Mnemiopsis leidyi
Encyclopedia
The warty comb jelly or sea walnut (Mnemiopsis leidyi) is a species
of tentaculate
ctenophore
(comb jelly), originally native to the western Atlantic coastal waters. Three species have been named in the genus
Mnemiopsis, but they are now believed to be different ecological forms of a single species M. leidyi by most zoologists.
s. Unlike cnidarians, Mnemiopsis doesn't sting. Their body contains 97% water. They are small animals, having a maximum body length of roughly 7–12 cm (2.8–4.7 ) and a diameter of 2.5 centimetre (0.984251968503937 in).
It is euryoecious, tolerating a wide range of salinity
(2 to 38 psu), temperature (2–32 °C or 35.6–89.6 F), and water quality.
Mnemiopsis is a carnivore
that consumes zooplankton
including crustacean
s, other comb jellies, and eggs and larvae of fish
; it is sometimes known to eat smaller individuals of its own kind. It also has several other predators. Many are vertebrate
s, including species of bird
s and fish
. Some predators include other members of gelatinous zooplankton
such as Beroe ctenophores and various Scyphozoa
(jellyfish).
This comb jelly has the capacity for self fertilization, as they are hermaphroditic. They have gonad
s that contain the ovary
and spermatophore
bunches in their gastrodermis
. This animal carries 150 eggs along each meridional canal. Eggs and sperm
are released into the water column where external fertilization takes place. The spawning commences at late evening or at 1:00 or 2:00 a.m. The spawning eggs develop a thick outer layer within 1 minute after touching the seawater. As many as 10,000 eggs can be produced from large specimens in areas with good prey abundance. Egg production can start when the animals reach about 15 mm in length. Egg production increases with ctenophore size, and it is unclear when senescence
occurs.
Mnemiopsis leidyi was introduced in the Black Sea
in the 1980s, where only one species of comb jelly, the small sea gooseberry Pleurobrachia pileus occurred until then. The most likely cause of its introduction is accidentally by merchant ships' ballast water. The first Black Sea record was in 1982.
By 1989, the Black Sea population had reached the highest level, with some 400 specimens per m³ of water (>10 animals/cubic foot) in optimal conditions. Afterwards, due to depletion of foodstocks resulting in lower carrying capacity
, the population dropped somewhat.
In the Black Sea, M. leidyi eats eggs and larvae of pelagic fish
. It caused a dramatic drop in fish populations, notably the commercially important anchovy
Engraulis encrasicholus (known locally as hamsi, hamsiya, hamsa, etc), by competing for the same food sources and eating the young and eggs. Biological control was tried with Beroe ovata, another comb jelly, with some degree of success; it appears as if a fairly stable predator-prey dynamic has been reached.
1999 – Caspian Sea
In 1999 the species was introduced in the Caspian Sea
. The result was that 75% of the zooplankton
was depleted, thereby affecting the entire food chain
of the lake.
2006 – North and Baltic Seas
Since then, the species has apparently spread throughout the Mediterranean basin
and the northwestern Atlantic. In 2006, it was first recorded in the North Sea
, and since October 17, 2006 in the western Baltic Sea
, namely the Kiel Fjord
and The Belts
. Up to 100 animals/m³ (/cubic ft) were counted in the Baltic, whereas the population density in the North Sea was at a much lower 4 animals/m³ (about 1 animal/9 cubic ft) at most.
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One year later, the Baltic population of M. leidyi was found to have spread east to the Gotland Basin
and the Bay of Puck
. The impact of the species on the already heavily stressed Baltic ecosystem
is unknown. The species overwinters in the deep waters where temperature does not drop below 4 °C (39.2 °F); the fact that the Baltic is heavily stratified, with the waters above and below the halocline
mixing little, is believed to aid its survival.
Apart from the widespread P. pileus, 3 comb jelly species are occasionally drifted into the Baltic from the North Sea but do not seem to be present as a stable population of significant size: Bolinopsis infundibulum, Beroe cucumis and Beroe gracilis. The second species might potentially be used for biological control.
