The legal targets are binding. We are a party to the Convention on Biological Diversity, and the Aichi targets that you've heard so much about are a legal commitment.
We also have commitments under the UN Convention on the Law of the Sea. Article 192 requires all states “to protect and preserve the marine environment”, with no qualification to that duty.
There's further guidance about creating networks of protected areas in both the biodiversity treaty and the UN sustainable development goals.