The study looked at how small and large sea creatures respond to low oxygen levels in the Gulf of Mexico. They found that small creatures like worms and clams can survive in low oxygen, while bigger animals like fish can move away to find food. The area with the lowest oxygen had fewer types of small creatures but more types of larger animals. This was because small fish and invertebrates stayed there when bigger fish left. The size and depth of the small creatures' homes also affected the number of larger animals in the area.