It talks about red tides and hypoxia, but it doesn't say that they saw evidence of those occurrences in the areas they were observing.
They didn't; but the study supports the linkage between agricultural runoff and blooms that induce hypoxia elsewhere.
They mention problems with hypoxia at the end of Mississippi river, but they don't really show that they have any evidence to show that it's related to algal blooms or nutrient runoff. I suspect that there are a lot of different pollutants in the Mississippi river, what ties the hypoxia to the nutrients?
Pollutants that don't enhance phytoplankton growth don't participate in the process that causes hypoxia; they're just pollutants. Excess nutrients like nitrogen and phosphorus do enhance phytoplankton growth.
The article mentions bacteria that eats the algae uses up oxygen. However green algae is the biggest source of oxygen in the oceans. I'm having a hard time buying the argument that more green algae results in a net loss of oxygen levels in the water.
Hypoxia is a problem on the sea floor. The algae die and sink to the bottom and get consumed by the bacteria. That's where the oxygen depletion occurs, not at the surface where the algae are growing.
Shrimp eat algae. So unless the runoff is causing toxic blooms, I would think that the shrimp population would thrive during algal blooms.
Shrimp breathe (respire), too, and they inhabit the bottom of the water body. If they are in waters that become hypoxic, they have to leave.
It sounds like they gathered some good information with their research. However the tone of the article seems to imply that these algal blooms are bad. All they've done so far is show that the nutrients appear to effect algae growth, but they don't know what type of algae or if it's good or bad.
I think it's more appropriate to say that excess algal blooms can be (but aren't always) bad. They don't really say that they've seen detrimental effects from this process in the Sea of Cortez, leading me to think that they haven't.