The route of dispersal of M. leidyi to the North Sea/Baltic region is unknown. It might have occurred naturally by drifting individuals, or with ballast water of ships, either from its natural range or from the Black Sea, via the Mediterranean and eastern Atlantic. At least technically possible given the species' euryhaline
habits is an alternate route of dispersal through continental Europe
, being carried with ballast water in ships travelling from the Black Sea to the Rhine Estuary via the Rhine-Main-Danube Canal
. The latter route is known to be the point of entry into continental Europe for numerous invasive freshwater
neozoons from the Ponto-Caspian region, such as the zebra mussel
, the quagga mussel
, the amphipods Dikerogammarus villosus
and Chelicorophium curvispinum
, and the polychaete
Hypania invalida.
Its mitochondrion shows several interesting features. It is 10 kilobases in length making it the smallest animal mitochondrial DNA sequence known to date. It has lost at least 25 genes, including atp6 and all the tRNA genes. The atp6 gene has been relocated to the nuclear genome and has acquired introns and a mitochondrial targeting presequence. All tRNA genes have been genuinely lost along with nuclear-encoded mitochondrial aminoacyl tRNA synthetase
s. The mitochondrial rRNA molecules possess little similarity with their homologs in other organisms and have highly reduced secondary structures.
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
of tentaculate
Tentaculata
Tentaculata is a class of comb jellies. The common feature of this class is a pair of long, feathery, contractile tentacles, which can be retracted into specialised ciliated sheaths. In some species, the primary tentacles are reduced and they have smaller, secondary tentacles...
ctenophore
Ctenophore
The Ctenophora are a phylum of animals that live in marine waters worldwide. Their most distinctive feature is the "combs", groups of cilia that they use for swimming, and they are the largest animals that swim by means of cilia – adults of various species range from a few millimeters to in size...
(comb jelly), originally native to the western Atlantic coastal waters. Three species have been named in the genus
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
Mnemiopsis, but they are now believed to be different ecological forms of a single species M. leidyi by most zoologists.
Description and ecology
Mnemiopsis have a lobed body that is oval-shaped and transparent, with four rows of ciliated combs that run along the body vertically and glow blue-green when disturbed. They have several feeding tentacleTentacle
A tentacle or bothrium is one of usually two or more elongated flexible organs present in animals, especially invertebrates. The term may also refer to the hairs of the leaves of some insectivorous plants. Usually, tentacles are used for feeding, feeling and grasping. Anatomically, they work like...
s. Unlike cnidarians, Mnemiopsis doesn't sting. Their body contains 97% water. They are small animals, having a maximum body length of roughly 7–12 cm (2.8–4.7 ) and a diameter of 2.5 centimetre (0.984251968503937 in).
It is euryoecious, tolerating a wide range of salinity
Salinity
Salinity is the saltiness or dissolved salt content of a body of water. It is a general term used to describe the levels of different salts such as sodium chloride, magnesium and calcium sulfates, and bicarbonates...
(2 to 38 psu), temperature (2–32 °C or 35.6–89.6 F), and water quality.
Mnemiopsis is a carnivore
Carnivore
A carnivore meaning 'meat eater' is an organism that derives its energy and nutrient requirements from a diet consisting mainly or exclusively of animal tissue, whether through predation or scavenging...
that consumes zooplankton
Zooplankton
Zooplankton are heterotrophic plankton. Plankton are organisms drifting in oceans, seas, and bodies of fresh water. The word "zooplankton" is derived from the Greek zoon , meaning "animal", and , meaning "wanderer" or "drifter"...
including crustacean
Crustacean
Crustaceans form a very large group of arthropods, usually treated as a subphylum, which includes such familiar animals as crabs, lobsters, crayfish, shrimp, krill and barnacles. The 50,000 described species range in size from Stygotantulus stocki at , to the Japanese spider crab with a leg span...
s, other comb jellies, and eggs and larvae of fish
Fish
Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...
; it is sometimes known to eat smaller individuals of its own kind. It also has several other predators. Many are vertebrate
Vertebrate
Vertebrates are animals that are members of the subphylum Vertebrata . Vertebrates are the largest group of chordates, with currently about 58,000 species described. Vertebrates include the jawless fishes, bony fishes, sharks and rays, amphibians, reptiles, mammals, and birds...
s, including species of bird
Bird
Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...
s and fish
Fish
Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...
