Nano-TiO2 and elevated temperature impair intestinal health in crabs via a mussel-based food chain†

Nano-titanium dioxide (nano-TiO₂) is a ubiquitous contaminant in the marine environment that accumulates in sediments and biological tissues. Coupled with global warming, these challenges can enhance the deleterious properties of nano-TiO₂, leading to compounded pollution effects on marine life and ecosystems. This study investigated the effects of nano-TiO₂ and increased temperatures on the Japanese swimming crab's gut microbiota and digestive system, Charybdis japonica, through different scenarios. We employed three exposure scenarios: direct exposure (DE) of the crabs to warming and nano-TiO₂, indirect exposure (IE) through consumption of mussels Mytilus coruscus subjected to the same conditions, and combined exposure (CE), where crabs were directly exposed to warming and nano-TiO₂ while consuming affected mussels. Additionally, a control group was established, comprising Japanese crab C. japonica and thick-shelled mussel M. coruscus that were reared under standard temperature (22 °C, the average annual temperature in the region where the mussels and crabs were sampled) and 0 mg L⁻¹ nano-TiO₂ concentration conditions. The findings indicated that warming and nano-TiO₂ disrupted the crabs' ATP production, digestive responses, and body chemical composition, leading to intestinal flora dysfunction. Notably, nano-TiO₂ exerted a stronger impact on the crabs' digestive enzymes and intestinal flora than warming alone; however, the concurrent presence of warming and nano-TiO₂, especially under the direct exposure (DE) conditions, generally exacerbated the negative effects of nano-TiO₂. This research provides valuable insights into the implications of nano-TiO₂ and elevated temperature on the digestive responses of marine crabs.