The effects of tench (Tinca tinca (L.)) and sticklebacks (Gasterosteus aculeatus L.) on planktonic and benthic communities in mesocosms in a shallow lake

The effects of introducing a zooplanktivorous fish, three-spined stickleback, (Gasterosteus aculeatus) and a benthivorous fish, tench (Tinca tinca) separately and in combination to replicated experimental enclosures with two density levels of white water lily (Nymphaea alba) were studied in Little Mere, UK. Numbers of Daphnia hyalina were high and only slightly diminished at reduced lily densities, probably due to stickleback predation, but there was no consequential effect on phytoplanktonic chlorophyll a concentrations. Tench reduced the numbers of gastropods but not of other macroinvertebrates, and in turn increased the biomass of periphyton growing on artificial substrata within the enclosures. The higher lily density reduced oxygen concentrations and pH values and increased total phosphorus and soluble reactive phosphorus concentrations but otherwise had little effect on water chemistry. There was little interactive effect of the fish species. The results are integrated with those of six other such enclosure experiments carried out in Little Mere since 1992.