The Ecological and Physiological State of the Ctenophore Mnemiopsis leidyi (Agassiz) in the Black Sea in Autumn 1996

Abstract

The survey was made in off-shore waters of the Black Sea near the Anatolian coast of Turkey during a research cruise of the R/V Bilim (24 Sept - 4 Oct 1996). The biomass of gelatinous macroplankton and the glycogen content in the body of the ctenophore Mnemiopsis leidyi were studied at 14 stations. Though the ctenophore still dominated the plankton in terms of biomass (average biomass + standard deviation 276 + 115 g/m2), this estimate was significantly lower than corresponding estimates obtained for the same months in recent years. A simultaneous reduction in the stock of small-sized fodder zooplankton and the large copepod Calanus euxinus indicates this case may be due to a general aggravation of trophic conditions for ctenophores. Data on the ctenophore’s body glycogen content varied from 21 to 44 μg/g fresh weight and accounted for 52.5 ± 14.2% of total polysaccharide content on average, the condition of M. leidyi observed during the conducted survey corresponded to that expected after a two-day fasting period. Tentative experiments have shown that metabolic rates of the examined ctenophores were notably reduced. The rate of oxygen consumption (R, μl O2 · ind-1 · h-1) was 1.7-1.8 less than that which would indicate a sufficient food supply; depending on the estimate of fresh body weight (W, g) at 12-14°C, it may be described by the following equation: R = 2.50 W0,83. Minimum metabolic demands of the entire population are evaluated as 91 cal · m-2 · day-1, that is 40% of the energy which would normally be assimilated from small-sized fodder mesozooplankton. However, in autumn the mesozooplankton production sustains only half of the food requirements of the ctenophores.