Megafauna: the ignored bioturbators

Bioturbation is a process caused by animals that move particles and water in sediments. This influences gas and solute exchange, and organic matter concentrations through the sediment column. Bioturbators play an important role in biogeochemistry and ecosystem functioning. To date, bioturbation research has focused on the invertebrate macrofauna present in the sediment. However, many larger marine animals (e.g. rays, sharks, whales) display foraging behaviours that disturb the sediment and thus potentially affect sediment biogeochemistry. We propose a categorization of vertebrate megafauna bioturbation based on their reworking behaviours, classifying them as 'pit creators', 'bulldozers', and 'trench diggers'. These categories underscore the diversity of impacts on sediment structure and biogeochemical processes. The need to investigate the topic comes from the limited knowledge surrounding the extent to which sediment biogeochemistry is influenced by megafauna activities. Additionally, the declining population of vertebrate megafauna due to climate change, overfishing, bycatch, and habitat loss and modification makes discerning the functional roles of these animals in the sediment a pressing issue. Understanding the ecological implications of megafauna bioturbation will be critical to support conservation strategies and protect marine ecosystems and the animals that shape them.