BULLETIN OF MARINE SCIENCE, 40(3): 437-441,1987

FIRST REPORT OF THE LITTLE-KNOWN SCYPHOMEDUSA DRYMONEMA DALMATINUM IN THE CARIBBEAN SEA, WITH NOTES ON ITS BIOLOGY

Ronald J. Larson

ABSTRACT The large (to 75 cm diameter and about 25 kg) scyphomedusa, Drymonema dalmatinum, is reported for the first time in the Caribbean Sea. Many of these medusae were observed in shallowwater in the Virgin Islands, as wellas along the coast of Puerto Rico. D. dalmatinum feeds mostly on aurita medusae, and can consume several of these at the same time. Extracellulardigestion occurswithin the oral arms ofD. dalmatinum whichapparently secrete proteases; gastric cirri are absent in large specimens. The oral arms are massive, comprising -50% ofthe total weight of the medusa, and have a surface area of several square meters in largespecimens. The large size of the oral arms allows for gorgingof prey when the latter are abundant. Laboratory-measured growth efficiencywas low (3-5%). In situ observations of D. dalmatinum showed that juvenile pelagicfishesare often associated with these medusae. Off Puerto Rico, an estimated 500 fishes, mostly Chloroscombus chrysurus, with fewer Car- anaxfusus, were seen swimming around one 75 cm diameter D. dalmatinum medusa. This speciesprobably serves as an important refuge for young pelagicfishes.

Large scyphomedusae of the family (Cyanea, Desmonema) are com- mon in polar and temperate oceans, but they rarely occur in the tropics. In the northwestern Atlantic, the only previously reported cyaneid is Cyanea capillata (Mayer, 1910; Larson, 1976). However, this species is restricted to waters ofless than about 20°C (Mayer, 1914; Hoese et al., 1964). The previously unreported occurrence of the large cyaneid Drymonema dalmatinum Haeckel, 1880 in the Caribbean Sea is surprising, especially considering the amount of biological col- lecting that has taken place there. The presence of D. dalmatinum in the Caribbean was first made known to me in 1973 by Professor C. E. Cutress, of the University of Puerto Rico. He had collected several small specimens from the south coast of Puerto Rico, near La Parguera. In 1974-1975, I was fortunate to observe many D. dalmatinum specimens of various sizes near Puerto Rico and in the Virgin Islands, some of which were collected for laboratory studies. This paper concerns in situ and laboratory observations of behavior, prey capture, feeding and growth of D. dalmatinum medusae. Historical Account. -Drymonema dalmatinum was first described by Haeckel (1880) from material collected off the Dalmatian coast of the Adriatic Sea. A year later, Haeckel (1881) described a second species, D. victoria, from material col- lected by the H.M.S. CHALLENGER,near Gibraltar. Muller (1883) described a third species, D. gorgo, from Brazil. Antipa (1892) described yet a fourth species, D. cordelio, from the Gulf of Smyrna in the Adriatic Sea. Mayer (1910) reviewed the genus Drymonema, and concluded that there was only a single Mediterranean species, namely D. dalmatinum. He also suggested that D. gorgo was probably not a valid species. Later, Stiasny (1940), after reviewing the genus, concluded that D. dalmatinum was the only valid species within this genus, the others being JUnIor synonyms. After examination of 20 Drymonema specimens collected from Puerto Rico and the Virgin Islands (deposited in the National Museum of Natural History,

