Potentially Harmful Phytoplankton in Trisik Coastal Lagoon, Kulon Progo, Yogyakarta, Indonesia

Lagoon is one of the coastal ecosystems that provide habitat for many coastal organisms, including phytoplankton. However, some phytoplankton species could bloom excessively, known as harmful algal blooms (HABs). In this study, we aimed to investigate the potentially harmful and toxic phytoplankton species in Trisik coastal lagoon, Kulon Progo, Yogyakarta, Indonesia. Five 2 l water samples were collected then pooled together. Then, put in five 150 ml glass bottles, preserved in 5% Lugol’s iodine solution, wrapped with aluminum foil, transported back to the laboratory and observed under light microscope. Environmental parameters such as temperature, pH, salinity, and TDS were also measured. This study identified three potentially harmful classes, Bacillariophyceae (3 taxa), Cyanophyceae (1 taxa), and Dinophyceae (5 taxa) from Trisik coastal lagoon. This lagoon has a higher temperature value (33.9 °C) than the recommended temperature range that might support the presence of harmful phytoplankton. This present study highlights the presence of potentially harmful phytoplankton in Trisik coastal lagoon, which therefore may contribute to a better regulation of Trisik coastal lagoon by the local government.