Sampling | Net Tow | HABs

Part of the ongoing ORHAB project mission is to educate the general public on the importance of the ORHAB studies and the potential impact of HABs on public health and the economy. In an effort to provide a basic understanding of the ORHAB project and also to generate an interest in science in our youth, this page will feature a variety of ORHAB research topics.

A Lesson In Sampling:

What is Sampling?

Sampling is a way of understanding something about a large environment by studying only a small portion of that environment. For example, ORHAB technicians sample seawater off the coast to monitor the numbers and types of phytoplankton in the water.

Phytoplankton are small single-celled plants that can't be seen with the naked eye. Most are several times smaller than a strand of hair. Imagine what it would be like trying to count all the phytoplankton in the ocean!

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Using a Net Tow

There are many sampling methods that researchers can use. One technique that is commonly used by ORHAB researchers is called the net tow. A net tow is done by dragging a net along the surface of the seawater, often for about a minute. The net that is being "towed" or dragged is made of a fine mesh with a circular opening on one end, called the mouth, and a container at the opposite end that can be removed, called the cod end.

As the net is towed through the seawater, the water passes through the net and phytoplankton that are trapped inside the net are too big to go through the mesh. Typically the mesh of the net is 20 micrometers in size, or about the size of a pin head. What size net do you think is used to catch fish?

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HABs - Harmful Algal Blooms

Once a sample has been collected, researchers can then analyze the sample under high powered microscopes that can enlarge things 100-200 times their normal size. They determine what kinds of plankton are present in the seawater. Most of the phytoplankton collected by a net tow are food for zooplankton, shellfish and fish (like anchovies and sardines).

Only a few phytoplankton species (< than 100 species) are known to be toxic. Some phytoplankton, though, can be harmful because they make poisons, and these are the organisms that ORHAB is especially interested in. These tiny phytoplankton alone are typically not dangerous to humans; however, the toxins (poisons) that they produce can be concentrated by creatures higher up in the food chain. For example, fish and shellfish feed on algae as part of their normal diet. When they eat toxic algae, they don't appear to be affected by these poisons, but when marine mammals, such as sea lions and sea otters, and humans eat the toxin-containing shellfish, they can become sick or even die.

Toxic algae can be present in the ocean in high numbers, so they're typically called harmful algal blooms. These harmful algal blooms, or HABs, can be difficult to detect since there is often no visible difference in the seawater when they occur. ORHAB researchers are monitoring HABs, collecting as much data as possible about the toxic phytoplankton species and the ocean environment that is their home. With enough data, researchers will begin to determine which factors cause HABs. They hope to eventually predict when harmful algal blooms happen, resulting in safer seafood for everyone!

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