Summary

Database for mesozooplankton species identification, size distribution and carbon biomass from Southern and Central California. Samples collected with a 1-m diameter ring net or a 0.71-m diameter CalBOBL bongo net on selected CalCOFI cruises from 1951 to present. Analyses by the Ohman lab, SIO, together with the SIO Pelagic Invertebrates Collection.

Ohman lab mesozooplankton database (ZooDB) website: http://www.calcofi.org/field-program/field-net.html

Methods

1. Cruises

The mesozooplankton for this time series are enumerated from samples from CalCOFI springtime cruises for the period 1951-present (Lavaniegos and Ohman 2003, 2007; Ohman et al. 2009). In addition to the springtime (usually April, range: March-May) cruises, all cruises available for the years 1969 and 1984 were analyzed in order to document seasonal variability. Between 1951 and 1999 a fall cruise for each decade was analyzed for copepod species by Rebstock (2001).

The two study regions selected are off Southern California (CalCOFI lines 80 through 93, shore to station 70, inclusive) and Central California (CalCOFI lines 60 through 70, shore to station 90, inclusive).

All samples have been collected with a 1-m diameter net from 1951-1977 or, from Dec. 1977 to present, a 0.71-m diameter CalBOBL Net (bongo net; Ohman and Smith 1995). For details on net sampling protocols at sea, see: http://www.calcofi.org/cruises/264-art-nets.html.

2. Sample selection

For each cruise, only nighttime samples collected within the study region are analyzed, to minimize artifacts associated with daytime net avoidance and diel vertical migration. Night is defined as 1 h after sunset until 1 h before sunrise. Stations shallower than 140 m (1951-1968) or 200 m (1969-present) are omitted.

For most taxa, samples within a cruise are pooled for purposes of enumeration, except for 16 cruises in Southern California (SC) and 6 cruises in Central California (CC), where each sample was analyzed individually (= a nonpooled sample). Euphausiids are analyzed from all nighttime stations individually (nonpooled); see separate methods for the Brinton and Townsend Euphausiid Database.

3. Pooling of Samples

3.1. Removal of large organisms

First, large organisms (>25 mm total length) are removed from each selected nighttime sample. Each specimen is then identified and measured to the nearest mm. These organisms are not returned to the original sample but stored in individual jars by station number. A removal label listing the organisms removed by taxa is inserted in the original sample jar.

3.2. Subsampling for pooling

A volume of each sample corresponding to 50 m3 (vol. = 50*(volume of sample/ volume of H20)/(percent of tow/100)) of seawater filtered in situ is then removed from each sample using a Stempel pipette. All subsamples from a given cruise are combined into a single jar, thus becoming the pooled sample representative of the sampling domain for that cruise. A detailed removal label is then added to each original sample jar. The pooled sample is labeled with the contents of the sample.

4. Analysis

4.1. Pooled sample analysis

The pooled sample is then subsampled using a Stempel pipette and twenty to twenty-five percent of the pooled sample is enumerated by trained microscopists using a dissecting microscope, with occasional reference to taxonomic details under a compound microscope. All zooplankton are identified to the lowest taxonomic level practical for our expertise (over 400 taxa; usually species) and measured to the nearest half mm for size classes from 0.5 mm to 3 mm and to the nearest 1 mm for specimens larger than 3 mm (measurements are made as described in Isaacs et.al. 1969). Starting with the 2006 pooled sample the number of taxa was reduced to 161 and all other procedures remain the same.

4.2. Nonpooled sample analysis

For each nonpooled sample, 1/8 of the sample is analyzed. A Stempel pipette is used for subsampling and the sample is counted following the same protocol as the pooled sample.

5. Data entry

All data for the pooled and/or nonpooled samples are entered into Excel spreadsheets then uploaded to a MySql database at: https://oceaninformatics.ucsd.edu/zoodb/secure/login.php.

6. Carbon biomass

The carbon biomass of each taxon is reconstructed from the enumerations by size category within taxon, using body length-carbon regressions found in the electronic supplement to Lavaniegos and Ohman (2007).

7. References

  • Isaacs, J.D., A. Fleminger, and J.K. Miller. 1969. Distributional Atlas of zooplankton biomass in the California Current Region: Spring and Fall 1955-1959. CalCOFI Reports 10: 1-252.
  • Lavaniegos, B.E. and M.D. Ohman. 2003. Long term changes in pelagic tunicates of the California Current. Deep-Sea Research Part II 50: 2493-2518.
  • Lavaniegos, B.E. and M.D. Ohman. 2007. Coherence of long-term variations of zooplankton in two sectors of the California Current System. Progress in Oceanography 75: 42-69.
  • Ohman, M.D., B.E. Lavaniegos, and A.W. Townsend. 2009. Multi-decadal variations in calcareous holozooplankton in the California Current System: Thecosome pteropods, heteropods, and foraminifera. Geophysical Research Letters 36: L18608 [doi: 10.1029/2009GL039901].
  • Ohman, M.D. and P.E. Smith. 1995. A comparison of zooplankton sampling methods in the CalCOFI time series. CalCOFI Report 36: 153-158.
  • Rebstock, G.A. 2001. Long-term changes in the species composition of calanoid copepods off Southern California. Ph.D. thesis, University of California, San Diego.