Developing the options for managing marine pests: specificity trials on the parasitic castrator, Sacculina carcini, against the European crab, Carcinus maenas, and related species

A multidisciplinary integrated approach using Pachygrapsus marmoratus to assess the impact of port activities on mediterranean marine protected areas

The establishment of marine protected areas is considered the main global strategy to halt the loss of marine biodiversity. Since most of marine areas are open systems, this form of habitat protection cannot prevent their contamination due to human activities performed outside of their borders. Innovative approaches to assess the health status of protected marine habitats are therefore needed. Here we developed a multidisciplinary approach that combines ecological characteristics, bioaccumulation of inorganic and organic pollutants, cell damage (micronuclei frequency, nuclear alterations and LPO) and enzymatic (AChE, CAT, IDH, LDH, GST and CAT) markers focused on an intertidal brachyuran crab, Pachygrapsus marmoratus, to assess the impacts of contaminant exposure on Mediterranean coastal habitats. As study sites we selected two protected areas and two sites within industrial ports of the Ligurian Sea. Our results showed that the selected crab species is an excellent bioindicator. Individuals collected in sites with the highest levels of heavy metal pollution showed the highest signals of stress responses at both cellular and enzymatic levels, coupled with a high incidence of the parasite Sacculina carcini, a signal of impairment of their standard development and reproduction cycle. We could also prove that one of the selected marine protected areas showed the same intensity of impact as its adjacent port site. Our multidisciplinary approach proved to be a valuable tool to assess the environmental quality and health of protected and disturbed Mediterranean coastal environments and to inform efficient management and protection schemes for such habitats.

Sacculina carcini impact on energy content of the shore crab Carcinus maenas L

The impact of Sacculina carcini infection on the nutritional status of the shore crab Carcinus maenas was investigated in the western Dutch Wadden Sea for a period of 20 months. About 3.3% of the population was sacculinized, i.e. externally infected with S. carcini and only 0.7% presented scars of previous infection. The results of mixed linear models showed that sacculinized and non-sacculinized crabs had similar morphometric condition, while the energy density of parasitized crabs (externa excluded) was significantly reduced by about 4.3% overall, and by up to 5.8% in crabs under 40 mm carapace width. However, when Sacculina externa was included in the energy determinations, the difference in energy density decreased to 1.2%, while total energy content of the pair infected crab-parasite including externa was 30.8% higher than non-sacculinized crabs of similar size. The total energy content of ovigerous females (eggs included) was even higher, near doubling the energy of similar-sized crabs. The same way, total energy content of Sacculina externa was about 4 times lower than total energy of egg mass. The results suggest that the rhizocephalan parasite is efficient in consuming the energy that the host may allocate for growth and maintenance, but require future studies to disentangle the impact of the degree of internal infection and the implications for the dynamics of the population.

Crustacean Fauna of the Aral Sea and its Relation to Ichthyofauna During the Modern Regression Crisis and Efforts at Restoration

The regression and salinization of the Aral Sea, largely caused by water diversion for irrigation, is among the most severe ecological disasters of the 20th century, and has had severe health and economic consequences for the local population. Introductions of alien species to enhance commercial fisheries before the regression had already impacted the ecology of this system. Crustaceans made up about one-quarter of the original metazoan species and constituted the principal food for native and introduced fish. From 1960 on, crustaceans were recorded at numerous fixed sampling stations, including thanatocoenoses (dead animals from sediment cores). We use this previously unpublished information to document changes in species abundance and discuss their causes in the context of species interactions and changes to physical and chemical parameters. Competition from alien crustaceans led to declines in or even extinction of some native species, but eventually severe salinization became the main detriment, and resulted in the complete collapse of commercial fisheries. This seriously hurt a critical trade, which provided the principal protein source for the local population. We document how comparatively modest conservation efforts enabled the northern Small Aral Sea to partially recover and commercial fishing to resume.

