I popped into the Tropics for some testing and spawned right next to a volcano. Surrounding the volcano, and a patch of seaweed, were untextured edges. Not full blocks, just edges. I'll include a screenshot.

Using Tropicraft 1.12.2 (7.1.3.62) and Forge (14.23.2.2639)

How much memory are you running the game with? And are you running any other mods? Have you tried running with the recommended version of forge (2611)?

This is a known bug with CTM, when you add/remove a texture pack while ingame. Restarting the game should fix it.