, Volume 451, Issue 1–3, pp 121–129 | Cite as

The impact of El Niño events on populations of mesopelagic hydromedusae

  • Kevin A. Raskoff


For over 10 years, the midwater ecology group at MBARI has compiled video and accompanying physical data with the ROV Ventana operating in mesopelagic depths of Monterey Bay, CA in order to elucidate patterns in midwater ecology. Two El Niño events have occurred during this time period, in 1991–92 and in 1997–98. The oceanographic metric of spiciness combines temperature and salinity data into one sensitive measurement. Although temperature and salinity measurements alone revealed no clear patterns, clear signals of spiciness were observed that corresponded to water mass intrusions into the deep waters of the bay during the two El Niño events. During these events, some seldom-seen species were observed in high numbers in the midwater, while historically common species became rare. During non-El Niño years, the leptomedusa Mitrocoma cellularia(A. Agassiz, 1865) was common in the surface waters (0–50 m) of Monterey Bay, but it was not abundant at depth, while the trachymedusa Colobonema sericeum Vanhöffen, 1902 was found in relatively high numbers at mesopelagic depths. During the last two El Niño events, M. cellulariawas observed in higher numbers at mesopelagic depths, whereas C. sericeum was scarce. M. cellularia was found in a wider range of temperatures, salinities, and dissolved oxygen values than was C. sericeum. Transport and tolerance hypotheses are proposed to explain differences in the presence and numerical density of the medusae.

Cnidaria blooms Mitrocoma Colobonema jellyfish ROV 


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Copyright information

© Kluwer Academic Publishers 2001

Authors and Affiliations

  • Kevin A. Raskoff
    • 1
    • 2
  1. 1.Monterey Bay Aquarium Research InstituteMoss LandingU.S.A.
  2. 2.Department of BiologyUniversity of CaliforniaLos AngelesU.S.A.

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