Physiological characteristics of the ctenophore Beroe ovata in Caspian Sea water

Abstract

Riparian countries of the Caspian Sea have been evaluating the pros and cons of the predatory ctenophore Beroe ovata as a control agent against the invasive ctenophore Mnemiopsis leidyi, which has enormous adverse impacts on the fishery resources as well as on the biodiversity in this once fertile sea. To assess the viability of B. ovata establishment in the Caspian Sea, the survival and some physiological characteristics (feeding, respiration, reproduction and growth) of the predatory ctenophore were studied in Caspian Sea water (12.6 ppt salinity) conditions using animals transported from the Black and Marmara Seas to a laboratory on the Iranian Caspian coast. The findings of the study showed that when salinity was gradually decreased from 22 to 12.6 ppt, B. ovata were able to adapt well to Caspian Sea water. Most of the predatory ctenophores began to swim actively and to feed on M. leidyi within 15 to 30 min following each step of acclimation. The feeding rate of B. ovata ranged from 14 to 765% of body wet weight and was highest for smaller individuals (i.e. 13 to 16 mm). Over the measured weight range of 0.23 to 3.87 g wet wt, the weight-specific respiration rate was independent of weight. The daily specific growth rate of adult ctenophores was 7 to 11% of body wet wt. B. ovata specimens were spawned and their eggs were hatched in Caspian Sea water, but the larvae survived for only a few hours. The energy budget of B. ovata calculated from food consumption, respiration and growth rates revealed a mean assimilation efficiency of 0.72 ± 0.1, a gross growth efficiency (K 1 ) of 0.48 ± 0.12 and a net efficiency (K 2 ) of 0.66 ± 0.06. Based on these physiological data, we suggest that in the Caspian Sea, B. ovata will be able to ingest M. leidyi intensively. However, concerning the reduction of the M. leidyi population and consequently the reversal of its adverse impact on this ecosystem, the failure of larval growth observed under experimental conditions (most probably due to poor handling) remains the main obstacle to overcome in the successful establishment of B. ovata in the Caspian Sea.

Phytoplankton distribution in the Caspian Sea during March 2001

“…pollution, eutrophication and invasive species) (Dumont, 1995). Recently, the impact of the accidentally introduced ctenophore Mnemiopsis leidyi (Ivanov et al, 2000) has been tremendous on the Caspian ecosystem causing sharp decreases in zooplankton levels (S. Bagheri & A. E. Kideys, unpublished data), pelagic fish stocks and other higher components of the ecosystem (Shiganova et al, 2001;Kideys, 2002;Kideys et al, 2004).…”

The problem of invaders in the Caspian Sea in the context of the findings of new zoo- and phytoplankton species from the Black Sea

“…Appearance of this obligate predator exclusively feeding on zooplankton-eating ctenophores such as Mnemiopsis leidyi triggered restoration of the Black Sea ecosystem (Shiganova et al, 2003). Our experimental introduction of Beroe ovata into the Caspian Sea for inhibiting Mnemiopsis population and restoring the Caspian ecosystem demonstrated that Beroe ovata can live, propagate, and feed on Mnemiopsis in the Middle and Southern Caspian regions (Kideys et al, 2004). Introduction of this alien species can possibly restore the Caspian ecosystem similarly to the Black Sea; such introduction is not only justified but essential.…”

Mnemiopsis leidyi Invasion and Biodiversity Changes in the Caspian Sea

“…During spring and summer of 2001, mass (estimated as 250,000 tons, or 40% of the population) mortalities of sprat were reported at the sea surface (Davis et al, 2003). The fish catch value was halved again in 2002, resulting in great economic losses (Kideys et al, 2004(Kideys et al, , 2005. Fishermen even stopped fishing during most part of 2003, due to lack of fish (Fazli and Roohi 2003).…”