The native habitat of the ctenophore M. leidyi is the Atlantic coast of North and South America where it can live over a broad range of salinity and temperature conditions. M. leidyi is a polymorphic speci...
The native habitat of the ctenophore M. leidyi is the Atlantic coast of North and South America where it can live over a broad range of salinity and temperature conditions. M. leidyi is a polymorphic species with wide environmental tolerance and high phenotypic variability. It may reach high numbers in conditions of abundant prey (zooplankton concentrations) in optimal salinity and temperature conditions in native areas. It is a self-fertilizing hermaphrodite, pre-adapted to rapid colonization (Kremer, 1976). Pianka reported that up to 100% normal development has been repeatedly obtained from self-fertilized eggs of single ctenophores, and the significance of out-breeding in ctenophores is controversial. In addition, M. leidyi has an ability to regenerate from fragments larger than one quarter of an individual. It is also a generalist carnivorous feeder. It was accidentally introduced first into the Black Sea in the early 1980s, possibly with ballast water from the northwestern Atlantic coastal region. From the Black Sea, it spread north to the Sea of Azov, south to the Sea of Marmara and to the eastern Mediterranean. In 1999, it reached the Caspian where it is currently expanding at an even more rapid rate than in the Black Sea. In 2005, it was found in the Adriatic Sea. In 2006, it was first recorded in the North Sea and the Baltic Sea.
The problem was resolved by Seravin (1994), who revised the Mnemiopsis genus with the conclusion that it included only one polymorphic species of lobate ctenophore - Mnemiopsis leidyi Agassiz 1865. Both M. mccradyiand M. gardeni are synonyms of this species (Seravin, 1994).
Genetic analyses of the Black Sea and the North and South American individuals were made by K. Bayha (Bayha et al., 2002), who confirmed the identification made by L.A. Seravin (1994). Thus, the taxonomical status of the Black Sea Mnemiopsis, is in accordance with the taxonomical guide of Costello et al. (2001).
M. leidyi is characterized by the presence of two large mobile lobes referred to as lateral or oral lobes). The oral lobes are derivatives of the ctenophore body (spherosome). Four smaller lobes are situated under the two principal oral lobes. Closing over one another by their distal edges, they completely envelop the mouth area of the animal (Agassiz, 1860; Mayer, 1912; Seravin, 1994).
Under the oral lobes, four smaller lobes are located called auricles. When oral lobes are closed, they completely cover the auricles. At the oral edge of the body, on either flattened side, there is a tentacular apparatus. The central part of the tentacular apparatus is located above the lip of the slit-like mouth. Right and left of the tentacular bulb, fascicles of thin tentacles extend over the sides of the body following special deep grooves. Both sides of the long slit-like mouth are bordered with a row of short simple tentacles, which are continuous with those of the deep lateral furrows.
M. leidyi was first discovered in the northwestern Black Sea in November 1982 (Pereladov, 1988) where it most probably was introduced with ballast waters from the northern American coastal area. By the autumn of 1988 it was found everywhere in the Black Sea (Vinogradov et al., 1989). M. leidyi spread to the Sea of Azov via the Kerch Strait in August 1988 (Studenikina et al., 1991); a first peak followed in September 1989. It can live in the Sea of Azov only during warm seasons, dying when temperature reaches 3°C and re-appears every spring or summer depending on direction of the current (Shiganova et al., 2001). Then probably in 1989-1990 it spread to the Sea of Marmara with the Black Sea currents (Shiganova, 1993). It now occurs year-round in the upper water layer of the Sea of Marmara. M. leidyi was first recorded in Saronikos Gulf during late spring-summer 1990, as well as in the neighbouring, eutrophic Elefsis Bay (Aegean Sea). Swarms were observed during summer in several coastal areas of the Aegean Sea (Skyros, Limnos and Alonissos Islands, Halkidiki Peninsula) in 1991-1996. Furthermore M. leidyi populations were rare along the Limnos coasts in summer 1997, 1998, and 1999 (Shiganova et al., 2001). Further east, M. leidyi appeared in Mersin Bay in spring 1992 (Kideys and Niermann, 1994), and in Syrian coastal waters in October 1993 (Shiganova, 1997).
