What is a Plankton Net?

A plankton net is a device that can be used to catch plankton (little plants and animals that live in the ocean). Scientists use special plankton nets with high volumes, but anyone can make a plankton net by tying a leg pantyhose to the end of a metallic ring with a handle. This can be dipped into the water from a slow-moving boat to collect plankton for observation under a microscope. Keep dragging the plankton net until it is obvious that there are many little bits of organic material caught in it. That's the plankton.

Plankton exist everywhere in the pelagic (illuminated) zone of the ocean, but are at relatively low concentrations in most places, requiring a plankton net to concentrate them for observation. The plankton you are likely to catch will be small, generally 2 mm in diameter or less, so you'll need a magnifying glass, or, better yet, a microscope to view them. Plankton only lives for a couple days after you remove it from the ocean with a plankton net, so you'd better look at it fast. It can be preserved for slightly longer by putting it in the refrigerator. If you want to preserve the planktonic organisms for a while after they die, add alcohol to the seawater so it becomes 70% alcohol.

Some of the organisms you may find using a plankton net include copepods (1-2 mm crustaceans), amphipods (slightly larger shrimp-like crustaceans), tunicates (sac-like filter feeders), cladocerans ("water fleas"), ostracods ("seed shrimp," 0.2 to 30 mm wide), chaetognaths ("arrow worms," about 10 mm), and bits of algae. If you have a more powerful microscope, you can see the smallest planktonic organisms, including rotifers and various larvae of larger animals.

Plankton engage in bust-and-boom cycles, where their numbers increase rapidly in warmer weather and drop in cooler weather. This is because their ultimate food source, the algae, is very sensitive to environmental conditions. The most numerous plankton is in the tropics, where the temperature and nutrient levels are ideal.

A plankton net is a specialized tool designed for marine research that captures tiny aquatic organisms known as plankton. Its primary use is to collect samples from bodies of water for scientific analysis, allowing researchers to study the diversity, population, and health of plankton communities, which are crucial for the marine food web.

A plankton net operates on a simple principle: it is towed through the water, either vertically or horizontally, and plankton are filtered by the net's fine mesh. The mesh size is small enough to trap plankton but allows water to pass through. Collected specimens are concentrated in a collection container, known as a cod end, at the base of the net.

There are several types of plankton nets, each tailored for specific research needs. The most common include the vertical net, used for sampling at various depths; the horizontal net, for surface sampling; and the bongo net, which has dual side-by-side cones for simultaneous sampling. Each type helps in assessing plankton distribution and abundance.

Plankton sampling is vital for understanding marine ecosystems. Plankton are the foundation of the aquatic food chain, and their populations indicate the health of marine environments. Sampling helps scientists monitor biodiversity, detect environmental changes, and predict fishery stocks, as many fish species rely on plankton for food during their larval stages.

Plankton nets are versatile and can be used in various aquatic environments, including oceans, seas, lakes, and rivers. However, the design might vary slightly depending on the specific conditions of the water body, such as salinity, depth, and the type of plankton being studied.

Researchers take great care to ensure that plankton samples are not damaged during collection. They use nets with appropriate mesh sizes to gently capture the organisms without harm. Additionally, the towing speed is regulated, and the cod end is often designed with a soft lining to cushion the collected specimens, preserving them for accurate analysis.