I don't know the specifics of the place you're talking about, but it's always a good question to ask what the goals are of having either an individual MPA or an MPA network. Often it is thought to be what the place was like before fishing happened, but in many cases that's not reasonable. Fishing by first nations has been taking place in some of these places for thousands of years, so there is no fishing precedent specifically. It may be appropriate to manage some of the fisheries more strictly within such a place. We also don't necessarily know all of the impacts by some of those fishing activities, or how the ecosystem has changed, as was mentioned, with climate change.
One of the things that MPAs have been shown to do is that by having less fishing effort and less impact from extractive activities, they tend to have less variability. They tend to be more consistent in terms of the fish that are there, which can be a benefit and can show us just how much change is happening in the places that are fished more severely or more intensely.