Early Larval Development and Annual Gametogenesis of the Brooding Oyster Ostrea circumpicta (Pilsbry, 1904) in the Shallow Subtidal Benthic Ecosystem in Jeju Island, Off the South Coast of Korea.

The subtropical brooding oyster Ostrea (= Striostrea) circumpicta (Pilsbry, 1904) occurs at high density in the shallow, subtidal, rocky bottom in Jeju Island, off the south coast of Korea, where the sea surface temperature and salinity varies annually from 13 to 25°C and 30 to 33 ppt, respectively. In this study, the annual gametogenesis and early larval development of O. circumpicta was examined, using histology and scanning electron microscopy (SEM). Histology indicated that the females and males initiated gonial mitosis in September, shortly after sexual resting in August. In December, ripe eggs first appeared in the follicles, and most of the females exhibited fully mature oocytes in May, as the water temperature reached 17 to 18°C. Spawning females were dominant in June and July, when the trochophore and strait- hinged veliger larvae were also identified in the branchial chambers, their size ranging from 111 to 130 µm and 135-205 µm in diameter, respectively. The veliger larvae in the brooding chamber exhibited a well- developed velum and digestive tract, suggesting that the larvae are engaged in feeding in the branchial chamber. Unlike other marine bivalves in temperate coastal ecosystems, O. circumpicta has a long period of gonad maturation and a short resting phase. It has been believed that such a long period of reproductive maturation is associated with a low level of food in the environment and the comparatively large size of the oocytes, which may require a relatively longer time to accumulate necessary nutrients to produce large eggs in a food-poor environment.

Spatial variability in long-term changes of climate and oceanographic conditions in Korea.

I evaluated long-term changes in hydrological conditions (temperature, salinity and dissolved oxygen) in Korean sea waters in relation to the regional land climate change (air temperature and precipitation) based on available meteorological and oceanographic data. Regression analyses, spatial patterns and cross-correlations on the climatologic and hydrological factors suggested that industrialization processes and related urban heat-island effects during the past 37 years from 1968 to 2005 in South Korea have increased land surface temperatures by 1.267 degrees C, at least for the urban areas, and subsequently increased sea surface temperatures by 0.975 degrees C and decreased salinities by 0.229. The influence of land surface temperature on the sea water temperature reached at least 75-m depth. Regarding the causality in the land-ocean climate changes, air-temperature changes preceded sea water temperature change by 0-2 months in spring and summer; but the sequence could be reversed, possibly because of potential heat held by the ocean. This study demonstrated that human factors have been driving warming influences on regional sea waters, impacting marine ecosystems and changing dominant fish species in commercial fishery catches of Korea.