Host plasticity supports spread of an aquaculture introduced virus to an ecosystem engineer

Role of native and invasive non-native marine invertebrate species as carriers for pathogens Vibrio spp. and ostreid herpesvirus-1 µVar

Invasive non-native species (INNS) are expanding their geographic range due to climate change, maritime traffic (primary route) and aquaculture (secondary route), resulting in the potential spread of microbes associated with them. Few studies have investigated the INNS-pathogen phenomenon. In this study, marine invertebrate species (native and INNS) were sampled monthly over 3 mo and screened by PCR for the ostreid herpesvirus-1 microvariant (OsHV-1 μVar) and Vibrio bacteria. Both pathogens are negatively associated with bivalve aquaculture. Sample sites included a shipping port, an oyster farm, a marsh nature reserve and a riverine site. Crustacea, Mollusca, Polychaeta, Tunicata and Porifera were sampled. Vibrio spp. were detected in 54.3% (n = 319/588) across all taxa and sample sites. The first detection of V. salmonicida associated with Atlantic salmon Salmo salar was detected in the INNS beaked barnacle Austrominius modestus. OsHV-1 μVar (7.7%, 45/588) was detected in Crustacea, Mollusca and Polychaeta at non-culture sites and in mussels Mytilus spp. at a much lower temperature (average sea surface temperature, SST, 11.25°C) than previously recorded. The shipping port had the highest Vibrio diversity and OsHV-1 μVar detection. Over half (51.1%) of 'recently dead' shore crabs Carcinus maenas had either pathogen detected compared to 29.4% of living crabs. OsHV-1 μVar detection was significantly higher in dead crabs (24.4%) compared to living crabs (5.9%). Findings from this study contribute a better understanding of the role of estuarine native and INNS as vectors/carriers of pathogens and of how the spread of INNS might facilitate the spread of pathogens.

Impacts of Climate Change on Marine Foundation Species

Marine foundation species are the biotic basis for many of the world's coastal ecosystems, providing structural habitat, food, and protection for myriad plants and animals as well as many ecosystem services. However, climate change poses a significant threat to foundation species and the ecosystems they support. We review the impacts of climate change on common marine foundation species, including corals, kelps, seagrasses, salt marsh plants, mangroves, and bivalves. It is evident that marine foundation species have already been severely impacted by several climate change drivers, often through interactive effects with other human stressors, such as pollution, overfishing, and coastal development. Despite considerable variation in geographical, environmental, and ecological contexts, direct and indirect effects of gradual warming and subsequent heatwaves have emerged as the most pervasive drivers of observed impact and potent threat across all marine foundation species, but effects from sea level rise, ocean acidification, and increased storminess are expected to increase. Documented impacts include changes in the genetic structures, physiology, abundance, and distribution of the foundation species themselves and changes to their interactions with other species, with flow-on effects to associated communities, biodiversity, and ecosystem functioning. We discuss strategies to support marine foundation species into the Anthropocene, in order to increase their resilience and ensure the persistence of the ecosystem services they provide.

Extrinsic and intrinsic drivers of parasite prevalence and parasite species richness in a marine bivalve

Parasite species richness is influenced by a range of drivers including host related factors (e.g. host size) and environmental factors (e.g. seawater temperature). However, identification of modulators of parasite species richness remains one of the great unanswered questions in ecology. The common cockle Cerastoderma edule is renowned for its diversity and abundance of parasites, yet drivers of parasite species richness in cockles have not been examined to investigate the association of both macro and microparasite communities. Using cockles as a model species, some of the key drivers of parasite prevalence and parasite species richness were investigated. Objectives of this 19-month survey were to determine the influence of the environment, host-parasite dynamics and parasite associations on parasite species richness and prevalence at two different geographic latitudes, chosen based on environmental differences. The highest parasite species richness was recorded in the northern sites, and this was potentially influenced by a range of interactions between the host, the pathogens and the environment. Parasite prevalence increased with host size and age, and parasite species richness increased with reduced salinity. A number of interactions between parasites, and between parasites and pathologies may be influencing parasite infection dynamics. New and concerning information is also presented regarding interactions between parasites and their environment. A number of parasites and potential pathogens (bacteria, Trichodina ciliates, metacercariae, trematode sporocysts) may be advantaged under climate change conditions (warming seas, increased precipitation), increasing disease incidence, which may prove detrimental not just for cockles, but for other bivalve species in the future.