In 2005, M. leidyi was found in the Gulf of Trieste (Adriatic Sea) (Shiganova and Maley, 2008). But later it was not recorded there.
M.leidyi was first found in the Caspian Sea in autumn 1999, where it was introduced probably with ballast waters of oil tankers (Ivanov et al., 2000). In 2000 it spread across all areas of the Caspian with a salinity of minimum 4.3‰ (Shiganova et al., 2001; 2003). In the Caspian Sea in 2001it reached twice the maximum numbers recorded in the Black Sea in 1989 (Shiganova et al., 2004b).
The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.
M. leidyi is able to occupy and establish itself in any temperate or subtropical productive or eutrophicated coastal area, semi-closed seas or estuaries where salinity is not less than 4‰ and temperature not higher than 28°C.
M. leidyi is a hermaphrodite with two fascicles of gonads (ovaries and testicles) in its gastrodermis. The gonads of the Black Sea Mnemiopsis are located along eight meridional canals of the gastrovascular system. They are localized in the spaces between the ctens (comb flappers). The rows of ovaries face the principal symmetry planes - saggital and tentacular. On the opposite side of each meridional canal, rows of testicles extend. Thus, in adjacent canals, the rows of testicles are arranged in a mirror-like manner, which is characteristic of Lobata. Gonads are formed in the central parts of the canals from the level of the statocyst almost up to the extreme ctens toward the oral edge of the body.
All the planktonic Ctenophora are simultaneous hermaphrodites capable of self-fertilization; therefore, a single adult individual may give birth to a viable posterity (Hirota, 1972; Pianka, 1974; Reeve and Walter, 1978, Shiganova, 2000). Planktonic ctenophores may sire before they reach the size of an adult individual. Pianka (1974) described cases of pedogenesis (sexual maturity and ability of reproducing of larvae and juvenile individuals) and dissogeny (reproduction with the existence of two periods of sexual maturity of the same animal at the larva and adult stages) in the reproduction of M. leidyi.
The genetic analysis of ctenophores from different parts of the recipient habitat performed jointly with the Hellenic Centre for Marine Research using sequences of DNA ribosomes showed for the first time that cross-impregnation of M. leidyi is widely spread reaching up to 50% (Kasapidis et al., in press).
The fecundity of M.leidyi depends on the size of the ctenophores. Previously, this has been shown for the individuals from the North American waters as well (Baker and Reeve, 1974; Kremer, 1975). Larger individuals produce more eggs; in experiments, the largest animals spawned 9990 (Baker and Reeve, 1974) and 14,000 (Kremer, 1975) eggs. Baker and Reeve, (1974) observed six individuals for 23 days after their hatching. These individuals began to produce eggs in 13 days after hatching when they reached a mean length of 26 mm; their maximal fertility exceeded 12,000 eggs.
The fecundity of the Black Sea ctenophores, as confirmed by recorded data, also changes depending on the body size. According to experimental data, in the Black Sea, Mnemiopsis begins to reproduce at a total length of 29–35 mm. Its maximal fertility (6200 eggs/individual.) was registered for an individual 92 mm long. The mean fertility calculated for freshly hauled ctenophores comprised 2534±1818 eggs/individual at a temperature of 25°C. The time for beginning production depends on the water temperature. The first egg spawning in the Black Sea was noted at 21°C, though intensive reproduction begins at a temperature of 23°C and the reproduction intensity increases with the temperature growth up to 25-26°C. Already at 27°C, one observes a decrease in the reproduction rate and at 28°C no Mnemiopsis reproduction was observed in the sea (Shiganova, 2000).
Eggs of M. leidyi represent spheres are 0.3–0.4 mm in diameter with a thin non-structured membrane. The outer eggs acquire a thick outer capsule during 1 min of their contact with seawater. At a temperature of 22–23°C, approximately a day later, a cydippide larva emerges from the egg.
The larva is completely formed under the egg capsule when its length reaches approximately 0.3 mm; in so doing, it acquires the characteristic shapes of the body and cilia. When the embryo obtains mobility, the capsule loses its elasticity and its shape becomes variable. Before hatching, the embryo already has double rows of minor tentacles.
