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R ghe SEA iVettk of Chesapeahe X conarcl Schultz crni .ÖaviJ , (.......-hesapeahe g cargo BIOLOGICAL ,ralorcrtory Perplexing Problem The summer sea nettle, Chrysaora quinquecirrha DeSor (formerly .Daetylatnetra quinquecit-rha) has been a problem since Colonial days. Each year this pest appears in Chesapeake Bay with regularity and certainty by late June, .reaching a peak of abundance during July and August. It may -.disappear in late August, or September in Virginia waters, but in the upper bay it may vanish anytime from September to November. When it is abundant, swimming declines in hay waters. No other animal in Chesapeake Bay is so detrimental to recreational activities. It also causes con' siderable economic loss to beach operators and to fishermen. Chrysaora is not unique to Chesapeake Bay. This type a nettle ranges from New England to the tropics, and ated species occur in oceanic waters in most temperate t tropical seas. •". . However, it is „.. rnore abundant in the • ay arid iii the lower parts of its tributary streams and creeks than in . xxiy other body of:water, Jellyfish vary in abundance in swimming areas from day to day, largely because of wave action and water currents. Strong wave action causes the sea nettle to swim slowly by feeble rhythmic contractions into deeper water. However, as soon as the turbulence ceases, it again moves slowly to the surface and is at the mercy of surface currents that may transport them to the beaches again. The sea nettle is well adapted to live and reproduce in salinities from 7 0/00 (parts per thousand) to 35 0/00, but it dies when the salinity is lower than 5 0/00. Maryland and Virginia, assisted by the Federal Government, are studying the biology of the summer sea nettle and possible methods of controlling its abundance. These investigations are underway at the Chesapeake Biological Laboratory, Solomons, Maryland, and at the Virginia Institute of Marine Science, Gloucester Point, Virginia. Other Jellyfishes Offer No Trouble Three other prominent jellyfishes are seen in the Bay: one, the nearly flat, white moon jellyfish, Aurelia aurita (Linnaeus), which may grow to more than a foot in diameter, is abundant in the lower bay in the summer, but less so in the upper bay. It is not a problem because its sting is scarcely felt by swimmers. Another white species, Rho pilema verrilli (Fewkes) is too rare in the bay to be of any concern. The third sea nettle, the red winter jellyfish, with short tentacles, Cyanea capillata (Linnaeus), makes its appearance in December and disappears by the end of May. Because of its winter occurrence and very weak sting, it is unimportant in relation to the activities of man. No Economic Value Here Attempts have been made to make some economic use of jellyfishes. For example, in Japan, Hong Kong, and Taiwan, Rho pilema, when dried, is used for food. Sometimes this or related kinds of medusae may be bought in local Chinese markets. However, when Chrysaora medusae become dried on fish nets the stinging cells can remain for at least 10 years. Then, when the nets are disturbed, the stinging cells float in the air and fishermen that breathe them sneeze violently, as any old timer will testify. There is no record of any economically profitable use of the sea nettle. BIOLOGY A Simple Animal, Related to the Polyps The summer sea nettle, which may reach 9 inches in diameter, is the medusa stage of an organism that belongs to the Phylum Coelenterata in the Animal Kingdom. It is a relatively simple animal related to corals, sea anemones, and hydras, all of which have two layers of differentiated cells (higher forms have 3 layers); the inner layer surrounds the digestive cavity and the outer layer contains the stinging NTER JELLYFISH cells. These medusae, bell- or umbrella-shaped, are composed of a translucent gelatinous mass with beautiful radial symmetry. The sea nettle medusa lacks a brain. It does have 8 nerve centers in the margin of the bell that serve to coordinate the pumping contractions of the bell and the feeding activities. Underneath the edges of the bell are numerous, long (over 4 feet in large medusae), threadlike, contractible, fishing tentacles as shown on the cover. They have thousands of minute stinging cells, the nematocysts, in their outer tissue layer. There are four long, lacy tissues, the oral arms, suspended from the center of the bell. In the bell cavity are tiny finger-like digestive glands. The summer jellyfishes are milky white in the upper and middle parts of the bay. However, in the lower bay many of them are beautifully decorated with 16 short red bars on the convex side of the umbrella. A chemical analysis of the medusa reveals that they consist of about 3% protein and salts and 97% water. Reproduction — bryos, or planulae, become covered with cilia and then begin to swim. They escape from the female into the water, where they are dependent on currents for movement