A case study of local ecological knowledge of shellfishers about edible cockle (Cerastoderma edule) in the Ria de Aveiro lagoon, Western Iberia

BACKGROUND

The cockle is available to numerous fishing villages in Europe, especially Portugal. In the Ria de Aveiro, there is a lack of a fisheries management program and the need for new ecological studies on cockle biology, ecology, and conservation. We shared local ecological knowledge (LEK) highlights about the cockle-Cerastoderma edule (Linnaeus 1758) in the Ria de Aveiro in favor of adaptive management of this bioresource.

METHODS

Semi-structured interviews with sixty shellfishers in this coastal lagoon were carried out during April and May 2021. LEK data on the biology and ecology of the cockle were analyzed using an ethical-emic approach and the model of integration of different individual skills. These informal data were compared with previously published data for the species, the Fish Base, and GBIF databases.

RESULTS AND DISCUSSION

The average minimum size of the cockle for capture was 23.4 mm, and the average capture per tide was 137.12 kg. The areas with the highest productivity and the most shellfish were RIAV1 and RIAV2. Cockles inhabit areas of sand and mud at an average depth of 2.71 cm. Feeds are mainly small particles, plankton, mud, and algae. The main predators were crabs, European plaice, and bird species. Cockles spawn primarily in late spring and summer. As of 2010, there was a slight decrease in cockle stocks in the Ria de Aveiro due to overfishing, increased rainfall, and changes in the sediment. Considering and analyzing this knowledge is essential for a better understanding of the environmental context the cockles thrive in the view of users of the natural resource.

CONCLUSION

Informal data shared by shellfishers in the Ria de Aveiro were typical of filter-feeding bivalves. LEK may assist in planning future management plans for cockles, and unrefuted data may serve as untestable hypotheses. Ethnobiological studies in the Ria de Aveiro lagoon with other species may improve the management of this system since multiple fisheries are carried out in this coastal area.

Co-occurrence of pathogen assemblages in a keystone species the common cockle Cerastoderma edule on the Irish coast

Despite coinfections being recognized as the rule in animal populations, most studies focus on single pathogen systems. Pathogen interaction networks and the drivers of such associations are lacking in disease ecology studies. Common cockle Cerastoderma edule populations are exposed to a great diversity of pathogens, thus making them a good model system to investigate. This study examined the diversity and prevalence of pathogens from different taxonomic levels in wild and fished C. edule on the Irish coast. Potential interactions were tested focussing on abiotic (seawater temperature and salinity) and biotic (cockle size and age, and epiflora on shells) factors. No Microsporidia nor OsHV-1μVar were detected. Single infections with Haplosporidia (37.7%) or Vibrio (25.3%) were more common than two-pathogen coinfected individuals (9.5%), which may more easily succumb to infection. Fished C. edule populations with high cockle densities were more exposed to infections. Higher temperature and presence of epiflora on cockle shells promoted coinfection in warmer months. Low seawater salinity, host condition and proximity to other infected host species influenced coinfection distribution. A positive association between two Minchinia spp. was observed, most likely due to their different pathogenic effect. Findings highlight the major influence that ecological factors have on pathogen interactions and host–pathogen interplay.

Connectivity dynamics in Irish mudflats between microorganisms including Vibrio spp., common cockles Cerastoderma edule, and shorebirds

