Negative effects of Microcystis blooms on the crustacean plankton in an enclosure experiment in the subtropical China

Effects of Microcystis blooms on the crustacean plankton were studied using enclosure experiments during July-September, 2000. Eight enclosures were set in the hypereutrophic Donghu Lake. Different nutrient concentrations through additional nutrient and sediment in enclosures were expected to result in different abundance of Microcystis. From July to early August, the phytoplankton community was dominated by Chlorophyta, Cryptophyta, Bacillariophyta and Cyanophyta other than Microcystis aeruginosa. M. aeruginosa showed a rapid increase during early August in all enclosures and predominated. Crustacean plankton was dominated by the herbivorous Moina micrura, Diaphanosoma brachyurum and Ceriodaphnia cornuta, and the predaceous Mesocyclops sp. and Thermocyclops taihokuensis. During the pre-bloom period, the dynamics of M. micrura population appeared to be mainly affected by the predaceous cyclopoids. With the development of Microcystis blooms, such interaction between M. micrura and cyclopoids seemed weakened, especially when the Microcystis biomass was high. But there was no apparent influence on the interaction between Leptodora kindti and its zooplanktonic prey. The density of two cyclopoids decreased with the enhancement of Microcystis. The density decline of M. micrura was caused by both predation and inhibition by Microcystis. The low food availability of other edible phytoplankton during the blooms led to low densities of both C. cornuta and D. brachyurum by late August. It appears that dense Microcystis blooms exert strong negative effects on the herbivorous cladocerans and the predaceous cyclopoids.

Diversity and Abundance of Copepods in Taninthayi Coastal Waters, Myanmar

Diversity and abundance of copepods occurring in Taninthayi coastal waters were studied and analyzed from the samples collected by R/V DR.FRIDTJOF NANSEN during the Myanmar ecosystem survey 2018.Seventy-nine copepods species belonging to calanoids(51 species),cyclopoids(21 species),and harpacticoids(7 species)were identified in the copepods community of Taninthayi coastal waters.Copepods species number and density were high at the nearshore stations(Sts 799,842,788)and low at the offshore stations(Sts 846,802,823).The resulted diversity index values of copepods were varied from 2.61 to 3.78 in species diversity index(H'),from 0.89 to 0.97 in the evenness index(E'),and from 2.51 to 7.50 in species richness index(D').According to the correlation matrix,the abundance of copepods was positively correlated with temperature,chlorophyll a and fluorescence,and negatively correlated with salinity and oxygen.