Fig. 2. Rate of growth of five young medusae of Chrysaora quinquecirrha. One medusa (D) died July 26

Polychaetous annelids were seen in numerous medusae in lower St. John Creek, confirming observations made by Cargo and Dormer in 1963 (MS),3 which indicated that these worms were an important item in the natural diet of the local sea nettle. Therefore, in mid-June we began feeding Nereis succinea (Frey and Leuckart) and Nereis virens Gars to the medusae twice a week, and the medusae increased in diameter as much as 12 mm per week. From mid-June to the first of September, three medusae grew from 12 mm to 75 mm in diameter. They had dusky gonads in September and may have spawned in our tank. In a concurrent experiment an assistant fed these annelid worms exclusively to 5 medusae held in aerated river water, which grew from an average diameter of from 8.8 mm to 53.7 mm from July 12 to August 27 (Fig. 2).

The significance of salinity for the survival of polyps appears to be important since no polyps were found in such creeks as Parker and Fishing Creeks (Calvert County, Maryland) which are subject to flushing with fresh water from heavy rainstorms. Also, we have not found polyps in the upper Potomac and the Magothy Rivers, which normally have low salinities during the spring. Another factor is the great amount of sediment deposited in small creeks, resulting from heavy rains, whereas in large rivers, such as the Potomac, strong tidal currents might clean the substrata.

Our survey of the geographical distribution of the polyp stage suggested these forms were most common in areas where the salinity is greater than 5% and less than 20%. Therefore, with the assistance of a summer student, salinity tolerance experiments were conducted. We found that most of the polyps died and others encysted at salinities of 5% and lower and at 25% and higher. The best survival was at 10, 15, and 20%. Artificial sea salts ("Rila Marine Mix") were used for the experiments.

The salinity tolerance studies with polyps resulted in some unexpected responses. The polyps previously held at about 15%, upon a change in salinity of 5% downward and 5 to 10% upward began strobilation within 4 days. This occurred despite a reduction in temperature from 25° C to 20° C. The apparent onset of strobilation in the field in the spring of 1965 coincided with a sharp rise in temperature along with a drop in salinity. These observations suggest further

3 Some observations on the macro-organisms taken by Chrysaora quinquecirrha in the vicinity of Solomons, Maryland in 1963. Unpublished manuscript.

investigations are needed to determine the role that salinity and temperature play in the initiation of strobilation. The effect of artificial salts is also a factor which must be examined before conclusions can be drawn concerning the influence of salinity on strobilation.

High salinity appears to be a factor limiting the distribution of the polyps. For example, in Chesapeake Bay between the mouth of the Potomac River and the Chesapeake Bay Bridge-Tunnel and in lower Tangier Sound, where the salinity varied from 19% to 25%, the 17 dredge-samples collected were without · Chrysaora polyps, whereas among 40 samples taken from the upper Bay Bridge to the mouth of the Potomac, where salinities were lower and varied from 7% to 18%, polyps occurred in 18 collections (Fig. 1).

The occurrence of sexual reproduction in local waters in 1965 was verified by placing two trays of cleaned oyster shells at the end of CBL pier on July 19 and 23. These shells were prepared from live oysters which were cleaned by natural processes in the woods for 5 weeks. They were then reasembled into oyster boxes by propping open the two shells with a small pebble and holding them together with rubber bands. We had previously observed that under natural conditions oyster boxes were particularly favorable habitats for polyps. One tray was inspected on October 8 and many polyps and cysts were found. On November 18 a tray with 137 shells were examined and colonies of polyps and pedal cysts were found on 126 shells, each colony consisted of from 1 to more than 100 cysts and polyps.

We concluded that planulae, resulting from natural sexual reproduction of medusae during July, August, and September, became attached to our cleaned oyster shells (described above) where they developed into polyps that produced a large number of cysts before the water temperature had lowered significantly. In one of our experimental aquaria, a polyp kept between 21° C and 23° C formed 52 cysts and 6 polyps by October 12. Polyps held in other aquaria since the previous spring produced numerous cysts during the summer and early autumn. Early in the spring, many cysts were observed in close association with polyps. We had assumed that these cysts formed from polyps as a result of the increasing coldness of the water as winter approached. However, there appear to be several other causes of cyst formation when conditions are unfavorable for the survival of the polyps. For example, we have induced 100% cyst formation in aquaria in the following ways: (a) by causing an oxygen-depleted situation associated with some hydrogen sulphide, in which the polyps formed cysts within a few weeks; (b) by rapidly reducing the water temperature to below 4° C, the polyps encysted within 72 hours; (c) by raising the temperature slowly, the polyps encysted within 48 hours when the temperature reached 34° C to 36° C; (d) when the salinity was raised to over 30% and lowered to 5%. Cysts also were formed when heavy bacterial fouling occurred in aerated aquaria. When the polyps were encysting under these conditions, we observed a differentiation of the cell layers, and found that only the cell-protoplasm migrated into the cyst, leaving a thin, transparent remnant of endodermal and ectodermal layers with nematocysts intact. differentiation of cell layers enabled us to predict and observe encystment. If pedal cysts are returned to favorable conditions, some develop into polyps within a few weeks, and later produce more polyps and cysts.

