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Dec. 2005, M.Ohman

Best Practices" for Zooplankton Sampling Within PaCOOS

The choice of zooplankton sampling gear, deployment methods, and sample processing methods are all closely linked to the scientific objectives of the research program. Here we assume that the following are some of the key objectives within PaCOOS pertaining to the holozooplankton. These objectives are assumed to apply to each subregion within PaCOOS.

OBJECTIVES:

  1. To assess spatial, seasonal, and interannual variations in total mesozooplankton biomass;
  2. To assess spatial, seasonal, and interannual variations in total euphausiid biomass;
  3. To assess spatial, seasonal, and interannual variations in abundance of "sentinel zooplankton species," defined as those species which are recognized to signify underlying changes in the physical and chemical ocean environment; at present these include several species (and species groups) of planktonic copepods, euphausiids, salps, and doliolids
  4. To assess California Current-wide coherence and alongshore continuity of regionally measured properties of the zooplankton assemblage

For each of these specific objectives we recommend the following types of approach as the "Best Practices" matched to the corresponding objective:

SAMPLING GEAR

Objectives 1. & 3,4. Vertically hauled 202-mm mesh nets, minimum diameter 0.5-m, dyed black or dark blue; sampling to 200 m depth, bottom-depth permitting; otherwise to within 10 m of the bottom
Acceptable alternatives: 0.75 - 1.0 m diameter nets

Objectives 1., 2A), 3, 4. Obliquely hauled bongo frame, 0.71-m diameter, with one 333-mm mesh mesh and one 505-mm mesh, dyed black or dark blue; sampling to 200 m depth as above - LOPC (Laser Optical Particle Counter) mounted in mouth of 333 net for vertical distribution information
Acceptable alternatives: 0.61-m diameter bongo Omitting LOPC if cost prohibitive

Objectives 2B) & 4. Multi-frequency hydroacoustic system for acoustic backscatter, principally to assess fine-scale vertical and horizontal spatial distribution of euphausiid-sized organisms (number and specific frequencies of transducers to be determined and standardized; essential that transducers be regularly calibrated)
Acceptable alternatives: unclear; needs to be reviewed by competent bioacousticians

SAMPLE PROCESSING METHODS

Objectives 1. & 4. Size-based reconstruction of biomass from microscopic enumerations of taxa within size categories; conversion to carbon biomass using appropriate Length-Carbon regressions
Acceptable alternatives: Probably optical scanning (e.g., Zooscan) measures of size and abundance; remains to be validated

Objectives 2A. & 4. Enumerations of total euphausiid abundance by microscopy and size-based reconstruction of biomass from Length-Carbon regressions
Acceptable alternatives: Possibly optical scanning (e.g., Zooscan) measures of size and abundance; remains to be validated

Objectives 2B. & 4. Standardized processing techniques for hydroacoustic surveys agreed to by experts in krill and fisheries bioacoustics Acceptable alternatives: None

Objectives 3. & 4. Microscopic identification of particular taxa with known merit as sentinel species
Acceptable alternatives: None