. Some predators include other members of gelatinous zooplankton
Gelatinous zooplankton
Gelatinous zooplankton is the term used to describe the fragile animals that live in the water column in the ocean. They have very delicate bodies that are easily damaged or destroyed. Gelatinous zooplankton are often transparent. All jellyfish are gelatinous zooplankton, but not all gelatinous...
such as Beroe ctenophores and various Scyphozoa
Scyphozoa
Scyphozoa is a class within the phylum Cnidaria, sometimes referred to as the "true jellyfish".The class name Scyphozoa comes from the Greek word skyphos , denoting a kind of drinking cup and alluding to the cup shape of the organism....
(jellyfish).
This comb jelly has the capacity for self fertilization, as they are hermaphroditic. They have gonad
Gonad
The gonad is the organ that makes gametes. The gonads in males are the testes and the gonads in females are the ovaries. The product, gametes, are haploid germ cells. For example, spermatozoon and egg cells are gametes...
s that contain the ovary
Ovary (plants)
In the flowering plants, an ovary is a part of the female reproductive organ of the flower or gynoecium. Specifically, it is the part of the pistil which holds the ovule and is located above or below or at the point of connection with the base of the petals and sepals...
and spermatophore
Spermatophore
A spermatophore or sperm ampulla is a capsule or mass created by males of various animal species, containing spermatozoa and transferred in entirety to the female's ovipore during copulation...
bunches in their gastrodermis
Gastrodermis
The gastrodermis is the inner layer of cells that lines a gastrovascular cavity of Cnidarians....
. This animal carries 150 eggs along each meridional canal. Eggs and sperm
Sperm
The term sperm is derived from the Greek word sperma and refers to the male reproductive cells. In the types of sexual reproduction known as anisogamy and oogamy, there is a marked difference in the size of the gametes with the smaller one being termed the "male" or sperm cell...
are released into the water column where external fertilization takes place. The spawning commences at late evening or at 1:00 or 2:00 a.m. The spawning eggs develop a thick outer layer within 1 minute after touching the seawater. As many as 10,000 eggs can be produced from large specimens in areas with good prey abundance. Egg production can start when the animals reach about 15 mm in length. Egg production increases with ctenophore size, and it is unclear when senescence
Senescence
Senescence or biological aging is the change in the biology of an organism as it ages after its maturity. Such changes range from those affecting its cells and their function to those affecting the whole organism...
occurs.
As an invasive species
1980s – Black SeaMnemiopsis leidyi was introduced in the Black Sea
Black Sea
The Black Sea is bounded by Europe, Anatolia and the Caucasus and is ultimately connected to the Atlantic Ocean via the Mediterranean and the Aegean seas and various straits. The Bosphorus strait connects it to the Sea of Marmara, and the strait of the Dardanelles connects that sea to the Aegean...
in the 1980s, where only one species of comb jelly, the small sea gooseberry Pleurobrachia pileus occurred until then. The most likely cause of its introduction is accidentally by merchant ships' ballast water. The first Black Sea record was in 1982.
By 1989, the Black Sea population had reached the highest level, with some 400 specimens per m³ of water (>10 animals/cubic foot) in optimal conditions. Afterwards, due to depletion of foodstocks resulting in lower carrying capacity
Carrying capacity
The carrying capacity of a biological species in an environment is the maximum population size of the species that the environment can sustain indefinitely, given the food, habitat, water and other necessities available in the environment...
, the population dropped somewhat.
In the Black Sea, M. leidyi eats eggs and larvae of pelagic fish
Pelagic fish
Pelagic fish live near the surface or in the water column of coastal, ocean and lake waters, but not on the bottom of the sea or the lake. They can be contrasted with demersal fish, which do live on or near the bottom, and reef fish which are associated with coral reefs.The marine pelagic...
. It caused a dramatic drop in fish populations, notably the commercially important anchovy
Anchovy
Anchovies are a family of small, common salt-water forage fish. There are 144 species in 17 genera, found in the Atlantic, Indian, and Pacific Oceans. Anchovies are usually classified as an oily fish.-Description:...
