Hundreds of sections of Reddit, the popular online message board, were unavailable Friday in what appeared to be a protest by many of the site’s moderators after the abrupt dismissal of a high-ranking company employee.

The move affected nearly 300 individual discussion areas — so-called subreddits that focus on individual topics like technology, art and business. Subreddits are generally moderated by self-appointed members of the community, not official Reddit employees. The shutdowns, which began Thursday evening, appeared to expand rapidly on Friday.

They began shortly after Victoria Taylor, Reddit’s director of talent, was dismissed Thursday afternoon. On Friday, the volunteers posted a document online that asked for better communication with official staff, as well as improved software tools for community management.

In a telephone interview on Friday, Reddit’s interim chief executive, Ellen Pao, said, “I’m sorry we let our community down yesterday.” She added, “We should have informed our community moderators about the transition and worked through it with them.”