Oithona davisae, the Most Predominant Copepod in Tokyo Bay, a Highly Eutrophic Embayment: Why Are They So Predominant?

Abstract

Oithona davisae is a planktonic cyclopoid copepod species, known to be extremely abundant and often predominates in coastal marine embayment. To understand why this animal is so successful, we have been looking into its swimming ability to escape from predators. Here we show how O. davisae escapes from the moon-jelly Aurelia aurita, which devours zooplankton and occurs in a huge number in embayments including Tokyo Bay. Direct observations revealed that O. davisae is agile enough to escape from the moon-jelly’s ephyra larvae, which appear much more numerously than adult moon-jelly. This agility reducing the predation mortality may be crucial for O. davisae to predominate in this bay and somewhere else that are full of predators. Direct observations by the use of video cameras suggested that O. davisae may be recognized as a genius in escaping from predators, comparing with some other planktonic animals such as Acartia (larger copepod), barnacle cypris, decapod zoeas, etc., being less agile than O. davisae.