student diving
Tokuda shark diving in Haleʻiwa. (Photo credit: Ocean Ramsey; One Ocean Diving.)

A senior in the University of Hawaiʻi at Mānoa’s Global Environmental Sciences (GES) program, is the lead author of a published scientific study on the food webs in the Mariana and Kermadec ocean trenches. This rare achievement by an undergraduate student is the result of Andrew Tokuda’s passion and keen interest in natural science, exceptional mentors and impactful research opportunities available to students in the School of Ocean and Earth Science and Technology (SOEST).

The study, published in Deep Sea Research and conceived by Tokuda’s mentor and research advisor, UH Mānoa oceanographer Jeffrey Drazen, was the first to analyze interactions between echinoderms, such as sea stars, urchins and sea cucumbers; crustaceans, such as amphipods and shrimps; and fishes in these trenches in the western Pacific Ocean.

student on a boat
Andrew Tokuda onboard the R/V Kilo Moana during an abyssal food webs cruise.

Given the remote location and challenging conditions in the ocean’s hadal zone—depths between 20,000 to 36,000 feet—little is known about the sources of nutrition and how energy cycles through food webs in these ecosystems.

“It has been thrilling to be able to work with samples from one of the most inaccessible habitats on the planet,” said Tokuda. “It is one of the things that has made this research experience incredible.”

“Our research showed that food webs in the Mariana and Kermadec trenches are very complex and dynamic!” said Tokuda. “We gained numerous insights from this work such as the possibility of multiple sources of nutrition in each trench, food web interactions being depth-dependent, and even trench topography influencing food input to trench communities.”

In each trench, Tokuda, Drazen and their co-authors collected organisms using baited traps, remotely-operated vehicles and sediment cores. With partial support from the UH Mānoa Undergraduate Research Opportunities Program, they assessed the various isotopes of carbon and nitrogen in the ecosystem to determine how nutrients flow through food webs and analyzed predator-to-prey relationships.

Their findings suggest that hadal inhabitants are strongly connected to a variety of larger scale physical and chemical processes and that these animals may ultimately have a substantial impact on the carbon cycle, which is essential for all life on Earth.

For more on the story, see SOEST’s website.

–By Marcie Grabowski