Green mould on pepper seedlings

Some of my pepper seedlings have a green mould-like substance on the surface of the compost, any ideas what it is, is it harmful, and what I might need to do about it?

Thanks in advance 

could be, I've tried not to water them too much after I read on here that they preffered to be on the dry side.  I might try scraping the top bit of the compost off.