The definition of the word "biosocial" is:
of, pertaining to, or entailing the interaction or combination of social and biological factors.
As the word suggests, biosocial contains aspects of both biology and sociology. A biosocial task, then, is anything one does which connects the two things. For example, cutting down all the trees in a primitive forest is an act which has purely biological ramifications--unless it is the forest from which a tribe of people gain their sustenance. Then it becomes a biosocial action because it changes how a culture lives.
Social behaviors can also be affected by biological factors, such as how people dress (depending on the weather) and what they eat (depending on what is available in their environment).
The word task does imply something more deliberate than, say, inadvertently polluting water which then changes the fishing habits of people downstream; however, anything which impacts both the biology and social behavior of something else would be considered a bisosocial act.