The effect of the egg-predator Carcinonemertes conanobrieni on the reproductive performance of the Caribbean spiny lobster Panulirus argus

BACKGROUND

The Caribbean spiny lobster Panulirus argus is heavily fished throughout its Greater Caribbean and Gulf of Mexico distribution, suggesting a heightened susceptibility to a fisheries collapse. In 2017, a nemertean worm, Carcinonemertes conanobrieni was described from ovigerous females of P. argus in Florida, USA. A year later, the presence of the same egg predator was recorded along the southern Caribbean coast (Colombia). The effect of this egg predator on the reproductive performance, including fecundity, embryo mortality, and reproductive output, of its host is unknown. This study tested whether C. conanobrieni affects embryo mortality, fecundity, and reproductive output in brooding females of P. argus.

RESULTS

Artisan fishers caught 90 ovigerous lobsters near Pueblo Viejo, Magdalena, Colombia. Each ovigerous female was examined for the presence/absence of the egg predator. Lobster egg mortality (%), fecundity (nº eggs female-1), and reproductive output (%) were estimated. Prevalence of C. conanobrieni in the studied population was 87.78%. The mean intensity of C. conanobrieni (all life stages) in the population was 11.68 (± 1.98) egg predators per brood mass sample. Infected females brooding late-stage embryos exhibited lower fecundity, lower reproductive performance values, and higher embryo mortality compared to infected females brooding early-stage embryos. Embryo stage and worm infection level negatively impacted fecundity and reproductive output. Worm infection level and the number of adult nemertean worms also negatively affected embryo mortality.

CONCLUSIONS

These results demonstrate an adverse effect of C. conanobrieni on the reproductive performance of P. argus. The interactive impact of this egg predator, natural stressors, and anthropogenic stressors on individual P. argus reproductive performance could facilitate losses at large-scale fisheries levels.

Invasion history shapes host transcriptomic response to a body-snatching parasite

By shuffling biogeographical distributions, biological invasions can both disrupt long-standing associations between hosts and parasites and establish new ones. This creates natural experiments with which to study the ecology and evolution of host-parasite interactions. In estuaries of the Gulf of Mexico, the white-fingered mud crab (Rhithropanopeus harrisii) is infected by a native parasitic barnacle, Loxothylacus panopaei (Rhizocephala), which manipulates host physiology and behaviour. In the 1960s, L. panopaei was introduced to the Chesapeake Bay and has since expanded along the southeastern Atlantic coast, while host populations in the northeast have so far been spared. We use this system to test the host's transcriptomic response to parasitic infection and investigate how this response varies with the parasite's invasion history, comparing populations representing (i) long-term sympatry between host and parasite, (ii) new associations where the parasite has invaded during the last 60 years and (iii) naïve hosts without prior exposure. A comparison of parasitized and control crabs revealed a core response, with widespread downregulation of transcripts involved in immunity and moulting. The transcriptional response differed between hosts from the parasite's native range and where it is absent, consistent with previous observations of increased susceptibility in populations lacking exposure to the parasite. Crabs from the parasite's introduced range, where prevalence is highest, displayed the most dissimilar response, possibly reflecting immune priming. These results provide molecular evidence for parasitic manipulation of host phenotype and the role of gene regulation in mediating host-parasite interactions.

