Does nori seaweed need a hechsher?

Answer: Yes (cRc).

Reason: Non-kosher crustaceans are occasionally mixed into plain nori sheets.

Source:

• cRc: requires certification, due to reports that non-kosher crustaceans are occasionally mixed into plain nori sheets, and shared oven lines with non-kosher product.

Related questions:

• Do soy sauce and tofu need a hechsher? Yes (cRc).
• Does raw fish need a hechsher? Raw fish from a kosher species may be bought without one, with care about the knife (cRc).

References: cRc (askcrc.org), “Nori Seaweed”