Checking the Ocean’s Pulse with Plankton

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Phronima plankton. Photo: NOAA Fisheries/Jonathan Whitney.

By Joseph Bennington-Castro

At the very core of the marine food web you’ll find plankton, which are tiny organisms that propagate and feed the rest of the ocean’s marine life — indirectly feeding everyone who enjoys seafood. Plankton, by definition, are small drifters that are largely microscopic and live in the deep ocean, making it a challenge for scientists to study them.

But make no mistake: What these creatures lack in size or locomotion, they more than make up in importance. In a sense, plankton are the “lifeblood” of the ocean and studying them allows scientists to metaphorically give the ocean a blood test or check its pulse to determine its overall health, among other things.

Seeking to better understand the health and productivity of Hawaiʻi’s coastal ocean, PIFSC scientists kicked off a project last week to collect and study the plankton and micronekton (small intermediate-stage organisms that develop from plankton) off the leeward coast of Oʻahu.

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Jar of plankton. Photo: NOAA Fisheries/Joseph Bennington-Castro.

The NOAA Fisheries researchers and their partners will be comparing the data they collect with similar leeward surveys conducted 1951 through 1978, earning the project the moniker “Trawling Through Time.” Ultimately, the project will help the research team, led by chief scientist Dr. Donald Kobayashi from the PIFSC Ecosystems and Oceanography Program, determine if and/or how the pelagic marine ecosystem and underlying oceanography of the leeward region has changed over time.

For this project, the researchers are conducting a series of bongo net surveys and midwater trawls off the NOAA Ship Oscar Elton Sette.

The bongo nets scoop up unsuspecting zooplankton, or animals that spend all or part of their life as free-floating plankton. The scientists are conducting day and night bongo net surveys at various depths, including 200 meters and 400 to 500 meters. They painstakingly sort the plankton by size (using mesh screens of various scales) in the ship’s wet lab, while the Sette continues to bob on the ocean.

Dr. Jonathan Whitney, a scientist with PIFSC-JIMAR (Joint Institute for Marine and Atmospheric Research), leads the plankton team. Dr. Erica Goetze from the University of Hawaiʻi at Mānoa (UHM) Department of Oceanography and her recent graduate Dr. Michelle Jungbluth (now at San Francisco State University) assist Whitney as experts with copepods, one of the most abundant plankton. One of the objectives of the “Trawling Through Time” project is to determine if copepod abundance or diversity has changed over time. Also part of this important team are Zora McGinnis from the NOAA Fisheries Pacific Islands Regional Office and Shilpa Lal, a graduate student at the UHM Department of Oceanography.

The midwater trawls pick up micronekton, a category of organisms that sit between plankton and nekton, or larger marine animals that can swim freely without their motions being driven by ocean currents. Typically serving as food for nektonic species, micronekton are situated in the middle of the food web and include marine animals like small fish, cephalopods, crustaceans, and jellyfish. They have increased swimming ability compared with plankton, helping them to avoid the nets scientists use to collect them.

On the 4th day at sea, the team conducted a deep tow with a midwater trawl, reaching a depth of about 1,000 meters. Bringing the net back up was a slow and tedious process, as they had to pick out numerous snipe eels and other mesopelagic fishes (those living at depths of 200 to 1000 meters) from the meshes in the forward part of the net as it was hauled back aboard the ship.

The trawl was quite successful, however, and the researchers collected various unusual-looking mesopelagic fish and micronekton, which they excitedly categorized back in the wet lab.

PIFSC JIMAR scientist Dr. Johanna Wren leads the the trawl team, which also includes Dr. John Denton from the American Museum of Natural History in New York City, Justin Ossolinski and Rory Driskell from the PIFSC Science Operations Division, recently retired PIFSC scientist Robert Humphreys Jr., and UHM undergraduate Yuuki Niimi. Dr. Denton is an expert in myctophids (lanternfishes), a family of fish that’s ubiquitous in the world’s oceans and one of the most abundant type of fishes around. One of the objectives of the project is to determine if myctophid abundance or diversity has changed over time.

The scientists are finishing the last of their their bongo net surveys and midwater trawls, and will then begin analyzing their data back on land. Given scientific concerns about the impact of climate change and other anthropogenic (human-related) factors on coastal fisheries and ecosystems, this research is vital to help scientists understand ocean resiliency, health, and productivity.

Learn more about the project here. And check out some of the team’s other collections below.