Inhibitory Effects Of Gracilaria Lemaneiformis On Phytoplankton Growth And Its Application For The Integrated Aquaculture.

In recent years,with the frequent occurrence of harmful algal blooms in inland waters and coastal waters of China,more and more experts and scholars pay attention to the bioremediation studies.Previous studies have shown the growth inhibition of macroalgae on phytoplankton,which provides a theoretical basis for the use of macroalgae to improve the marine environment.In the present study,Gracilaria lemaneiformis is selected as the experimental material.The inhibiting effects of Gracilaria on phytoplankton of freshwater and seawater and the actual suppression on harmful algal blooms in the in situ field experiments were carried.This seaweed could be as bioremediation material and integrated culture with abalone in coastal waters.The main results are as follows:1.The dry powder of seaweed G.lemaneiformis can significantly inhibit the growth of freshwater phytoplankton,pseudanabaena and Chlorella vulgaris(P<0.05)under the indoor experiment conditions.The concentrations of dry powder added were higher,and the inhibitory effects were more obvious,showing the effect of concentration gradient.2.In the field experiments,the fresh G.lemaneiformis and its dry powder inhibited significantly the growth of phytoplankton(P<0.05),and reduce phytoplankton cell densities with a concentration gradient effects.The fresh G.lemaneiformis can significantly increase phytoplankton species biodiversity(P<0.05),but the effects of Gracilaria dry powder on phytoplankton species number were not obvious.3.In order to study the effects of different modes of abalone mariculture on phytoplankton community structure and water environment,the field survey was made in four mariculture areas,including abalone culture area,Gracilaria-abalone polyculture area,transition area and control area in Shen'ao Bay from May to June,2016.Eighty-four phytoplankton species were recorded in this survey.The diatoms were the most dominant population with 71 species,accounting for 84.52% of the total phytoplankton species.The average densities of phytoplankton were significantly lower before the seaweed harvested than after harvesting in the survey areas(P<0.05).The average densities of phytoplankton in Gracilaria-abalone polyculture area were significantly lower than that in abalone culture area before harvesting(P<0.05).There was no significant difference between the densities of phytoplankton in the two areas after harvesting.The analysis of water physicochemical factors showed that the concentrations of total nitrogen(TN),total phosphorus(TP)and chlorophyll-a(Chl-a)in the Gracilaria-abalone polyculture area was the lowest.The phytoplankton community structure was significantly affected by TN,TP,water temperature(T)and salinity(Sal).4.The G.lemaneiformis-ablone polyculture systems can reduce the nutrient loading of abalone culture,and decrease the concentrations of nitrogen and phosphorus,and play an important role in improving water quality and sustaining aquaculture systems health.Therefore,abalone-seaweed polyculture mode is one of the worthy popularized integrated aquaculture systems in the coastal areas.