Reply #3: Red tide is the result of protozoa. [View All]

[Mendocino]

Certain protozoa, under certain conditions produce enough
toxins that result in red tide.  

Simply put, dead zones are large masses of oxygen depleted
water in which animals move out of or die. The dead zones
generally are the result of over-fertile waters that bloom
into massive algae beds. The algae eventually die, sink into
the depths and break down. When organic materials decompose,
they consume oxygen. Thus the water becomes oxygen poor.

Dead zones have also appeared in the Gulf of Mexico and Lake
Erie. The watersheds of both the Gulf and Erie are largely
agricultural, with excessive levels of fertilizers, organics
and silt flowing into them. They are also shallow and warm,
which adds to the problem.