Distribution and Behavior of the Marine Luminescent Ostracod Vargula hilgendorfii

Abstract

The distribution and behavior of the marine luminescent ostracod, Vargula hilgendorfii, were investigated on the shoreline of Kumamoto Prefecture and in a laboratory setting. Vargula hilgendorfii mainly inhabit sand/mud bottoms near the shore and are completely nocturnal. From March 1999 to January 2000, baited traps enclosing cock liver, were set one to three times every month (except for August) at the Nishime site to collect V. hilgendorfii. Ovigerous females were collected from April to October and small individuals from June to December, indicating that V. hilgendorfii winter in the adult form. In the summer of 1999, baited traps were set for 24 hours at varying depths under a floating pier at the Ryugu site and the numbers of V. hilgendorfii in each trap were counted every three hours. All the V. hilgendorfii were collected within 1 m of the sea bottom between 6 p.m. and 6 a.m. Vargula hilgendorfii luminescence was observed both at the Nishime site and in the laboratory, from July to October in 1999 and 2001. On the shoreline, V. hilgendorfii luminesced for just a few seconds, mainly when predators such as Portunus pelagicus, R sanguinolentus, Takifugu niphobles, Plotosus lineatus attacked, although the predators still often ate them. In the laboratory, males luminesced more often than juveniles and females, and more frequently when in a group of males, than when in a group with females. Most males appear to luminesce to threaten predators or other males, rather than for courting females.