The Effectsof Modified Clay On Bentonic Organisms In Mitigation Of Harmful Algal Blooms (HABs)

Modified clay is considered an effective protective measure against harmful algalbloom (HAB) and has been applied successfully in China, Japan, South Korea, andAustralia.We present results on the effect of modified clay on marine benthos inHABs’ controlling. We choose3marine benthos as experiment subject: Apostichopusjaponicas Selenka, Patinopecten yessoensis, Scrippsiella trochoidea.The main resultsare shown follow:1Effects of modified clay on the infant of Apostichopus japonicas.The halflethal concentration（LC50）of modified clay on the infant of A.japonicas was6.01g/Lin the96h acute test. In chronic toxicity tests, the growth rates and survival rates inmodified clays were almost as same as control groups. When less than1.0g/Lmodified clay added, the moisture, ash, sugar, fatty acid and protein contents of thetissues had no significant changes. After60days incubation experiments with theconcentration of1.0g/L modified caly, there was no significant effect on thealuminum content of the tissues. Meanwhile, the study studied the removing ofharmful algal Prorocentrum donghaiense, and the efficiency concentration ofmodified clay was0.1g/L and0.5g/L, which could simutaneously reduce the mortalityof the juvenile A.japonicas. Thus, there were no negative impacts of the modified clayflocculation on the benthic A.japonicas, and the modified clay treatment was aneffective and reliable strategy to mitigate the harmful algaes.2Effects of modified clay on the infant of Patinopecten yessoensis.The half lethalconcentration（LC50）of modified clay on the infant of P. yessoensis was2.3g/L, andthe safe concentration was0.23g/L, which was more than two times higher than thefield application concentration（0.1g/L）in96h acute toxicity test. The chronic toxicity test showed the influence of modified clay on the survival rate, shell length and heightwas insignificant when the concentration of clay increased from0.1to1.0g/L. Andthe feeding of P. yessoensis infant was effected by modified clay, with highermodified clay concentration leading to greater influence. We also studied the effectsof P. yessoensis infant when harmful algae（Prorocentrum donghaiense）bloom wascontrolled by modified clay. Compared with the control, the addition of modified clayimproved the survival rate of P. yessoensis from22%to38%. Meanwhile, it improved3times than control group, when we picked out the P. yessoensis before the additionof clay and then put P. yessoensis into the culture. To sum up, the addition of modifiedclay not only controlled HABs effectively, but also improved the survival of P.yessoensis infant. It was a meaningful technology to mitigate HABs.3Effects of modified clay on cysts of Scrippsiella trochoidea. Concentrationsof modified clay（0,0.1,0.5, and1.0g/L）were added to cultures, and observationswere made oncysts of S.trochoidea under controlled laboratory conditions. Resultsindicate that the removal rate of algal cells reached97.7%at the clay concentrationof1.0g/L. The cyst formation rate increased from4.6%to24.6%when theconcentration of clay was increased from0to1.0g/L. Two cyst metamorphs wereobserved: spinal calcareous cysts and smooth noncalcareous ones. The proportion ofthe spinal cysts decreased from76.9%to24.1%when clay concentration increasedfrom0to1.0g/L. In addition, modified clay affected cyst germination. Thegermination rate decreased with the increases in the clay concentrations.Non-calcareous cysts had a lower germination rate and a longer germination time. Weconclude that modified clay could depress algal cell multiplication and promoteformation of temporal cysts of S. trochoidea, which may help in controlling HABoutbreaks.In addition, the author also investigated the effects of nitrate and ammonium onthe growth and encystment of S. trochoidea. We incubated S. trochoidea in modifiedf/2media without nitrogen and silicate in flasks. The flasks were divided into twogroups. Nitrate was added as a nitrogen source in the first group, and ammonium was added in the second group. The concentrations of the nitrogen compounds were0,10,30,60, and90μM. The duration of the experiment was14days. The results indicatethat NO3-N favors cell growth, and cultures with a higher concentration of NO3-Nwere ineffective at forming cysts. In contrast, NH4-N promoted cell growth and cystformation. At similar concentrations as NO3-N, NH4-N had a toxic effect on cellgrowth and increased the cyst formation rate. Thus, the NH4-N concentration is animportant factor for controlling encystment. We believe that the impact of ammonia ininducing cyst formation may be a useful feedback mechanism in ecological systems.