The data were collected as part of the Horizon Europe project BIOcean5D – Marine Biodiversity Assessment and Prediction Across Spatial, Temporal and Human Scales. The aim of the study was to explore public reasoning, deliberation processes, and collective reflections related to marine biodiversity and ecosystem services, with a particular focus on plankton. This dataset comprises anonymised verbatim transcripts of group discussions conducted during a series of Deliberative Monetary Valuation workshops held across Europe. The transcripts capture lay participants’ deliberations, arguments, questions, and interactions throughout the workshops, providing qualitative insights into how preferences, values, and viewpoints were formed and discussed in a deliberative setting. In total, 15 workshops were conducted between October 2023 and February 2024 in the following locations: Poland (Poznań and Sopot), Italy (Padova and Chioggia), the Basque Country (Vitoria-Gasteiz and Bilbao), Germany (Bremerhaven and Hannover), and France (Rennes and Brest). All transcripts have been anonymised to remove direct and indirect identifiers prior to publication. For each workshop, the dataset includes (i) transcripts in the original language of the discussion without speaker labels, and (ii) English-language workshop transcripts translated from the original language, in which speakers are identified using randomised speaker IDs to preserve anonymity while allowing analysis of interaction patterns. The prefixes "Mod_" and "Expert_" are used to identify moderators and experts, respectively. Transcription and translation of the workshop discussions were carried out by an external service provider, with the exception of the German workshop transcripts. Prior to participation in the workshops, all participants were required to provide informed consent. The study design and consent procedures were approved by the Ethics Committee of Martin-Luther-Universität Halle-Wittenberg (Ref. Nr.: 2309JGE). Accordingly, no ethical concerns were identified. The transcripts complement the questionnaire-based dataset derived from the same workshop series and are intended to support qualitative, mixed-methods, and methodological research on deliberation, public engagement, and environmental valuation (please refer to "Related works").