International shipping as a potent vector for spreading marine parasites

Phylogeography of Pennella (Copepoda: Siphonostomatoida: Pennellidae) indicates interoceanic dispersal mediated by cetacean and fish hosts

Copepods of the genus Pennella parasitize a wide range of marine animals, including cetaceans, teleosts, and cephalopods worldwide. Their taxonomy is unclear, as there is incongruence between morphological and genetic data and incomplete species coverage. This study provides new morphological and genetic (COI) data from 23 specimens of Pennella cf. filosa (syn. P. balaenoptera) from western Mediterranean whales and a swordfish. First, their position in the phylogeny of Pennella was assessed and species delimitation revisited using all available Pennella COI sequences (n = 189), obtained from Mediterranean and north Pacific specimens from 18 host species (including multiple cetaceans and teleosts). Second, it was investigated whether the geographic location, degree of host vagility, or host taxonomic identity help explain genetic differentiation. Five distinct haplotype groups with varying genetic divergence were distinguished. Although the presence of sibling species cannot be ruled out, species delimitation methods could not find interspecific genetic differences, leaving the taxonomy of the genus unresolved. The observed genetic differentiation could not be attributed to geography or host type. This suggests that members of the genus Pennella show low specificity for definitive hosts and interoceanic dispersal mediated by some vagile definitive hosts. The use of more genetic markers for addressing these questions in the future is encouraged.

Marine transmissible cancer navigates urbanized waters, threatening spillover

Inter-individual transmission of cancer cells represents a unique form of microparasites increasingly reported in marine bivalves. In this study, we sought to understand the ecology of the propagation of Mytilus trossulus Bivalve Transmissible Neoplasia 2 (MtrBTN2), a transmissible cancer affecting four Mytilus mussel species worldwide. We investigated the prevalence of MtrBTN2 in the mosaic hybrid zone of M. edulis and M. galloprovincialis along the French Atlantic coast, sampling contrasting natural and anthropogenic habitats. We observed a similar prevalence in both species, probably due to the spatial proximity of the two species in this region. Our results showed that ports had higher prevalence of MtrBTN2, with a possible hotspot observed at a shuttle landing dock. No cancer was found in natural beds except for two sites close to the hotspot, suggesting spillover. Ports may provide favourable conditions for the transmission of MtrBTN2, such as high mussel density, stressful conditions, sheltered and confined shores or buffered temperatures. Ships may also spread the disease through biofouling. Our results suggest ports may serve as epidemiological hubs, with maritime routes providing artificial gateways for MtrBTN2 propagation. This highlights the importance of preventing biofouling on docks and ship hulls to limit the spread of marine pathogens hosted by fouling species.

Anthropogenic Vector Ecology and Management to Combat Disease Spread in Aquaculture

Anthropogenic vectors (transfer mechanisms) can facilitate the introduction and spread of aquatic disease in marine farming regions. Preventing or interrupting pathogen transfers associated with movements of these vectors is key to ensuring productivity and profitability of aquaculture operations. However, practical methods to identify and manage vector risks are lacking. We developed a risk analysis framework to identify disease risks and management gaps associated with anthropogenic vector movements in New Zealand's main aquaculture sectors - Chinook salmon (Oncorhynchus tshawytscha), green-lipped mussels (Perna canaliculus), and Pacific oysters (Crassostrea gigas). Vectors within each sector were identified and assigned categorical risk scores for (i) movement characteristics (size, frequency, likelihood of return to sea), (ii) biological association with pathogens (entrainment potential, contribution to previous aquaculture disease outbreaks) and (iii) available best practice biosecurity methods and tools, to inform unmitigated and mitigated risk rankings. Thirty-one vectors were identified to operate within the national network and association with livestock was found to be a primary driver of vector risk rankings. Movements of live growing stock and culture substrates (e.g., mussel ropes) in shellfish farming had high-risk vector profiles that are logistically challenging to address, while vessel vectors were identified as the salmon farming sector's priority. The framework and rankings can be used to inform both research and management priorities in aquaculture and other primary production systems, including risk validation, vector roles in disease epidemiology, compliance with permit conditions, policy development, and treatment options.

Thermal optima of cercarial emergence in trematodes from a marine high-temperature ecosystem, the Persian Gulf

Global warming may alter the dynamics of infectious diseases by affecting important steps in the transmission of pathogens and parasites. In trematode parasites, the emergence of cercarial stages from their hosts is temperature-dependent, being highest around a thermal optimum. If environmental temperatures exceed this optimum as a consequence of global warming, this may affect cercarial transmission. However, our knowledge of cercarial emergence patterns of species from high temperature environments is currently very limited. Here, we investigated the effect of temperature on the emergence of two common trematode species from an abundant mud snail Pirenella cingulata in the Persian Gulf, the warmest sea on Earth. Infected snails were incubated in the laboratory at 6 temperatures from 10 to 40 °C for 3 days. We found an optimal temperature for cercarial emergence of 32.0 °C and 33.5 °C for Acanthotrema tridactyla and Cyathocotylidae gen. sp., respectively, which are the warmest recorded thermal optima for any aquatic trematode species. Emergence of both species dropped at 40 °C, suggesting upper thermal limits to emergence. Overall, Persian Gulf trematodes may be among the most heat-tolerant marine trematode species, indicating a potential for dispersing to regions that will continue to warm in the future.

Incorporating Microbial Species Interaction in Management of Freshwater Toxic Cyanobacteria: A Systems Science Challenge

Water resources are critically important, but also pose risks of exposure to toxic and pathogenic microbes. Increasingly, a concern is toxic cyanobacteria, which have been linked to the death and disease of humans, domesticated animals, and wildlife in freshwater systems worldwide. Management approaches successful at reducing cyanobacterial abundance and toxin production have tended to be short-term solutions applied on small scales (e.g., algaecide application) or solutions that entail difficult multifaceted investments (e.g., modification of landscape and land use to reduce nutrient inputs). However, implementation of these approaches can be undermined by microbial species interactions that (a) provide toxic cyanobacteria with protection against the method of control or (b) permit toxic cyanobacteria to be replaced by other significant microbial threats. Understanding these interactions is necessary to avoid such scenarios and can provide a framework for novel strategies to enhance freshwater resource management via systems science (e.g., pairing existing physical and chemical approaches against cyanobacteria with ecological strategies such as manipulation of natural enemies, targeting of facilitators, and reduction of benthic occupancy and recruitment). Here, we review pertinent examples of the interactions and highlight potential applications of what is known.