Comb Jellies invade and disrupt the Black & Caspian Sea ecosystems!
Though the jelly-like comb jellies are classified in a different animal phylum than jellyfish (which signifies a distant relationship), they also share the jellyfish's fondness for zooplankton, along with the eggs and larvae of fish and invertebrate animals. Ctenophores commonly found in the Black Sea are Pleurobrachia pileus, Mnemiopsis (different species), and Beroe ovata.
Mnemiopsis is a comb jelly native to the Atlantic coastal region between Massachusetts and southern Argentina. In its natural range, it has been known to heavily impact ecosystems by consuming vast quantities of zooplankton, eggs, and the larvae of fish and invertebrates that would otherwise support populations of more desirable species. Mnemiopsis was first observed in the Black Sea in the early 1980s, where it is thought to have been transported and dropped by the ballast water of freighters arriving from distant shores in the western Atlantic.
By the late 1980s, populations of Mnemiopsis soared, populations of its favored zooplankton food plummeted, and, coincidentally, commercial catches of the zooplankton-eating anchovy (Engraulis encrasicolus) were drastically reduced. A few years ago, Mnemiopsis was accidentally introduced into the Caspian Sea, where a similar impact is beginning to be seen.
Mnemiopsis sp. - comb jelly
Highly transparent, elongated body, round in cross-section, with semi-transparent rows running the length of the animal. Size: less than 1 inch to 4 inches. No sting.
Jellyfish are free-swimming members of the phylum Cnidaria. They have several different basic morphologies that represent several different cnidarian classes including the Scyphozoa (about 200 species), Staurozoa (about 50 species), Cubozoa (about 20 species), and Hydrozoa (about 1000-1500 species that make jellyfish and many more that do not)[1][2]. The jellyfish in these groups are also called, respectively, scyphomedusae, stauromedusae, cubomedusae, and hydromedusae; "medusa" (plural "medusae") is another word for jellyfish. Jellyfish are found in every ocean, from the surface to the deep sea. Some hydrozoan jellyfish, or hydromedusae, are also found in fresh water. Most of the information about jellyfish that follows in this article is about scyphozoan jellyfish, or scyphomedusae. These are the big, often colorful, jellyfish that are common in coastal zones worldwide.
In its broadest sense, the term jellyfish is sometimes used also to refer to members of the phylum Ctenophora. Although not closely related to cnidarian jellyfish, ctenophores are also free-swimming planktonic carnivores, are also generally transparent or translucent, and occur in shallow to deep portions of all the world's oceans. Ctenophores move using eight rows of fused cilia that beat in metachronal waves that diffract light, so that they sparkle with all of the colors of the rainbow. The rest of this article deals only with jellyfish in the phylum Cnidaria.
Body systems
Jellyfish don't have specialized digestive, osmoregulatory, central nervous, respiratory, or circulatory systems. They digest using the gastrodermal lining of the gastrovascular cavity, where nutrients are absorbed. They do not need a respiratory system since their skin is thin enough that the body is oxygenated by diffusion. They have limited control over movement, but can use their hydrostatic skeleton to accomplish movement through contraction-pulsations of the bell-like body; some species actively swim most of the time, while others are passive much of the time. Jellyfish are composed of more than 90% water; most of their umbrella mass is a gelatinous material - the jelly - called mesoglea which is surrounded by two layers of epithelial cells which form the exumbrella (top surface) and subumbrella (bottom surface) of the bell, or body.
Jellyfish do not have a brain or central nervous system, but rather have a loose network of nerves, located in the epidermis, which is called a "nerve net". A jellyfish detects various stimuli including the touch of other animals via this nerve net, which then transmits impulses both throughout the nerve net and around a circular nerve ring, through the rhopalial lappet, located at the rim of the jellyfish body, to other nerve cells. Some jellyfish also have ocelli: light-sensitive organs that do not form images but which can detect light, and are used to determine up from down, responding to sunlight shining on the water's surface.
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