In the case of plastic bags, they seem to be commonly mistaken for squid and jellyfish, eaten by the albatross and sea turtles, to name just two species.
So while the bag-free aesthetic on land is an improvement, the potential for downstream benefits is even greater.
You fix that by improving the sanitation system so that garbage is not dumped into the ocean, not by trying to stop the creation of garbage going into the system.
350 million metric tons of plastic are produced each year and that number is growing by 4% per annum. Plastic bags are not going to change that, and plastic is only one type of long lived material in our garbage.
The solution is to not dump garbage into rivers and oceans and to create effective sanitation systems in developing countries.
But people in Germany forgoing the use of plastic bags, thinking that they are saving a seal or something are just misguided. Germany has an effective sanitation system -- India, Thailand, China, Myanmar do not. Nothing you throw away in Germany is going to end up in the ocean.