Have a look at another nice pack for UE4. Free of charge in November!
The set features an underwater environment with rock meshes, terrain materials, algae, schools of fish. You'll get an animated eel, particle effects, submarine wreckage and downed Japanese WWII planes.
It includes five rock meshes that make use of displacement and tessellation that also come with material instances for you to adjust the sand amount on top of them. Please note that all vegetation is paintable using vegetation tools. The author also noted that terrain material has parallax enabled and contains two layers.
Technical Details
You can learn more and get the pack here.