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We evaluated the potential of the marine bristleworm Hediste diversicolor (Polychaeta) to recycle side streams from aquaculture and biogas production. Polychaetes were fed along a gradient from pure aquaculture sludge (SS) to pure solid biogas digestate (SBD) in 33% steps, with a positive control reared on fish feed (FF). Worms fed with FF showed the highest specific growth rate; there were no significant differences in growth rates among worms fed pure SS, pure SBD or their mixtures. While the diets differed significantly in protein concentrations, the worms showed comparable protein concentrations at the end of the 30 d rearing period (42-47% of dry weight). Lipid content in the worms was positively correlated with that in their diets. The worms on mixtures of SS and SBD with different ratios showed similar amino acid profiles. Fatty acid (FA) composition in the polychaetes reflected diet, where increased fractions of SBD resulted in an increase in long-chain polyunsaturated FAs, such as arachidonic (C20:4 n-6) and eicosapentaenoic (C20:5 n-3) acids, whereas increased ratios of SS increased docosapentaenoic (C22:5 n-3) and docosahexaenoic (C22:6 n-3) acids. These results suggest that polychaetes can recycle organic nutrients from aquaculture and biogas side streams into high-quality proteins and lipids, and can potentially serve as ingredients for aquafeeds.

Side streams from aquaculture production such as fish sludge poses ample opportunities for biological upcycling, as the sludge contains high amounts of nutrients, energy and valuable biochemicals, making it an ideal food for extractive species. Sludge has been proposed as a feed stock for polychaete production, which in turn can be utilized live in shrimp aquaculture or as an aquafeed ingredient. However, the biosafety of such value chains has not yet been addressed. We conducted an experiment exposing the polychaete Hediste diversicolor to aquaculture sludge spiked with four different fish pathogens (Mycobacterium salmoniphilum, Yersinia ruckeri, Infectious Pancreatic Necrosis (IPN) and Infectious Salmon Anaemia (ISA)) known to cause diseases in Atlantic salmon (Salmo salar L.). Moreover, we assessed whether heavy metals and other potentially hazardous elements present in fish sludge bioaccumulates in the polychaetes. Neither of the bacteria nor viruses could be detected in the polychaetes after 14 days of continuous exposure. Seven of the 15 elements we analysed showed bioaccumulation factors significantly below one, meaning biodilution, while the other eight did not differ from one, meaning no bioaccumulation. None of the elements showed a significant bioaccumulation. Further on, none of the heavy metals found in the polychaetes at the end of our experiment exceeded the EU regulatory maximum levels for fish feed ingredients. The current results suggest that a H. diversicolor can reared on aquaculture sludge, and aquaculture sludge may serve as feed stock for polychaete production without the product exceeding EU regulations for contaminants in animal feed., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:Arne M. Malzahn reports financial support was provided by Norwegian Seafood Research Fund. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Finding alternative protein and lipid sources for aquafeeds is crucial for the sustainable growth of fed aquaculture. Upcycling industrial side streams and byproducts using extractive species can reduce waste and help reduce the sector's dependence on fish meal and fish oils. Polychaete worms ( Hediste diversicolor ) and black soldier fly ( Hermetia illucens ) larvae (BSFL) are promising candidates for converting waste materials into valuable protein and lipid sources. However, further research and evaluations are needed to ensure the safety and regulatory compliance of these alternative feed sources, especially regarding prions spreading potential in the unlikely case that prions would be introduced in the value chain via feedstocks. In the present investigation, BSFL and juvenile polychaetes that had received a massive dose of scrapie prions through immersion and oral inoculation were found to harbour detectable prions using an ultrasensitive amplification method known as PMCA. This observation suggests that both H. diversicolor and BSFL have the potential to serve as mechanical vectors for prions diseases. However, it is important to note that insects, lacking the prion protein gene, are incapable of propagating prions. Therefore, the quantity of prions present in the larvae will inevitably be lower than the amount of prions they encountered. This is the first study to report on the fate of prions through ingestion by these marine and terrestrial invertebrate species., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© 2024 The Authors.)

