if you are in the united states and if these are published online, in an open forum that does not require any login, then you are clearly dealing with documentary evidence, which is clearly exempt from irb. you are doing the same exact thing as going to the university archives and doing research about the still living presidents of the university. one good way to test this is to see if the data that you are trying to use is in the internet archive. if there is a login required to get the information you are using, then there may be an assumption of privacy, which then brings up issues of the subject. you also have the question of harm, as these people are using pseudonyms they likely have an assumption that if people found out there could be harm involved. however the key distinction that you need to deal with right now is... are you dealing with the people? or are you dealing with documents? If you are going to talk or participate in the community, then you are dealing with people. then it is participant observation, which might not be exempt and you might still need informed consent, but you might not, depending on many factors... mainly depending on the harm question. if you intervene in their life in any way (this does not include re-publication) such as emailing them, chatting with them, then if there is possible harm involved, you will likely need informed consent forms as you are constructing them as a defined human subject of research, if there is no possible harm, and you are merely participating as a member of the community and documenting your participation then you are presenting it as an ethnography. if you are just going to capture the texts that are freely available on the internet, then you are dealing with documents. document research is exempt. so... what i'm saying is... your methods determine the ethics you must follow, define your methods.