There was no formal organizer of Sunday’s protests; people found out about the rallying points over social media, mostly on Twitter and Facebook, the platforms most used by Cubans. The thousands of Cubans who took to the streets — protesters and pro-government activists alike — wielded smartphones to capture images and send them to relatives and friends or post them online. On Monday, Cuban authorities were blocking Facebook, WhatsApp, Instagram and Telegram, said Alp Toker, director of Netblocks, a London-based internet monitoring firm. “This does seem to be a response to social media-fueled protest,” he said. Twitter did not appear to be blocked, though Toker noted Cuba could cut it off if it wants to. While the recent easing of access by Cuban authorities to the internet has increased social media activity, Toker said, the level of censorship has also risen. Not only does the cutoff block out external voices, he said, it also squelches “the internal voice of the population who have wanted to speak out.”