from place to place. During this pelagic larval stage, the planulae are white in color and smaller than a grain of salt. After a few days they settle and attach to hard objects on the bottom. The attached planula looks like a tiny white speck, the center of which soon bulges outward and then develops into a flower-like polyp shaped like an ice cream cone. This is the sessile, or attached, stage in the life cycle of jellyfishes. They are sometimes abundant on the underside of oyster shells, on bottles, cans and anything else available in shallow water in the numerous, small, protected creeks and in the bay. They should be looked for especially on oyster shells. The growing polyp (1/25 inch in diameter and 1/8 inch tall) first forms 8 small tentacles around its outer free margin. There is a small cup-shaped mouth at the center, thus the name "scyphistoma" (cup and mouth) for this stage of sea nettle. As the polyp grows, 16 tentacles are formed. They are greatly extensible and retractile, and bear numerous stinging cells. These nematocysts are discharged when touched by an organism. For example, tiny protozoans are paralyzed and held by the tentacles, then quickly moved toward and deposited in the mouth of the polyp. Polyps will eat any organism they can sting and hold with the tentacles. Tentacles Nerve Centers Sexual and Asexual Medusae of Chrysaora have separate sexes. The ovaries and testes are shaped like a 4-leaf clover within the bell. The olive- to dusky-colored ovaries of the mature female are distinguishable from the males, which have whitish or pinkish testes. The entire bell of the male appears more whitish in the water than that of females when viewed from above. The gonads are sexually mature from July onward to the end of the season. Sperm apparently are set free in the water from the testes. They fertilize the eggs within the ovaries, where development begins. Soon the developing em- MOON JELLYFIS Asexual reproduction in Chrysaora is highly developed. One common method is by the formation of stolons, These are small tubular projections from the side of a polyp that extend outward then downward to touch the hard substrate, at which point a new polyp, or cyst, grows. The cyst is shaped like a cupcake and is always attached to the hard substrate. It is reddish brown and measures 1/2 mm thick and about 2 mm (1/16 inch) in diameter. Another method of reproduction, strobilation, occurs mostly in the spring and early summer. The distal or outer 2/3 of the polyp forms into disk-like buds, which measure 1 to 3 mm in diameter. Soon the outer one begins to pulsate and then breaks away to swim freely in the water. It is called an ephyra. The latter has 8 flap-like extensions, called lappets, around the margin. When this ephyra reaches 1/4 inch in diameter (6 or 7 mm), tentacles begin to form and soon it looks like the adult medusa or jellyfish, which is the sexual stage. The summer sea nettle has remarkable ability to reproduce itself. Each polyp may produce about 5 ephyral discs (some form over 10) at a time, and this may occur as many as 4 times in a season. Thus, if a polyp produced a total of 50 cysts and polyps in one season, and then in the spring and summer if each of the 50 polyps formed 20 discs, it is possible that 1,000 medusae could result from a polyp within a year. When we consider that the bay has literally millions of shells, many of them bearing numerous polyps, it is easy to understand why we have a problem with jellyfishes. The abundance of polyps and cysts varies greatly under natural conditions. One shell had 1200 polyps on it; however, usually there are fewer than 25 polyps and cysts. Many shells have none. A polyp that sets in July may reproduce itself more than 50 times by the start of the winter. Cysts are made at the base, or foot, of the polyp, and the polyp then moves a little distance away and forms a new cyst. If living conditions for the polyp are unfavorable, the polyp can withdraw completely into a cyst and remain protected until conditions improve. Chrysaora polyps thus may pass the winter in an encysted condition. Polyps can survive for several years, and perhaps even longer. When the water temperature rises to about 17°C (63°F) in the spring, a new polyp grows out of the center of the cupcake-shaped cyst and within a few days strobilation starts. The male and female medusae reproduce sexually, forming sperm and eggs and then larvae, whereas the polyp reproduces asexually by forming cysts, stolons, and ephyrae. These two alternating methods of reproduction, asexual and sexual, illustrate an interesting well-known phenomenon in nature, the "alternation of generations". Fast Growth, Wide Variety of Food Growth from the ephyra stage to a mature jellyfish is very rapid. Diameter increases as much as 1 or 2 inches per week in the early part of the season. Under favorable conditions, from the jellyfish point of view, a size of 6 to 8 inches across is reached in 5 weeks. By late summer