The Annelida phylum is composed of a myriad of species exhibiting key phenotypic adaptations. They occupy key ecological niches in a variety of marine, freshwater and terrestrial ecosystems. Importantly, the increment of omic resources is rapidly modifying the taxonomic landscape and knowledge of species belonging to this phylum. Here, we comprehensively characterised and annotated a transcriptome of the common ragworm, Hediste diversicolor (OF Müller). This species belongs to the family Nereididae and inhabits estuarine and lagoon areas on the Atlantic coasts of Europe and North America. Ecologically, H. diversicolor plays an important role in benthic food webs. Given its commercial value, H. diversicolor is a promising candidate for aquaculture development and production in farming facilities, under a circular economy framework. We used Illumina next-generation sequencing technology, to produce a total of 105 million (M) paired-end (PE) raw reads and generate the first whole-body transcriptome assembly of H. diversicolor species. This high-quality transcriptome contains 69,335 transcripts with an N50 transcript length of 2313 bp and achieved a BUSCO gene completeness of 97.7% and 96% in Eukaryota and Metazoa lineage-specific profile libraries. Our findings offer a valuable resource for multiple biological applications using this species., Competing Interests: Declaration of competing interest The authors declare no competing interests (financial, professional, or personal relationships) that could influence the work here reported., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Marine annelids are a globally distributed and species-rich group, performing important ecological roles in macrobenthic communities. Yet, the availability of molecular resources to study these organisms is scarcer, comparatively with other phyla. Here, we present the first complete mitogenome of the Atlantic ragworm Hediste diversicolor (OF Muller, 1776). The mitogenome (15,904 bp long) contains 13 protein-coding genes, 22 transfer RNA, and two ribosomal RNA genes, all encoded in the same strand. Gene arrangement and composition are identical to those observed in two available congeneric species, Hediste diadroma and Hediste japonica . The phylogenetic analysis using both maximum-likelihood and Bayesian inference methods reveal a well-supported monophyly of genus Hediste and the already reported paraphyletic relationships within the subfamilies Nereidinae and Gymnonereidinae. Our results highlight the relevance of increasing the molecular sampling within this diverse group of marine fauna., Competing Interests: No potential conflict of interest was reported by the author(s)., (© 2021 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group.)

Omega-3 ( ω 3 or n -3) long-chain polyunsaturated fatty acids (PUFA), including eicosapentaenoic acid and docosahexaenoic acid (DHA), play physiologically important roles in vertebrates. These compounds have long been believed to have originated almost exclusively from aquatic (mostly marine) single-cell organisms. Yet, a recent study has discovered that many invertebrates possess a type of enzymes called methyl-end desaturases ( ω x ) that enables them to endogenously produce n -3 long-chain PUFA and could make a significant contribution to production of these compounds in the marine environment. Polychaetes are major components of benthic fauna and thus important to maintain a robust food web as a recycler of organic matter and a prey item for higher trophic level species like fish. In the present study, we investigated the ω x enzymes from the common ragworm, Hediste diversicolor , a common inhabitant in sedimentary littoral ecosystems of the North Atlantic. Functional assays of the H. diversicolor ω x demonstrated unique desaturation capacities. An ω 3 desaturase mediated the conversion of n -6 fatty acid substrates into their corresponding n -3 products including DHA. A further enzyme possessed unique regioselectivities combining both ω 6 and ω 3 desaturase activities. These results illustrate that the long-chain PUFA biosynthetic enzymatic machinery of aquatic invertebrates such as polychaetes is highly diverse and clarify that invertebrates can be major contributors to fatty acid trophic upgrading in aquatic food webs. This article is part of the theme issue 'The next horizons for lipids as 'trophic biomarkers': evidence and significance of consumer modification of dietary fatty acids'.

Ocean acidification may affect zooplankton directly by decreasing in pH, as well as indirectly via trophic pathways, where changes in carbon availability or pH effects on primary producers may cascade up the food web thereby altering ecosystem functioning and community composition. Here, we present results from a mesocosm experiment carried out during 113 days in the Gullmar Fjord, Skagerrak coast of Sweden, studying plankton responses to predicted end-of-century pCO2 levels. We did not observe any pCO2 effect on the diversity of the mesozooplankton community, but a positive pCO2 effect on the total mesozooplankton abundance. Furthermore, we observed species-specific sensitivities to pCO2 in the two major groups in this experiment, copepods and hydromedusae. Also stage-specific pCO2 sensitivities were detected in copepods, with copepodites being the most responsive stage. Focusing on the most abundant species, Pseudocalanus acuspes, we observed that copepodites were significantly more abundant in the high-pCO2 treatment during most of the experiment, probably fuelled by phytoplankton community responses to high-pCO2 conditions. Physiological and reproductive output was analysed on P. acuspes females through two additional laboratory experiments, showing no pCO2 effect on females' condition nor on egg hatching. Overall, our results suggest that the Gullmar Fjord mesozooplankton community structure is not expected to change much under realistic end-of-century OA scenarios as used here. However, the positive pCO2 effect detected on mesozooplankton abundance could potentially affect biomass transfer to higher trophic levels in the future.