The Warty Comb Jelly Mnemiopsis leidyi.

The Warty comb jelly (Mnemiopsis leidyi) or sea walnut as it is sometimes known, is a species of ctenophore (commonly known as comb jellies) that originated in the western Atlantic waters (Encyclopaedia of life, 2014). For a time there was believed to be up to 3 species in this genus of comb jelly but that has since been revised down to a single species with differing ecological forms (Hansson, 2006).

The Mnemiopsis leidyi under stress glowing a blue-green colour.

Source: http://news.bbc.co.uk/2/hi/science/nature/6719965.stm, accessed on the 13th of May 2014.

The Warty comb jelly has a lobed oval-shaped, transparent body (Encyclopedia of life, 2014). They have 4 rows of ciliated combs, that will glow a blue-green colour when disturbed, they have many feeding tentacles - but unlike jellyfish do not have stinging nematacytes. There body is 97% water, with a body length of around 8-12 cm and a diameter of 2cm (Hansson, 2006).

Diagrams of the size and subumbrellar cavity of M. leidyi. 

Source: http://people.bu.edu/jrf3/BI547/BI547_IMAGES.html, accessed on the 13th of May 2014.

M. leidyi is a carnivorous organism that mainly eats zooplankton, other comb jellies, eggs and larvae. Its main predators are larger fish and birds (Kube, et al. 2007). M. leidyi have the ability to self-fertilise (they are hermaphroditic), the comb jelly can carry up to 150 at any one time and release both eggs and sperm into the water column during spawning. As many as 10,000 eggs can be fertilised in one spawning event (Hansson, 2006).

Sampling the M. leidyi found within the Black Sea.

Source: http://www.cefas.defra.gov.uk/our-science/ecosystems-and-biodiversity/non-native-species/invasive-comb-jellyfish-(m-leidyi).aspx, accessed on the 13th of May 2014.

In the 1980's M. leidyi was released into the Black Sea through the ballst water of passing cargo ships, 1989 the population had exploded to well over a million individuals (Tucker, 2012). This number suffered a small decline due to overconsumption of food stocks. The population of M. leidyi within the Black Sea mainly subsist on eggs and pelagic fish, this has had a damaging effect on fish numbers including the very lucrative anchovy species Engraulis encrasicholous (Zaika, et al 1990). Beroe ovate, a larger species of comb jelly was introduced as a form of biological control and had some success. Recent reports show that it appears that a stable predator-prey dynamic has occurred between M. leidyi and the other species within the Balck Sea (Hansson, 2006). The Warty comb jelly has now also spread to the Caspian Sea and the Baltic Sea, each time destroying the fish and zooplankton numbers with the introduction of Beroe ovate having no effect in these locations (Zaika, Tucker, 2012).

The spread of M. leidyi through the Caspian Sea.

Source: http://www.grida.no/graphicslib/detail/comb-jelly-mnemiopsis-leidyi-spreading-through-the-caspian-sea-invasive-species_11bd#, accessed on the 13th of May 2014.

References:

Hansson, H. G. (2006). Ctenophores of the Baltic and adjacent Seas - the invader Mnemiopsis or here. Aquatic Invasions 1(4): 295-298.

Kube, S., Postel, L., Honnef, C., Honnef, A. (2007). Mnemiopsis leidyi in the Baltic Sea - distribution and overwintering between autumn 2006 and spring 2007. Aquatic Invasions. 2 (2): 137-145.

Mnemiopsis leidyi. Encyclopedia of life. Accessed on the 13th of May 2014.

Tucker, A. (2012). How can a jellyfish this slow be so deadly? It's invisible. Smithsonian Magazine.

Zaika, V. and Sergeyeva, N. (1990). Morphology and development of Mnemiopsis leidyi in the Black Sea. Zoological Journal. 69 (2): 5-11.