Q: What carnivorous plants live in the oceans?

A: This is very easy to answer! None!

Marine environments are very challenging for vascular plants. While some oceanic algae such as kelp can become very large, none are known to be carnivorous.

The ocean covers most of the world (albeit much of it is pelagic), so I carefully chose the phrasing "known to be carnivorous." Will the answer be different in 2, 5, or 20 years?

The carnivorous bladderwort Utricularia benjaminiana can survive in moderately brackish waters.

Lowland Nepenthes are sometimes found at the water's edge, but this is not the same as it being a marine species. By the same token, vast regions of carnivorous habitat in the southeastern USA are occasionally submerged by ocean water during hurricanes.

Page citations: Rice, B.A. 2006a; Taylor, P. 1989; personal observation.