Experimental feeding rates of gelatinous predators Aurelia aurita and Mnemiopsis leidyi at low northern Baltic Sea salinity

The effect of the northern Baltic Sea's low salinity on feeding rates of a native scyphozoan Aurelia aurita and a recent invader to southern Baltic Sea, ctenophore Mnemiopsis was investigated experimentally. Incubations with Acartia spp. prey (4.19-25.16 indiv. l(-1)) were used to estimate clearance rates for both predators. Mnentiopsis leidyi digestion times were measured for several natural prey items. Wet weight (ww):length/diameter relationships as well as clearance rates (0.49 +/- 0.15 1 g(ww)(-1) h(-1) [mean +/- SE] for M. leidyi [mean oral-aboral length +/- SD = 9.6 +/- 1.5 mm]; and 0.18 +/- 0.07 1 g(ww)(-1) h(-1) [mean +/- SE] for A. aurita [mean bell diameter SD = 37.3 +/- 6.9 mm]) and digestion times at salinity 5.7 were within the ranges reported from higher salinities. These preliminary results suggest that the low salinity does not significantly depress the feeding rates or potential predatory impact of these gelatinous predators.