In the subsurface waters of the Black Sea, at a temperature of 21-23°C, the embryonic development is completed over 20-24 h, while at a temperature of 25-26°C it takes 17-20 h. The size of the larva hatched is 0.3-0.4 mm
The larva is spherical in shape with eight rows of meridional canals with comb flappers; it is provided with double tentacles (tentilla) typical of a cydippid individual. The larva of M. leidyi can fully retract both tentacles into tentacular sheaths located on the sides of the body between the oral and aboral poles.
When the size of the larva reaches about 5 mm, oral lobes start to develop on either side of the mouth aperture At this time, the lower parts of the vertical meridional and paragistal canals lengthen. The primary tentacular bulbs also subside at this time and are located close to the mouth aperture on both sides. At this stage, the Mnemiopsis larvae resemble representatives of the Bolinopsis genus. The auricles are the last to appear after the lobes are already formed.
Physiology and Phenology
Size of ctenophore and morphological features are different in different conditions. The largest size M. leidyi reached in temperate conditions with salinity 18-20‰ in the Black Sea was 160-180 mm, with mean range of adult individuals 30-120 mm). In the Sea of Azov and the Caspian Sea M. leidyi is smaller: mean length of adult individuals is 20-30 mm, with maximal 65 mm. In lower salinity conditions M. leidyi is a smaller size.
M. leidyi is a polymorphic species with wide environmental tolerance. Therefore it could establish in different environmental conditions of the southern seas and recently in the Baltic Sea. Conditions determine its morpho-physiological features in a possible range of phenotypic alternative development.
Physiological features in different environments determine the seasonal cycle, which includes fecundity, reproduction time and duration, population growth and size, pattern of distribution and finally population predation rate on zoo- and ichthyoplankton. Minimal population size and absence in the inshore waters in spring occurs after cold winters (Shiganova, 2007).
The feeding mechanism of adult lobate ctenophores may be subdivided into two groups. In the first group, the prey may be captured only by pre-oral lobes; in the second, both lobes together with secondary hunting tentilla are in action. Most of lobate ctenophores including M. leidyi feature the second type of feeding. If the prey is active and relatively large as, for example, a copepod, it is captured mainly by the lobes either through mantling the prey by mucus or through simple closing the lobes. Relatively inactive preys such as nauplii or eggs get into the mouth passing by the lobes. Using these two feeding mechanisms, M. leidyi has wider possibilities of capturing preys of different sizes and kinds than if only one feeding mechanism was used. The food particles ingested are rapidly transported to the aboral edge of the gastrovascular atrium and digested there. Therefore, when examining the contents of the gastrovascular atriums of the ctenophores sampled from the sea, food accumulation is registered deep in the gastrovascular atrium. During the digestion, the protective cover of the prey is destroyed and the liquefied contents transferred to the infundibulum of the ctenophore and distributed through the canals of the gastrovascular system. The minor liquefied remains are removed via the anal pores at the aboral edge of the body; meanwhile, chitinous shells of crustaceans and mollusk valves are removed through the mouth. The observations of the feeding behavior of ctenophores under laboratory conditions showed that, in the course of digestion, the ingestion and removal of undigested remains proceed independently and continuously (Reeve and Walter, 1978).
Almost exclusively, the ctenophores of the Lobata order are zooplankton-feeding predators; occasionally phytoplankton and detritus were encountered in their gastrovascular cavities (Reeve and Walter, 1978).
According to most of the scientists who studied the feeding of Mnemiopsis, it is capable of feeding (or, at least, of ingesting and killing) any organisms available to be captured by its oral lobes - holoplanktonic organisms, planktonic larvae of benthic animals (meroplankton), and fish eggs and larvae (Nelson, 1925; Main, 1928; Tsikhon-Lukanina et al., 1993). Similar to the majority of lobate ctenophores, M. leidyi is capable of excessive feeding; even if its gastrovascular atrium is full, it continues hunting and vomits large amounts of undigested food in mucous clots (Harbison et al., 1978).
