Refractometer

All posts tagged Refractometer

By John Harrod, Manager, DuPont Environmental Education Center

Over the summer and last weekend at WildFest, Blue Crabs were caught in the DuPont Environmental Education Center’s freshwater tidal pond. Most visitors were surprised to find crabs here since they are usually associated with brackish (slightly salty) and salt water along the Atlantic and Gulf coasts.

An excited summer camper with a Blue Crab. Photo by John Harrod.

  Blue crabs can live in fresh water. To find out the salinity content of our pond, I borrowed a refractometer from the Delaware Nature Society’s technical monitoring program. The pond registered a salinity reading of 0 parts per million (ocean water is 32+ ppm).

Pete Zeigler demonstrating use of a hand refractometer. Photo by John Harrod.

 Growing up to 9 inches, this crustacean is an opportunistic bottom-dwelling predator that feeds on anything it can find including live and dead fish, clams, snails, and detritus (decayed organic matter).

A recent catch at WildFest that could grow up to 9 inches. Photo by Laura Orth.

 This predator is also prey of wildlife including eel, striped bass, other blue crabs and catfish. As its scientific name – Callinectes sapidus – indicates, people enjoy them too. It translates, “beautiful swimmer that is savory.”

 To learn more about DNS technical monitoring program visit here.