Invasive Non-Native Crustacean Symbionts: Diversity and Impact

Invasive non-native species (INNS) pose a risk as vectors of parasitic organisms (Invasive Parasites). Introducing invasive parasites can result in ecological disturbances, leading to biodiversity loss and native species illness/mortality, but occasionally can control INNS limiting their impact. Risks to human health and the economy are also associated with INNS and invasive parasites; however, we understand little about the diversity of symbiotic organisms co-invading alongside INNS. This lack of clarity is an important aspect of the 'One Health' prerogative, which aims to bridge the gap between human, wildlife, and ecosystem health. To explore symbiont diversity associated with the invasive crustacean group (including: crab, lobster, crayfish, shrimp, amphipod, isopod, copepod, barnacle, other) (n = 323) derived from 1054 aquatic invertebrates classed as INNS across databases, we compile literature (year range 1800-2017) from the native and invasive range to provide a cumulative symbiont profile for each species. Our search indicated that 31.2% of INN crustaceans were known to hold at least one symbiont, whereby the remaining 68.8% had no documented symbionts. The symbiont list mostly consisted of helminths (27% of the known diversity) and protists (23% of the known diversity), followed by bacteria (12%) and microsporidians (12%). Carcinus maenas, the globally invasive and extremely well-studied green crab, harboured the greatest number of symbionts (n = 72). Additional screening is imperative to become more informed on invasive symbiont threats. We reveal that few studies provide truly empirical data that connect biodiversity loss with invasive parasites and suggest that dedicated studies on available systems will help to provide vital case studies. Despite the lack of empirical data, co-invasive parasites of invasive invertebrates appear capable of lowering local biodiversity, especially by causing behavioural change and mortality in native species. Alternatively, several invasive parasites appear to protect ecosystems by controlling the impact and population size of their invasive host. We provide a protocol that could be followed to explore symbiont diversity in invasive groups as part of our case studies. The consequence of limited parasite screening of INNS, in addition to the impacts invasive parasites impart on local ecologies, are explored throughout the review. We conclude in strong support of the 'One Health' prerogative and further identify a need to better explore disease in invasion systems, many of which are accountable for economic, human health and ecological diversity impacts.

Impacts of crustacean invasions on parasite dynamics in aquatic ecosystems: A plea for parasite-focused studies

While there is considerable interest in, and good evidence for, the role that parasites play in biological invasions, the potential parallel effects of species introduction on parasite dynamics have clearly received less attention. Indeed, much effort has been focused on how parasites can facilitate or limit invasions, and positively or negatively impact native host species and recipient communities. Contrastingly, the potential consequences of biological invasions for the diversity and dynamics of both native and introduced parasites have been and are still mainly overlooked, although successful invasion by non-native host species may have large, contrasting and unpredictable effects on parasites. This review looks at the links between biological invasions and pathogens, and particularly at crustacean invasions in aquatic ecosystems and their potential effects on native and invasive parasites, and discusses what often remains unknown even from well-documented systems. Aquatic crustaceans are hosts to many parasites and are often invasive. Published studies show that crustacean invasion can have highly contrasting effects on parasite dynamics, even when invasive host and parasite species are phylogenetically close to their native counterparts. These effects seem to be dependent on multiple factors such as host suitability, parasite life-cycle or host-specific resistance to parasitic manipulation. Furthermore, introduced hosts can have drastically contrasting effects on parasite standing crop and transmission, two parameters that should be independently assessed before drawing any conclusion on the potential effects of novel hosts on parasites and the key processes influencing disease dynamics following biological invasions. I conclude by calling for greater recognition of biological invasions' effects on parasite dynamics, more parasite-focused studies and suggest some potential ways to assess these effects.

Observations and Experiments on the Biology and Life History of Riseriellus occultus (Heteronemertea: Lineidae)

Studies on the biology and life history of nemerteans are scarce, mostly because these animals are nocturnal. In order to broaden the knowledge base on the life history of nemerteans as a prerequisite for comparative analyses, we studied a population of Riseriellus occultus (Heteronemertea: Lineidae) inhabiting the rocky intertidal in southern Brittany near Concarneau (France) for more than 10 years. Our studies show that R. occultus is an iteroparous, perennial species exclusively inhabiting rocky shore crevices that result from onionskin weathering of the granite. From September through October R. occultus reproduces by external fertilization and develops via a planktonic pilidium larva, which, under laboratory conditions, metamorphoses after about six weeks. Adults of R. occultus are nocturnal macrophagous predators that preferentially feed on the gastropods Gibbula umbilicalis and Patella species, but also consume the bivalve Mytilus edulis. Since R. occultus devours the snail inside the shell, we fixed individuals while feeding, and serially sectioned them. Reconstruction of the sections shows that R. occultus swallows the entire soft body and finally detaches the columellar muscle from the shell. Estimates on the density of R. occultus inside the rock crevices provide evidence for clustered distribution and locally high abundance on the rocky shore. These data strongly suggest that R. occultus affects the structure of the rocky shore gastropod community. Although our data are still fragmentary with respect to the ecology of this species and its role in the local food web, our knowledge has grown to such extent that R. occultus can now be regarded as one of the few well characterized nemertean species.

