Survival alternatives and environmental interactions of Thalassiosira rotula across three trophic levels

Thalassiosira rotula, a ubiquitous diatom in coastal seas, exhibits different bloom potentials in response to distinct trophic levels, complicating the prevention and management of its blooms. However, the reproductive mechanisms of T. rotula under various trophic levels and their response to environmental changes are relatively understudied within current scholarly discourse. This study examined the population dynamics of T. rotula, and analyzed the interactions of environmental factors, through a harmful algal bloom simulation experiment within a trophic gradient system. The results indicated that T. rotula at oligotrophic levels primarily used nutrients for resting spore formation, while at eutrophic and mesotrophic levels, it utilized nutrients for both vegetative cell proliferation and resting spore formation. Eliminating resting spores and disturbing alternatives of survival strategies could mitigate T. rotula blooms. Different trophic levels altered T. rotula's absorption threshold for DIP but not for DIN. The reintroducing of nitrogen into the low N:P ratio environments caused by excess nitrogen consumption could trigger T. rotula blooms. Thus, focusing on the reintroducing of nitrogen is crucial when managing the re-blooms of T. rotula in seawater. Trophic levels indirectly affected T. rotula's reactive silicate absorption by influencing its growth, physiology, and cell cycle. T. rotula blooms could be controlled by intervening in the physiological and ecological traits of this algae. Nutrient restriction significantly impacted T. rotula's photosynthetic efficiency, affecting water pH and dissolved oxygen levels. Both nitrogen and phosphorus deficiencies promoted resting spore formation under sufficient reactive silicate, restricted to specific-sized vegetative cells before the decay phase. The findings may be insightful for comprehending T. rotula's survival strategies in response to fluctuations in trophic levels and devising effective measures to mitigate harmful algal blooms.