As far as I know, there isn't any. At all. Not even algae. The reason is clear: no sunlight, no photosynthesis, so plants would starve in the deep sea - they have no other way of gaining food. read more
All these factors have led to fascinating adaptions of deep sea life for sensing, feeding, reproducing, moving, and avoiding being eaten by predators. Light. The deep sea begins below about 200 m, where sunlight becomes inadequate for photosynthesis. read more