d^-1から白化後期段階の-7.0mmol m^-2 d^-1に激減した。これは昼間の石灰化量の減少と夜間の溶解量の増加によるものであり、炭酸塩の溶解を示す。大気-海水間のCO₂フラックスは白化初期段階が-1.8mmol m^-2 d^-1、白化後期段階が-1.1mmolm^-2 d^-1であり、どちらも大気から海水へCO₂が吸収された。
白化の初期段階と後期段階でP/R比 (=1.2) はほとんど変化しなかったことから、白化によって褐虫藻の光合成活性は変化しないことが示唆された。サンゴの白化により石灰化速度は光合成速度に較べ著しく減少した。白化はサンゴにダメージを与え、サンゴ-褐虫藻の共生系の炭素代謝に大きく影響した。

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Three types of symbiotic dinoflagellates L (large), B (brown) and G (green) found in hermatypic corals from a fringing reef of Sesoko Island (Okinawa, Japan) differed morphologically, physiologically and biochemically. Colonies of the hydrocoral Millepora intricata hosted symbionts of type L only; scleractinian corals containing type B only were Pocillopora damicornis, type G only were Seriatopora caliendrum and S. hystrix, and both types B and G were found living together in Stylophora pistillata and Echinopora lamellosa. The symbiotic dinoflagellates (SD) differed considerably in cell size, shape and structural elements in coccoid state in hospite. SD of these types also differed in photosynthetic capacities, primary production, pigment accumulation and maximum rates of cell division and degradation.
Corals hosting various types of SD significantly differed in light-resistance. Scleractinian corals with symbionts of both types B and G, in the same colony, acclimated to bright light by increasing the relative number of symbionts of type G and acclimated to dim light by increasing the SD number of type B. It was shown that scleractinian corals can photo-acclimate through formation of optimal composition of SD types under various light intensities.

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