Comparison between introduced and native ctenophores in Nordic waters -feeding rates and survival in low food conditions

The ctenophore Mnemiopsis leidyi was introduced to Nordic waters in the middle of the last decade. Recordings of the species raised the question about impact of this comb jelly in the recently invaded ecosystems. It is known that ctenophores can consume large amounts of zooplankton prey. Still, quantitative measurements of feeding rates, based on field data, are scarce both for invaders and native species. We measured the time required by the invasive M. leidyi and the native Bolinopsis infundibulum to digest different naturally occurring prey species in Swedish and Norwegian waters. The prey and predator specific digestion times were used together with in situ prey concentrations and gut contents of M. leidyi and B. infundibulum to calculate clearance rates. Further survival in conditions without food was investigated in the two species at laboratory in temperature 10°C, where animals after the period of starvation were fed Artemia. The major findings are: I) Mnemiopsis and Bolinopsis were seen to feed with similar rates on their major prey groups. II) Both ctenophores species survived and started to grow again after a two month long period without food. Together with field data of ctenophore abundance and carbon content requirements for the species, possible impact by invading and indigenous ctenophores, on natural zooplankton populations in Nordic waters are discussed. The capacity of ctenophores to survive in conditions with low or no food, are considered in connection to transfer of ctenophores within ships ballast water