Introduction of M. leidyi into the Black Sea had catastrophic effects on ecosystem and fish stocks. In 1997, an accidental invasion occurred in the Black Sea when the ctenophore Beroe ovata was released with ballast waters. B. ovata is a predator feeding on planktivorous comb jellies and M. leidyi above all. As with its predecessor, B. ovata arrived with ballast waters from the same coastal waters of North America (Seravin et al., 2002).
B. ovata is the best candidate to control M. leidyi population size as shown in the Black Sea by a natural experiment. B. ovata is only able to eat planktivorous ctenophores. It controls its own population size by stopping reproduction in the absence of available prey; large adult individuals are eliminated and others stay near the bottom without movements until prey is available.
Optimal conditions for M. leidyi are temporal or subtropical climates. Climatic conditions control epidemics of M. leidyi even in optimal environments and spread to adjacent seas from the Black Sea to the Sea of Azov or eastern Mediterranean or from the Southern Caspian to the Middle and Northern Caspian (Shiganova et al., 2007).
Only few animals are known to feed on M. leidyi, foremost of which are the scyphomedusan Chysaora quinquecirrha and the ctenophore Beroe ovata (Purcell et al., 2001).
Chrysaora quinquecirrha scyphomedusae is a main predator of M. leidyi in North American waters. It has strict seasonal development. It first appeared in May or June in the tributaries of the mesohaline region of Chesapeake Bay when temperatures exceed 17°C, and about a month later in the mainstem of the bay. Polyps and medusae of C. quinquecirrha are found in Chesapeake Bay at salinities above 5 and below 25. Abundances of Mnemiopsis and C. quinquecirrha medusae have been shown to vary inversely in tributaries of Chesapeake Bay. Ctenophores in the tributaries are numerous in spring before the medusae are large or abundant, then decrease or disappear when medusae become numerous, and rebound when the medusae die in the autumn. Predation rates on ctenophores by medusae were sufficient to eliminate ctenophores from the tributaries, where medusae were abundant, but not in the main bay, where medusae were less abundant. Densities and biomasses of medusae and ctenophores also vary inversely in the mainstem Chesapeake Bay.
Firstly, medusa C. quinquecirrha does not always overcome population of M. leidyi and it consumes mainly small size of M. leidyi and secondly, more importantly, C. quinquecirrha is a dangerous animal for people.
The vermform larval sea anemone, Edwardsia leidyi, frequently infects M. leidyi . It is unknown to what extent this endobiont is parasitic. Infected ctenophores often are as vigorous as uninfected ones. Anemones cannot live in the low salinity and although tissue damage results, M. leidyi can regenerate tissue.
Therefore the only invertebrate predator that was proposed was a Bero species endemic to the eastern seaboard of the Americas. This species is found in estuaries in both North and South America and is often closely associated with populations of M. leidyi and create feedback predator-prey.
The species of Beroe ovata has two outstanding advantages: firstly, it is highly specific in its feeding, so that even its larval stage feeds on M. leidyi. Secondly, its reproductive rate and fecundity are almost as great as that of M. leidyi, so that its population can grow at similar rates to its prey (Gezamp, 1997).
Interannual variation in abundance of Mnemiopsis is strongly related to predator abundance in US waters. Kremer (1976) reported the population abundance in Narragansett Bay decreased dramatically in September, 1974 with increasing numbers of the ctenophore predator, B. ovata.
The harvest fish, Peprilus alepidotus (Herman et al., 1968; Harbison, 1993; Gesamp, 1997) and butterfish, Peprilus triacanthus (Oviatt and Kremer, 1977), are predators on M. leidyi, the latter appearing to be nutritionally adequate for juvenile butterfish, insofar as the carbon requirement is concerned.
In Narragansett Bay, for example, the butterfish occurs, and may be primary predator on Mnemiopsis. Grazing experiments led Oviatt and Kremer (1977) to conclude that this predator accounts for the local late summer - early autumn decline of M. leidyi. However, the field evidence is less convincing.
Theharvestfish, P. alepidotus, and butterfish P. triacanthus, because of the low salinities in much of Chesapeake Bay (5-7‰), are found mostly in the southern bay (11-15‰) (Purcell et al., 2001). Oviatt and Kremer (1977) estimated that butterfish could eat 4 to 184 mL ctenophore /hour per g fish DW-1, and that this predation probably accounts for the autumn decline of the Mnemiopsis population in Narragansett Bay. No estimates of fish predation on Mnemiopsis exist elsewhere.
