Observations on the Moon Jelly, Aurelia aurita, and the Spider Crab, Libinia d u b i a ~

ABSTRA{:T

�9 : i : i : ' : ~ i / i : ( : ~ - Observations of an association between Aurelia aurita and Libinia dubia are reported. Numerous small spider crabs were noted on these occasions~ clinging to the medusae , and two individuals were found to have penetrated into the m e s o g l e a and were feeding upon the medusan t i ssue . This asso- ciation is considered one of chance contact.

Associations of several animals with jellyfishes have heen observed in *.he Chesapeake Bay. Small harvestf ish, Peprilus aIepidotas, arid but terf ish, Poronot~s triacanthus, lead a commensal and ectoparasi t ic existence with the se-r net t le , Chry- saora quinquecirrha (Mansueti , 1963: 40-80). Certain crustaceans are also known to associate with jellyfishes. The amphipod, Hyperia galba, is a widely d is t r ibu ted parasi te . f tile moon jel ly and tile p ink jellyfish, Cyanea capillala (Dahl, 1959:1749). Add i t imrd associati(ms of amphipods and scyphozoan medusac have been recent ly re- ported by Bowman et al. (1963). Young blue crabs, Callinectes sapidus, h' tve f requent ly been observed clinging to the umbrel las of sea net t le , Chrysaora ((uinquecirrha, but have never been observed to feed upon them.

A large group of moon jellies was seen in the Chesapeake Bay near the mouth of the Pa tuxen t l?dver on 26 August 1963. The water dep th in th is area was approximate ly 100 feet, bu t the medusae were not observed at depths greater than 10 feet. Small spider crabs, Libinia dubia, were found living ~)n and within many of the medusae in this group. They were also foun(t on "rod within scat- tered moon jellies in the same area on the 2nd and again on the 9th of September 1963. Concur- reut ly , numerous young harvcstf ish were observed feeding upon tile medusae.

Eleven specimens of L. dubia were collected frmn 10 jellyfish. The carapace hmgths of these crabs ranged from 10 to 25 mm, with an average of 15 ram. The length of the carapace of a large male crab, by comparison, is over 100 ,nm ( I la thbun , 1925). Seven of tile spider crabs collected were clinging to the vent ra l surface ~,f the subumbrel la , two were clinging to the manubr ium between the oral arms, and two were in tile mcsoglca of the jellyfish (see Fig. 1).

The medusae were apparent ly in good condi- t ion, except for the holes t.hat the crabs h:td cut in them. Several crabs appeared to be feeding upon a l iving medusa when la ter observed in the labora- tory. The er:tbs pulled f ragments of t issue from

Cont r ibu t ion No. 248, Na tura l Ilesourees Ins t i t u t e (if the Univers i ty of Mary land , Chesa- peake Bi(/h)gieal L'~borat~)ry, S(~lomons, Mary- hmd.

OBSERVATIONS ON TIIE MOON JELLY AND THE SPIDER CRAB 195

Fig. 1 . - -Diagrammat ic cross section of a medusae of Aurelia aurita showing typical mesogleal excavat ion by small Libinia dubia.

the exumbrel la with thei r ehelipeds and t rans- ferred them to the i r mouth parts . None of the crabs showed any ill effect from eat ing or l iving in the medusa.

The occurrence of spider crabs in and upon A. aurita apparen t ly depends upon chance contac t of the jellyfish with the shallow bo t tom or wi th aquat ic p lants where this non-swimming crab normally occurs. The presence of floating aquat ic grasses in the area where the jellyfish were found suggests t h a t th is had happened. The hab i t s of these two animals, one planktonic and the o ther benthonic , are so different t h a t an associat ion in which one of them is dependent upon the o ther is considered to be unlikely.

I t hank Mr. David G. Cargo for his helpful advice and for reviewing th is manuscr ip t , and Mrs. A. J. Mansuet i for drawing the i l lustrat ion.

L I T E R A T U R E C I T E D

BOWMAN, T. E., C. ]). ME~'ERS, AND S. D. IIIcKS. 1963. Notes on the associat ions between hypcri id amphipods and medusae in Chesapeake and Nar raganse t t Bays and the Niant ic River. Ches. Sci. ~(8):I~I-6.

DAHL, E. 1959. The amphipod, Hyperia galba, an ect()parasite of the jellyfish, Cyanea capil- lain. Nature 183:17~9.

MANS(;ETL R. J. 1963. Symbiotic behavior be- tween small fishes and jellyfishes, with new da ta on t h a t t)etween the Stromateid, Peprilus alepidotus, and the Scyl)homedusa, Chrysaora quinqueeirrha. Copeia 1963(I):40-80.

MINER, R. W. 1950. Field Book of Se'~shore Life. G. P. Putnam's Sons, N. Y. X V q- 888.

RATHBUN, J. Z. 19~5. The spider crabs of America. U. S. Nat. Mus. Bull. 129. Washington, p. 318.

])~ICHARD JACttOWSKI

Chesapeake Biological Laboratory Solomons, Maryland