Passing the gut of juvenile flounder, Platichthys flesus: differential survival of zoobenthic prey species

We studied the resistance of benthic prey organisms (Ostracoda, Hydrobia spp., Macoma balthica) to digestion by juvenile flounder, Platichthys flesus (L.), in a series of aquarium experiments. Results showed that some food species are able to survive the gut passage (Ostracoda 53 to 75%, Hydrobia spp. 46 to 92%). This has ecological implications, as increasing eutrophication of the Baltic Sea favours prey species that are nondigestible for the juvenile flounder. Thus, seemingly small changes in food-web structure may have unpredictable effects for the predatory fish. Received: 8 March 1997 / Accepted: 14 March 1997