We’ve Got Crabs

The triangle of saltmarsh ot the southern end of Pier One at Brooklyn Bridge Park is an experiment. It’s cordgrass (Spartina alterniflora), which thrives even though it’s flooded by salt water at high tides. In flower now, it will send many seeds off on the currents, searching for mudflats. Key to its success, though, is the matrix of roots in the mud. Two other keys are ribbed mussels and fiddler crabs; together the three species anchor an incredibly productive and important ecosystem, nursery for many fish species and acting as kidneys by cleaning water.

Now, neither the mussels nor the crabs were “planted” with the cordgrass when this went in two years ago. That’s what I mean by experiment. But the fiddler crabs (Unca pugnax, I think) have found the marsh. Could there be mussels in there as well? This is a male; I also saw one female. Females lack the big bull-fiddle claw, which the males used to show off and protect their tunnels. Now I only saw two individuals, and places like Four Sparrow and Pelham bay are absolutely scurrying with them (these two observed at high tide, mind you), but everybody starts small. UPDATE: returning four days later at lower tide, I saw several more and their tunnels; they sense your vibrations as you approach and hide just before you get a good look at them, so try sitting on the rocks and waiting until they emerge again.Just a few feet away, I found evidence of a second species of native crab, the Blue or Blue Claw (Callinectes sapidus). The Hudson has a robust population of this species, according to this. This was a young one, 1.75″ long. Being delicious, it has been scarfed up by something; those are additional bits of chitinous remains above the overturned carapace. Those points on the sides of the carapace are tell-tale for this species.

[Crab and crab shell were photographed in the water. Image may thus appear larger than is actually the case.]