most of the medusae are less than 6 inches across, indicating slower growth. Possibly this results from a reduced food supply through overpopulation of jellyfish, or the medusa may become mature at smaller sizes later in the summer. Sea nettles do not seek or voluntarily swim to their food but drift with water movements. They extend their long thread-like tentacles in many directions. When touched, they discharge a highly toxic venom which almost instantly paralyzes small fishes and other aquatic organisms that adhere to the tentacles. The latter contract and draw the food organism into the oral arms. Gradually, the food item is moved by ciliary action into the mouth, thence into the gastric cavity of the bell, where powerful juices, secreted by the digestive glands, digest the food in 8 to 12 hours at room temperature. A small fish will be completely absorbed, except for the undigestible, veil-like remains that are later ejected by the medusa. The commonst food of this sea nettle consists of small fishes, worms, oyster and other shellfish larvae, sea walnuts, and many kinds of small marine invertebrates and protozoans. 0 1 $‘4 Nematocyst capsule Stinging /\ ; filament released >01 1 - Cell containing nematocyst The Stinging Cells Are Poisonous When vacationers touch a sea nettle, the stinging cells or nematocysts are stimulated to discharge microscopic "darts," which can penetrate the thinner skin of legs, arms, or exposed parts of the body. Each stinging nematocyst is a lemon-shaped cell with a trigger-like hair. This large cell, situated in the surface layer of the tentacles, oral arms and bell, contains a coiled thread. The thread, coated with the cenom, is quickly everted when the "trigger" is touched. The venom discharged is a complex protein substance and not "formic acid," as sometimes reported. It irritates the affected skin, producing a stinging sensation almost instantly. A few people have an allergic reaction that may hospitalize them. Most people stung show only inflamed skin that may last for a few hours. Various substances have been used by bathers in an attempt to reduce the burning sensation, for example, baking soda, salt, ammonia water, and sand rubbed on the stung area. Each of these home remedies helps but none is fully satisfactory. Ointments, such as vaseline, if spread thickly on the skin, are effective shields, but such substances are so messy that few people use them. Recently it was reported that the proteolytic en- zyme, papain, one of the active ingredients of most commercial meat tenderizers, gave almost instant relief for most people when applied immediately. It is more effective if applied quickly to the skin after an attack. The stung area should be rnoisetened, then richly sprinkled with the tenderizer, and briskly rubbed. A second application is often needed to stop the burning sensation, but some itching may still remain in more severe attacks. Since the stinging thread can penetrate only the thinner layers of the skin, one can usually grasp the bell side of a jellyfish with the hands without danger. The skin of the palm side of the hand is usually too thick to be penetrated by the "dart" of the nematocyst. The Sea Nettle Population Keeps Changing Records of relative abundance of the summer sea nettle have been kept by the staff of the Chesapeake Biological Laboratory since 1960. These data show considerable fluctuation. This sea nettle was scarce in 1960 and 1961, but has been abundant since then. Medusae usually reach a peak of abundance in July and August and then decrease gradually and disappear by November. However, in 1963, 1966 and 1969, they disappeared suddenly by early September. Marine biologists are trying to discover the causes of such changes. They have speculated that heavy rains, considerable sedimentation, some unknown jellyfish disease, or perhaps a predator might cause these changes. Not enough knowledge is as yet available to determine the correct answers. Perhaps each affects this species. 2000 LaJ 0, 1962 1963 1.1 64 1966 1965 1000 Es 2 1967 1968 69 1970 1500 500 I IA Å i t, 1 ANNUAL SEASONS MONTHS MAY TO DECEMBER Enemies of the Jellyfish An important predator that might influence relative abundance is the shell-less nudibranch, or sea slug, a marine mollusk about 1/4 to 3/4 of an inch long. It prefers to eat jellyfish polyps but also feeds on hydroids. Nudibranchs actively seek the polyps and are able to detect them at a distance of several inches. One large individual of Cratena pilata (Gould) kept in the laboratory ate 500 polyps in a 3-day period. Biologists believe that if the nudibranchs became abundant, jellyfish might be reduced in numbers. The life history of the nudibranch is not yet well understood. They appear to be abundant in June and again in October and November. Nudibranchs are hermaphroditic (each individual is both male and female), but selffertilization is not possible. They mate and then both lay eggs in a jelly-like coiled string