Engraulis encrasicholus (known locally as hamsi, hamsiya, hamsa, etc), by competing for the same food sources and eating the young and eggs. Biological control was tried with Beroe ovata, another comb jelly, with some degree of success; it appears as if a fairly stable predator-prey dynamic has been reached.
1999 – Caspian Sea
In 1999 the species was introduced in the Caspian Sea
Caspian Sea
The Caspian Sea is the largest enclosed body of water on Earth by area, variously classed as the world's largest lake or a full-fledged sea. The sea has a surface area of and a volume of...
. The result was that 75% of the zooplankton
Zooplankton
Zooplankton are heterotrophic plankton. Plankton are organisms drifting in oceans, seas, and bodies of fresh water. The word "zooplankton" is derived from the Greek zoon , meaning "animal", and , meaning "wanderer" or "drifter"...
was depleted, thereby affecting the entire food chain
Food chain
A food web depicts feeding connections in an ecological community. Ecologists can broadly lump all life forms into one of two categories called trophic levels: 1) the autotrophs, and 2) the heterotrophs...
of the lake.
2006 – North and Baltic Seas
Since then, the species has apparently spread throughout the Mediterranean basin
Mediterranean Basin
In biogeography, the Mediterranean Basin refers to the lands around the Mediterranean Sea that have a Mediterranean climate, with mild, rainy winters and hot, dry summers, which supports characteristic Mediterranean forests, woodlands, and scrub vegetation...
and the northwestern Atlantic. In 2006, it was first recorded in the North Sea
North Sea
In the southwest, beyond the Straits of Dover, the North Sea becomes the English Channel connecting to the Atlantic Ocean. In the east, it connects to the Baltic Sea via the Skagerrak and Kattegat, narrow straits that separate Denmark from Norway and Sweden respectively...
, and since October 17, 2006 in the western Baltic Sea
Baltic Sea
The Baltic Sea is a brackish mediterranean sea located in Northern Europe, from 53°N to 66°N latitude and from 20°E to 26°E longitude. It is bounded by the Scandinavian Peninsula, the mainland of Europe, and the Danish islands. It drains into the Kattegat by way of the Øresund, the Great Belt and...
, namely the Kiel Fjord
Kiel Fjord
Kiel Fjord is an approximately long fjord or firth of the Baltic Sea along the shores of Schleswig-Holstein, Germany. Formed by glacial movement during the last Ice Age, it lies between the Danish Wold and Wagria. It originates at the Hörn in centre-city Kiel and merges into the Bay of Kiel.The...
and The Belts
The Belts
The Belts are two straits in the Danish archipelago, Little Belt and Great Belt.See also the march across the Belts.See also danish straits....
. Up to 100 animals/m³ (/cubic ft) were counted in the Baltic, whereas the population density in the North Sea was at a much lower 4 animals/m³ (about 1 animal/9 cubic ft) at most.
Gotland Basin
The Gotland Basin is the large central basin in the Baltic Sea between Sweden and the Baltic countries. It is subdivided into the Gdansk Deep , the Western Gotland Basin and the Eastern Gotland Basin. Within the Eastern Gotland Basin is the Gotland Deep which is an anoxic basin...
and the Bay of Puck
Bay of Puck
The Bay of Puck or Puck Bay , historically also known as the Bay of Putzig , is a shallow western branch of the Bay of Gdańsk in the southern Baltic Sea, off the shores of Gdańsk Pomerania, Poland. It is separated from the open sea by the Hel Peninsula.The bay has an average depth of 2-6 metres...
. The impact of the species on the already heavily stressed Baltic ecosystem
Ecosystem
An ecosystem is a biological environment consisting of all the organisms living in a particular area, as well as all the nonliving , physical components of the environment with which the organisms interact, such as air, soil, water and sunlight....
is unknown. The species overwinters in the deep waters where temperature does not drop below 4 °C (39.2 °F); the fact that the Baltic is heavily stratified, with the waters above and below the halocline
Halocline
In oceanography, a halocline is a subtype of chemocline caused by a strong, vertical salinity gradient within a body of water. Because salinity affects the density of seawater, it can play a role in its vertical stratification...
mixing little, is believed to aid its survival.
