Benthic Station

Benthic organisms are creatures that live on the seafloor. We will collect a sample of seafloor sediment using a device called a Peterson Grab (see pictures below). Seabed sediments and organisms can give a good indication of the overall health of the seabed. This is very important because the decomposition of organic matter on the seabed represents a major source of nutrients used by phytoplankton near the ocean surface.

o A healthy seabed has a rich, ocean/earthy smell mud, and contains many decomposers, such as brittle stars. This means that organic matter is being broken down abundantly on the seabed, which releases nutrients (particularly phosphate, nitrate, and iron) into the water. Therefore, when we get upwelling currents across the seabed, we have the potential to carry large amounts of nutrients up to the euphotic zone where the phytoplankton live. When the phytoplankton have lots of nutrients and sunlight, they reproduce rapidly, providing abundant food and oxygen for other marine life. Message: healthy seabed = healthy ocean with lots of life.

o An unhealthy seabed has a black color and perhaps a rotten egg smell. It supports very few decomposers or other organisms. This means that few nutrients will be available for phytoplankton even if upwelling is occurring. This means the phytoplankton don’t reproduce much and therefore don’t produce much food and oxygen for other organisms. Message: unhealthy seabed = unhealthy ocean with not much life.

Setting and preparing to lower the Peterson Grab.

Once onboard, the grab is opened and the seabed sediments are placed in a bucket.

We wash the sediments through a screen to free the organisms contained in the mud.

A small brittle star—an important seabed decomposer, and a good indicator of a healthy seabed.

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Modified from pages developed by John Turbeville.