A study on microzooplankton community from the coastal waters of eastern Arabian Sea: Emphasis on the dominance of heterotrophic dinoflagellates

Abstract We studied the community composition of microzooplankton (MZP) from the surface waters off Candolim, Goa. The MZP communities were examined for the year 2013, covering different seasons and four stations (Near-shore: G3 & G4, offshore: G5 & G6). A total of 30 species belonging to 24 genera were recorded, which include loricate ciliates (LC: 14 species of 13 genera), aloricate ciliates (ALC: 5 species of 3 genera), heterotrophic dinoflagellates (HDS: 11 species of 8 genera) and copepod nauplii. The MZP abundance in the coastal waters varied spatially irrespective of different seasons, with higher abundance in the offshore stations (G5 & G6, 38–127 cells L-1) and lower abundance in the near-shore stations (G3 & G4, 20–97 cells L-1). The MZP community composition showed the dominance of HDS (16–85%) in the near-shore stations during most of the seasons and inferiority during NEM (16–18%,). Moreover, all the coastal waters (near and offshore) were dominated by HDS (58–85%) during spring inter-monsoon. The dominant species of HDS were Dinophysis apicata, Dinophysis caudata, Porocentrum micans, Protoperidinium breve, Protoperidinium latistriatum, and Protoperidinium granii. The statistical analysis (Spearman's rank correlation) depicts that the MZP abundance and community composition were mainly controlled by salinity (r = 0.4–0.7). Whereas the dominance of HDS in the coastal waters could be the reason for its mixotrophic nature and diverse feeding mechanism. Thus, a strong positive correlation between the HDS and LC (r = 0.73–0.92) showed the feeding ability of HDS in their relative community.