The solitary ascidian, Halocynthia aurantium, which is commonly called the sea peach because of its coloration and general shape, is a valuable organism of benthic marine population in the northern region of the East Sea, Korea. It is seldom found at a depth of less than 10 meters and the sea peach is frequently observed in large populations between 20 and 100 meters. It appears to prefer attachment to vertical rocks faces and artificial cement blocks exposed to the currents. Mass mortality and reduction of resources in sea peach, H. aurantium, were occurred in the benthic area of the northern region of the East Sea because of the rapid fluctuation of environmental factors such as temperature and salinity due to mass rainfall in summer and going up north of a strong warm current in winter. Therefore, we examined the effects of temperature and salinity on embryonic development of fertilized eggs, tadpole larva to metamorphosis, and attachment to siphon development. Laboratory-raised larvae were studied using a two-factorial experimental design with four levels of temperature(8, 12, 16 and 20℃) and four levels of salinity(20, 25, 30 and 34 psu). The ascidian larvae of H. aurantium survived environmental conditions between temperature of 8～20℃ and salinity of 25～34 psu and exhibited positive growth at 8～16℃ and 30～34 psu. Fertilized eggs have not developed at lower salinity of 20 psu irrespective of temperature range tested and have showed an abnormal development at the salinity of 25 psu between higher temperatures of 20 and 24℃. This result suggests that temperature increase and salinity reduction depending on environmental fluctuation may have significant impacts on population variation of H. aurantium in the northern region of the East Sea.

The clam, Gomphina melanaegis, which is commonly called the sandy beach clam because of its habitat, is a valuable organism in the sandy coast of East Sea, Korea. It is frequently observed in large populations between 0.5 and 5 meters. We have released 50,000 seedling, ranging from the diameter of approximately 3 mm, 2007, and 1,000,000 seedling, ranging from the diameter of approximately 0.2 mm, plus 100,000 adult individuals, ranging from the shell length of approximately 20～40 mm, 2008 at Jinha beach. The spawning period of G. melanaegis, was from June to August, and the main spawning occurred in July. This investigation was carried out to elucidate population distribution on the stocking area of sandy beach clam, G. melanaegis. The relationship between shell length and ring radius in each ring was investigated as a regression line. The relationship between the shell length and shell height of released young clam was SH=1.0105SL-4.7764 (R2=0.7905). The relationship between the shell length and total weight of released young clam was TW=0.0013SL2.3966(R2=0.71). It draws a deduction that the ring of this clam was produced once a year during the duration between June and August.