Introduction
Shell-boring polychaetes of the genus Polydora and related taxa (Polydorini) are among the most important pests of farmed molluscs (Simon and Sato-Okoshi, 2015). These worms bore into shells, inducing the formation of mud blisters filled with sediment and faecal material (Blake and Evans, 1973; Read 2010). In oysters, infestation can induce health problems, higher susceptibility to environmental stressors, mortality, and influence negatively product quality and its market value (Korringa, 1954). Numerous non-native polydorin pests have been transported worldwide through the translocation of infected oyster adults and juveniles (Fossi et al., 2026). Recently, new non-native pests P. caeca and P. websteri have been reported in oyster farms in the Adriatic Sea, Italy (Mikac et al., 2025). Despite their recognized impact, the management of Polydora infestations remains challenging. A wide range of physical and chemical treatments has been proposed in different experimental and geographical contexts, often showing variable effectiveness and limitations related to host safety or operational feasibility. This study aims to identifyand experimentally test the most effective and applicable protocols for the removal of shell-boring polychaetes in Italian oyster farms within the framework of the PolyFREE project.
Materials and Methods
A literature-based assessment of removal treatments for shell-boring polychaetes was conducted through a systematic search of peer-reviewed articles, technical reports and grey literature. Protocols were comparatively evaluated using a multi-criteria scoring system based on: (i) quality of the test, (ii) efficacy against the parasite, (iii) host safety, (iv) operational applicability, and (v) environmental and economic sustainability. Experimental trials will be conducted accross four seasons on naturally infested oysters from two Italian farms, under controlled laboratory conditions, using replicated treatment groups and untreated controls. Treatment efficacy will be assessed by evaluating the abundance of residual live Polydora remaining inside oysters after their treatment and a few-days stabilization period. Worms will be extracted by immersion in a phenol solution. Oyster mortality and treatment-associated stress will also be monitored during the post-treatment stabilization period. Subsequently, the most promising protocol(s) will be tested under field conditions in oyster farming facilities located in the Emilia–Romagna region.
Results and perspectives
The literature review identified a broad range of physical and chemical treatments for the control of shell-boring polychaetes in aquaculture systems worldwide. A total of 37 publications were examined and comparatively evaluated. The evaluation highlighted substantial variability among treatments, particularly regarding treatment efficacy, oyster tolerance, and practical applicability under farming conditions. Based on the overall assessment, three non-chemical physical treatments were selected for experimental validation: (1) freshwater immersion followed by air drying, (2) hypersaline immersion followed by air drying, and (3) prolonged desiccation. Results of the experimental phase, currently underway, will be presented at the conference. They will provide the first comparative validation of Polydora treatment protocols under controlled laboratory and field conditions in oyster farming systems of the Emilia–Romagna region. Information on successful treatment protocols will be communicated to oyster producers, and workshops will be organized if needed. The PolyFREE project is expected to contribute to the development of standardized, sustainable and low-impact management strategies against shell-boring polychaete infestations in Mediterranean oyster aquaculture.
Acknowledgment
This work was supported by GALPA Costa Emilia-Romagna through the PolyFREE project, funded under the PN FEAMPA 2021–2027 programme (Priority 3, Specific Objective 2.B), within the call "Azioni pilota rivolte all'introduzione di altre specie e sviluppo di sistemi di acquacoltura sostenibile", aimed at promoting technological innovation and sustainable aquaculture practices.
References
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