Introduction

Collecting a wide range of zooplankton and ichthyoplankton (fish eggs and larvae) on the level of the water’s surface as well as at depth is one method used by scientists to evaluate the sustainability of the ecosystems in our oceans. The output of this plankton at the beginning of the food chain, the place and scope of adult spawning populations, the movement of ocean currents, and the distribution of fish larvae and lobsters to and away from nursery regions can all be strongly affected by observations of this plankton.

The Neuston net and the Bongo net are two helpful pieces of equipment when sampling plankton. Due to its design like a manta ray, the Neuston net, often referred to as the manta net, is used to collect samples from the ocean’s very surface layer, also referred to as the neuston layer. After a neuston tow, the microscopic animals captured at the cod end of the net are placed into a sieve, and organisms such as crab megalopae (crab larvae), larval fish, and Velella (colonial jellyfish found only in the neuston) are preserved for a later laboratory investigation.

 

Describe plankton.

Plankton is a term used to describe creatures that spend most of their life at the water’s surface. In the plankton of fresh or marine waters, viruses, bacteria, protists, fungi, and animals with sizes ranging from nanometers to several centimeters can be discovered. A variety of affordable, simple-to-assemble nets are a simple technique to sample planktonic species. A plankton net can be constructed in a variety of ways (e.g., see Microcosmos Curriculum Guide, Kendall Hunt Publishers). 

 

Describe Plankton Net.

A plankton net is a piece of equipment used to gather samples of plankton in bodies of still water. It is made up of a cod end, a nylon mesh net, and towing line and bridles. One of the most traditional, straightforward, and affordable ways to sample plankton is with plankton nets. Both horizontal and vertical sampling techniques can be utilized with the plankton net. It enables analysis of plankton in environmental water samples using quantitative methods (cell density, cell colony, or biomass) as well as qualitative methods (e.g., chlorophyll-a as a primary phytoplankton production).

 

History of Plankton Net

Upon returning from Mauritius and making his way to the UK in 1816, John Vaughan Thompson invented a plankton net. A little unchanged form that he subsequently named Sapphirina’s marine bioluminescence captured his attention, and he felt “under enormous debts to this lovely little animal, which by its glorious presence in the water inspired me to initiate the use of a muslin hoop-net, which when it failed to obtain me a sample, brought up such a profusion of other marine organisms completely invisible while in the sea, as to induce a continuing use of it on every advantageous chance.” From 1828 through 1834, he wrote six memoirs in which he shared the results of his research.

 

During the Beagle survey voyage on January 10, 1832, Charles Darwin used a plankton net for the second time that is known in history. He drew a picture of the net in his journal, and it appears that the drawing was inspired by the trawl net that John Coldstream had described to Charles Darwin in a letter. Robert Edmond Grant may have brought Thompson’s concept to Darwin’s attention in Edinburgh earlier. A sack constructed of bunting that is four feet deep and fastened to a semicircular bow is what Darwin refers to as this “contrivance”; it is held upright and dragged behind the ship by lines. The following morning, he said, “The sheer volume of creatures the net gathers provides a complete explanation for how so many large-sized animals can exist so far from a populated area. Several of these small organisms that are so low on nature’s scale have the most beautiful features and vibrant colors. It inspires a sense of amazement that something so beautiful might appear to have been made for such a little reason.”

 

Components of Plankton Net

• Bridle and towing line

The upper portion of a plankton net is called the towing line and bridle, and it is used to maintain the net in place. Triangle bridles are attached to nylon rope towing lines that can be adjusted to the user’s preferred amount of tension.

• Mesh nylon net

The central section of the plankton net, which is made of nylon mesh, is used to filter the plankton out of the water sample according to the mesh’s size. Also, due to its funnel-like design, it is feasible to efficiently gather plankton of varied sizes. Nets come in a variety of mesh sizes based on the target microorganism to be captured and the state of the water body. The size of the plankton in the water sample decreases as the mesh size increases.

As an illustration, a net mesh size between 25 and 50 m in diameter should be chosen in order to collect small invertebrates with a diameter of 50 to 1500 m, as this is enough to successfully filter out the desired creature.

A plankton net with a mesh greater than 100 m should be selected in eutrophic water conditions, though, to prevent the net from being clogged.

• Cod end

At the funnel’s end, the cod end is situated in the lowest portion of the plankton net. The valve that opens and closes the collecting cylinder is both present.

• Use

Towing the net horizontally behind a slow-moving boat is a typical technique for gathering a plankton sample. The net needs to be rinsed with the test water before being used to harvest plankton. By rotating the valve into the vertical position, the operator should make sure that the cod end is completely closed. At the side of the boat that is traveling slowly, the plankton net is then dropped horizontally to the water’s surface. It takes 1.5 minutes to complete the sampling. Following this, the plankton sample is obtained by opening the cod end above it and twisting the valve horizontally to collect it in a sample container. When the specimen is collected, it can be looked at using a microscope to detect the type of phytoplankton or zooplankton, or cell growth can be done to ascertain the density of plankton in the water source.

 

Structure of Plankton Net

The collection of phyto- and zooplankton samples has involved the employment of a wide range of nets and other tools. Of all the plankton-collecting tools, the plankton tow net has reportedly been in use since Johannes Müller originally developed it in 1846.

 

The plankton net is pulled through the water by a metal ring that is connected to a filtering cone. Seiwell provides comprehensive instructions on how to cut designs for standard nets (1929). Typically, some type of silk bolting cloth similar to that used for sifting flour serves as the filtering material that forms the net. According to the count of meshes per linear inch, it is designated from 0000 to 25. They differ from typical weaving in which the strands cross alternately without a binding turn because the aperture size cannot be easily adjusted due to the way the strands are weaved. The crucial characteristics to think about are the sizes of the openings between the strands since they influence the size of the tiniest organisms that the net will be able to capture. Many of the creatures living in the plankton pass easily through the meshes of the finest weave bolting cloth, as has been frequently demonstrated through comparison with centrifuged water and by inspection of the stomach lining of filter-feeding animals. In actuality, the smallest size of the organisms that need to be collected should be identified, and the coarsest net appropriate for this size should be utilized. For reference, the sizes of conventional bolting cloth are listed in Table 59 by their respective diameters. During prolonged use in the water, the aperture sizes shrink. Normal, X (extra heavy), XX (extra double heavy), and XXX are the types of silk that are utilized (extra triple heavy). For any given number of fabrics, the heavier quality lead to a slight difference in the aperture size as well as the number of meshes per inch. The heavier strands of stramin, a strong screening material with an aperture of 1 mm, have certain drawbacks since they make towing through the water more difficult. Stramin is usually used for larger nets or ring trawls.

 

How to use a plankton net

The first step is to locate a body of water, after which you must figure out how to maneuver the net through it. A plankton net is typically towed by a boat for researchers. What alternative means might you have to transfer water through the plankton net because you most likely don’t have access to a boat? If you choose to tow your plankton net, secure a piece of sturdy string to the wedding band so you can draw the net through the water. In the bottle, the plankton will gather concentration. To ensure that the plankton on the inside of the net is washed into the collection bottle, rinse the inside of the net with water after towing the plankton net. After finishing, cut the rope that is tying the bottle’s mouth shut and carefully take the bottle out. Take a look at the water in your collection bottle. Do you still see motion in the particles after the water has stopped moving? So those are your zooplankton, if you have any. Put a few drops of water from your collection jar into a viewing dish with an eye dropper if you took observational equipment to the collecting site. Look through a hand lens or a microscope at the plankton in the viewing dish.