Apart from the widespread P. pileus, 3 comb jelly species are occasionally drifted into the Baltic from the North Sea but do not seem to be present as a stable population of significant size: Bolinopsis infundibulum, Beroe cucumis and Beroe gracilis. The second species might potentially be used for biological control.
The route of dispersal of M. leidyi to the North Sea/Baltic region is unknown. It might have occurred naturally by drifting individuals, or with ballast water of ships, either from its natural range or from the Black Sea, via the Mediterranean and eastern Atlantic. At least technically possible given the species' euryhaline
Euryhaline
Euryhaline organisms are able to adapt to a wide range of salinities. An example of a euryhaline fish is the molly which can live in fresh, brackish, or salt water. The European shore crab is an example of a euryhaline invertebrate that can live in salt and brackish water...
habits is an alternate route of dispersal through continental Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
, being carried with ballast water in ships travelling from the Black Sea to the Rhine Estuary via the Rhine-Main-Danube Canal
Rhine-Main-Danube Canal
The Rhine–Main–Danube Canal , located in Bavaria, Germany, connects the Main and the Danube rivers across the European Watershed, running from Bamberg via Nuremberg to Kelheim...
. The latter route is known to be the point of entry into continental Europe for numerous invasive freshwater
Freshwater
Fresh water is naturally occurring water on the Earth's surface in ice sheets, ice caps, glaciers, bogs, ponds, lakes, rivers and streams, and underground as groundwater in aquifers and underground streams. Fresh water is generally characterized by having low concentrations of dissolved salts and...
neozoons from the Ponto-Caspian region, such as the zebra mussel
Zebra mussel
The zebra mussel, Dreissena polymorpha, is a small freshwater mussel. This species was originally native to the lakes of southeast Russia being first described in 1769 by a German zoologist Peter Simon Pallas in the Ural, Volga and Dnieper rivers. They are still found nearby, as Pontic and Caspian...
, the quagga mussel
Quagga mussel
The quagga mussel is a subspecies of freshwater mussel, an aquatic bivalve mollusk.It is one of seven Dreissena species and has an average life span of 3 to 5 years....
, the amphipods Dikerogammarus villosus
Dikerogammarus villosus
Dikerogammarus villosus, also known as the killer shrimp, is a species of amphipod crustacean native to the Ponto-Caspian region of eastern Europe, but which has become invasive across the western part of the continent. In the areas it has invaded, it lives in a wide range of habitats and will kill...
and Chelicorophium curvispinum
Chelicorophium curvispinum
Chelicorophium curvispinum is a species of amphipod crustacean. It lives in salt, brackish and fresh water, and may reach in length. It occurs in the Caspian Sea, the Black Sea and adjoining rivers, and in river systems emptying into the southern Baltic and North Sea....
, and the polychaete
Polychaete
The Polychaeta or polychaetes are a class of annelid worms, generally marine. Each body segment has a pair of fleshy protrusions called parapodia that bear many bristles, called chaetae, which are made of chitin. Indeed, polychaetes are sometimes referred to as bristle worms. More than 10,000...
Hypania invalida.
Genomics
The ~155 megabase genome of Mnemiopsis leidyi has been sequenced.Its mitochondrion shows several interesting features. It is 10 kilobases in length making it the smallest animal mitochondrial DNA sequence known to date. It has lost at least 25 genes, including atp6 and all the tRNA genes. The atp6 gene has been relocated to the nuclear genome and has acquired introns and a mitochondrial targeting presequence. All tRNA genes have been genuinely lost along with nuclear-encoded mitochondrial aminoacyl tRNA synthetase
Aminoacyl tRNA synthetase
An aminoacyl tRNA synthetase is an enzyme that catalyzes the esterification of a specific amino acid or its precursor to one of all its compatible cognate tRNAs to form an aminoacyl-tRNA. This is sometimes called "charging" the tRNA with the amino acid...
s. The mitochondrial rRNA molecules possess little similarity with their homologs in other organisms and have highly reduced secondary structures.
External links
- Research group Limnology at Ghent University, Belgium
- Ctenophores from the São Sebastião Channel