Phytoplankton communities in different season in the coastal area of Kawasi, the western part of Obi Island, North Maluku, Indonesia

Plankton communities are one of the groups monitored to assess environmental conditions. West Obi Island is known for its fisheries resources and is one of Indonesia’s largest Nickel mining areas in North Maluku, Indonesia. However, few studies have discussed phytoplankton structure in this region, and this study aimed to assess the distribution and community structure in the western part of Obi Island, Halmahera Selatan. Vertical sampling was conducted to collect phytoplankton and zooplankton from 13 stations during the dry and wet seasons in 2023. We identified 46 species phytoplankton during dry season and 24 species during wet season. During the wet season, phytoplankton is more abundant at specific locations, such as ports and estuaries, and less abundant in coral reef areas. In contrast to the wet season, there was a significant increase in phytoplankton abundance across all locations during the dry season, which could relate to nitrate. Chaetoceros sp., Coscinodiscus sp., and Rhizosolenia sp. were the predominant genera in both seasons. During the dry season, phytoplankton were predominantly concentrated in the strait area between Obi and Mala-Mala Island. In contrast, the phytoplankton were more concentrated in the harbor and estuary areas in the wet season.