Sarcasm aside, metal straws don't float, and fish and birds don't try to eat them. And unless you have some fancy expensive metal straws, in a corrosive sea salt environment the ones generally available rust in a matter of years.

Bioplastic straws are a superior solution.

Compostable straws can be made of bioplastics, but require high temperatures to biodegrade, meaning generally temperatures not found in nature (outside of volcanic areas).