TRURO — Since the once-thriving salt-marsh ecosystem called East Harbor was partially reopened to tidal flow in 2002, ocean organisms have been rapidly recolonizing the estuary. Researchers now hope to understand its changing ecology by documenting the success of horseshoe crabs, which have recently been found spawning in East Harbor (sometimes called Pilgrim Lake). Scientists from the Cape Cod National Seashore, the Center for Coastal Studies, and Antioch University of New England are about to dig into two projects to collect baseline data and document horseshoe crab behavior in the partially restored tidal lagoon. The work, to begin in April and continue for two years, builds on an effort that began in 2018 and was slowed by the government shutdown the following year. … ▶