Corrosion Under Prop

After changing the oil in the foot of my motor today I just happened to spin the prop and heard a 'gritty" kind of noise, so I pulled the prop. Turns out it was fishing line, but I also noticed some corrosion I wasn’t expecting to see. Seems to brush off easily enough, but still concerns me.

Can someone tell me what I’m seeing?

'07 198 DLX Carolina Skiff
FS90 Suzuki

this is why they tell you to pull prop and grease that whole area every year