Final answer:
The mobula ray appears closer to the surface than it actually is due to the refraction of light, which causes objects in water to look shallower than their actual depth. This refractive effect also explains why a person's legs look shortened when wading in water. Bioluminescent marine creatures, like anglerfish, are adapted to the darkness of deep waters where refraction doesn't affect the visibility of objects since sunlight doesn't reach such depths.
Step-by-step explanation:
The phenomenon that causes a mobula ray, which is 3 meters above the surface of the ocean, to appear at a different position than its actual depth when observed from above is known as refraction. When light travels from water to air, it speeds up and changes direction. This bending of light rays makes objects in water appear closer to the surface than they really are. Hence, a fish or any object under water appears at 3/4 of the actual depth due to this refractive effect.
When it comes to someone wading in a pool, their legs look very short due to the same principle of refraction. The light rays from their legs bend when they move from water to air, making the legs appear shorter and closer to the surface than they really are.
In the context of marine life, like the mentioned anglerfish living at depths where no sunlight penetrates, its adapted bioluminescence is essential for survival in its dark environment, which is unaffected by the optical phenomenon affecting how deep things appear.