Feeding, respiration and growth of ctenophore Beroe cf ovata in the low salinity conditions of the Caspian Sea

Abstract

The ctenophore Beroe cf ovata, which spontaneously entered the Black Sea in the 1990s and suppressed the previous ctenophoran invader Mnemiopsis leidyi by its predatory impact, is currently considered for intentional introduction to the Caspian Sea as well. In order to assess its impact on Mnemiopsis in the Caspian, Beroe was transported during 2002 from the Black Sea and the Bosporus to the Khazerabad laboratory (Mazandaran), on the Caspian coast of Iran, where experiments on its survival in Caspian water, and on various physiological characteristics (feeding, respiration, reproduction and growth) of both ctenophore species were performed. Beroe cf ovata was found to adjust to Caspian salinity conditions without problems. Beroe also readily fed on Mnemiopsis, but rejected all zooplankton food. The feeding rates measured are such that it can be predicted that Beroe will suppress Mnemiopsis in the Caspian at the same rate as it did in the Black Sea. The mean daily ration of Beroe was found to be 26-43% of its body weight. The daily specific growth rate of Beroe cf ovata makes up 0.1 (10%) of its body weight in conditions of food ad libitum. Under favourable food conditions, the population of Beroe was able to double its biomass in 10 days. An energy budget for Beroe cf ovata is provided.