"Warty comb jelly Sea walnut"

Type Description

Mnemiopsis have an oval-shaped and transparent lobed body, with four rows of ciliated combs that run along the body vertically and glow blue-green when disturbed. They have several feeding tentacles. Unlike cnidarians, Mnemiopsis does not sting. Their body comprises 97% water. They have a maximum body length of roughly 7–12 centimetres (3–5 in) and a diameter of 2.5 centimetres (1 in). 

Habitat

The native habitat of the ctenophore, Mnemiopsis, is in temperate to subtropical estuaries along the Atlantic coast of North and South America (Mayer,1912). M. leidyi is tolerant of a wide range of salinity, temperature and water quality conditions over a broad range of inshore habitats. Since its unintentional introduction to the Black Sea, Mnemiopsis has spread to adjacent bodies of water, inhabiting waters of salinities ranging from 3% in the Sea of Azov to 39‰ in the eastern Mediterranean, and temperatures ranging from 4oC in winter to 31oC in summer (Dumont and Shiganova).

Reproductive Information

Mnemiopsis leidyi is a free-spawning, simultaneous hermaphrodite capable of self-fertilization (Costello, 2001). It possesses gonads containing both the ovary and the spermatophore bunches in their gastrodermis. Total numbers of simultaneously forming eggs depends of food availability and on temperature - 2-3000 eggs per day production by adults at high food concentrations is common. The embryo is formed completely within the original egg cover. It has size of about 0.12-0.14mm and acquires its specific form and tentacular structures. When the larva attains mobility the egg cover softens and became flexible. The life span of egg producing individuals may be many months (Costello, 2001).

Lifecycle

"Totally planktonic life history; early tentaculate larvae resembling Cydippida ctenophores but metamorphoses into the mature lobate form. No current evidence of resting stages (Costello, 2001).
The embryo acquires a double rows of cilia, a well-developed pair of lateral tentacles, and a large, apical sense-organ. The entodermal part of the gastro-vascular system consists of 6 lateral diverticula from a central chamber; 2 of these lateral branches lead into the bases of the tentacles and the other 4 lead outward toward the 4 double rows of cilia. The ectodermal buccal pouch or stomodeum has become a long, laterally compressed tube, with its broad axis 90* from the tentacular axis of the animal. Until this time the animal swims about quite freely within the egg-envelope at this stage its cilia may be observed beating in a normal manner and its tentacles to elongate or contract in response to stimuli. Soon after this the larva breaks through the egg-envelope and escapes into the water. Here it passes the development stages which are very similar to those of the young Pleurobrachia.

The tentacles acquire numerous lateral filaments and elongate greatly, as in Pleurobrachia. When the animal is 5mm long, the oral lobes begin to develop as two simple outgrowths on both sides of the mouth in the sagittal plane of the animal. At the time when the oral lobes begin to develop, the meridional ventral canals and the paragastric tubes begin to elongate downward. The former give rise to the characteristic loops in the oral lobes. Four meridional vessels extend downward and fuse with the circum-oral vessel. The primary tentacle-bulbs migrate downward to lie close by the sides of the mouth. The auricles appear last of all, after the lobes have developed to some extent. When attaining 10mm long the animal becomes ellipsoidal in outline. The appearance of its lobes and auricles resembles to that in the adult of Bolinopsis. Afterward the deep, lateral furrows extend upward to the level of the apical sense-organ and the animal acquires the characteristic of Mnemiopsis ( Mayer, 1912 ). The embrional development takes about 20-24 hours in the Black Sea upper water layer by 23 degrees C. The size of hutched larvae is 0.3-0.4mm."

Nutrition Information

A wide range of zooplanktonic prey; varies with ctenophore development. Early cydippid stages utilize protozoa and microzooplankton, lobate forms feed primarily on crustaceans (often copepods, cladocera) mollusc larvae, eggs, and young fish larvae (Costello, 2001).

General Impact Information

"Mnemiopsis ledyi is a major zooplankton predator and is associated with fishery crashes (Costello, 2001). A carnivorous predator on edible zooplankton (including meroplankton), pelagic fish eggs and larvae, M. leidyi causes negative impacts right through the foodchain of the areas it has invaded. In the Black Sea and the Sea of Azov, the zooplankton, ichthyoplankton and zooplanktivorous fish stocks all underwent profound changes.
The pelagic ecosystem of the Black Sea was degraded, manifesting as sharply decreased biodiversity, abundance, and biomass of the main components of the pelagic ecosystem-zooplankton (Dumont and Shiganova). Fish stocks in the Black Sea and Sea of Azov have suffered due to predation on eggs and larval stages of food supplies (Shiganova 2003). Effects on the ecosystem in the Caspian Sea were faster and stronger than in the Black Sea. In 2001, repercussions were felt at all trophic levels, including that of the top predator, the Caspian seal (Dumont and Shiganova).

A cascading effect occurred at the higher trophic levels, from a decrease in zooplankton stock and collapsing planktivorous fish, to vanishing predatory fish and dolphins. Similar effects occured at lower trophic levels: from a decrease in zooplankton stock to an increase in phytoplankton, which was released from zooplankton grazing pressure. The majority of these effects were top-down, but a few were also bottom-up. Similar effects, but less pronounced, were recorded in the Sea of Marmara. Effects on Mediterranean food webs have, so far, remained insignificant. Salinity is probably supraoptimal there, and several predators prevent M.leidyi from reaching outbreak levels.
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General Management Information

"Biological: Eradication may be impossible in practice. A variety of predators (including medusae and fish) consume M. leidyi in its native regions. Reduction of M. leidyi populations in the Black Sea occurred after one of its predators, the ctenophore Beroe ovata, was introduced to the region (Costello, 2001).
One of the factors that provoked high level of population development of M. leidyi in the Black Sea but was not observed within its natural range-estuarial waters of North America was the absence of a predator feeding on M. leidyi and controlling its population size (Purcell et al., 2001). In 1997, another invader, the ctenophore Beroe ovata Mayer 1912, was found in the northeastern Black Sea. It is a predator feeding on planktivorous comb jellies - especially M. leidyi (Konsulov and Kamburskaya, 1998). As with its predecessor, B. ovata arrived with ballast waters from the same coastal waters of North America (Seravin et al., 2002). Development of B. ovata considerably decreased the population of M. leidyi that had deformed the Black Sea ecosystem for over a decade. The reduction of the M. leidyi population limited its influence on the ecosystem and consequently we observed a recovery of the main components of the Black Sea pelagic ecosystem – zooplankton (including meroplankton), phytoplankton, dolphins and fish as well as their eggs and larvae (Shiganova et al.,2000a,b; 2001 c).

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General Pathway Information

In the early 1980s, Mnemiopsis leidyi was accidentally introduced via the ballast water of ships to the Black Sea where it had a catastrophic effect on the entire ecosystem. It was also introduced into the Caspian Sea via the ballast water of oil tankers.

Notes

References