I have a mer civilization that does have magic, with a technological advancement to about flintlock musket level, so nothing overly complicated. I need the soldiers to have effective weaponry, underwater. With the drag force water has I haven't been sure if swords or slingshots would be effective weapons. I know harpoons would work but they aren't suitable for close combat. The magic is more personal and doesn't really work to change the rules of underwater combat, though magic users ability to have area effects is why close combat is so important. This primarily for mer vs. mer combat. I'm not looking for really technical details more about which weapons would work. I am also dealing with a civilization that can trade and scavenge from and with land dwellers but are themselves still using stone and wood.
And no I'm not looking at open warfare, so please no more wmds