Abstract: To clarify ecological effects of co-culture of macroalgae and saline cladocerans, two co-culture aquatic systems were established via addition of macroalgae, i.e.Ulva pertusa or Ulva intestinalis, into the static culture water with water fleas Moina mongolica. We investigated the impacts of those two macroalgae on the static water purification effect and the reproduction and population performance of the water fleas. The results showed thatthe two macroalgae had significant effects on the levels of ammonia, pH and DO in the co-cultured water (P<0.05). The water chemical parameters varied in a similar pattern for both systems. The levels of ammonia in both systems decreased to the minimum value (0.016 mg·L^-1) after 12 days, and then kept stable. Both pH value and DO level were elevated with increasing biomass of the two macroalgae. The pH values varied between 8.2 and 9.0 and DO levels between 4.2 and 6.4 mg·L^-1. The two macroalgae differentially affected the reproduction and population growth of M. mongolica in the coculture systems. The average neonates, intrinsic increase rate (r_m), finite increase rate (λ), and generation cycle (T) were increased with the increases of U. pertusa biomass. When U. pertusabiomass peaked at 2.5 g·L^-1, those parameters declined. In contrast, the average lifespan declined with the increasing biomass of U. pertusa. There were better ecological effects in the co-culture system based on U. pertusa than in the control. There was no significant difference between co-culture system based on U. intestinalisand the control (P>0.05). U. pertusa, with the biomass of 2.5 to 3.5 g·L^-1, played dual roles in both water purification and culture of aquatic animals in the co-culture system, beneficial to the purification of ammonia and DO in water and the growth and reproduction of M. mongolica. These findings provide useful insights into optimization of a large-scale culture technique and development of novel culture mode for M. mongolica.

Key words: ecosystem services value, ecology-economy, harmonious development, Yanqi Basin.