Rhizocephalan infection in the Patagonian stone crab Danielethus patagonicus

The system formed by a still-unidentified rhizocephalan infecting the Patagonian stone crab Danielethus (Platyxanthus) patagonicus (A. Milne-Edwards, 1879) was analyzed in northern Patagonia. Out of 3222 crabs sampled, mean prevalence of externae was 2.1%, while corrected mean prevalence based on observations of externae, scars or other indicators of infection was slightly higher (3.01%; N = 2100). Prevalence was higher in males (4.47%) than in females (1.44%). Parasitized males were morphologically feminized, while females showed no hyper-feminization. Although most parasitized crabs showed only 1 externa, 2 externae were observed in some individuals. The parasite externae were only present in intermediate-sized crabs (26.6-99.7 cm carapace width). While scanning electron microscopy images allowed detection of the 'smooth-surface-balloon' type of retinacula on the inner surface of the externae, typical of the Sacculinidae and Peltogastridae, the position of the mantle opening relative to the stalk, the receptacle location and the shape of the externae suggest that the parasite belongs to either the genus Sacculina or to the recently erected Parasacculina (Polyascidae).

Effects of climate variability on an estuarine green crab Carcinus maenas population

The increase in frequency and intensity of extreme climate events over the last few decades has been leading to profound changes in estuarine and marine ecosystems worldwide, with strong implications for the species inhabiting these ecosystems as well as for the services provided by them. In this study, we analysed the effects of climate variability on the temporal and spatial variations in population dynamics of the green crab Carcinus maenas in the Mondego estuary (Portugal), between 2003 and 2018. In this 15-year period, a greater recruitment of C. maenas was observed during drought periods, periods which was matched by an increase in secondary production. Ontogenic stage segregation was also observed, with juveniles being found mainly in the further upriver areas of the estuary. The estuarine population was mainly composed of the green morphotype, with the orange and red morphotypes present in more downstream areas of the estuary. Redundancy analysis (RDA) showed high spatial and temporal variability of C. maenas in the estuary which was related with environmental changes over the 15-year period. A correlation between C. maenas biological features and several local-scale (salinity and river runoff) and large-scale (North Atlantic Oscillation index and Eastern Atlantic pattern) environmental variables was identified through cumulative sums analysis (CUSUM), indicating a strong environmental control on C. maenas population dynamics. This paper shows the importance of relatively long-term datasets to unravel the effects of extreme weather events due to climate change on key epibenthic estuarine species, and also how they might cope with a changing marine environment.

A new molecular phylogeny-based taxonomy of parasitic barnacles (Crustacea: Cirripedia: Rhizocephala)

Rhizocephalans are abundant members of marine ecosystems and are important regulators of crustacean host populations. Morphological and ecological variation makes them an attractive system for evolutionary studies of advanced parasitism. Such studies have been impeded by a largely formalistic taxonomy, because rhizocephalan morphology offers no characters for a robust phylogenetic analysis. We use DNA sequence data to estimate a new phylogeny for 43 species and use this to develop a revised taxonomy for all Rhizocephala. Our taxonomy accepts 13 new or redefined monophyletic families. The traditional subdivision into the suborders Kentrogonida and Akentrogonida is abandoned, because both are polyphyletic. The three ‘classical’ kentrogonid families are also polyphyletic, including the species-rich Sacculinidae, which is split into a redefined and a new family. Most species of large families remain to be studied based on molecular evidence and are therefore still assigned to their current genus and family by default. We caution against undue generalizations from studies on model species until a more stable species-level taxonomy is also available, which requires more extensive genus- and species-level sampling with molecular tools. We briefly discuss the most promising future studies that will be facilitated by this new phylogeny-based taxonomy.

Infestation of parasitic rhizocephalan barnacles Sacculina beauforti (Cirripedia, Rhizocephala) in edible mud crab, Scylla olivacea

Screening of mud crab genus Scylla was conducted in four locations (Marudu Bay, Lundu, Taiping, Setiu) representing Malaysia. Scylla olivacea with abnormal primary and secondary sexual characters were prevalent (approximately 42.27% of the local screened S. olivacea population) in Marudu Bay, Sabah. A total of six different types of abnormalities were described. Crabs with type 1 and type 3 were immature males, type 2 and type 4 were mature males, type 5 were immature females and type 6 were mature females. The abdomen of all crabs with abnormalities were dented on both sides along the abdomen’s middle line. Abnormal crabs showed significant variation in their size, weight, abdomen width and/or gonopod or pleopod length compared to normal individuals. The mean body weight of abnormal crabs (type 1–5) were higher than normal crabs with smaller body size, while females with type 6 abnormality were always heavier than the normal counterparts at any given size. Sacculinid’s externa were observed in the abdomen of crabs with type 4 and type 6 abnormalities. The presence of embryos within the externa and subsequent molecular analysis of partial mitochondrial COI region confirmed the rhizocephalan parasite as Sacculina beauforti. Future in-depth descriptions of the life cycle and characteristics of S. beauforti are recommended as it involves a commercially important edible crab species and the effect on human health from the consumption of crabs is of crucial concern.

