Shannon Point Marine Center

The native habitats of the ctenophore, Mnemiopsis, are temperate to subtropical estuaries along the Atlantic coast of North and South America, where it is found in an extremely wide range of environmental conditions (winter low and summer high temperatures of 2 and 32 • C, respectively, and salinities of <2-38). In the early 1980s, it was accidentally introduced to the Black Sea, where it flourished and expanded into the Azov, Marmara, Mediterranean and Caspian Seas. We compile data showing that Mnemiopsis has high potentials of growth, reproduction and feeding that enable this species to be a predominant zooplanktivore in a wide variety of habitats; review the population distributions and dynamics of Mnemiopsis in U.S. waters and in the Black Sea region; and examine the effects of temperature and salinity, zooplankton availability and predator abundance on Mnemiopsis population size in both regions, and the effects of Mnemiopsis on zooplankton, ichthyoplankton and fish populations, focusing on Chesapeake Bay and the Black Sea. In both regions, Mnemiopsis populations are restricted by low winter tem-

Analysis of the gastrozooids (stomachs) of 646 colonies of tl-11: cystoncct siphonophore Rhizophysa eysenhardti collected by hand in the Gulf of Californi i showed that these specimens had fed only on fish larvae. Siphonophore density during blcom conditions averaged 0.038 + 0.004 individuals * rnp3 in an open-water channel, and 0.91 +: 0.55 in a shallow cove. Siphonophore feeding was greater in the cove where fish larval: were more abundant than in the channel, and during dawn and dusk in the cove when pre J were more available. Gastrozooid analysis and behavioral experiments showed that sipho.rophores fed only in the light. Digestion of fish larvae required 3-7 h, increasing with prey size. Food was assimilated by the siphonophores with 72% efficiency. Each siphonophore was estimated to consume an average of 8.8 fish larvae during a day in the cove. The heavy predation on fish larvae by R. eysenhardti suggests that both fish mortality and siphonophore population growth may be strongly affected.

Gelatinous zooplankton are conspicuous p'redators during summer in Chcsapeakc Bay. Inverse correlations of the abundances of gelatinous predators and their zooplankton prey have led to speculation that these predators may control their prey populations. We measured predation on copepods by hydromedusae, scyphomedusae, and ctcnophorcs in the mesohalinc region of the bay in May-October 1987 and 1988. WC simultaneously asscsscd the possibility of food limitation in Acartia tonsa by measuring its phyto-and microzooplankton food resources and rates of adult female egg production. WC conclude that A. tonsa populations arc not limited by gelatinous zooplankton predation and rarely by food. Other predators (c.g. fish, adult copepods) and environmental limitations (e.g. temperature, hypoxic bottom waters) probably affect A. tonsa abundances in this region.

of the Patuxent River, a tributary of Chesapeake Bay. We synthesize existing and newly collected data to examine spatial and temporal variation in bottom DO, the prevalence of hypoxia-induced mortality of fishes, the tolerance of Patuxent River biota to low DO, and the influence of bottom DO on the vertical distributions and spatial overlap of larval fish and fish eggs with their gelatinous predators and zooplankton prey. We use this information, as well as output from watershed-quality and water-quality models, to configure a spatially-explicit individual-based model to predict how changing land use within the Patuxent watershed may affect survival of early life stages of summer breeding fishes through its effect on DO. Bottom waters in much of the mesohaline Patuxent River are below 50% DO saturation during summer. The system is characterized by high spatial and temporal variation in DO concentrations, and the current severity and extent of hypoxia are sufficient to alter distributions of organisms and trophic interactions in the river. Gelatinous zooplankton are among the most tolerant species of hypoxia, while several of the ecologically and economically important finfish are among the most sensitive. This variation in DO tolerances may make the Patuxent River, and similar estuaries, particularly susceptible to hypoxia-induced alterations in food web dynamics. Model simulations consistently predict high mortality of planktonic bay anchovy eggs (Anchoa mitchilli) under current DO, and increasing survival of fish eggs with increasing DO. Changes in land use that reduce nutrient loadings may either increase or decrease predation mortality of larval fish depending on the baseline DO conditions at any point in space and time. A precautionary approach towards fisheries and ecosystem management would recommend reducing nutrients to levels at which low oxygen effects on estuarine habitat are reduced and, where possible, eliminated.

