Table of Contents

• Coverage
• Dataset Description
  • Methods & Sampling
  • Data Processing Description
  • BCO-DMO Processing Description
• Data Files
• Parameters
• Instruments
• Deployments
• Project Information
• Funding

This study was carried out within the temperate to subtropical Southern California Bight and surrounding coastal areas between 32° and 35° N, and 117° and 120° W. Specific locations sampled fall within the CalCOFI and CCE-LTER programs' quarterly survey grid from lines 76.7 to 93.4 and stations 26 to 55.

Sampling took place during February 2021 and April 2021 on R/V Bob and Betty Beyster cruises BBB2102 and BBB2104 and on R/V Shearwater cruise SW2104. Each cruise was composed of one or more day trips using one of the two research vessels. The two-three letters in the cruise ID number indicate the research vessel and the four digits indicate YYMM.

Zooplankton were collected using a 71-centimeter (cm) diameter dual Bongo plankton net system equipped with a small CTD to record depth and physical variables during horizontal net tows at a ship speed of 1.5-2.5 knots down to 30-33 meters (m) depth. The Bongo was equipped with two nets, one with a 53-micrometer (µm) and the other with a 202 µm mesh size, and a flowmeter mounted in the center of each of the two nets.

Once the nets were retrieved, they were gently rinsed with saltwater. The content of the cod-ends was then concentrated onto a sieve of 50 µm mesh size, transferred into glass jars, and preserved in buffered 3.7% formaldehyde. The 53 µm samples were split using a 10-milliliter (mL) Hensen Stempel Pipette and sorted under a dissecting microscope. Zooplankton were identified based on morphological characteristics and measured using an eyepiece micrometer. The 202 µm samples were size fractioned into two replicate small (202 - 999 µm), one large (1000 - 4999 µm), and one extra large (> 5000 µm) size fractions, split into appropriately sized subsamples using a Folsom splitter, and analyzed by ZooScan. The organism's images were then identified manually and sized using ImageJ. In most identified taxonomic groups, up to 30 individuals were size-measured and a target of 50 individuals were counted per sample. Length measurements represent the total body length for all organisms except copepodites where prosome length was measured instead. Width measurements were taken at the widest part of the body.

Known problems or issues: Unicellular organisms such as dinoflagellates, diatoms, and tintinnids are underrepresented in the samples due to their small size and fragile structure.

The flowmeter was calibrated between cruises to accurately calculate the volume of water strained by the 53 and 202 µm nets and the abundance of zooplankton.

- Imported original file "Zooplankton abundance data from Bongo plankton net tows.xlsx" into the BCO-DMO system.
- Marked 'nd' as a missing data value (missing data are blank/empty in the final CSV file).
- Created local and UTC date/time fields in ISO 8601 format; removed original separate date and time columns.
- Rounded numeric fields.
- Saved the final file as "915900_v1_zooplankton_abund_and_size.csv".

NSF Award Abstract:
Like many species of small pelagic marine fish, recruitment and productivity of Northern Anchovy fluctuate by orders of magnitude among years. When abundant, the anchovy support a wide range of marine species, including marine mammals, seabirds and a diverse group of marine fishes. Anchovy, which previously thrived during periods of cool-water temperatures and strong coastal upwelling, are currently booming with abundances far in excess of any historical record, even though the California Current Ecosystem is experiencing an unprecedented marine heat wave. This unexpected occurrence challenges the most basic understanding of the mechanisms driving population dynamics in the species. This project is investigating the effects of trophic relationships on population productivity by capitalizing on the immediate research opportunity afforded by the novel, yet ephemeral, state of a local marine heat wave. Findings from the work are being used to develop a mechanistic model of coastal pelagic fish population dynamics generally, and anchovy dynamics in particular. Funded field and lab work are supporting opportunities for undergraduate training and research, and are generating open-access data that serve the research and teaching/training communities into the future.

This RAPID project augments the scheduled Fall research cruises jointly run by the California Cooperative Oceanic Fisheries Investigation and the California Current Ecosystem Long-Term Ecological Research programs. Together, these programs conduct regional oceanographic surveys that include anchovy spawning grounds and larval nursery areas. The RAPID-augmented sampling is designed to test the emerging hypothesis that anchovy populations are trophodynamically mediated at the larval stage, whereby high recruitment results from increased trophic transfer efficiency from the base of the food web. Larval diets and prey selection analyses are being paired with amino acid compound-specific isotope analysis (δ15N) of the larvae and prey field to generate detailed information on larval trophic ecology. Larval diets and plankton community structure are being related to available data on upwelling and productivity to assess environmental and biological drivers to trophic transfer efficiency. Collectively, these analyses are revealing how food chain length is regulated at the larval level through prey selection, at the prey level through community composition, and at the base of the food chain via coastal upwelling and primary production. Furthermore, this project is establishing whether the current trophic level of anchovy larvae is equal to that of historic population booms and if this is the result of favorable feeding conditions throughout their habitat. Findings from the study are generating a mechanistic understanding of the trophic underpinnings of small pelagic fish population productivity in coastal upwelling systems.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

Location Description:
This study is carried out within the temperate to subtropical Southern California Bight and surrounding coastal areas between 32° and 35° N, and 117° and 120° W. Specific locations sampled fall within the CalCOFI and CCE-LTER programs quarterly survey grid from lines 76.7 to 93.4 and stations 26 to 55.

Project Affiliations:
California Current Ecosystem Long-term Ecological Research Program (CCE-LTER)
California Cooperative Oceanic Fisheries Investigations (CalCOFI)