[zxcmx]

If you don't find the OHI (https://www.conservation.org/projects/ocean-health-index) credible, I'm not sure there's much more I could write that would convince you. Sorry :/

The point is that the oceans are large, there are different concerns, and conditions vary across location and species.

If you want to answer a question like "how healthy are our oceans?" you need to first work out what that might mean, and then measure that systematically like the project I linked you to.

[pmiller2]

Why do we need to attach a number to it for it to be a valid concern? The ocean is undoubtedly changing in ways that, if allowed to continue, will cause massive ecosystem damage, leading to secondary effects on land, such as increased warming and higher CO2 levels. Why is that not enough to convince anyone who matters to do anything?

[zxcmx]

There are lots of things being done, but much more could be done - and for that we need to convince governments, which takes data.

In particular we need to convince governing bodies that action is in their direct and immediate economic interest, which again takes data.