Star Wars: The Clone Wars - Season 4 Episode 5 -

"Mercy Mission" Plo Koon's clone legion "The Wolfpack", R2-D2 and C-3PO are sent to repair power & communication systems on the planet of Aleen after a series of devastating earth-quakes; but the droids discover a severe ecological imbalance between the planet's subterranean ecology and surface biospheres.