Given the diversity of biodiversity citizen science projects' design and objectives, a major challenge is to better understand the factors influencing their successes. We study an online communication space where participants to a participative biodiversity monitoring program share their data and freely interact. A quantitative analysis of the comments' distribution among participants reveals the multiplicity of epistemic and social roles they endorse: helping collective identification of plants and insects, moderating the respect of the scientific protocol, or maintaining community's life. By building a typology of these comments, we show how this space of discussion favors exchanges and reflections about esthetical, interpersonal, biological and methodological aspects. We argue that the existence of such spaces favors all together the production of high-quality data, science learning, and individual commitment towards environmental issues. Maybe more importantly, they allow citizens to build and strengthen collective epistemic and affective relationships with science