Effects of predation by the scyphomedusan Chrysaora quinquecirrha on zooplankton populations in Chesapeake Bay, USA

Abstract

The diet, digestion times, and d e n s~t~e s of Chrysaora quinquecirrha medusae, and densities of their prey were quantified in order to evaluate the importance of this conspicuous scyphomedusan on zooplankton populations in Chesapeake Bay, USA, and its tributaries. Medusae consumed a variety of zooplankton prey, but copepods, mostly Acartia tonsa, averaged 55 % of the prey items in gut contents collected during July and August from 2 tr~butaries of Chesapeake Bay in 1987 and 1988, a n d 7 1 % of the prey in gut contents from the main bay in [1987][1988][1989][1990]. Medusae showed positive selection for copepods, but negative selection for copepod naupli~. Digestion tlmes of copepods by medusae averaged 3.5 h. A n~ultiple regression equatlon related digest~on times to temperature and the number of ingested copepods, but not to medusa slze. Predation rates (numbers of copepods consumed medusa-' d-') increased with increasing prey density, medusa diameter, and temperature These results p r o v~d e a means of predicting C. quinquecirrha feeding in sjtu. Greater numbers of prey in medusae at n~ghttime than during the day probably were due to greater prey densit~es at night. Daily predation effects (percentage of the copepod standing stock consumed d.') were calculated from feeding rates, and the d e n s~t~e s of medusae and copepods. Medusa densities (peaks of 11 to 16 m-3) and predation effects (peaks of 42 to 94 % d-l of the copepods consumed) were much greater in the 2 tributar~es than at a nearshore station in the bay (peaks of 2 medusae m-3 and 3 % d-' of the copepods consumed). Ingestion of zooplankton provided a n average of 145 % of the nitrogen needed to balance excretion in medusae <45 mm In diameter, but supplied only 65 % of the n~trogen needs of medusae > 4 5 mm. Other prey, including ctenophores, fish eggs and larvae, and large polychaete worms are additional contributions to the diet. Predation by C. quinquecirrha medusae may control copepod populations in some tributaries of Chesapeake Bay, as suggested by high predat~on effects and declining copepod populations throughout the summer.

Predation by the scyphomedusan Chrysaora quinquecirrha on Mnemiopsis leidyi ctenophores

“…Densities of Chrysaora quinquecirrha and Mnemiopsis leidyi were measured with a 1 m diameter, 1.6 mm mesh net with flowmeter towed at 1 m depth in Broad Creek (bottom depth < 4 m), from 0 to 4 m at Stn 5 (bottom depth 5 m), and from 0 to 11 m at Stn 4 (bottom depth 20 m, pycno-and oxycline at 11 m). Medusae and ctenophores were counted from samples preserved in 5 % formalin, and the preserved sizes converted to live diameter (medusae) and volume (ctenophores), as in Purcell (1992 and1988, respectively).…”

“…Recent studies to quantify predation by Chrysaora quinquecirrha on zooplankton have emphasized gut content analyses (Purcell 1992, Purcell e t al. 1994a, yet virtually no ctenophore remains were found in the gut contents.…”

Modeling the seasonal autochthonous sources of dissolved organic carbon and nitrogen in the upper Chesapeake Bay

“…Mortality rates for phytoplankton were increased in the spring and fall to account for sinking and sedimentation following the spring bloom (Malone et al, 1996(Malone et al, , 1988 and mixing of the water column associated with the fall overturn (Boicourt, 1992). Mortality rates for zooplankton were increased during the summer and early fall to reflect high seasonal predation by ctenophores (Stoecker et al, 1987) and the jellyfish Chrysaora quinquecirrah (Baird and Ulanowicz, 1989;Purcell, 1992). Atlantic menhaden, bay anchovies, other filter-feeding fish, and larval fish may also exert high predation pressure on both phytoplankton (mostly menhaden predation) and zooplankton at different times of the year (Baird and Ulanowicz, 1989;Hartman et al, 2004;Lewis and Peters, 1994).…”

Development, biological regulation, and fate of ctenophore blooms in the York River estuary, Chesapeake Bay

“…Chrysaora ingestion rates on copepods (mostly Acartia) were calculated using Eq. (6) (copepods medusa -1 d -1, Table 1) (Purcell 1992), and converted to copepod C ingested (CI CqAc , mg copepod C medusa) by multiplying by 6 µg C copepod -1 (Roman 1977). Chrysaora population C ingestion rates on copepods…”