We investigated predation on bivalve veligers by the scyphozoan Chrysaora quinquecirrha and the ctenophore Mnemiopsis leidyi. We found that the medusa stage of C. quinquecirrha captures, but does not digest, veliger larvae: 99% of oyster veligers (Crassostrea virginica) caught by medusae were egested alive within 7 h of capture, and 98% survived for 24 h after egestion; 98% of oyster, mussel (Mytilus edulis), and clam (Mulinia lateralis) veligers placed on the oral arms of medusae were

Acoustic target-strength (TS) measurements are presented for tethered and free-swimming individual Chrysaora hysoscella (Scyphozoa) and Aequorea aequorea (Hydrozoa) medusae in Namibian waters. Tethered individual C. hysoscella (17e54 cm total umbrella diameter) and A. aequorea (19e28 cm total umbrella diameter) were ensonified at 38 kHz using a portable echosounder. Mean TS values for individual medusae at this frequency ranged from ÿ67.3 to ÿ52.8 dB for C. hysoscella and from ÿ65.4 to ÿ50.1 dB for A. aequorea. There was a positive relationship between medusa diameter and TS for both species. TS of individual medusae varied cyclically over time by about 15 dB, probably because of the periodic contraction of the medusae whilst swimming. C. hysoscella was parasitized by hyperid amphipods (maximum infestation O1800 parasites per medusa). A fluid-cylinder scattering model was used to determine the expected backscatter from the parasites, and it suggested that even at the highest observed level of infestation the jellyfish itself remained the major contributor to total backscatter at 38 kHz. Single-target echoes from targets identified by trawling as medusae were obtained from vessel-mounted echosounders at 18, 38, 120, and 200 kHz. Triangulation between echosounder beams to identify targets detected simultaneously at all four frequencies increased confidence that echoes were in fact from single targets. The 38-kHz TS values from free-swimming medusae corresponded with values obtained from tethered animals at the same frequency, providing strong evidence that the TS estimates were robust. TS values at all four frequencies (Chrysaora hysoscella mean umbrella diameter 41 cm, TS at 18 kHz ¼ ÿ60:0 dB, 38 kHz ¼ ÿ65:5 dB, 120 kHz ¼ ÿ68:0 dB, and 200 kHz ¼ ÿ70:5 dB. Aequorea aequorea mean inner-umbrella diameter 6.5 cm, TS at 18 kHz ¼ ÿ66:0 dB, 38 kHz ¼ ÿ66:5 dB, 120 kHz ¼ ÿ71:5 dB, and 200 kHz ¼ ÿ73 dB) were consistent with previously published data. Given these robust TS estimates, the possibility may now exist for multi-frequency identification and evaluation of these jellyfish species in some circumstances, and for the use of acousticsurvey techniques to estimate jellyfish abundance.

Science has rapidly expanded its frontiers with new technologies in the 20th Century. Oceanography now is studied routinely by satellite. Predictive models are on global scales. At the same time, blooms of jellyfish and ctenophores have become problematic, especially after 1980. Although we have learned a great deal about gelatinous zooplankton ecology in the 20th Century on local scales, we generally have not scaledup to estimate the extent, the causes, or effects of large blooms. In this age of global science, research on gelatinous zooplankton needs to utilize large-scale approaches and predictive equations. Some current techniques enable jellyfish populations (aerial, towed cameras), feeding (metabolic rates, stable isotopes), and dynamics (predictive modeling) to be studied over large spatial and temporal scales. I use examples of scyphomedusae (Aurelia spp., Cyanea capillata, Chrysaora quinquecirrha) and Mnemiopsis leidyi ctenophores, for which considerable data exist, to explore expanding from local to global scales of jellyfish trophic ecology. Regression analyses showed

