In this study, we histologically investigated the late stage of oogenesis, spermatogenesis, and pseudo-egg development processes of the pseudo-dioecious coral Galaxea fascicularis to form a base from which to elucidate the mechanisms of coral sexual reproduction. This coral has a large egg size and individual polyps, which are suitable for studying the mechanism of sexual reproduction. The histological analysis revealed that germinal vesicle breakdown of this coral begins 3 days before spawning in both female oocytes and male pseudo-oocytes. Spermatogonium, spermatocytes, spermatids, and sperm were observed in the male testicular lobules from 2 months to 1 day before spawning. The findings of our study might allow for the elucidation of the mecha-nisms of sexual reproduction in this species and facilitate the development of methods for its aquaculture.
The study quantifies different sources of error in the visual censuses of 12 fish species on a fringing coral reef. Each species was censused 24 times within a period of four days. We assumed that in this narrow time window, true abundances of species were constant, and that the variation observed in the estimates was due to short-term environmental oscillations, inter-observer differences, and chance events. ANOVA revealed that the environmental variance in four species, inter-observer variance in three species, and chance variance in one species contributed most to the censusing results. In the remaining four species, the variance components were similar in magnitude. We conclude that identifying important sources of error variance, which allows for the informed correction of censusing methods, could increase the precision and comparability of density estimates.
Increases in atmospheric CO2 cause decreases in calcium carbonate saturation, which is predicted to affect the calcification process of most marine calcifiers. At the same time, the increase of seawater pCO2 is also known to increase the productivity of primary producers. Giant clams host symbiotic dinoflagellates (‘zooxanthellae’: Symbiodinium spp.) that provide nutrition and use CO2 as their primary source for photosynthesis. This leads to the hypothesis that increased seawater pCO2 rise could positively affect the production of giant clam zooxanthellae, and dampen effects of CO2 on host giant clams. To test this hypothesis, we measured the shell growth rate, photosynthesis rate, respiration rate and zooxanthellae density of the juvenile Tridacna crocea reared under three different pCO2 conditions. Results revealed that negative shell growth of juvenile Tridacna crocea was observed once seawater Ωarag reached less than 2.33. Additionally, although zooxanthellae density in T. crocea increased with seawater pCO2 rise, zooxanthellae productivity did not change, suggesting that the productivity per zooxanthella decreased in high pCO2 seawater. Our findings suggest future seawater pCO2 rise will not increase productivity of zooxanthellae, thus giant clam will be negatively impacted in the coming centuries.