Occurrence of the polychaete larvae in the Ca Mau mangrove habitats

Abstract

The study was conducted to determine the occurrence and abundance of the polychaete larvae to serve as a baseline for protection and development of this species in the mangrove habitats in Ca Mau. Polychaetes samples were collected from 9 mangrove shrimp fields in Dam Doi, Nam Can, and Ngoc Hien districts, Ca Mau province (3 fields/district). The study was carried out through 9 sampling periods, once a month, from January to September 2022. The zooplankton samples including Polychaetes larvae were collected at three points of each site (inlet, center, and the back of the field) using zooplankton nets with a mesh size of 60 µm. Samples were preserved in formalin 4 %. The density of zooplankton and polychaete larvae were determined in Sedgewick- Rafter counting chamber. The results showed that the density of zooplankton were highest in April with 646,001 ind/m3 and lowest in January with 171,592 ind/m3 . In study locations, Dam Doi area were recorded with highest density 613,019 ind/m3 of zooplankton compared to Nam Can and Ngoc Hien. The density of polychaete fluctuated during study period with the highest in January and lowest in July. Dam Doi also was highest density of polychaete larvae than other locations. Polychaete larvae were effected by percentage of mangrove coverage. The results also indicated that the polychaetes can reproduce year round but January can be the peak.