The Effects of Grass Carp on Aquatic Plants, Plankton and Benthos in Ponds

The effects of the grass carp (Ctenopharyngodon idella Val.)on aquatic plant biomass, water quality, phytoplankton, chlorophyll a, zooplankton and benthic fauna were investigated between May and September 2000 in earthen ponds at Cifteler- Sakaryabasi Aquaculture and Research Station. (PDF has 8 pages

Herbivore regulation of plant abundance in aquatic ecosystems.

Herbivory is a fundamental process that controls primary producer abundance and regulates energy and nutrient flows to higher trophic levels. Despite the recent proliferation of small-scale studies on herbivore effects on aquatic plants, there remains limited understanding of the factors that control consumer regulation of vascular plants in aquatic ecosystems. Our current knowledge of the regulation of primary producers has hindered efforts to understand the structure and functioning of aquatic ecosystems, and to manage such ecosystems effectively. We conducted a global meta-analysis of the outcomes of plant-herbivore interactions using a data set comprised of 326 values from 163 studies, in order to test two mechanistic hypotheses: first, that greater negative changes in plant abundance would be associated with higher herbivore biomass densities; second, that the magnitude of changes in plant abundance would vary with herbivore taxonomic identity. We found evidence that plant abundance declined with increased herbivore density, with plants eliminated at high densities. Significant between-taxa differences in impact were detected, with insects associated with smaller reductions in plant abundance than all other taxa. Similarly, birds caused smaller reductions in plant abundance than echinoderms, fish, or molluscs. Furthermore, larger reductions in plant abundance were detected for fish relative to crustaceans. We found a positive relationship between herbivore species richness and change in plant abundance, with the strongest reductions in plant abundance reported for low herbivore species richness, suggesting that greater herbivore diversity may protect against large reductions in plant abundance. Finally, we found that herbivore-plant nativeness was a key factor affecting the magnitude of herbivore impacts on plant abundance across a wide range of species assemblages. Assemblages comprised of invasive herbivores and native plant assemblages were associated with greater reductions in plant abundance compared with invasive herbivores and invasive plants, native herbivores and invasive plants, native herbivores and mixed-nativeness plants, and native herbivores and native plants. By contrast, assemblages comprised of native herbivores and invasive plants were associated with lower reductions in plant abundance compared with both mixed-nativeness herbivores and native plants, and native herbivores and native plants. However, the effects of herbivore-plant nativeness on changes in plant abundance were reduced at high herbivore densities. Our mean reductions in aquatic plant abundance are greater than those reported in the literature for terrestrial plants, but lower than aquatic algae. Our findings highlight the need for a substantial shift in how biologists incorporate plant-herbivore interactions into theories of aquatic ecosystem structure and functioning. Currently, the failure to incorporate top-down effects continues to hinder our capacity to understand and manage the ecological dynamics of habitats that contain aquatic plants

Influence of Trout Cage Culture On Water Quality, Plankton And Benthos Anatolian Dam Lake

The effects of rainbow trout cage culture on water quality, phytoplankton, zooplankton and ben- thos were investigated in a cage farm of 30 ton capacity in Kesikköprü dam lake. Water tempera- ture did not differ among stations while dissolved oxygen and pH values were slightly lower in the station with cages. Significant and insignificant increases were detected in concentrations of ammonia, nitrate, orthophosphate and chlorophyll a in the cage station. Also, the abundance of phytoplankton, zooplankton and benthos was highest in the cage station. The composition of phy- toplankton was not fundamentally different among stations except for a higher abundance of Chlorophyceae and Cyanophyceae species in the cage station in November. The composition of zooplankton and benthos did not differ among stations; rotifers and gastropods were dominant, respectively