Overview on the European green crab Carcinus spp. (Portunidae, Decapoda), one of the most famous marine invaders and ecotoxicological models

Green crabs (Carcinus, Portunidae) include two species native to Europe--Carcinus aestuarii (Mediterranean species) and Carcinus maenas (Atlantic species). These small shore crabs (maximal length carapace, approximately 10 cm) show rapid growth, high fecundity, and long planktonic larval stages that facilitate broad dispersion. Carcinus spp. have a high tolerance to fluctuations of environmental factors including oxygen, salinity, temperature, xenobiotic compounds, and others. Shipping of Carcinus spp. over the past centuries has resulted in its invasions of America, Asia, and Australia. Classified as one of the world's 100 worst invaders by the International Union for Conservation of Nature, Carcinus spp. are the most widely distributed intertidal crabs in the world. Their voracious predatory activity makes them strong interactors in local communities, and they are recognized as a model for invasiveness in marine systems as well as a sentinel species in ecotoxicology. This review shows an exhaustive analysis of the literature on the life cycle, diversity, physiological tolerance, genomic investigations, ecotoxicological use, historical invasion, control programs, and putative economical valorization of shore crabs.

Reservoirs and alternate hosts for pathogens of commercially important crustaceans: a review

There is a considerable body of literature describing the causative agents of many diseases of crustaceans. Given that many of these crustaceans support commercially important fisheries, it is somewhat surprising that comparatively little information is available regarding the natural transmission pathways and reservoirs of many of the disease-causing agents. In this paper we review what is known about reservoirs and alternate hosts for several important diseases of commercially important crustaceans and provide recommendations on future areas of research.

Laboratory observations on the feeding behavior and feeding rate of the nemertean Procephalothrix simulus

The feeding behavior of the nemertean Procephalothrix simulus and the effects of extrinsic factors on the feeding rates of this nemertean were experimentally studied. Procephalothrix simulus showed a typical macrophagous feeding strategy and consumed various food items. When capturing freshwater Tubifex sp., the nemerteans successfully ingested prey in all attacks, and they did not evert the proboscis in 25% of capture events. When capturing marine Saccocirrus gabrillae, the nemerteans failed to consume prey in more than half of the attacks, and they always everted the proboscis. There was a positive relationship between nemertean body weight and the rate of successful attacks, and a negative relationship between nemertean body weight and the duration of feeding events. The feeding rate of P. simulus increased when the temperature was raised from 5 degrees C to 30 degrees C but was significantly inhibited at 32 degrees C. Food intake was significantly reduced in media diluted to a practical salinity of 20 and 10 and in medium with the salinity elevated to 45. Dark conditions induced higher food intake, but prey density had no significant effect on feeding rate. These results suggest that P. simulus is a predator successfully adapted to the variable environmental conditions of the intertidal habitat.

Effects of small weirs on fish parasite communities

In this study, we examined the impacts of small weirs on the parasite community of gudgeon and toxostome in a medium-sized river. We tested changes on parasite species diversity using indices that capture both richness and abundance characteristics, and we examined parasite community structure with null models (co-occurrence index C score) and a multiple discriminant function analysis (MDFA). Our results showed that parasite community diversity of gudgeon is strongly influenced by weirs with a maximum diversity upstream of the weirs. Weirs also induce change in abundance of gudgeon parasite species particularly during summer. Nevertheless, we obtained that weirs had no effect on the parasite co-occurrence patterns. In addition, similarity indices indicate that the parasite faunas of newly established limnophilic species (roach and bleak) are host-specific and are rarely transmitted to other fish species. We conclude that fish parasite communities responded in different ways to the presence of impassable weirs, but, in a general tendency, changing environmental conditions induced by weirs may represent an ecological risk.

