The Experts below are selected from a list of 270 Experts worldwide ranked by ideXlab platform

Tahei Tahara - One of the best experts on this subject based on the ideXlab platform.

Jennifer E Purcell - One of the best experts on this subject based on the ideXlab platform.

  • Single-target echo detections of jellyfish
    ICES Journal of Marine Science, 2004
    Co-Authors: Andrew S. Brierley, Conrad Sparks, Helen Boyer, Jennifer E Purcell, Bjørn Eric Axelsen, David C. Boyer, Christopher P. Lynam, Carol A Didcock, Mark J. Gibbons
    Abstract:

    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 (17-54 cm total umbrella diameter) and A. Aequorea (19-28 cm total umbrella diameter) were ensonified at 38 kHz using a portable echosounder. Mean TS values for individual medusae at this frequency ranged from −67.3 to −52.8 dB for C. hysoscella and from −65.4 to −50.1 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 >1800 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 = −60.0 dB, 38 kHz = −65.5 dB, 120 kHz = −68.0 dB, and 200 kHz = −70.5 dB. Aequorea Aequorea mean inner-umbrella diameter 6.5 cm, TS at 18 kHz = −66.0 dB, 38 kHz = −65.5 dB, 120 kHz = −68.0 dB, and 200 kHz = −73 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 acoustic-survey techniques to estimate jellyfish abundance.

  • predation on zooplankton by large jellyfish aurelia labiata cyanea capillata and Aequorea Aequorea in prince william sound alaska
    Marine Ecology Progress Series, 2003
    Co-Authors: Jennifer E Purcell
    Abstract:

    Large jellyfish are conspicuous members of many coastal plankton communities. They are potentially important as competitors for zooplankton prey with fish larvae and zooplanktivorous fish, as well as being predators of fish eggs and larvae. Nevertheless, few data exist on predation effects of large medusae on zooplankton in situ. Biovolumes and densities of Aurelia labiata, Cyanea capillata and Aequorea Aequorea medusae combined, measured in fishing seines, were generally low (<1 l per 1000 m 3 and <10 medusae 1000 m -3 ) at 24 to 44 stations during July in 1998 and 1999 in Prince William Sound (PWS), Alaska. Their diets contained mainly copepods, larvaceans and clado- cerans, and also a variety of meroplankton. Few fish eggs and larvae were eaten. Multiple regression analyses showed that the numbers of the main prey taxa in the gut contents usually were significantly correlated with medusa diameter and prey density. Digestion rates for copepods and cladocerans at 14°C averaged 3 h for A. labiata, 2 h for C. capillata and 1.5 h for larvaceans by both predators. Calculations using the above data indicated that individual medusa consumed 100s to 1000s of prey daily. Because of high prey densities and low medusa densities, predation effects on small copepods were low (mean ≤ 0.3% of the standing stock d -1 ). Larvaceans experienced greater predation at an average of ≤ 8.3% of the standing stock d -1 . These predation effects were underestimated in 1998, because sampling did not include the numerous aggregations of A. labiata, and also in 1999, when small hydromedusae were abundant (mean 59 medusae m -3 ). During this study, predation by medusae probably did not reduce prey availability to Age 0 sandlance, herring and walleye pollock, with diets consisting primarily of small copepods; however, medusa predation may have affected larvacean availability to Age 0 pink salmon, which consume them extensively.

  • Predation on zooplankton by large jellyfish, Aurelia labiata, Cyanea capillata and Aequorea Aequorea, in Prince William Sound, Alaska
    Marine Ecology Progress Series, 2003
    Co-Authors: Jennifer E Purcell
    Abstract:

    Large jellyfish are conspicuous members of many coastal plankton communities. They are potentially important as competitors for zooplankton prey with fish larvae and zooplanktivorous fish, as well as being predators of fish eggs and larvae. Nevertheless, few data exist on predation effects of large medusae on zooplankton in situ. Biovolumes and densities of Aurelia labiata, Cyanea capillata and Aequorea Aequorea medusae combined, measured in fishing seines, were generally low (

  • prey selection and dietary overlap among zooplanktivorous jellyfish and juvenile fishes in prince william sound alaska
    Marine Ecology Progress Series, 2001
    Co-Authors: Jennifer E Purcell, Molly V Sturdevant
    Abstract:

    The potential for competition for food among zooplanktivorous species of gelatinous zooplankton and fishes has been the subject of much speculation. Here, we evaluate the dietary over- laps among 2 scyphomedusan species, Aurelia labiata and Cyanea capillata, 1 ctenophore species, Pleurobrachia bachei, 1 hydromedusan species, Aequorea Aequorea var. albida, and juveniles (Age-0) of 4 forage fish species, walleye pollock Theragra chalcogramma, Pacific sandlance Ammodytes hexapterus, Pacific herring Clupea pallasi, and pink salmon Oncorhynchus gorbuscha. Zooplankton samples collected in July-August 1995 to 1998 showed great similarity among years (86 to 96%), which allowed valid dietary comparisons between pelagic coelenterates and fishes col- lected in different years during that period. The predators fell into 2 groups, one that ate primarily crustacean prey (A. labiata, P. bachei, juvenile walleye pollock, sandlance, and herring), and another that ate mostly larvaceans (C. capillata, A. Aequorea, and juvenile pink salmon). Species within the first group showed significant positive selection for crustacean prey and significant negative selec- tion for larvaceans. The opposite trends were observed in the second group. Dietary overlaps were higher among crustacean-eating species (63 ± 13%) and larvacean-eating species (66 ± 10%) than when comparing crustacean- with larvacean-eating species (24 ± 14%). Dietary overlaps among pelagic coelenterate species (41 ± 21%) and among fish species (42 ± 25%) were similar, while over- laps between pelagic coelenterate and fish species averaged 50 ± 21%. These pelagic coelenterate and fish species were collected together in 45 purse seine sets taken in Prince William Sound in July 1999. We conclude that the diets of pelagic coelenterate and forage fish species overlap substantially, and that the species co-occur spatially and temporally. Therefore, the potential for competition for prey exists for these zooplanktivores in Prince William Sound.

Tomotsumi Fujisawa - One of the best experts on this subject based on the ideXlab platform.

Hikaru Kuramochi - One of the best experts on this subject based on the ideXlab platform.

Haruko Hosoi - One of the best experts on this subject based on the ideXlab platform.