If you have a prawn or seamoth in the cyclops reapers will attack you and knock you around a little bit trying to get to the smaller vehicle, but won't damage the cyclops, provided they dont knock you below the crush depth.

Will a Reaper attack a Cyclops?

Normally reapers will completely blank the cyclops but this one suddenly started to snap its jaws and ram my cyclops in the middle. This happened several times and the reaper always targeted the cyclop's flanks rather than the cockpit or tail.

Can leviathans destroy Cyclops?

I returned to the Lost River after applying a MK2 depth enhancement to my cyclops, hoping to go explore the lava area down there. Everything was peachy the last three times I had gone, but this time there was a juvenile ghost leviathan in there.