Resolution of fine biological structure including small narcomedusae across a front in the Southern California Bight

• Published in: Journal of Geophysical Research: Oceans Vol. 117; no. C4
• Main Authors: McClatchie, Sam, Cowen, Robert, Nieto, Karen, Greer, Adam, Luo, Jessica Y., Guigand, Cedric, Demer, David, Griffith, David, Rudnick, Daniel
• Format: Journal Article
• Language: English
• Published: Washington, DC Blackwell Publishing Ltd 01.04.2012; American Geophysical Union
• Subjects: Acoustics; Biological oceanography; Chemical oceanography; Cladocera; Earth sciences; Earth, ocean, space; Exact sciences and technology; Fish eggs; Fluorescence; fronts and jets; Geophysics; ichthyoplankton; Instrumentation; Marine; Narcomedusae; Oceanography; Physical oceanography; Predators; Sardinops; Scomber; Southern California Bight; zooplankton; Southern California; U. S. Channel Islands; California; San Nicolas Island; United States; INE, USA, California, Southern California Bight; INE, USA, California, San Nicolas I; eggs; predators; salinity; Chordata; density; Surface layer; fine-grained materials; concentration; samplers; Spray; North America; in situ; Frontal zone; Temperature gradient; offshore; Vertebrata; markets; fluorescence; Pisces; fish; temperature; oxygen; color imagery
• ISSN: 0148-0227; 2169-9275; 2156-2202; 2169-9291
• DOI: 10.1029/2011JC007565

We sampled a front detected by SST gradient, ocean color imagery, and a Spray glider south of San Nicolas Island in the Southern California Bight between 14 and 18 October 2010. We sampled the front with an unusually extensive array of instrumentation, including the Continuous Underway Fish Egg Sampler (CUFES), the undulating In Situ Ichthyoplankton Imaging System (ISIIS) (fitted with temperature, salinity, oxygen, and fluorescence sensors), multifrequency acoustics, a surface pelagic trawl, a bongo net, and a neuston net. We found higher fluorescence and greater cladoceran, decapod, and euphausiid densities in the front, indicating increased primary and secondary production. Mesopelagic fish were most abundant in oceanic waters to the west of the front, market squid were abundant in the front associated with higher krill and decapod densities, and jack mackerel were most common in the front and on the shoreward side of the front. Egg densities peaked to either side of the front, consistent with both offshore (for oceanic squid and mesopelagic fish) and shelf origins (for white croaker and California halibut). We discovered unusually high concentrations of predatory narcomedusae in the surface layer of the frontal zone. Potential ichthyoplankton predators were more abundant either in the front (decapods, euphausiids, and squid) or shoreward of the front (medusae, chaetognaths, and jack mackerel). For pelagic fish like sardine, which can thrive in less productive waters, the safest place to spawn would be offshore because there are fewer potential predators. Key Points We sampled a front with an extensive array of instrumentation at high resolution We discovered unusually high concentrations of predatory narcomedusae Fish spawning offshore of the frontal zone could avoid potential predators