Effect of temperature on clearance rate, daily ration and digestion time of Mnemiopsis leidyi from the southern Caspian Sea

The effect of temperature on the main feeding parameters of Mnemiopsis leidyi from the southern Caspian Sea was studied in 2002. The clearance rates and daily rations were estimated from laboratory experiments in a wide range of temperatures from 12 to 27 ºC for M. leidyi of 12–17 mm in length. Clearance rate values changed from 52.5 to 107.3 ml ind-1 h-1. The coefficient Q10 in temperature 12 - 20 ºC was higher than that in 20 - 27 ºC (3.81 and 1.91, respectively). The specific daily ration changed from 1.56±0.19 to 0.24±0.05 mg C mg C-1 day-1 when temperature decreased from 27 ºC to 12 ºC. The direct relationship occurred between daily ration and temperature (R2=0.99). The digestion time decreased with temperature rise and did not display any clear relation to quantity of digested food.

Ctenophores-invaders and their role in the trophic dynamics of the planktonic community in the coastal regions off the Crimean coasts of the Black Sea (Sevastopol Bay)

The abundances, biomasses, and population structures of two introduced ctenophore species-Mnemiopsis leidyi and Beroe ovata-were monitored along with mesoplankton in the near-shore waters of the northern Black Sea (Sevastopol Bay and adjacent regions) over a period of four years (2000-2003), after the B. ovata invasion. The annual dynamics of the M. leidyi population were similar in these years: very low abundances and biomass values were observed during the major part of the year ( unlike previous years) with a short-term peak in the summer-early autumn. B. ovata development during the growth in the M. leidyi biomass resulted in a sharp fall in the M. leidyi biomass down to extremely low values. The interannual differences in the populations of both ctenophore species were reflected by their quantitative parameters: the maximum biomass of M. leidyi varied from 790 g/m(2) in 2001 to 211-266 g/m(2) in other years. The maximum biomass values of B. ovata (38.9 and 32.5 g/m(2)) were observed in 2001 and 2003, respectively. In 2000-2003, from July to September, during the peak in mnemiopsis development, the population consumed from 1.9 +/- 0.4 to 13.4 +/- 5.7% of the mesoplankton biomass per day, while in the years of B. ovata absence, these values were as high as 30-40%. For the first time, the grazing rate of microzooplankton by M. leidi larvae was estimated. In August 2003, the maximum daily consumption rate was as great as 23-25% of the microzooplankton biomass. The daily rations of the mnemiopsis larvae on microzooplankton were close or even higher than those on mesoplankton