Amphipoda, Hyperiidae) with Ctenophora Off North Carolina, U.S.A

NOTES AND NEWS

NOTES ON THE OCCURRENCE OF HYPEROCHE MEDUSARUM (KRØYER) (AMPHIPODA, HYPERIIDAE) WITH CTENOPHORA OFF NORTH CAROLINA, U.S.A.

LAWRENCE B. CAHOON, CRAIG R. TRONZO and JEFFREY C. HOWE Department of Biological Sciences, University of North Carolina at Wilmington, Wilmington, North Carolina 28403, U.S.A.

Hyperiid amphipods are frequently found associated with other members of the zooplankton, particularly gelatinous forms (Raymont, 1983). Reviews of these associations by Madin & Harbison (1977) and Harbison et al. (1977) in- dicate patterns of association specificity that suggest obligate parasitism or other highly coevolved relationships. The hyperiid amphipod Hyperoche medusarum (Kr0yer) has frequently been captured in association with gelatinous zooplankters, including the ctenophores Pleurobrachia bachei A. Agassiz, 1860 (cf. Brusca, 1970), P. pileus (0. F. Muller, 1776) (cf. Evans & Sheader, 1972) and the medusans Cyanea capillata (L., 1758) and Tima formosa A. Agassiz, 1862 (cf. Bowman et al., 1963). Raymont (1983) considers the relationship between H. medusarum and ctenophores a strong and common one. Evans & Sheader (1972) reported that H. medusarum rejected the medusans Cyanea capillata (L., 1758) and Aurelia aurita (L., 1758) as hosts in the presence of Pleurobrachia. The association with ctenophores appears to be parasitic; H. medusarum is reported to consume host tissue and to have little ability to capture or consume other prey types (Evans & Sheader, 1972). Raymont (1983) describes H. medusarum as a boreal-arctic species, occurring in colder waters in both hemispheres. Previously the southern-most reported occurrence of H. medusarum in the northwest Atlantic Ocean was in Chesapeake Bay (Bowman et al., 1963) in March and April, when water temperatures are beginning to rise. We report here the association of H. medusarum with two previously unreported host species, the ctenophores Beroe ovata Chamisso & Eisenhardt, 1821, and Mnemiopsis leidyi A. Agassiz, 1865. Furthermore, we report a signifi- cant southward extension of the known range of H. medusarum in the northwest Atlantic. 96

We observed and captured ctenophores with associated amphipods while diving at two sites (34° 10.5' N 77°44. 7' W; 34° 10.2' N 77°41.0' W) on August 16 and 20, 1984, respectively. The two sites are approximately 5 and 10 km east of Masonboro Inlet, North Carolina. Water temperatures were ca. 24°C. We believe the occurrence of H. medusarum in relatively warm water far south of Cape Hatteras (considered a biogeographical boundary to boreal species by Cerame-Vivas & Gray (1966)) in the summer to be the result of anomalous weather and circulation patterns. Prevailing summer winds along the North Carolina coast are southwesterlies. A northeasterly wind event from August 10 to August 12 (Wilmington Star-News) might have pushed mid- Atlantic Bight water south of Capes Hatteras and Lookout (Bumpus, 1955). Such anomalous circulation events have been invoked as explanations for southward displacement of other cool water species (Cerame-Vivas & Gray, 1966). The association of H. medusarum with previously unreported hosts is likely to be a consequence of the displacement of our amphipod specimens from their normal range. Although H. medusarum's preferred host, Pleurobrachia, occurs off North Carolina, it is less commonly encountered than Beroe and Mnemiopsis. We encountered no Pleurobrachia during our sampling dives. The apparent suitability of Beroe and Mnemiopsis as hosts, coupled with normal movement and migration activity by the amphipods and their hosts during transport into North Carolina waters easily account for our observations. Aside from a description of new hosts and an extended known range for H. medusarum, the value of our observations lies in reinforcing our awareness of the importance of circulation patterns in determining the identity of the neritic zooplankton of a given coastal area. It would be especially interesting to know how responsive zooplankton distribution patterns are to anomalous circulation events.

LITERATURE CITED

BOWMAN,T. E., C. D. MEYERS& S. D. HICKS, 1963. Notes on associations between hyperiid amphipods and medusae in Chesapeake and Narragansett Bays and the Niantic River. Chesapeake Sci., 4: 141-146. BRUSCA,G. J., 1970. Notes on the association between Hyperoche medusarum A. Agassiz (Amphipoda, Hyperiidea) and the ctenophore, Pleurobrachia bachei (Müller). Bull. Southern California Acad. Sci., 69: 179-181. BUMPUS,D. F., 1955. The circulation over the continental shelf south of Cape Hatteras. Trans. American Geophys. Union., 36: 601-611. CERAME-VIVAS,M. J. & I. E. GRAY, 1966. The distributional pattern of benthic invertebrates of the continental shelf off North Carolina. Ecology, 47: 260-270. EVANS,F. & M. SHEADER,1972. Host species of the hyperiid amphipod Hyperoche medusarum (Krøyer) in the North Sea. Crustaceana, (suppl.) 3: 275-276. HARBISON,G. R., D. C. BIGGS& L. P. MADIN, 1977. The associations of Amphipoda Hyperiidea with gelatinous zooplankton II. Associations with Cnidaria, Ctenophora and Radiolaria. Deep-Sea Res., 24: 465-488.