Comparison of Common Plankton Counting Equipment
Selecting the proper plankton counting device depends on the size of the organisms, sample concentration, desired accuracy, and laboratory workflow. The Sedgwick-Rafter Cell, Bogorov Counting Chamber, Hemocytometer, Folsom Plankton Splitter, and Palmer-Maloney Counting Cell each serve different purposes in plankton analysis and are commonly used in limnology, oceanography, aquaculture, fisheries, and environmental monitoring.
| Equipment | Best For | Organism Size | Typical Sample |
|---|---|---|---|
| Glass Sedgwick-Rafter Cell | Routine phytoplankton & zooplankton | 20 µm–5 mm | Freshwater & marine |
| Plastic Sedgwick-Rafter Cell | Field and teaching applications | 20 µm–5 mm | Freshwater |
| Bogorov Counting Chamber | Large zooplankton | 0.3–20 mm | Concentrated net samples |
| Hemocytometer | Microalgae cultures | 2–100 µm | Laboratory cultures |
| Folsom Plankton Splitter | Sample splitting | Any size | Large plankton collections |
| Palmer-Maloney Cell | Small phytoplankton | 2–200 µm | Concentrated algae samples |
Glass Sedgwick-Rafter Counting Cell:
The glass Sedgwick-Rafter (S-R) cell is the standard chamber for quantitative plankton analysis. It has an internal volume of exactly 1 mL (50 × 20 × 1 mm) and is typically engraved with a grid to aid counting under a compound microscope.
Advantages
- Standardized 1 mL counting volume
- Excellent optical clarity
- Resistant to scratches and chemicals
- Highly accurate and repeatable
- Suitable for long-term laboratory use
Limitations
- Fragile
- More expensive than plastic versions
- Requires careful cleaning
Plastic Sedgwick-Rafter Cell:
Plastic S-R cells provide the same basic chamber dimensions but are manufactured from clear acrylic or other plastics.
Advantages
- Lightweight
- Break-resistant
- Lower cost
- Ideal for student laboratories
- Suitable for field work
Limitations
- Scratches more easily
- Optical quality generally lower than glass
- Shorter service life
Bogorov Counting Chamber:
The Bogorov chamber was developed specifically for counting larger zooplankton.
Its long, serpentine channel spreads organisms into a single layer, making identification and counting much faster than with a Sedgwick-Rafter cell.
Advantages
- Very fast counting
- Minimal organism overlap
- Excellent for copepods and cladocerans
- Easy sorting under a stereomicroscope
Limitations
- Not suitable for tiny phytoplankton
- Not intended for dense algal samples
Typical organisms
- Copepods
- Cladocerans
- Rotifers
- Fish larvae
- Insect larvae
Hemocytometer
Originally developed for blood cell counts, the hemocytometer has become one of the most common tools for counting cultured microalgae.
It contains an engraved precision grid with a chamber depth of 0.1 mm, allowing accurate calculation of cells per milliliter.
Advantages
- Extremely accurate
- Small sample volume
- Ideal for laboratory cultures
- Inexpensive
Limitations
- Small counting area
- Not ideal for mixed environmental samples
- Larger zooplankton cannot be counted
Typical applications
- Algal cultures
- Biofuel research
- Hatcheries
- Aquaculture
- Cell density determination
Folsom Plankton Splitter
The Folsom Plankton Splitter is not a counting chamber but an essential laboratory instrument for reducing large plankton samples to manageable sizes while maintaining representative proportions.
The circular chamber divides a thoroughly mixed sample into two equal halves. Repeated splitting can produce increasingly smaller subsamples (e.g., 1/2, 1/4, 1/8, 1/16), making large collections practical to analyze.
Advantages
- Produces statistically representative subsamples
- Reduces counting time dramatically
- Preserves organism proportions
- Standard equipment for marine plankton laboratories
Limitations
- Requires careful mixing before splitting
- Does not count organisms directly
- Less suitable for very small sample volumes
Typical applications
- Marine plankton surveys
- Oceanographic research
- Fisheries assessments
- Large zooplankton collections
- Long-term monitoring programs
Palmer-Maloney Counting Cell
The Palmer-Maloney counting cell is specifically designed for concentrated phytoplankton samples.
Its chamber depth of approximately 0.4 mm provides a shallower sample than a Sedgwick-Rafter cell, allowing small algae to remain in better focus at higher microscope magnifications.
Advantages
- Excellent for small phytoplankton
- Improved focus at high magnification
- Better visualization of individual algal cells
- Requires only a small sample volume
Limitations
- Not suitable for large zooplankton
- Small chamber volume increases counting time for dilute samples
Typical organisms
- Diatoms
- Cyanobacteria
- Green algae
- Dinoflagellates
- Small flagellates