Both species can eat M. leidyi but they are subtropical- temperate coastal species endemic of North America. They are not found in low salinity in the Chesapeake Bay, although in experimental conditions P. triacanthus lived two weeks in salinity 4%. Among the disadvantages of the introduction are that its reproductive biology is poorly known, its eggs and larvae may be vulnerable to predation by M. leidyi (Gezamp, 1997) and their introduction would be very expensive transcontinental measurement.
Thus, the food web involving M. leidyi seems to be relatively simple based on available information. Only a few predators identified to date are very significant. Moreover, the distributional and/or seasonal ranges of occurrence for M. leidyi and its predators frequently do not overlap.
Only these species specialize on the Mnemiopsis feeding. But a variety of fishes are known to consume gelatinous species, not only ctenophores (Harbison, 1993; Purcell et al., 2001). Some more tolerant for temperate regions with low salinity basin species were proposed for introduction into the Black Sea by the Gezamp group of experts (Gezamp, 1997).
The Baltic cod, Gadus morhua callarias, is a commercially valuable temperate species, but this species inhabits cooler waters than Caspian Sea waters. It lives in the Baltic Sea near the bottom where the temperature is not higher than 14°C. Although this species is omnivorous, the main food of cod is small pelagic fish and benthic animals. It is not yet known, if it can eat M. leidyi, however it eats other ctenophores, particularly Beroe cucumis (Kamshilov, 1960). Disadvantages are that it will also eat commercially valuable small pelagic fish and it lives in cooler waters than Caspian Sea.
Oncorhynchus keta, the chum salmon, is an anadromous salmonid of high commercial value. It appears, in contrast to other representatives of the genus, to have gelatinous zooplankton as a major component of its diet. It spawns in the rivers and its early ontogenetic stages develops in fresh water, and is therefore not vulnerable to predation by M. leidyi. It is easily cultured, and its populations can be controlled in the rivers. However, it is not know if it eats M. leidyi. Among potential disadvantages are the facts that it is omnivorous on small pelagic fish, it may not be able to establish itself in the rivers that flow into the Caspian Sea, because of pollution and dams, and it may compete with native sturgeons.
Although a group of experts from the international commission of the Joint Group of Experts on the Scientific Aspects of Marine Pollution (GESAMP) (IMO/FAO/UNESCO-IOC/WMO/WHO/IAEA/UN/UNEP) (GESAMP, 1997) proposed the introduction of potential predators for M. leidyi into the Black Sea, their suggestions were not intentionally implemented. However, a predator of M. leidyi, Beroeovata accidentally appeared in the Black Sea in 1997 for the first time. It is a great natural experiment which provides an excellent example and shows the way to combat population of Mnemiopsis in the Caspian Sea.
M. leidyi is a real ecosystem engineer. It affects physical conditions of several recipient productive ecosystems; for example in - the decrease in water transparency, hydrochemical - change nutrients contents and biota. After M. leidyi invasion cascading effects occurred at the higher trophic levels, from a decreasing zooplankton stock to collapsing planktivorous fish to dolphins (bottom-up). Similar effects occurred at lower trophic levels: from a decrease in zooplankton stock to an increase in phytoplankton, relaxed from zooplankton grazing pressure (top-down) and from increasing bacterioplankton to increasing zooflagellata and infusoria (Shiganova at al., 2004 a,b).
M. leidyi may be mixed with other representatives of another Lobata species of genus Bolinopsis. B. infundibuilum, occursin the northern Atlantic, North, Baltic and Barrens Sea (Greve, 1970; Seravin, 1998) and the subtropical species B. vitrea, which occurs in the Mediterranean Sea and southern coastal America (Shiganova et al., 2004c; Oliveiro and Migotto, 2006). Oral lobes of both species originate about half-way between the mouth and the infundibulum while in M. leidyi oral lobes originate near the level of the infundibulum.
Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.
There should be strict control of ballast waters in harbours to avoid introduction of alien species.