Data in the Digital Publishers Revenue Index Report from the Association of Online Publishers (AOP) and Deloitte showed that the previous year-on-year growth of 80% in the first quarter had dropped to 21.5% in the second, The Drum reported.
Those figures hid some contrasting fortunes, as spending on smartphones continued to increase strongly, at 44%, while that on tablets dropped back -9%.
Overall digital advertising revenues were up 5.9%, with the greatest rise coming in the sponsorship format (+34%).
Other growth formats included classified (+19%), desktop video (+15%) and recruitment (+4%). Only display (-4%) registered negative growth.
Just over one quarter of participants had displayed annual growth of more than 25% for the first time since early 2014 and all expected to see growth over the next 12 months.
Tim Cain, AOP managing director, said the Q2 report "once again highlights that advertising revenue reflects the increasing consumption of media on mobile and will remain a key focus for publishers during the next quarter.
"Publishers and advertisers alike need to recognise the impact of cross-device, particularly mobile, when planning budgets and understand the value different devices hold along the path to purchase," he added.
Recent figures from the Audit Bureau of Circulations showed that digital magazine circulations increased during the first half of the year, with current affairs titles such as the Economist and The Week recording double digit growth.
Almost half of audited digital titles, however, had reported falls in circulation, a development attributed in part to slowing tablet sales.
"Publishers are now aiming to achieve growth through increasing advertising revenue rather than simply cutting costs," said Howard Davies, media partner at Deloitte.
He described the optimism surrounding digital marketing as "refreshing to see" and said this was "largely down to the continuing growth of mobile and video advertising revenue that has been prevalent in the last 12 months and [which] looks set to continue."
Data sourced from The Drum, Fipp; additional content by Warc staff