The reproductive cycle of Diopatra neapolitana was studied over two years in Redondela (NW Spain), considering both the monthly evolution of the percentage of individuals with oocytes and the variation of the mean oocyte size. Moreover, since three other species of Diopatra have recently been documented in regions geographically close to NW Spain, we first confirmed the identity of this species by carrying out a morphological identification of a representative number of the specimens collected. Our data showed a discontinuous reproductive season, with a period of proliferation and maturation of oocytes from January to September and asynchronous spawning events between July and October. Then, a resting period in the months of November and December was observed. We also explored the influence of some relevant environmental factors (namely, water temperature, photoperiod, salinity, primary production and upwelling index) on the observed reproductive cycle. The results suggest that water temperature is one of the most important drivers of the reproductive cycle for this species. Particularly, in Ría de Vigo, the reproductive cycle seems to be influenced by upwelling events of deep cold water that occur frequently between March and September, and that could act as a spawning-inducing switch.

This study highlights the rise of polychaete fisheries, while also emphasises the challenges of managing them in a data-deficient context, which poses a threat to their sustainability. Taking advantage of the long history of polychaete harvesting in Galicia (NW Spain), a comprehensive review of various kinds of information spanning the past two decades —including regulatory measures, fishing statistics, and management strategies— was conducted. Data from NW Spain underline the need for accurate species identification and improved landing records. Also, they reveal significant gaps in biological and ecological knowledge that hinder the effective implementation of ecological indicators as mandated by recent European legislation. By detecting management shortcomings, this manuscript contributes to the dialogue on sustainable resource utilization, proposing enhancements for future resilience and sustainability of the Galician polychaete fishery. Indeed, this analysis not only deepens the understanding of regional fishing dynamics but also seeks to inform policy-making for the preservation of this critical resource.