Unless it's for a saltwater aquarium, I wouldn't use wood found in the or around the ocean and brackish areas. It's likely to be too salty and give off a high pH for most freshwater aquariums. Treating the wood is the same for either fresh or salt though which is first baking it or boiling it for a short time. Too long and it will disintegrate into mush, then if you're worried about tannins, letting it soak in water for a few weeks to months, depending on how much it gives off tannins.