Seasonal occurrence and reproduction of Hypnea charoides (Rhodophyta) in Thng Ping Chau, N.T., Hong Kong SAR, China

Seasonal occurrence and reproduction in populations of Hypnea charoides Lamouroux were investigated along two coastal shores, A Ma Wan and Lung Lok Shui, in Tung Ping Chau, N. T., Hong Kong SAR, China, from 1996 to 1999. Annual growth of these populations was initiated in early winter (November-December) and ended in late spring (April-May). Mean length of H. charoides in A Ma Wan was significantly negatively correlated with photoperiod (r = -0.359, n = 38, p < 0.05) and seawater temperature (r = -0.669, n = 38, p < 0.05). Vegetative plants were dominant but relatively high abundance in tetrasporic plants was observed at the end of each growing season. Percentage occurrence of tetrasporic plants was significantly positively correlated with seawater temperature in samples collected at -I m CD (r = 0.635, n = 19, p < 0.05), -2 m CD (r = 0.690, n = 13, p < 0.05) and from drifted populations (r = 0.705, n = 17, p < 0.05), suggesting that increase in seawater temperature might induce tetrasporogenesis of H. charoides in A Ma Wan. Plants in Lung Lok Shui were mostly vegetative but 100% tetrasporic samples were collected at -I m CD during an unusual growth period in October 1998. High abundance of tetrasporic plants was also observed at a depth of -10m CD on 9 April 1998 (97.5%) and 22-Apri11999 (90%). Significantly negative correlation was found in percentage occurrence of vegetative plants at -10 m CD with photoperiod (r = -0.553, n = 14, p < 0.05) and seawater temperature (r = -0.855, n = 8, p < 0.05). Dominance of vegetative and tetrasporic plants and rarity of cystocarpic plants in both A Ma Wan and Lung Lok Shui suggested that the life span of H. charoides might be very short and/or majority of the plants underwent apomeiosis to complete their life cycles in Tung Ping Chau.