Cryptogamie, Algologie, 2016, 37 (2): 109-120 © 2016 Adac. Tous droits réservés doi/10.7872/crya/v37.iss2.2016.109 Seasonal variation in the occurrence and abundance of mangrove macroalgae in a Malaysian estuary Md. Masum BiLLAH a,b* , Abu Hena Mustafa kAMAL a , Mohd Hanai Bin iDris a & Johan Bin isMAiL a a Faculty of Agriculture and Food sciences, Department of Animal science and Fishery, university Putra Malaysia Campus Bintulu, Bintulu-97008, sarawak, Malaysia b education and research Center for Marine resources and environment, Faculty of Fisheries, kagoshima university, 50-20 shimoarata 4-Chome, kagoshima 890-0056, Japan Abstract – Mangrove macroalgae produce substantial proportion of biomass, which contributes to the coastal ecosystems. Relatively less is known for the seasonal variation in the occurrence and biomass of mangrove associated macroalgae. Consequently, mangrove macroalgae epiphytic on the pneumatophores of Avicennia marina (Forsk.) Vierh., were sampled from the Miri estuary of Sarawak during the four seasons of Malaysia namely southwest monsoon, northeast monsoon, and two inter-monsoons to elucidate seasonal variation in the occurrence and biomass production of macroalgae. Over the sample period, 11 species of mangrove macroalgae were identiied from 6 genera. Six of these species such as Caloglossa leprieurii (Montagne) J.Agardh, C. adhaerens R.J.King & Puttock, C. stipitata E.Post, C. ogasawaraensis Okamura, Bostrychia kelanensis Grunow and Dictyota sp. were found to be common in each sample time. Considering four seasonal samples, maximum frequency of occurrence was observed for C. ogasawaraensis (66 ± 10%) and maximum biomass was observed for B. kelanensis (248 ± 95 g m –2 ). Marked seasonal variations were observed in the frequencies of occurrence and the biomass for the most of the dominant macroalgal species. To the best of our knowledge this is the irst time to report the seasonal pattern data for occurrence and abundance of macroalgae from the mangrove systems of Malaysia. Mangrove macroalgae / Pneumatophores / Seasonal distribution / Sarawak / Malaysia INTRODUCTION Mangroves grow on tropical and subtropical protected coasts (Hoque et al., 2015a). Mangrove forests are distributed in almost 124 countries, covering an area of about 1% of the world (Saenger, 2002). Mangroves support distinct macroalgal assemblages as epibionts in the intertidal and subtidal portion of the tree such as dead branches, prop roots, pneumatophores, branches and roots (Dawes et al., 1999; * Corresponding author: k4302867@kadai.jp; masum_imsf07@yahoo.com