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Seasonal variations in growth, alginic acid and mannitol contents of Sargassum wightii and Turbinaria conoides growing in the Gulf of Mannar near Mandapam have been followed for a period of two and a half years from August 1965 to J a n u a r ~ 1'308. 3Iarl;ed seasonal changes occur in the growth of these two brown algae with a slow growth in the population up to July or -1ugust and a rapid growth from October to December when reproductive receptacles were noticed in both the species. Results obtained on the alginic acid and mannitol contents indicate that these two carbohydrates vary with tile seasonal growth behaviour of the two brown algae investigated. Yield of alginic acid is high during the peak growth and fruiting periods, Mannitol content is at its maximum in the early stages of the growth cycle from May to August and minimum after the initiation of the reproductive receptacles.

Essential micro-nutrients such as manganese, copper, lead and zinc were analysed in three species of Gracilaria for 12 months from August 1994 to July, 1995. Comparative data on the interspecific variation of essential micro-nutrients have been explained. Seasonal variation of the trace element within the species were also analysed. Zinc content was found to be maximum in all the species of Gracilaria. In general, the decreasing trend of essential micro-nutrients was Zn>Pb>Cu>Mn. Manganese and copper content were found to be comparatively higher in G. edulis whereas lead dominated in G. crassa.

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.

Seasonal variation in growth and biochemical constituents such as protein, carbohydrate and lipid in Hypnea valentiae, Acanthophora spicifera, Laurencia papillosa, Enteromorpha compressa, Ulva lactuca and Caulerpa recemosa were observed for one year from April, 1995 to March 1996. Carrageenan content was estimated from H. valentiae, A. spicifera and L. papillosa. In general, peak growth and biomass of these algae occurred during the period June -August and January - March. The maximum values in these algae varied from 12.5 to 13.2% for protein, 13.0 to 13.3% for carbohydrate and 10.3 to 12.0% for lipid. The yield of phycocolloid recorded 11.3%, 6.0% and 8.1% in H. valentiae, A. spicifera and L. papillosa respectively.