The Feeding Ecology Of Snails On Benthic Algae

The study of different density gradient of two common snails named Radix sp.and Bellamya sp form Lake Dishui, Lingang, Shanghai. Meanwhile, the studycompared the effects on water suspended solids, nutrient, nitrogen and phosphorus inthe sediment and benthic algae grazed by two kinds of snails.(1)The snails activitied can increase the concentration of total nitrogen in water,the higher concentration of snails, the higher concentration of total nitrogen andammonia nitrogen. And the concentration of total nitrogen increased prominentlywhen adding0.09kg/m2(1g) Radix sp. and1.77kg/m2(20g) Bellamya sp.respectively (p<0.05), and the concentration of ammonia nitrogen increased radicallywhen adding0.18kg/m2(2g) Radix sp. and1.77kg/m2(20g) Bellamya sp.respectively (p<0.05). And the concentration of total phosphorus increased radicallywhen added0.18kg/m2(2g) Radix sp. and7.07kg/m2(80g) Bellamya sp. respectively(p<0.05), with the increasing of snails concentration, the concentration of totalphosphorus was rising. The concentration of total phosphorus decreased comparedwith pre-experiment in control group. The snails activitied can also affect thefluctuation of ratio between N and P, the amplification of total phosphorus is higherthan the amplification of total nitrogen in experiment groups. All indicates that theactivity of snails in low density can reduce the contents of suspended substance inwater, and improved the transparency of the water effectively; snails activities in highdensity can strengthen the disturbance of water, prompt the bottom sedimentresuspension, Increase suspended solids and reduce the transparency of water. Theconcentrations of suspended substance in water decreased radically when adding0.09kg/m2(1g) Radix sp. and0.44kg/m2(5g) Bellamya sp. respectively (p<0.05); theconcentration of organic detritus in water decreased radically when adding0.09kg/m2(1g) Radix sp. and0.44kg/m2(5g) Bellamya sp. respectively (p<0.05) and withincreasing snails, the concentration of organic detritus decreased prominently. Theconcentrations of inorganic ash in water decreased radically when adding0.09kg/m2 (1g) Radix sp. and0.44kg/m2(5g) Bellamya sp. respectively (p<0.05) compared withcontrol groups. The concentrations of inorganic ash in water increased radically whenadded1.41kg/m2(16g) Radix sp. and7.07kg/m2(80g) Bellamya sp. respectively(p<0.05). Comparison between two snails herds activities on the influence of waterquality indicated that the influence on total nitrogen, total phosphorus and suspendedsolids was more apparent than that of Bellamya sp. when added the same density ofthem. With the same density, the increase of total nitrogen and phosphorus inexperiment groups of Radix sp. was far higher that of Bellamya sp.(p<0.05). Thedecrease of suspended solids in experiment groups of Radix sp.is higher that ofBellamya sp.(p<0.05).(2)In control groups, the percentage of total nitrogen and total phosphorus insediment all decreased. The total nitrogen of sediment has fallen by0.32%, the totalphosphorus decreased by0.11%.In the experimental groups, with the increasing of thedensity of snails, the percentage of total nitrogen in the sediment was rising. And thepercentage of total nitrogen increased radically when added0.09kg/m2(1g) Radix sp.and0.44kg/m2(5g) Bellamya sp. respectively (p<0.05). In the experimental group,with the increasing of the density of snails, the percentage of total phosphorus in thesediment was rising. And the percentage of total phosphorus increased radically whenadding0.09kg/m2(1g) Radix sp. and0.44kg/m2(5g) Bellamya sp. respectively(p<0.05). The amplification of total nitrogen in sediment was higher than totalphosphorus in the experimental groups. Comparison between two snails herdsedactivities on the influence of sediment indicated that the influence on total nitrogenand total phosphorus is more apparent than that of Bellamya sp. when adding thesame density of them. With the same density, the increase of total nitrogen andphosphorus in experiment groups of Radix sp. was far higher that of Bellamya sp.(p<0.05).(3)The radula of Radix sp. were more closely packed, the number of radula unitis larger than Bellamya sp., and the number of sawtooth of radula unit was also largerthan Bellamya sp.. The density of benthic algae decreased because of the increasedensity of snails, and when reached a certain density, the density of benthic algaeremained at a low level, changed a bit. And in control groups, the density of benthicalgae and all kinds of benthic algae increased prominently. When added0.09kg/m2(1g) Radix sp. and1.77kg/m2(20g) Bellamya sp.,the total density of benthic algaewas different significantly (p<0.05). The density of Chlorophyta and Cyanobacteria was different significantly (p<0.05), when added0.18kg/m2(2g) Radix sp., thedensity of Bacillariophyta and other kind of algae was different significantly (p<0.05)when adding0.09kg/m2(1g) Radix sp. The density of Chlorophyta algae was notdifferent significantly, the density of Cyanobacteria algae was different significantly(p<0.05), when adding1.81kg/m2(20g) Bellamya sp., the density of Bacillariophytaalgae and other kind algae was different significantly (p<0.05) when added0.88kg/m2(10g) Bellamya sp.. The percentage of Cyanobacteria algae in the experimentalgroups was increased, the percentage of Chlorophyta algae gradually decreased, thepercentage of Bacillariophyta algae also had a certain degree of rising. The density offeeding on benthic algae of Radix sp. was higher than that of Bellamya sp., thedecrease of total density of algae and different phylum algae was larger inexperimental groups than that of Bellamya sp. when adding the same quality of0.44kg/m2(5g)(p<0.05). Radix sp. can feed filamentous algae in water, but it was not beable to prove that Bacillariophyta algae can feed filamentous algae.(4)Through field investigation found that seaweed rich river water quality isgood, when there is no snails and aquatic plants, channel points of difference wassmaller. No aquatic plants, with the increase of the density of snails, the greater thenegative impact of snails in water, when the snails coexist with aquatic plants, snailsless negative influence on the water. In areas with high levels of pollution onlyaquatic plants can only reduce the water hydration numerical indicators and does notreduce planktonic algae biomass, and the existence of the snails can reduce planktonicalgae biomass. Therefore, snails and the common role of aquatic plants can play apositive role in the aquatic.