As we steam westward along the second line of sampling, DBO-2, the research teams continue to collect CTD data, water and benthic samples, and plankton at each site. Janet Duffy-Anderson, a NOAA researcher, and Chrissy Hayes, a Knauss Fellow, are using bongo nets to capture a snapshot of the plankton populations in the Arctic. The term plankton includes zooplankton, small invertebrates that larger species of the ecosystem eat as food and ichthyoplankton, which are fish larva.
The bongo net that is deployed off the Healy has four nets and the anatomy of the equipment is very interesting. Two small nets sit at the top above two larger nets. The two different sizes are designed to collect different-sized organisms. The smaller nets with the 153um mesh and 20cm opening keep smaller animals in and allow larger animals to avoid entering. The larger nets have a 505um mesh and a 60cm diameter, which filter higher volumes of water and collect larger species. Once on the deck, they spray down the nets so that all of the organisms gather in the caught end at the bottom to be examined.
The nets are attached to a conducting cable that has electrical capabilities and allows the plankton team to attach a mini-CTD called a SEACAT right above the nets. They also have flow meters in all four of the nets that read the volume of water going through each one during the cast. Janet and Chrissy can then use the number of plankton they caught and the volume of water to calculate the density of organisms in each tow.
Janet works for NOAA, more specifically, for the fisheries division. She is looking at zooplankton, which are small organisms that are at the bottom of the food chain in the world's oceans and feed many of the larger consumers such as fish and whales. Many species of zooplankton in the Arctic are big and contain large amounts of lipids, or fats, because the water is cold. This means a higher caloric content that provides consumer species with a lot of energy and is also the reason why many organisms migrate here to feed in the summer. Over the past few years, Janet and her colleagues at NOAA have seen a decline in the lipid content of Arctic zooplankton. They are currently trying to collect samples to understand why.
Janet and Chrissy are also looking to answer two questions about fish populations in order to help commercial fisheries make informed decisions about where to fish and how much to catch. In their bongo net tows, they are identifying fish larva, or ichthyoplankton, species from the Bering up to the Chukchi Sea to observe any movement that may be happening in the populations. This helps fishermen make decisions about what species they should focus on and how far they need to go to get a worthwhile catch.
Within the scope of fish larvae, they are looking specifically at the Arctic and Saffron Cod populations. Arctic Cod is a lipid-rich species that provides a food source for many organisms in the Arctic ecosystem. They are, however, cold-water dependent and will move if the area where they live begins to warm. As the bottom water of the Arctic rises in temperature, scientists want to know where the Arctic Cod are going or if they are going to be replaced by the Saffron Cod, a more temperature variable species that can withstand warm waters, but has less caloric value. It will be interesting to follow Janet and Chrissy as they aim to answer these important questions.
A Question From the Crow's Nest
Many species of plankton have a diurnal migration. What does that mean?
Answer from previous post: The other major element that indicates high productivity other than carbon is Nitrogen.