The marine annelid trait manifesto: A call to rethink functional traits for ecological and conservation research

Samuel Delgado Mendes, Paulo Cesar de Paiva, MANOELA COTTA, Rodolfo Leandro Nascimento 

The Raunkiæran shortfall, defined as the scarcity of knowledge regarding species' attributes, represents one of the major obstacles to developing sound biodiversity conservation strategies and understanding ecological processes. In this context, despite the importance of marine annelids as dominant components of benthic ecosystems and key agents of marine ecosystem functioning, no comprehensive synthesis has centered on the knowledge gaps related to their functional traits. To address this limitation, we conducted a systematic review to quantify the extent of Raunkiæran shortfalls related to marine annelids. Specifically, we investigated which traits have been measured, how they have been applied, whether trait selection is mechanistically aligned with ecological questions, the computational reproducibility of published studies, and the socio-cognitive structure underpinning the research field focusing on filling these knowledge gaps. As a result, feeding mode, body size, motility, and bioturbation emerged as the most frequently assessed traits, within a research agenda that has increasingly shifted from labor-intensive realized trait measurements toward the use of potential traits derived from databases and literature compilations to answer ecological questions. Bibliometric analyses revealed that this field is geographically structured, being dominated by North Atlantic research networks. Persistent challenges were identified, related to flaws in trait nomenclature standardization, lack of documentation of intraspecific trait variation, scarcity of demonstrations of mechanistic trait–fitness relationships, trait coding resolution disparities, and the lack of integration of a truly eco-evolutionary perspective on trait-based approaches. Collectively, our findings reveal that the field has matured into a sophisticated research domain but remains constrained by pervasive issues that hamper a proper understanding of benthic community assembly, ecosystem functioning, and conservation. In this sense, we point out future directions for research to overcome each of these challenges.