AbstractsBiology & Animal Science

[Truncated abstract] In order to control algal blooms, it is necessary to better understand microbial interactions in aquatic ecosystems. However, present ecological models, mainly based on the simple 'top-down' (consumer) view of controlling algal blooms, do not always provide an accurate picture of planktonic dynamics due to the complicated nature of microbial interactions. This study has developed serial ecological models building on the classic 'Nutrient-Phytoplankton-Zooplankton-Detritus' (NPZD) model to better understand the significance of specific microbial interactions in aquatic ecosystems, such as the microbial loop and the viral shunt. These interactions are relevant to 'bottom-up' (resource) control of algal blooms in aquatic ecosystems. Using Lake Kinneret (Israel) as a study site, the significance of key microbial loop processes on nutrient supply and stoichiometry is further examined by applying a one dimensional coupled hydrodynamic-ecosystem model (DYRESM-CAEDYM) to a comprehensive dataset (1997-2001). In the first study, the potential significance two types of microbial interactions in aquatic ecosystems have been theoretically explored. The improved serial models for the microbial loop and the viral shunt illustrate the importance of 'bottom-up' (resource) control of algal blooms via these microbial interactions in aquatic ecosystems. In the second study, the relationship between phytoplankton internal nutrient stoichiometry and water column N:P ratios has been investigated in a dynamic lake environment. The results showed that the average internal N:P ratios of the phytoplankton community followed the total carbon biomass seasonal patterns. The seasonal patterns of the simulated dissolved inorganic N to total P (DIN:TP) ratios in the water column were a useful indicator for reflecting the N:P stoichiometry of the phytoplankton community and compared better than other indicators that were tested including total N: total P (TN:TP) ratios and dissolved inorganic N to dissolved inorganic P (DIN:DIP) ratios. However, the internal N:P ratio patterns of individual phytoplankton groups did not always reflect the DIN:TP ratio patterns. The stoichiometry of nutrient recycling pathways illustrated that the ability of bacteria to regulate phytoplankton stoichiometry is a significant factor that has ecosystem wide implications. The microbial loop has more considerable changes of the N:P ratios of the iv nutrient pools than the N:P ratios of the simulated phytoplankton groups, which further indicate its importance in regulating the N:P stoichiometry of the nutrient fluxes between bacteria, zooplankton, and inorganic and organic matters pools. In the third study, the analysis of C:N:P stoichiometric variations demonstrated the effect of bacterial competition for inorganic nutrients on the stoichiometry of phytoplankton. In particular, bacterial competition with phytoplankton for inorganic nutrients in the microbial loop plays a positive effect on phytoplankton primary production rather than the traditional…