Modelling the biological invasion of Carcinus maenas (the European green crab)

This paper proposes a system of integro-difference equations to model the spread of Carcinus maenas, commonly called the European green crab, that causes severe damage to coastal ecosystems. A model with juvenile and adult classes is first studied. Here, standard theory of monotone operators for integro-difference equations can be applied and yields explicit formulas for the asymptotic spreading speeds of the juvenile and adult crabs. A second model including an infected class is considered by introducing a castrating parasite Sacculina carcini as a biological control agent. The dynamics are complicated and simulations reveal the occurrence of periodic solutions and stacked fronts. In this case, only conjectures can be made for the asymptotic spreading speeds because of the lack of mathematical theory for non-monotone operators. This paper also emphasizes the need for mathematical studies of non-monotone operators in heterogeneous environments and the existence of stacked front solutions in biological invasion models.

Infestation of parasitic barnacle Sacculina spp. in commercial marine crabs

Commercial crab species infected of rhizocephalan cirripedes are reported from the coast of Parangipettai. Sacculina spp. were collected from brachyuran hosts Portunus sanquinolentus, Portunus hastatoides, Chaybdis feriatus, Charybdis variegate, Charybdis natator, Charybdis miles, Charybdis lucifera, Charybdis hoplites, Charybdis hellerii, Charybdis granulate, Charybdis amboinensis and Thalamita coeruleipes respectively.

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.

Evolution of sex determination and sexually dimorphic larval sizes in parasitic barnacles

The parasitic (rhizocephalan) barnacles include species of which larval sex is determined by the mother (genetic sex determination, GSD), male larvae are larger than female larvae, and a female accepts only two dwarf males who sire all the eggs laid by her. In contrast, other species of parasitic barnacles exhibit monomorphic larvae that choose to become male or female depending on the condition of the host they settle (environmental sex determination, or ESD), and a female accepts numerous dwarf males. Here, we ask why these set of traits are observed together, by examining the evolution of sex determination and the larval size. ESD has an advantage over GSD because each larva has a higher chance of encountering a suitable host. On the other hand, GSD has two advantages over ESD: the larval size can be chosen differently between sexes, and their larvae can avoid spending time for sex determination on the host. We conclude that, in species whose female accepts only two males, the male larvae engage in intense contest competition for reproductive opportunities, and male's success-size relation is very different from female's. Then, larvae with predetermined sex (GSD) with sexually dimorphic larvae is more advantageous than ESD. In contrast, in species whose females accept many dwarf males, the competition among males is less intense, and producing larvae with undetermined sex should evolve. We also discuss the condition for females to evolve receptacles to limit the number of males she accepts.

Ecological and developmental dynamics of a host-parasite system involving a sea anemone and two ctenophores

The lined sea anemone Edwardsiella lineata has evolved a derived parasitic life history that includes a novel body plan adapted for life inside its ctenophore hosts. Reputedly its sole host is the sea walnut, Mnemiopsis leidyi, a voracious planktivore and a seasonally abundant member of many pelagic ecosystems. However, we have observed substantially higher E. lineata prevalence in a second ctenophore species, the ctenophore predator Beroë ovata. The interplay among these 3 species has important conservation consequences as M. leidyi introductions are thought to be responsible for the severe depletion of numerous commercial fisheries in the Mediterranean basin, and both E. lineata and B. ovata have been proposed as biological controls for invasive M. leidyi. Over a 3-yr period (2004-2006), we collected 8,253 ctenophores from Woods Hole, Massachusetts, including M. leidyi, B. ovata, and a third ctenophore, Pleurobrachia pileus, and we recorded E. lineata infection frequencies, parasite load, and parasite location. We also conducted laboratory experiments to determine the likely mechanisms for parasite introduction and the effect of each host on parasite development. We observed peak E. lineata infection frequencies of 0% in P. pileus, 59% in M. leidyi, and 100% in B. ovata, suggesting that B. ovata could be an important natural host for E. lineata. However, in laboratory experiments, E. lineata larvae proved far more successful at infecting M. leidyi than B. ovata, and E. lineata parasites excised from M. leidyi exhibited greater developmental competence than parasites excised from B. ovata. Although we show that E. lineata is efficiently transferred from M. leidyi to B. ovata when the latter preys upon the former, we conclude that E. lineata larvae are not well adapted for parasitizing the latter species and that the E. lineata parasite is not well adapted for feeding in B. ovata; these developmental and ecological factors underlie the host specificity of this recently evolved parasite.

