What is the significance of this passage?

A sea otter dives. Long streams of sunlight wash through kelp trees, undulating like lazy belly dancers. A purple sea urchin creeps towards a kelp trunk. The otter dips, snatches up the urchin, carries it to the surface, where the sound of the waves breaking on the nearby shore is a bitter grumble. Devouring the urchin’s soft underbelly in neat nibbles, the otter twirls in the surf, then dives again. The urchin’s shell parachutes to the ocean bottom, landing in the dark, drifting hair of a corpse.