Size-specific clearance rates of the ctenophore Mnemiopsis leidyi based on in situ gut content analyses

摘要

The ctenophore Mnemiopsis leidyi can consume large amounts of zooplankton prey. However, quantitative measurements of feeding rates, based on field data, are scarce. We measured the time required by the invasive M. leidyi to digest naturally occurring prey species in the Gullmar fjord, Sweden. Digestion times were related to prey size and type, number of prey in the gut and size of the predator. Large prey species or many prey in the gut resulted in longer digestion times compared with small or few prey, but digestion time also varied with the size of M. leidyi. The prey- and predator-specific digestion times were used together with in situ prey concentrations and gut contents of M. leidyi to calculate the clearance rates. Clearance rate as a function of ctenophore size is presented for the most abundant mesozooplankton: Acartia sp., Oithona sp., Oikopleura dioica and Penilia avirostris. On the basis of the relation between digestion time and the carbon content ratio between prey and predator, we discuss the possible effects of mixed prey assemblages on the estimates of clearance rates.