What are these sea urchin tree balls?

Sea urchin tree balls, also known as "urchin balls," refer to a type of marine organism that has a spherical shape and is often found in coral reefs. These structures are composed of numerous sea urchin tests (the hard outer shells) and can be mistaken for natural debris or marine plants. They play a role in the ecosystem by providing habitat and food for various marine species, contributing to the overall biodiversity of their environment.