Aquaculture and transport in a changing environment: overlap and links in the spread of alien biota

Aquaculture has been practiced for some millennia. The speed and access of different transport modes in the spread of cultured species, their pests, parasites, diseases and associates, has changed over this time. There now exists an overlap and interlinking of different transport networks with further routes planned. Coupled with environmental changes and habitat alterations alien biota are presented with further opportunities to become more widely distributed. The certainty of the responsible pathway for the arrival of an alien species is not always easily deduced unless imported directly. A scheme for classifying different levels of certainty is proposed. Aquaculture itself consists of different cultivation intensities ranging from part to all of a species life-history and are classified accordingly in this account. It is inevitable that further species intended for cultivation will be utilized in different world regions and that other biota, some considered to be harmful, will also be transmitted. Nevertheless there are codes of practice such as those used by the IMO and ICES that can reduce some risks.

An experimental evaluation of host specificity: the role of encounter and compatibility filters for a rhizocephalan parasite of crabs

The encounter/compatibility paradigm of host specificity provides three qualitative pathways to the success or failure of a potential host-parasite interaction. It is usually impossible to distinguish between two of these (encounter and compatibility filters closed versus encounter filter open and compatibility filter closed) because unsuccessful infection attempts are difficult to observe in nature. We were able to open the encounter filter under experimental laboratory conditions. Our analytical system used the rhizocephalan barnacle, Sacculina carcini, a parasitic castrator of the European green crab, Carcinus maenas, and Pachygrapsus marmoratus, a native European crab that occurs with C. maenas but is not parasitized by S. carcini in nature. Penetration followed by unsuccessful infection of P. marmoratus crabs by parasitic barnacle larvae leaves a uniquely permanent record in the thoracic ganglion of the crabs. This provided us with a novel tool to quantify the encounter filter in a host-parasite system in nature. We demonstrated, in the laboratory, that the compatibility filter was closed and that, in nature, even where barnacle larvae were present, the encounter filter was also effectively closed. The closure of both filters in nature explains the failure of this potential host-parasite interaction, an outcome favored by selection in both host and parasite.

Coevolutionary arms races: increased host immune defense promotes specialization by avian fleas

We investigated the relationship between host defense and specialization by parasites in comparative analyses of bird fleas and T-cell mediated immune response of their avian hosts, showing that fleas with few main host species exploited hosts with weak or strong immune defenses, whereas flea species that parasitized a large number of host species only exploited hosts with weak immune responses. Hosts with strong immune responses were exploited by a larger number of flea species than hosts with weak responses. A path analysis model with an effect of T-cell response on the number of host species, or a model with host coloniality directly affecting host T-cell response, which in turn affected the number of host species used by fleas, best explained the data. Therefore, parasite specialization may have evolved in response to strong host defenses.

Causal mechanisms underlying host specificity in bat ectoparasites

In parasites, host specificity may result either from restricted dispersal capacity or from fixed coevolutionary host-parasite adaptations. Knowledge of those proximal mechanisms leading to particular host specificity is fundamental to understand host-parasite interactions and potential coevolution of parasites and hosts. The relative importance of these two mechanisms was quantified through infection and cross-infection experiments using mites and bats as a model. Monospecific pools of parasitic mites (Spinturnix myoti and S. andegavinus) were subjected either to individual bats belonging to their traditional, native bat host species, or to another substitute host species within the same bat genus (Myotis). The two parasite species reacted differently to these treatments. S. myoti exhibited a clear preference for, and had a higher fitness on, its native host, Myotis myotis. In contrast, S. andegavinus showed no host choice, although its fitness was higher on its native host M. daubentoni. The causal mechanisms mediating host specificity can apparently differ within closely related host-parasite systems.

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.