Populations of Cyclosalpa bakeri occurred during late summer at station P in the subarctic Pacific in 1987 and 1988. Salps were collected by divers for measurement of rates of feeding, metabolism, growth, and reproduction. These parameters were used to create the first complete carbon and nitrogen budget for a pelagic tunicatc. Egestion, ingestion, and filtration rates were determined from chlorophyll and pheopigment in the fecal material. Counts of diatoms in the guts indicated that pigment-based rates underestimated filtration by -50%. Salps ranging in size from 10 to 100 mm filtered from 0.05 to 10.0 liters h I. Respiration rate was 0.22 pmol 0, (mg C)-I h-l, and NH, + excretion was 0.034 pmol (mg C) I h-l. Growth was measured on salps maintained in aquaria. A model growth curve based on size-specific rates of increase in length gave maximum growth rates of 2% h-l and predicted a generation time of 24 d. Solitary generation salps would produce about 170 aggregate generation offspring during their lifetime, and each aggregate produces one solitary. Budgets for a 50-mm solitary salp indicate that daily rations of C and N were 6 1 and 54% of body C and N. Assimilation efficiency was 61% for C and 71% for N. Rates of filtration, metabolism, and growth were lower than those of some other salp species, but comparable, on a weight basis, to those of many other herbivores.

A steep increase in jellyfish biomass, primarily Chrysaora melanaster, over the eastern Bering Sea shelf was documented throughout the 1990s. Their biomass peaked in summer 2000 and then declined precipitously, stabilizing at a moderate level after 2001. The onsets of the outburst and decline coincided with transitions between climatic regimes. Specifically, 1989 marked the beginning of a period of moderate temperatures in the eastern Bering Sea, after the warm conditions of the late 1970s through the 1980s. Very warm conditions came to the eastern Bering after 2000, as evidenced by decreased ice cover in winter and increased total heat content and surface water temperatures in summer. We examined the relationships between jellyfish biomass and temperature, ice cover, atmospheric variables, current patterns, zooplankton biomass, and associated fish biomass in two regions of the Middle Shelf Domain (SE and NW) by use of Generalized Additive Models (GAM). We found density-dependent interactions within and between jellyfish biomass in the two regions related to the flow regime, and demonstrated a linkage between biophysical indices and jellyfish biomass. In particular, ice cover (SE and NW), sea-surface temperature in spring (SE) and summer (NW), and wind mixing (SE) all influenced jellyfish biomass. In addition, the importance of juvenile pollock biomass (SE) and zooplankton biomass (NW) suggest that jellyfish biomass was sensitive to the availability of prey. Since most climate models suggest continued warming is likely in the Bering Sea, the jellyfish populations may remain at moderate levels there but will likely shift northward into the Arctic Ocean.

Hypoxic conditions are common in many coastal environments such as Chesapeake Bay. While medusae appear to be quite tolerant of low dissolved oxygen (DO) concentrations, the effects of hypoxia on the benthic polyp stages are unknown. Chrysaora quinquecirrha (DeSor) polyps, and were subjected to 5 DO treatments (air-saturated [control], 3.5, 2.5, 1.5 and 0.5 mg l −1 ) in the laboratory. Polyp survival and development were documented over 24 d. Virtually no mortality occurred in any treatment during the first 5 d. Total polyp mortality after 24 d was 59.3% at the lowest DO concentration, whereas <3% mortality was observed in the air-saturated treatment. Formation of stolons and strobilae occurred in all treatments, however, the proportions of polyps undergoing stolonation and strobilation were significantly greater in all DO concentrations above 0.5 mg l −1 . Polyp encystment was not observed in any treatment over the course of the 24 d experiment. These results indicate that polyps can survive and asexually propagate even during prolonged exposure to hypoxic conditions.