Effect of dinoflagellates and diatoms on the feeding response and survival of Aurelia sp. polyps

Abstract

To investigate whether dinoflagellates and diatoms interact with the polyp stage of Aurelia sp., feeding responses to dinoflagellates and diatoms and the survival of polyps fed on phytoplankton or Artemia sp. were studied in laboratory experiments. Feeding responses to motionless diatoms, defined by the movement of the polyp tentacles, were seldom seen but responses to motile dinoflagellates were clearly observed. Meanwhile, the feeding response was significantly positively related to the equivalent spherical diameters of the dinoflagellates. Gastric cavity analysis indicated that micro-phytoplankton (Alexandriumcatenella, Akashiwo sanguinea), which were in high concentration, could be detected, but nano-phytoplankton (Prorocentrum donghaiense, Karenia brevis) were not detected, implying that nano-phytoplankton were not eaten by Aurelia sp. polyps. We also observed that dinoflagellates whether nano or micro lost their motility and became attached on Aurelia sp. polyps. Compared to feeding on Artemia sp. nauplii, survival of the polyps was significantly depressed after 91 days feeding on phytoplankton in all combinations of species and concentrations. High mortality of the polyps when feeding on a high concentration (80 mg C l−1) of dinoflagellates implied that the polyps may be harmed when they coexisted with dinoflagellate blooms, so that the mass occurrence of large numbers of Aurelia medusae in natural coastal waters was depressed.