This

These are

Polyps naturally form pedal cysts in the following ways: (a) The foot or base of the polyp spreads or divides into two or more parts, sometimes spreading to distances of 2 or 3 mm. The protoplasm of the polyp at each of the points of contact with the substratum then forms a reddish-brown opaque structure. about 0.5 mm thick and about 2 mm in diameter. The top is flat, with concentric rings and often of a lighter color in the center. The wall has a leathery texture. (b) Pedal cysts are formed from a stolon, which grows laterally from the stalk of the polyp and then curves downward to contact the substratum. This stolon may form either a pedal cyst or a new polyp.

The importance of pedal cysts in the life cycle of Chrysaora became apparent as our knowledge about them increased. They not only serve as a means of survival during unfavorable environmental conditions but their formation is especially important in asexual reproduction as suggested by Truitt (1939). Cyst formation is not necessarily induced by a gradual lowering of the water temperature; instead their abundance in late summer and autumn indicates a natural phase of the life cycle, which makes possible in early spring the sudden development of polyps from these cysts followed by an extremely abundant bloom of medusae as observed in the headwaters of the deep creeks tributary to the Bay. Although Chrysaora polyps are associated with numerous invertebrate organisms we have not yet seen any such organism feeding upon the polyps. On the other

hand, the polyps may ingest almost any available small marine organisms that they can catch. They readily take recently-hatched brine shrimp and a number of naturally occurring organisms, for example, amphipods, protozoa such as Stentor, Folliculina, Parafolliculina, diatomaceous accumulations, organic detritus, and unidentified worms (probably nemerteans).

The polyps share living space within oyster boxes with at least four species of fishes. The most abundant of these is the clingfish (Gobiesor strumosus Cope), which cleans a part or the entire inside area of an oyster box, then lays its eggs on the inside surfaces of both shells. In some of the trays containing oysters at the end of the CBL pier, over 25% of the boxes contained clingfish eggs under parental care. However, we have found polyps on the uncleaned part of the shell not used by the clingfish, thus both exist together. The other less numerous kinds of fishes using oyster boxes for nest are: the striped blenny, Chasmodes bosquianus (Lacépède); feather blenny, Hypsoblennius hentzi (LeSuer); and the naked goby, Gobiosoma bosci (Lacépède).

The medusae are preyed upon during late summer and autumn by at least two kinds of fishes in Chesapeake Bay. The most common and best known (Mansueti, 1963) is the harvest fish, Peprilus alepidotus (Linnaeus), the small young of which frequently accompany a medusa and feed heavily upon the tentacles and oral lappets, whereas schools of those longer than 50 mm may destroy scyphozoan medusae in minutes. Another predator unreported to our knowledge, is the orange filefish, Alutera schoepfi (Walbaum), juveniles of which were observed (DGC) on two occasions feeding actively on medusae of Chrysaora.

A number of individuals have assisted us in many ways. We appreciate the help of Miss Sara K. Wedeles, Cambridge University, Cambridge, England, in the growth and salinity tolerance experiments. We are also indebted to W. L. Dovel, E. A. Dunnington, Jr., and especially to H. T. Pfitzenmeyer of the Chesspeake Biological Laboratory, for securing occasional field samples and to other CBL staff members for their assistance.

Agassiz, L. 1862.

LITERATURE CITED

1862. Contributions to the natural history of the United States of America. 4:1-380, pls. 20–34.

Fraser, James. 1962. Nature adrift, the story of marine plankton. G. T. Foulis & Co., London. 178 pp. illus.

Kramp, P. L. 1961. Synopsis of the medusae of the world. Jour. Mar. Biol. Assn. United Kingdom. 40:1-469.

