The seasonal abundance and vertical distribution of rocketship siphonophores over a seven-year period, including the impact of the 1997--1999 ENSO, and their metabolic demand and prey requirements

The goal of this research was to study the role of rocketship siphonophores as predators in the mesopelagic waters of Monterey Bay. The first project assessed the abundance and vertical distribution patterns of these siphonophores over three years. The second studied their metabolic requirements and estimated their potential impact on their prey population. The third project assessed the impact of El Niño and La Niña on their abundance and vertical distribution.; The research was conducted using the Monterey Bay Aquarium Research Institute's Remotely Operated Vehicle Ventana, an ISE Hysub 40 that has been outfitted for scientific research. Quantitative, horizontal transects were conducted, and recorded on video, at 100 m depth intervals from 50 m to 1000 m over seven years (1993–1999). Rocketship calycophoran abundance was annotated from the video post-dive and counts were normalized to the volume of water transected. Oxygen consumption rates for the two numerically dominant species of rocketships (Lensia conoidea and Chuniphyes multidentata) were determined using the micro-Winkler method.; The vertical distribution of the study animals changed seasonally, coupled to the onset and cessation of upwelling in the bay. Both species had oxygen consumption rates within the range previously reported for other pelagic cnidarians, and Lensia conoidea had a significantly greater mass-specific oxygen consumption rate than C. multidentata. Minimum daily copepod requirements were estimated from oxygen consumption rates, yielding a demand of 3.5 and 1.6 prey siphonophore1 day1 for L. conoidea and C. multidentata respectively. The 1997–98 El Niño did not effect the overall abundance of these siphonophores, although it did significantly impact their seasonal abundance and distribution pattern. The 1998–99 La Niña period had a significantly higher abundance of rocketship siphonophores than either the previous El Niño or normal years.