So last week I went to a talk by a guest PhD student at the aquarium who studies the ecological impact of horseshoe crabs. The take away was basically that, in the area of study, which was across several mud flats in Great Bay, New Hampshire the HSCs are foraging in nearly 100% of available space across two weeks. Diligent little chelicerates.
She also found that that in areas where the HSCs were foraging the invertebrate population was about a third of that in undisturbed mud. Basically they are exerting some pretty intense predation pressure on these mud flats.
And that brings me to the real revelation: The HSC really is, like the sea star, a top predator of the inter-tidal zone. I have been telling it all wrong. When asked I generally tell people that horseshoe crabs eat "dead stuff" or "soft stuff" because they don't have teeth or jaws. While it's probably true that they're not terribly picky and will scavenge, they are in fact hunters as well. The really cool thing I learned was that they are capable of cracking soft shell clams with their legs. I had no idea that they were so capable at being awesome predators. It really has changed my already very favorable opinion of them. They're like the sharks of the mud flats,