The phrase "discernible effect" means that there is a noticeable or observable outcome or influence resulting from a particular action or situation. Full definition
The depreciation of the Australian dollar during the Asian crisis had little discernible effect on final consumer prices over the subsequent couple of years. (rba.gov.au)
The 2012 government reshuffle was said to be a «rise of the right» moment but has made little discernible effect on the overall direction of the government, aside from possibly the work done by Chris Grayling as justice secretary and Owen Paterson as environment secretary. (labour-uncut.co.uk)
They're there, yes, but they have so little discernible effect as to feel tokenistic; you might as well ignore them. (trustedreviews.com)