Int.J.Curr.Microbiol.App.Sci (2014) 3(8) 723-748 723 Original Research Article Comparison between the Diversity and Density of Marine Dinoflagellates in Northern and Southern zone of Malacca straits Mohamed Amar Naqqiuddin * , Norsalwani Muhamad Nor, Azura Alim, Idris Abdul Ghani, Hishamuddin Omar and Ahmad Ismail Department of Biology, Faculty of Science, Universiti Putra Malaysia, 43400, UPM Serdang, Selangor Darul Ehsan, Malaysia *Corresponding author ABSTRACT Introduction Dinoflagellates species are microscopic phytoplankton (Hallegraeff, 1988) and highly abundant in both marine and fresh waters. These organisms play important role for food web in the aquatic ecosystem. Some dinoflagellates live close to shore for the nutrients supply and lower salinity than open sea (Smetacek et al., 1991). A phytoplankton bloom becomes in contrast when the density reach over than 10 8 cell/L ISSN: 2319-7706 Volume 3 Number 8 (2014) pp. 723-748 http://www.ijcmas.com Keywords Dinoflagellates Phyrrophyta; Peridiniales; Ceratium furca; Straits of Malacca Dinoflagellates are the second most abundant phytoplankton group throughout the world. Other than incidents of harmful algal blooms, studies are carried out to keep track on changes to diversity, composition and abundance of dinoflagellates species almost annually. Nonetheless, there is insufficient information collected from previous studies. The main objective of this study is to distinguish the abundance, species composition and distribution of dinoflagellate in the northern and southern zone of Malacca Straits during northeast and pre southwest monsoon season. Samples were collected by using Van Dorm water sampler and observed under inverted and scanning electron microscope (SEM). Under Division Pyrrophyta, 71 dinoflagellates species from 21 genus, 13 families and six orders were identified in the northern zone while in southern zone, 53 species were found from 15 genus, 11 families and six orders. During northeast monsoon, Peridiniales dominated in both north and south zone with total density of 89.76% and 80.84% respectively. Peridiniales also constitute an important group during pre southwest monsoon with an average total density of dinoflagellates at 61.89% in north zone and 79.3% in south zone. Total concentration of dinoflagellates in north zone ranged from 18.02 cells/L to 180.01 cells/L during pre southwest monsoon season. For south zone, the range was from 7.93 cells/L to 99 cells/L during northeast monsoon season and was highest from 26.01 cells/L to 577.3 cells/L during pre southwest monsoon season. Overall, Ceratium furca was the most dominant in the northern zone during northeast monsoon season (maximum cell density reached 69.96 cells/L at Station 2) and during pre southwest monsoon in the southern zone of Malacca Straits.