Vertical and horizontal plankton tows for qualitative and quantitative samples

Summary

This video demonstrates the use of a plankton tow net for sampling both zooplankton and phytoplankton at varying depths in a lake. The net’s mesh size is adjustable to accommodate different types of plankton. The process involves lowering the net to the lake bottom, then pulling it back up to collect samples, which are trapped in a bottle. The video also covers the procedure for rinsing and concentrating the sample. Finally, it describes a horizontal tow technique to sample plankton residing at the lake surface, showcasing a thorough and practical approach to plankton collection.

Takeaways

• 😀 A plankton towed net is used to sample zooplankton or phytoplankton at different depths in water bodies.
• 😀 The mesh size of the net varies depending on the type of plankton being sampled, larger for zooplankton and smaller for phytoplankton.
• 😀 The net has a bottle at the end to trap the organisms as the net is pulled through the water.
• 😀 A weight is attached to the net to ensure it stays straight as it is lowered into the water.
• 😀 A clip at the bottom of the net ensures that no organisms fall through during sampling.
• 😀 The net is lowered to the bottom of the water body, then pulled back up slowly and steadily to collect the sample.
• 😀 After retrieving the sample, the net can be lowered and lifted again to rinse off any organisms stuck on the sides.
• 😀 The contents of the bottle are emptied into a labeled container for further analysis.
• 😀 The zooplankton sample can be concentrated by shaking the net and allowing excess water to drain out.
• 😀 The sample collection is not always quantitative but gives a clear representation of plankton residing in the area.
• 😀 A horizontal towed net can be used to sample plankton near the surface of the water as the boat moves back toward the ramp.

Q & A

What is a plankton towed net, and what is its purpose?

A plankton towed net is a device used to sample plankton, such as zooplankton or phytoplankton, from different depths in bodies of water. The net captures plankton as it is towed through the water, and a bottle at the end collects the organisms.

How does the mesh size of the towed net vary depending on the type of plankton being sampled?

The mesh size of the towed net is adjusted based on the type of plankton being sampled. For zooplankton, the mesh size is larger, while for phytoplankton, the mesh size is smaller to better capture these tiny organisms.

What role does the weight play in the functioning of the plankton towed net?

The weight ensures that the towed net stays relatively straight and vertical when it is lowered into the water. This helps the net maintain the correct position as it moves through the water.

Why is there a clip on the end of the plankton towed net?

The clip on the end of the towed net helps to secure the sample, ensuring that no plankton or water falls out of the net during the sampling process.

How is the sample collected from the plankton towed net?

Once the net is pulled back up from the water, the contents of the bottle at the end are evacuated into a labeled container, where the plankton sample is stored.

What is the purpose of shaking the net during the sampling process?

Shaking the net helps to concentrate the plankton sample by draining excess water from the sides, ensuring that the organisms remain in the bottle for easier collection.

What is a quantitative sample, and how is it achieved in this process?

A quantitative sample refers to a sample that allows for the measurement of plankton abundance. This is achieved by concentrating the sample in the bottle and capturing enough organisms for analysis.

What is the horizontal tow, and how does it differ from the other sampling method?

A horizontal tow involves towing the net along the surface of the water to collect plankton residing near the top of the lake. Unlike the depth-sampling method, the horizontal tow does not provide a quantitative measurement but offers insight into plankton distribution near the surface.

Why is the horizontal tow not considered a quantitative measurement?

The horizontal tow is not a quantitative measurement because it does not provide information about the exact amount of plankton present. It only samples plankton from the surface, without offering detailed data about plankton density or abundance at different depths.

What happens after the horizontal tow sample is collected?

After the horizontal tow sample is collected, the plankton is transferred to a container for analysis. The sample provides information on the plankton population that resides near the surface of the lake.