Actually, I don't believe specific sea creatures reach Ariel's domain, such as sharks, eels, and other villainous marine life. I think that's more Ursula's sector of the Ocean (but I might be wrong, this is just from memory. Haven't seen The Little Mermaid in a long time).
Even if this was the case, Jasmine is protected by many magical entities (connected with both Aladdin and Jafar). So magic can easily be used to take out the "marines" (lol, I made a funny :3). She could also reclaim the betel half's and ask Aladdin to go back into the cave to reclaim something else of value.