What Was Expected

Kelp and seagrass were not in any sub-tab, and rather just next to the coral decorations sub-tab.

What Happened

Kelp and seagrass sit at the end of the Coral Decorations sub-tab.

To Reproduce

Open the Creative inventory and navigate to the Nature tab. You won't see kelp or seagrass because it's hidden in the Coral Decorations sub-tab.