Prevalence and evolutionary relationships of haematozoan parasites in native versus introduced populations of common myna Acridotheres tristis

The success of introduced species is frequently explained by their escape from natural enemies in the introduced region. We tested the enemy release hypothesis with respect to two well studied blood parasite genera (Plasmodium and Haemoproteus) in native and six introduced populations of the common myna Acridotheres tristis. Not all comparisons of introduced populations to the native population were consistent with expectations of the enemy release hypothesis. Native populations show greater overall parasite prevalence than introduced populations, but the lower prevalence in introduced populations is driven by low prevalence in two populations on oceanic islands (Fiji and Hawaii). When these are excluded, prevalence does not differ significantly. We found a similar number of parasite lineages in native populations compared to all introduced populations. Although there is some evidence that common mynas may have carried parasite lineages from native to introduced locations, and also that introduced populations may have become infected with novel parasite lineages, it may be difficult to differentiate between parasites that are native and introduced, because malarial parasite lineages often do not show regional or host specificity.

Ecology and biogeography of marine parasites

A review is given of (mainly recent) work on the biodiversity, ecology, biogeography and practical importance of marine parasites. Problems in estimating species numbers have been thoroughly discussed for free-living species, and the main points of these discussions are reviewed here. Even rough estimates of the richness of most parasite groups in the oceans are premature for the following reasons: species numbers of host groups, in particular in the deep sea and the meiofauna, are not known; most host groups have been examined only insufficiently for parasites or not at all; even in some of the best known groups, latitudinal, longitudinal and depth gradients in species richness are only poorly understood or not known at all; effects of hosts on parasite morphology and geographical variation have been studied only in a few cases; there are few studies using techniques of molecular biology to distinguish sibling species. Estimates of species richness in the best known groups, trematodes, monogeneans and copepods of marine fishes, are given. Parasites are found in almost all taxa of eukaryotes, but most parasitic species are concentrated in a few taxa. Important aspects of the ecology of marine parasites are discussed. It is emphasized that host specificity and host ranges should be distinguished, and an index that permits calculation of host specificity is discussed. The same index can be applied to measure site specificity. Central problems in ecology are the importance of interspecific competition and whether equilibrium or non-equilibrium conditions prevail. Marine parasites are among the few groups of organisms that have been extensively examined in this regard. A holistic approach, i.e. application of many methods, has unambiguously shown that metazoan ecto- (and probably endo-) parasites of marine fish live in largely non-saturated niche space under non-equilibrium conditions, i.e. they live in assemblages rather than in communities structured by competition. Nestedness occurs in such assemblages, but it can be explained by characteristics of the species themselves. There is little agreement on which other factors are involved in "structuring" parasite assemblages. Few studies on metapopulations of marine parasites have been made. A new approach, that of fuzzy chaos modelling, is discussed. It is likely that marine parasites are commonly found in metapopulations consisting of many subpopulations, and they are ideally suited to test the predictions of fuzzy chaos. Some recent studies on functional ecology and morphology--especially with regard to host, site and mate finding--are discussed, and attention is drawn to the amazing variety of sensory receptors in some marine parasites. Effects of parasites on hosts, and some studies on the evolution and speciation of marine parasites are discussed as well. A detailed overview of biogeographical studies is given, with respect to latitudinal gradients in species diversity, reproductive strategies and host ranges/specificity. Studies of marine parasites have contributed significantly to giving a non-equilibrium explanation for latitudinal diversity gradients. Recent studies on longitudinal and depth gradients are discussed, as well as parasites in brackish water, parasites as indicators of zoogeographical regions and barriers, and parasites as biological tags. The practical importance of marine parasites in mariculture, as monitors of pollution, agents of human disease, the use of parasites for controlling introduced marine pests, and some related aspects, are also discussed.