The abundance and species assemblages of dinoflagellate cysts at sediments in the three estuaries of the Southern part of South Sulawesi

Harmful algal blooms (HAB) are a phenomenon of drastically increasing phytoplankton populations, which can cause problems in aquatic ecosystems. Dinoflagellate cysts are a type of phytoplankton that are the main source of causing the HAB phenomenon; this occurs due to unfavorable environmental conditions. The Southern Estuary of South Sulawesi has high fishery resources and high primary productivity. The coastal areas around these waters are widely used for anthropogenic activities that trigger nutrient increases. There are no studies on HAB, especially the abundance and community structure of dinoflagellate cysts at this location. This study aims to identify the types, abundance, and species assemblages of dinoflagellate cysts in the three estuaries of southern South Sulawesi. Sampling was carried out at three locations, namely the Pappa River Estuary, the Kelara River Estuary, and the Calendu River Estuary, in January 2022. Each location consists of 4 stations, 3 sub-stations with 3 repetitions sampling for each substation. Results showed that there were 34 species of dinoflagellate cysts belonging to 6 families, namely Gonyaulacaceae, Gymnodiniaceae, Osteropsidaceae, Peridiniaceae, Polykrikaceae, and Protoperidiaceae. The highest abundance of dinoflagellate cysts was at the Calendu River estuary station III, accounting for 82 cysts g−1, while the lowest abundance of dinoflagellate cysts was found at Pappa River estuaries stations I and II, accounting for 8 cysts g−1. The level of diversity, uniformity, and richness of dinoflagellate cysts was not significantly different in the three study sites. The family Osteropsidaceae was the most common type of dinoflagellate cyst found in the three study sites. The Osteropsidaceae family is a type of dinoflagellate cyst that contains toxins, so it can be assumed that the three research sites have the potential for HAB.