BULLETIN OF MARINE SCIENCE, 67(2): 845–856, 2000 845 CORAL REEF PAPER REPRODUCTIVE CYCLES OF DIADEMA SETOSUM AND ECHINOMETRA MATHAEI (ECHINOIDEA: ECHINODERMATA) FROM KUWAIT (NORTHERN ARABIAN GULF) Adel H. Alsaffar and Khalid P. Lone ABSTRACT A study was undertaken on the seasonal variations in the reproductive biology of Diadema setosum and Echinometra mathaei from the coral reefs of Kuwait. Sixteen monthly samples were taken for both species and gonads were processed for histological studies. Both species had peak spawning in summer months when maximum seawater temperature was between 24.2 and 28.8ºC. Peak spawning was seen for Diadema in April- May (24–28ºC), while this point for Echinometra was achieved in June (28.8ºC). The spawning peak was much broader for Diadema. The breeding season in both species coincided well with increasing seawater temperature and day-length. The gonad color was not related to sex and there was no difference in drained weight of male and female of both the species. Both spermatogenesis and oogenesis were histologically similar to other echinoid species described by other authorities. The Indo-Pacific echinoids Diadema setosum and Echinometra mathaei are distrib- uted from Japan to southern Australia and from Mexico to the Gulf of Suez (Khamala, 1971). Throughout their distribution, their ecology, biology and reproduction have been studied (Pearse, 1968, 1969; Kobayashi, 1969; Lessios, 1981; Illiffe and Pearse, 1982; Drummond, 1995). Reproduction in previously studied populations was either continu- ous or restricted to certain part of the year (Pearse and Cameron, 1991). Reproduction of these species has not been studied on the coral reefs of Kuwait. Despite the extreme difference in seawater temperatures (minimum 10.6ºC in January; maximum 32.8ºC in August with air temperature reaching beyond 50ºC), the populations of both species are well established at the coral reef, with E. mathaei being more prevalent than D. setosum. The population density of D. setosum has been reported to range from 3 to 15 urchins m −2 while that of E. mathaei exceeds 100 urchins m −2 (Downing and El-Zahr, 1987; Downing, 1992; Downing and Roberts, 1993; Carpenter et al., 1997; Harrison et al., 1997). Here we report the reproductive periodicity of these species and compare it with studies on these species elsewhere. MATERIALS AND METHODS Urchins were collected from Kuwait’s Kubbar Island reef (29º 04.25'N, 48º 29.50'E) from the sampling positions shown in Figure 1. Diadema setosum were taken from the reef edge at a depth ranging from 3 to 5 m, at a bearing of 140 o magnetic to the light tower on the Island. E. mathaei were taken from the reef flat at a position 70 m from the reef edge along the previous bearing at a depth ranging from 1–2 m. The urchins were collected in early morning in the middle of the lunar month (at full moon), or as soon as possible thereafter. Each month, 20 to 30 individual urchin of each species were collected by divers in mesh bags, transported to the laboratory and immediately laid on a table with the oral opening facing down to allow the excess of water to drain. The sampling was done for 16 mo starting from the month of November 1985 through February 1987.