437 438 BULLETIN OF MARINE SCIENCE, VOL. 40, NO.3, 1987

Smithsonian Institution, Washington, D.C.), I conclude that the Caribbean species is D. dalmatinum, as diagnosed by Stiasny (1940). Observations.-D. dalmatinum medusae (5-75 cm diameter) were observed near La Parguera, Puerto Rico, from November 1974 to January 1975, and in the Virgin Islands (Beef 1., Tortula 1., St. John 1., Guano 1., and Jost van Dyke 1.) during July 1975. These medusae were most numerous in the Virgin Islands, where scattered individuals occurred in passes between the islands. As many as 50 specimens were observed in a small bay near Monkey Pt., Guano Island. This giant medusa has also been observed off the east coast of Puerto Rico (C. Goenaga, pers. comm., 1974). It has also been seen at Flatts Inlet, Bermuda (D. Calder, pers. comm., 1986) and possibly on the Atlantic side of S. Florida (S. Cairns, pers. comm., 1977). Swimming Behavior. -On several occasions, the swimming behavior of D. dal- matinum was observed in situ. Most medusae were seen in the upper 5 m. Ori- entation was such that the exumbrella was most often upwards, with the tentacles trailing below (either downwards when there was no current or inclined when there was a current). The medusae were slow swimmers, pulsating only 2-20 times per minute, and pulsation rates decreased with increasing size of the medusa. The swimming pulsations were just sufficient to keep the medusa near the surface, but were not strong enough for horizontal movement owing to the considerable drag and weight of the tentacles and oral arms. Feeding Behavior.-During December 1974 at La Parguera, P.R., 13 D, dalma- tinum individuals seen at the water's surface, were examined for the presence of prey in their oral arms. Six specimens were found with partially-digested Aurelia aurita medusae in their oral arms; another specimen (30 cm diameter) contained three partially digested Aurelia (20 cm); another specimen (5 cm) was attempting to digest an Aurelia nearly four times it size; the other five contained no prey. Prey capture was observed in situ by moving an Aurelia medusa near a swim- ming D. dalmatinum, Upon contact with a tentacle of D. dalmatinum, the Aurelia was immediately caught and pulled upwards by a tentacle. Continued swimming activity of the Aurelia soon brought it into contact with additional D. dalmatinum tentacles, and within a few moments the oral arms also attached, completely enveloping the Aurelia within 30 minutes. Associations with Fishes. -Of the 13 D. dalmatinum medusae seen during De- cember 1974 at La Parguera, P.R., 5 had associatedjuvenile fishes. These medusae, ranging in size from 15 to approximately 75 cm in diameter, each had from 50 to about 500 fish (mostly Chloroscombus chrysurus) continuously circling around their oral arms (Fig. 1). The largest medusa (75 cm), which had the greatest number of fishes swimming around it, had its oral arms and umbrella nearly obscured from view by the school of encircling fishes. The medusa was slowly pulsating (2-5 pulsations per minute) near the surface, with its numerous tentacles (~5 mm in diameter) extended up to 10 m or more in various directions. The school of fishes consisted mostly of C. chrysurus (1-4 cm long), plus several larger Caranxfusus (10 cm), which were all swimming around the medusa in the same direction. When approached, the school of fishes moved closer and closer to the medusa until some of the fish were actually within the oral arms. No fishes were apparently captured by the medusa, although one medusa brought back to the lab had several dead fish in its oral arms. Associations with Amphipods. -Hyperiid amphipods belonging to the genus LARSON: NEW CARIBBEAN SCYPHOMEDUSA 439

Figure I. A 20 em Drymonema dalmatinum medusa swimming in an aquarium with associated juvenile Chloroscombus chrysurus fish (about 2 em in length). 440 BULLETIN OF MARINE SCIENCE, YOLo 40, NO.3, 1987

Brachyscelus were found on the exumbrella of several specimens of D. dalmatinum collected at La Parguera. This amphipod was also found on Aurelia aurita medusae from the same location. Laboratory Observations. - Prey capture and digestion were studied in the labo- ratory. A lO-cm Aurelia was placed in an aquarium with a 25-cm D. dalmatinum medusa. In the confines of the aquarium, Aurelia quickly became tangled in the tentacles of D. dalmatinum. Oral arms of the latter contacted and began to spread over its prey. Within 1.5 h, the oral arms of D. dalmatinum had completely enveloped the specimen of Aurelia. Digestion, which was extracellular, was com- pleted in 6-8 h. Examination of the lip margins of the oral arms of D. dalmatinum disclosed large numbers of nematocysts. These same cnidae were found discharged in a piece of Aurelia umbrella mesoglea that had been touched to the oral arm of D. dalmatinum. Evidently, since both the abaxial and adaxial surfaces of the oral arms are heavily ciliated and show much spontaneous muscular activity, envel- opment of the prey is by ciliary creeping aided by muscular contraction of the oral arms. Gastric cirri, which have been thought to be the primary structures responsible for production of extracellular proteases and for assimilation by scyphomedusae (Bodansky and Rose, 1922), were absent in D. dalmatinum specimens larger than 10 cm. Nevertheless, isolated pieces of D. dalmatinum oral arm liquified pieces of Aurelia mesoglea (control pieces of Aurelia mesoglea remained unchanged), suggesting that digestive enzymes are produced by the oral arms. Since the oral arms of D. dalmatinum appeared to have a very large surface area for enveloping prey during feeding, I estimated the total surface area of a 30-cm diameter specimen. A I-g piece of oral arm was allowed to creep over the 2 bottom of a dish. It spread over an area of 25 cm • The total mass of oral arms of this specimen equaled 2.3 kg (-50% of the total weight of the medusa). There- fore, the total surface area of the oral arms (each -0.5 m long) was estimated as several square meters. Such an extensive area allows Drymonema to envelop several large Aurelia simultaneously. Growth. -A 140-g wet weight (9.5 cm diameter) D. dalmatinum medusa was maintained in the laboratory on a diet of Aurelia medusae. After 1 week, the medusa had doubled its biomass, reaching 310 g (15 cm), having consumed 3.2 kg of Aurelia. Another D. dalmatinum was also maintained in the lab for 1 week. It grew from 165 g to 285 g, consuming 4.0 kg of Aurelia. Growth efficiency (new biomass/food biomass) was estimated to be 5% and 3%, respectively, for the two specimens.

