why are horseshoe crabs endangered?

Answer 1

They're not endangered.

Stressors they're facing include habitat loss / degradation, overharvest.

This situation may change as their traditional breeding beaches are submerged by rising ocean.

Answer 2

Eel fishermen used them for bait by the thousands and their blood is used for medical research so there is a black market. They don't reproduce fast enough to keep up with demand.

Answer 3

Because we are messing up the oceans by throwing sh*t in there.