20 Questions

Josh, Sandip, Greg, Julia and I went camping in Killalea State Park last week. There is a river system that flows into the Tasman Sea, and the river is mostly salty.

We were exploring the shores of the river and came upon this:






It was tough but bendable; felt like it was made of very tough sea matter. It was about the size of a medium pine cone. Most importantly, when Greg stepped on it, a thick, viscous, light greenish blue squidge (looked like Pert Plus) squeezed out of it in a trajectory.

Can you guess what it is?