Ecological response of Rotaria rotatoria (Bdelloid Rotifera) to unbalanced nitrogen in food: experimental insights from life history strategy and feeding behavior

Nitrogen (N) cycle in ecosystems has been overbalanced by human activities. However, it remains uncertain whether the altered N supply results in a change in the elemental composition of phytoplankton and, consequently, affects the life history strategy of zooplankton. To investigate these impacts, a simple lab-based food chain was established. Results show that lack or excess of nitrogen reduced algal density, cell volume, growth rate and chlorophyll content. Moreover, N content in algae significantly increased with increased N concentration in the medium, and reached saturation at concentrations ≥5 mg·L−1. Feeding on algae grown in a low-nitrogen or no nitrogen mediums resulted in faster decline in age-specific survival of rotifers, and slower population growth, as well as longer generation time. In order to make up for nutritional shortage, grazing and filtration rates increased. On the other hand, rotifers feeding on algae grown in high-N mediums (A50 and A200) had significantly shorter average lifespan and life expectancy at hatching. Therefore, nitrogen imbalances have adverse effects on the growth, development and reproduction of both primary producers and herbivorous zooplankton in the food chain.