Species-specific responses to trace elements in rotifer reproduction: A critical review

Trace elements are essential nutrients for aquatic organisms. Aquatic species rely primarily on external sources (diet and the environment) for trace mineral nutrition. Trace element bioavailability differs among species and is influenced by the forms of minerals (organic or inorganic) and environmental factors. Rotifers that belong to the Brachionus genus play a significant role in aquaculture operations (by serving as live feed source for marine larval rearing) and are also important in ecological studies with regard to aquatic ecosystems. Rotifers engage in cyclical parthenogenesis, enabling rapid population expansion through asexual reproduction and the formation of resting eggs via sexual reproduction. The generation of resting egg facilitates long-term preservation and enables a consistent supply of rotifers. Rotifers are often subjected to trace element conditions through indirect trophic transfer or direct exposure in rearing systems or fields. The nutritional and toxicological effects of essential trace elements, such as iron, zinc, selenium, and copper in rotifers have been studied. While we identified species-specific modifications in reproductive patterns and metabolic activities, such as inhibited or enhanced sexual reproduction in different rotifers, with distinct responses in neutral lipid accumulation in reproductive organs and oxidative defenses within the Brachionus plicatilis species complex under iron and zinc exposure. Accordingly, we hypothesized that specific trace elements function as nutrients for growth and essential metabolisms, while also controlling the transition of rotifer reproductive patterns. To strengthen our understanding, this paper presented a systematic literature review on the effects of various essential trace elements, especially iron, zinc, selenium, and copper on the reproduction of rotifers. We elucidated the mechanisms from multiple perspectives, including behavior, biochemical, and genetic. This review also discussed aspects of their influence on phytoplankton–zooplankton–larval interactions, given the importance of trace elements in the aquatic food web. Finally, we outlined the regulatory effects of trace elements on intra- and interspecific responses from individual and population ecological viewpoints, and the ecophysiological significance of interactions with other elements and environmental factors. Understanding the interactions of rotifers with trace elements and the mechanisms underlying species-speci