DISCUSSION D. dalmatinum is the largest known medusa in the tropical Atlantic, reaching at least 75 cm diameter and probably weighing about 25 kg. Its occurrence in the Caribbean may be sporadic, hence the absence of earlier reports. Stiasny (1940) noted that it was sporadically present in the Adriatic Sea, in fact, at intervals as long as 30 years apart! A. aurita appears to be the major prey of D. dalmatinum in both the Adriatic and Caribbean Seas (Stiasny, 1940; this report). Because D. dalmatinum appears to have such a low growth efficiency, at least in the laboratory, considerable amounts are evidently required. Nevertheless, Aurelia is seasonally abundant in inshore waters ofthe Caribbean Sea (unpub I. obs.), and could conceivably support LARSON:NEWCARIBBEANSCYPHOMEDUSA 441

small populations of Drymonema. Growth efficiencies measured in the laboratory for some other scyphomedusae are comparable: Larson (1986; 1987) found growth efficiencies of2-10% for Chrysaora quinquecirrha, and 7-12% for Pelagia noctiluca. Fraser (1969) found efficiencies of 37% for both A. aurita and C. cap- illata. However, in Fraser's study the prey had a much higher organic composition. Since D. dalmatinum was often seen with juvenile scombrids, sometimes in large numbers, this medusa may be locally important as a refuge for young pelagic fishes. Juvenile scombrids are also often associated with another large Caribbean scyphomedusa, Phyllorhiza punctata (unpub1. obs.). Mansueti (1963) reviews the literature on fish-medusae relationships. The Brachyscelus amphipods found on D. dalmatinum have not previously been reported from medusae, but have been observed on diver-collected cteno- phores and salps (Harbison et a1., 1977).

ACKNOWLEDGMENTS

I wish to thank the staff, and in particular C. Cutress, of the University of Puerto Rico, Mayaguez, for providing funding, laboratory space, and equipment. T. Bowman kindly identified the hyperiid amphipods and T. Bailey, D. Calder, K. Larson, and C. Mills provided helpful comments on the manuscript. A post-doctoral fellowship from Harbor Branch Institution provided financial support during manuscript preparation. This is contribution 584 of Harbor Branch Foundation.

LITERATURE CITED

Antipa, G. R. 1892. Eine neue Art von Drymonema. Jen. Z. Naturw. 27: 337-339. Bodansky, M., and W. C. Rose. 1922. Comparative studies of digestion. I: The digestive enzymes of coelenterates. Amer. J. Physio!. 62: 473-481. Fraser, J. H. 1969. Observations on the experimental feeding of some medusae and chaetognaths. J. Fish. Res. Bd. Can. 26: ]743-1762. Haeckel, E. 1880. System der Acraspeden. Zweite Hiilfte des System der Medusen. Jena. Pp. 361- 672. --. 188]. Report on the deep-sea medusae dredged by the H.M.S. Challenger during the years ]873-1876. Rep. Sci. Res. Challenger (Zoology) 4: 1-154. Harbison, G. R., D. C. Biggs and L. P. Madin. 1977. The associations of Amphipoda Hyperiidea with gelatinous zooplankton-II. Associations with , Ctenophora and Radio]aria. Deep- Sea Res. 24: 465-488. Hoese, H. D., Copeland, B. J. and J. M. Miller. 1964. Seasonal occurrence of Cyanea-medusae in the Gulf of Mexico at Port Aransas, Texas. Texas 1. Sci. 16: 391-393. Larson. R. J. 1976. Marine flora and fauna of the northeastern United States. Cnidaria: . N.O.A.A. Tech. Rept. N.M.F.S. Cir. 397. 18 pp. --. 1986. The feeding and growth of the sea nettIe Chrysaora quinquecirrha (Desor) in the laboratory. Estuaries, 9: 376-379. --. 1987. A note on the feeding, growth and reproduction of the epipelagic scyphomedusa Pelagia noctiluca (ForskAl). BioI. Oceanogr. 4: 447-454. Mansueti, R. ]963. Symbiotic behavior between small fishes and jellyfishes, with new data on that between the stromatoid Peprilus alepidotus and the scyphomedusa Chrysaora quinquecirrha. Copeia 1963: 40-80. Mayer, A. G. 1910. Medusae of the world. III. Pub!. Cameg. Inst. Wash. No. 109. Pp. ]-735. --. 1914. Effects of temperature on tropical marine . Pap. Tortugas Lab. 183: 1-24. Milller, F. 1883. Drymonema an der Kiiste von Brasi[ien. Zool. Anz. 6: 220-222. Stiasny, G. [940. Uber Drymonema dalmatina Haeckel. Zool. Jb. Anal. 66: 437-462.

DATEACCEPTED:June 3, 1986.

ADDRESS:Department oj Marine Sciences, University oj Puerto Rico, Mayaguez, Puerto Rico 00708. PRESENTADDRESS:Harbor Branch Institution, RR 1, Box 196A, Fort Pierce, Florida 33450.