These rust spots are known as surface rust. It doesn't damage the material, and you can easily remove it with a sharp kitchen sponge and stainless steel cleaner. If you encounter this, don't wait too long to clean it to prevent other parts from being affected.
But how and why does this surface rust specifically occur in that area? Metals react differently to saltwater depending on their alloy composition, and it cannot be entirely avoided. We use stainless steel (V4A) and titanium to minimize rust formation as much as possible.
We recommend rinsing the screws with freshwater and thoroughly drying them after each session.