Indian Journal of Marine Sciences Vol. 30, September, 2001, pp 161-165 Phenology of brown alga Coilodesme japonica (Phaeophyta, Dictyosiphonales) with respect to the host-specificity along Muroran coast, North Pacific Ocean, Japan Geetanjali V. Deshmukhe* & M. Tatewaki Institute of Algological Research Faculty of Science, Hokkaido Unversity, Muroran 051, Japan Received 11 May 2000, revised 23 April 2001 Coilodesme japonica – a brown temperate algal species grows epiphytically on three marine algal host species namely Cystosiera hakodatensis, Sargassum confusum and Dictyopteris divaricata. The distribution pattern, phenology and host-specificity in the field was studied. Out of the 3 hosts, C. hakodatensis was most favoured host by C. japonica (100% by May) followed by S. confusum. The least favourite host was D. divaricata (only 5% were epiphytized). The rhizoidal portion was less epiphytized in both the cases. Maximum number of C. japonica thalli and biomass were found on the size class 3 and 4. Host surface, age and biochemistry play important role in the C. japonica distribution and biomass colonization. The role of epiphytic plants in the marine community, their distribution and their effects on the host plants were well documented 1-3 . The epiphytes affect their host plants by several ways such as, they suppress the host plant growth. Reduced photosynthesis and reproduction rate of the host was also reported due to heavy epiphytism. On the other hand, several researchers suggested that the presence of epiphytes reduce the herbivory of the host plant 3,4 . The genus Coilodesme (Class: Phaeophyceae, Order: Dictyosiphonales, Family: Coilodesmeceae), predominantly grows epiphytically on several host species, and its geographical distribution is restricted to temperate and subtropical seas of the Northern hemisphere 5,6 . Coilodesme japonica Yamada, a spring annual is one of the obligatory epiphyte that grows mainly on brown macroalga Cystosiera hakodatensis (Yendo) Fensholt. Other two hosts preferred are brown macroalgae namely Saragassum confusum C. Ag. and Dictypteris divericata (Okam) Okamura. The study was particularly undertaken to study the distribution, biomass and phenology of C. japonica in nature and its preference to any particular host species. Materials and Methods Samples of C. japonica along with the three host species were collected from the intertidal zone and tide pools at Charatsunai, near the Institute of Algological Research, Muroran, Hokkaido (latitude: 42° 19’ N; longitude 141° 50’ E), at monthly intervals from February to July in the years 1991 and 1992. For observation purpose, one whole plant of C. hakodatensis (TCH) was sampled from 5 different tide pools. In the intertidal zone C. hakodatensis (ICH) and Sargassum confusum C. Ag. (ISC) were collected from randomly placed 1 m 2 quadrant (n = 5). Only one plant from each quadrant was collected because of the large size of the host plant. In the case of Dictyopteris divericata growing in the intertidal zone (IDD) 5 plants from randomly placed 0.25 rn 2 quadrants (n = 5) were collected. Numbers of epiphytized plants in all the types were recorded. Once brought to the laboratory, both Sargassum and Cystoseira plants were divided every after 15 cm and designated as class 0, 1, 2 (0 = 15 cm, 1 = 30 cm length, etc.) starting from the rhizoidal portion 1,7 . Epiphytes other than Coilodesme were recorded just for their presence. Number of epiphytic Coilodesme thalli was counted on each size class and length of each thalli was measured and recorded. After separating the host and epiphytes, both were dried in an oven at 120°C for 24 h. The biomass of —————— * Present address and contact for reprints: Central Institute of Fisheries Education, Seven Bungalows Versova, Bombay 400 061, India