Abstrak
This study aims to determine the structure of the plankton community as a water bioindicator. The location of the research was carried out at two points, namely station I in the estuary area and at station II close to settlements. Sampling was carried out 15 times for 2 months. The structure of the plankton community at high tide in Amal Baru coastal waters as the object of research includes abundance, diversity index, uniformity index, and dominance index. The types of phytoplankton found at the research site consisted of 3 classes, namely Bacillariophyceae, Coscinodiscophyceae and Dinophycea classes and zooplankton from Crustacea classes. The most common type of phytoplankton found at the research site is the Bacillariophyceae class because this class has good adaptability to its environment. Phytoplankton abundance index values obtained ranged from 14-94 cells/l and zooplankton abundance values obtained ranged from 4-16, including in the low category. The diversity index value is in the medium category with the uniformity index in the high uniformity category and low dominance. The chemical and physical factors of the Amal Baru coastal waters of the city of Tarakan at the research location are still good for the life of aquatic organisms.