Size-invariant aerobic scope across ontogeny in a giant deep-sea scavenger

Aerobic scope defines the energetic margin available for activity beyond maintenance and plays a central role in ecological performance. In many organisms, increasing body size or environmental stress can reduce this margin, a pattern often described as having "little left in the tank". However, species that rely on episodic but intense activity may require sufficient aerobic capacity from early life stages onward, particularly when individuals are relatively large at hatching or birth. Here, we examined the ontogenetic scaling of resting metabolic rate (RMR) and active metabolic rate (AMR) in the giant deep-sea scavenger Bathynomus doederleini across a broad size range (1.7-48.4 g) using intermittent-flow respirometry at 10 {degrees}C. RMR and AMR increased with body mass and exhibited nearly identical scaling exponents, resulting in a size-invariant factorial aerobic scope (median = 2.83). This pattern suggests that aerobic capacity is established early and maintained proportionally with maintenance costs, supporting locomotion and scavenging throughout ontogeny in an energy-limited environment.