NOAA Teacher at Sea
Onboard NOAA Ship Oscar Elton Sette
March 12 – March 26, 2012
Mission: Fisheries Study
Geographical area of cruise: American Samoa
Date: March 23, 2012
Plankton Net Operation
Learning how to work with the plankton net was so interesting. It required careful, meticulous, and orderly work. Emily Norton, University of Hawaii at Manoa, Biological Oceanography, is conducting daytime and nighttime tows targeting plankton. She’s particularly interested in collecting and studying copepods, a type of small crustacean which comprise ~80-90% of the plankton. Plankton is a name for a variety of plants and animals that live in the water column and are found throughout the world’s oceans. Plankton are important because they are an integral part of the food chain, and they can help scientists better understand currents and transport in the oceans. Helping with the plankton tow is Megan Duncan, oceanography participant, Joint Institute for Marine and Atmospheric Research at the University of Hawaii. Together we deployed the net starting around 11:00 p.m. Due to migration patterns known as diel vertical migration, plankton can be collected more easily at night.
- The net consists of a 1 meter metal ring with a fine mesh (200 um) net attached to collect the plankton.
- At the end of the long, conical net is a collection filter tube or “codend.” This is the final collection point for all of the specimens funneled into the mouth of the net.
- The flowmeter is then connected across the diameter of the metal ring, which measures the amount of water flowing past it.
- With a crane operator’s help the net is lowered into the sea with 230 feet wire out which calculates to approximately 200 feet deep. This is called an “oblique tow” method.
- The net remains in the water for 30 minutes.
- Once brought to the surface, the net is rinsed with sea water multiple times to ensure all of the plankton are completely flushed down into the cod end.
- The next step is filtering the plankton-rich seawater through a very fine sieve.
- The plankton are either observed under a microscope or immediately preserved using an ethanol solution, 95% ethanol 5% water.
- Labels are then placed inside the jar written in pencil on waterproof paper, and outside the jar using indelible marker.
- The plankton will be processed at a later date in the lab for quantitative analysis.
- In the lab, scientists study the plankton further, making observations and studying the DNA, Deoxyribonucleic Acid using PCR, Polymerase Chain Reaction, and sequencing. Similarities and differences (i.e. mutations) in the DNA sequences are used by scientists to determine how closely related populations of copepods are. This helps scientists infer how currents affect connectivity in the ocean.
Baby giant squid
juvenile fish, various species
Q:What fish have you had the most interest in and why?
A: The most common fish caught in the net is the lanternfish or myctohid. They represent nearly 85% of the ocean’s biomass. One interesting feature is their photophores which produce light that emit from their bodies.