Shellfish, including the key species the common cockle Cerastoderma edule, living and feeding in waters contaminated by infectious agents can accumulate them within their tissues. It is unknown if microbial pathogens and microparasites can subsequently be transmitted via concomitant predation to their consumers, including shorebirds. The objective of this study was to assess if pathogens associated with C. edule could be detected seasonally in the faeces of shorebirds that feed on C. edule and in the physical environment (sediment) in which C. edule reside, along the Irish and Celtic Seas. Two potentially pathogenic global groups, Vibrio and Haplosporidia, were detected in C. edule. Although Haplosporidia were not detected in the bird faeces nor in the sediment, identical strains of Vibrio splendidus were detected in C. edule and bird faecal samples at sites where the oystercatcher Haematopus ostralegus and other waders were observed to be feeding on cockles. Vibrio spp. prevalence was seasonal and increased in C. edule and bird faecal samples during the warmer months, possibly due to higher seawater temperatures that promote the replication of this bacteria. The sediment samples showed an overall higher prevalence of Vibrio spp. than the bird faecal and C. edule samples, and its detection remained consistently high through the sites and throughout the seasons, which further supports the role of the sediment as a Vibrio reservoir. Our findings shed light on the fact that not all pathogen groups are transmitted from prey to predator via feeding but bacteria such as V. splendidus can be. As most of the wading birds observed in this study are migratory, the results also indicate the potential for this bacterium to be dispersed over greater geographic distances, which will have consequences for areas where it may be introduced.

Viral Decoys: The Only Two Herpesviruses Infecting Invertebrates Evolved Different Transcriptional Strategies to Deflect Post-Transcriptional Editing

The highly versatile group of Herpesviruses cause disease in a wide range of hosts. In invertebrates, only two herpesviruses are known: the malacoherpesviruses HaHV-1 and OsHV-1 infecting gastropods and bivalves, respectively. To understand viral transcript architecture and diversity we first reconstructed full-length viral genomes of HaHV-1 infecting Haliotis diversicolor supertexta and OsHV-1 infecting Scapharca broughtonii by DNA-seq. We then used RNA-seq over the time-course of experimental infections to establish viral transcriptional dynamics, followed by PacBio long-read sequencing of full-length transcripts to untangle viral transcript architectures at two selected time points. Despite similarities in genome structure, in the number of genes and in the diverse transcriptomic architectures, we measured a ten-fold higher transcript variability in HaHV-1, with more extended antisense gene transcription. Transcriptional dynamics also appeared different, both in timing and expression trends. Both viruses were heavily affected by post-transcriptional modifications performed by ADAR1 affecting sense-antisense gene pairs forming dsRNAs. However, OsHV-1 concentrated these modifications in a few genomic hotspots, whereas HaHV-1 diluted ADAR1 impact by elongated and polycistronic transcripts distributed over its whole genome. These transcriptional strategies might thus provide alternative potential roles for sense-antisense transcription in viral transcriptomes to evade the host's immune response in different virus-host combinations.

Genomic Diversity of the Ostreid Herpesvirus Type 1 Across Time and Location and Among Host Species

The mechanisms underlying virus emergence are rarely well understood, making the appearance of outbreaks largely unpredictable. This is particularly true for pathogens with low per-site mutation rates, such as DNA viruses, that do not exhibit a large amount of evolutionary change among genetic sequences sampled at different time points. However, whole-genome sequencing can reveal the accumulation of novel genetic variation between samples, promising to render most, if not all, microbial pathogens measurably evolving and suitable for analytical techniques derived from population genetic theory. Here, we aim to assess the measurability of evolution on epidemiological time scales of the Ostreid herpesvirus 1 (OsHV-1), a double stranded DNA virus of which a new variant, OsHV-1 μVar, emerged in France in 2008, spreading across Europe and causing dramatic economic and ecological damage. We performed phylogenetic analyses of heterochronous (n = 21) OsHV-1 genomes sampled worldwide. Results show sufficient temporal signal in the viral sequences to proceed with phylogenetic molecular clock analyses and they indicate that the genetic diversity seen in these OsHV-1 isolates has arisen within the past three decades. OsHV-1 samples from France and New Zealand did not cluster together suggesting a spatial structuration of the viral populations. The genome-wide study of simple and complex polymorphisms shows that specific genomic regions are deleted in several isolates or accumulate a high number of substitutions. These contrasting and non-random patterns of polymorphism suggest that some genomic regions are affected by strong selective pressures. Interestingly, we also found variant genotypes within all infected individuals. Altogether, these results provide baseline evidence that whole genome sequencing could be used to study population dynamic processes of OsHV-1, and more broadly herpesviruses.