that is draped loosely on plants, hydroids, or shells, from late May through November. They hatch in less than a week. The larvae, or veligers, each bearing a tiny snail-like shell, are set free. For about two weeks they swim freely in the water and then lose their shell. Soon they begin to crawl about on the bottom. They grow rapidly and become mature adults within two months. Probably they pass the winter hidden in the bottom and emerge when the water reaches about 11°C. (52°F). The life span of Cratena may be less than one year. There are other predators that feed on jellyfishes, but none of them is effective in reducing sea nettle abundance. One, the juvenile harvestfish, Peprilus ale pidotus, swims in and out of the jellyfish tentacles with impunity. In some years about 1 in 100 medusae will be accompanied by one or more harvestfish. These fish feed on the tentacles and bell of jellyfishes. Larger harvestfish do not stay under the bell of a sea nettle, but travel in schools. They can destroy several medusae in a few minutes. The juvenile orange filefish, Alutera schoepfi, also feeds on these medusae. At least 4 small fishes that clear off part of a shell for their nests compete with Chrysaora for living space and destroy some polyps in the process. These are the clingfish, Gobiesox strumosus Cope; the striped blenny, Chasmodes bosquiannus Lacepede; the feather blenny, Hypsoblennius hentzi Le Sueur; and the naked goby, Gobiosoma bosci (Lacepede). None of them are abundant enough to measurably reduce the population of polyps. CONTROL EFFORT Man-Made Barriers Chemical and Biological Controls Under Study Numerous protective devices have been built to keep summer sea nettles out of swimming areas along the shores of the bay. However, most of them have been unsuccessful because they were not properly designed nor given adequate daily attention after installation. Bubble screens and water jets have been used experimentally to divert sea nettle away from bathing areas. So far, there is no known method of controlling the abundance of the summer sea nettle. The area of the bay is so large, and the volume of water so great, that it would be very difficult and expensive to change the abundance of sea nettles with chemicals or by scooping them up in large nets. Chemicals so far tested that kill the sessile polyp stage also kill oysters, crabs, and other marine organisms. It has been experimentally determined that sediment covering polyps to a depth of 1/8 inch stops asexual reproduction within a period of 3 or 4 weeks and that longer exposure causes a very high mortality. However, the application of silt to control the abundance of sea nettles may not be practical because the layer of sediment also kills small oysters and other sessile organisms. There is, however, a possibility that biological control might give some relief from the nuisance. This approach would attempt to attack some vulnerable stage in the life cycle of Chrysaora. The polyp, although perhaps not the weakest. stage, is one which is sessile or fixed in position on the bottom and may be attacked. The only predator so far discovered in the bay that voraciously eats the polyp stage, is Cratena, the local sea slug. It is being studied to determine its value for possible control of the abundance of sea nettles. Attempts are underway to culture it in the laboratory for this purpose. Continued research on the biology, on chemical and biological controls, on hormones that might retard or stop reproduction, on sea nettle barriers, and on substances that might neutralize the effect of the venom may help reduce the discomfort and considerable economic loss resulting from Chesapeake Bay's most troublesome pest. Successful sea nettle barriers along the open bay shore have been constructed of galvanized wire hardware cloth, fastened to wooden frames. The swimming area protected is encircled on 3 off-shore sides by posts set at 10-foot intervals, to which wooden frames are attached. The frames are removed each autumn, repaired, and then again placed on the posts in the spring. Fish netting hung on ropes or cables has been used with partial success in coves and other areas that are protected from strong waves and strong currents. The bottom line of the net is held down by lead weights or a heavy chain. These devices, however, become clogged with jellyfishes and other floating debris, which often pulls the net off the bottom or submerges the "corkline." Drifting timbers or trees tear holes in these nets, letting jellyfish into the swimming area. Strong wave action breaks up the medusa and its tentacles into small parts, which pass through the netting. The detached tentacles can still sting swimmers, as much as when attached to the bell. .A survey of these installations made it clear that whatever type of barrier is built, it requires daily servicing to be effective. The best type of barrier, still in the experimental stage, may be a combination of water jets and netting.