Littleford, R. A. 1939. The life cycle of Dactylometra quinquecirrha, L. Agassiz in Chesapeake Bay, Biol. Bull. 77(3):368–381, pls. 1-3.

and Truitt, R. V. 1937. Variation of Dactylometra quinquecirrka. Science. 86(2236): 427. Mansueti, R. 1955. The sea nettle, Chesapeake Bay's troublesome summer jellyfish. Maryland Tidewater News. Supplement No. 7. 12(3):1-2, 7 figs.

1963. Symbiotic behavior between small fishes and jellyfishes, with new data on that between the stromateid, Peprilus alepidotus, and the Seyphomedusa, Chrysaora quinquecirrha. Copeia. (1):40-80, figs. 1–5. Mayer, A. G. 1910. Medusae of the World. The Scyphomedusae. Carnegie Inst. Washington. 3:499–735, pls. 56–76.

Spangenberg, Dorothy B. 1965. Cultivation of the life stages of Aurelia aurita under controlled conditions. Jour. Exp. Zool. 159(3):303-318, figs.

Truitt, R. V. 1939. Stoloniferous, pedal disk, and somatic budding in the common sea nettle, Dactylometra quinquecirrha, L. Agassiz. Bull. Nat. Hist. Soc. Maryland. 9(5):38-39.

(The investigations reported herein have been supported by the Office of Water Resources Research, Department of the Interior; The Maryland Board of Public Works, and the University of Maryland.)

Mr. DOWNING. Thank you for a most interesting commentary.
What is the life span of a jellyfish?

Dr. CRONIN. Well, it's an endless cycle. The life span of the swimming medusae in the bay is from sometime early in the summer to about September. Then this form will die.

Meanwhile it has reproduced and its young have found the bottom and attached and will be there through the winter, and then will split off their progeny next spring, so that the medusae itself is short lived. Mr. DOWNING. It is asexual as well as bisexual?

Dr. CRONIN. Yes, this summer form is sexual, but the polyps reproduce by splitting at the base and a number of polyps can be formed in a chain. Mr. Cargo has occasionally seen so many that it is a bit discouraging, but sometimes conditions will affect this in ways that we are just beginning to understand.

Mr. DOWNING. The article which accompanied your statement indicated that they have 24 tentacles. Is this a uniform number? Dr. CRONIN. Not precisely. It varies around that number, but it is remarkably constant for the species.

Mr. DOWNING. Have you been able to isolate the irritant toxin?

Dr. CRONIN. As far as I know, the irritant for this species has not been isolated. Those of a number of other species have. The University of Miami has been very active in the field, and other centers as well. This species has not been investigated but should be.

Mr. DOWNING. I should think that would be awfully important. It has a burn not unlike sulphuric acid.

Dr. CRONIN. It certainly feels like an acid sting, but it is a different kind of irritant.

Mr. DOWNING. The sting is located in the tentacles?

Dr. CRONIN. Primarily yes, and along the long central parts of the mouth.

Mr. DOWNING. Is the entire tentacle capable of stinging?

Dr. CRONIN. Yes, the stings are located in individual tiny organs actually scattered along the entire tentacle, but all over it and a little on the top. As Mr. Garmatz demonstrated earlier, the top can be handled with reasonable safety.

Mr. DOWNING. Do they have the ability to migrate?

Dr. CRONIN. They have about the swimming ability that you see here in the tank, a slow pulsing. We think that they can respond by swimming toward the surface or toward the bottom, but they cannot migrate in any very clear direction. They are carried by the movement of the water primarily.

Mr. DOWNING. Do they have any special genes?

Dr. CRONIN. I think not. They have a few simple reactions, responses, but no concept of planning or thinking and rationalizing. Mr. DOWNING. Did I understand you to say that there were two female jellyfish in the tank?

Dr. CRONIN. Yes, sir; they are both females.

Mr. DOWNING. How can you tell?

Dr. CRONIN. Well, in the central area are brownish or pinkish masses which are the reproductive organs. In these two they are brown, so that they are females. If they were pink, they would be males.

Mr. DOWNING. I have noticed some nettles that were red.

Dr. CRONIN. Yes. This is a very nice picture that the National Geographic has loaned us of the red phase. This is a phase of the same species. It is exactly the same and only a percentage do develop this color pattern.

Mr. DOWNING. What caused the red color?

Dr. CRONIN. I don't know, Mr. Chairman. These are not significantly different, but they do comprise a small percentage of the form in Chesapeake Bay.

Our impression is that they are more common along the coast but I am not certain.