Here you can find a lot of corals, shels, seaweeds and starfishes. All seaweeds have vertex colors for animation by vertex shader. BigShell_1 - 2614 triangles
Support, URP and HDRP shaders are here:
My Discord group
BigShell_2 - 2708 triangles
BigShell_3 - 5322 triangles
BigShell_4 - 5322 triangles