Effects of bioturbation by three macrozoobenthic species and predation by necto-benthic mysids on cladoceran benthic eggs

摘要

The effects of bioturbation and predation by the amphipod Monoporeia affinis, the bivalve Macoma balthica and the polychaetes Marenzelleria spp. were studied on the number, vertical distribution and hatching of benthic eggs (ephippia) of the cladoceran Bosmina longispina maritima. It was hypothesised that the 3 functionally different macrobenthic species affect Bosmina ephippia to different degrees. In addition, it was hypothesised that macrofaunal bioturbation either inhibits or enhances predation by the necto-benthic mysid Mysis mixta on cladoceran benthic eggs. M. affinis and M. balthica caused a 48 and 23% decrease in the total number of Bosmina ephippia, respectively, indicating egg predation. In addition, M. balthica extended the distribution of eggs into deeper sediment layers. Both M. affinis and M. balthica suppressed the daily hatching rate of Bosmina, and the effect of the bivalves (reduction 92%) was stronger than that of the amphipods (34 to 78%). None of the benthic species promoted the predation of mysids on Bosmina eggs. Instead, both M. affinis and M. balthica reduced the number of ephippia in the sediment surface (by 79 and 43%, respectively), implying that these species decrease the ability of mysids to feed on cladoceran benthic eggs. M. balthica was the most harmful species for the recruitment of Bosmina, whereas the nonindigenous Marenzelleria spp. did not affect ephippia.