| Summary: | 碩士 === 國立中山大學 === 海洋科學系研究所 === 107 === This study studied the vertical movement behavior of Nerita costata and N. plicata in Dongsha intertidal zone. Experimental approaches were need to test why N. costata and N. plicata move vertically on the concrete wall. We found that the vertical distribution of Nerita spp generally followes the tide. During the high tide, the average vertical height of N. plicata was 15.3 cm, higher than that of N. costata. During the low tide, the average vertical height of N. plicata was 11.8 cm, higher than that of N. costata. We tested the relationship between temperature and the vertical movement of Nerita spp. N. plicata was 6 oC, lower than that of N. costata, when they were fixed on the substrate. Meanwhile, the average temperature of free moving snails was significantly lower than that of fixed-position living snails. Besides, the mean temperature of the wall got higher as the height increased. Both substrate and snails have the same source of heat. Significantly higher activity ratio of Nerita spp was detected when snails were hungry. We also found that there was a significant difference between the vertical height of N. plicata and that of N. costata under wet condition. So far, temperature, dessication, and foraging have been found to play roles in the vertical movement of Nerita spp.
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