It took me a couple tries to parse as well. At first I thought "counting" was a verb, leading to the impression that a horseshoe crab had been taught to count and was now counting alongside New York's citizen scientists. I figured perhaps it had something to do with prior research on crab computing: https://phys.org/news/2012-04-scientists-crab-powered.html

"Horseshoe crab census" would had been the obvious solution available

Horseshoe crab-counting...the hyphen makes a [UK English only?] difference.

I found it hard to read - I thought they may have crowd-sourced some telescope buffs.