does subsistence fishing (whether extensive or not) affect the corals in the sea?

Answer 1

Depends on how it is done. Hook and line fishing would have minimal effect. Hand nets wouldn't do too much either. But anchoring boats, drag nets on the bottom and using poisons to catch fish are obvious problems.

A less obvious problem is that people try to catch the tastiest fish first and rarely hesitate to catch all of them. That can really turn an eco-system upside down. What if that tasty fish feeds on a fish that eats coral?

Generally, the higher density and higher technology a society has, the more effects it has. But we've been altering eco-systems and killing off species for at least 11,000 years.