Uncovering the Mysteries of the Mesopelagic

By Beth Francis, Bangor University UK

Have you ever thought about the mysterious dwellers of the deep ocean? Six months ago, I thought of these species only as scary-looking creatures in horror movies and nature documentaries. Now, after flying across the world twice to study these alien-like inhabitants of the depths up-close, I was inspired to investigate the mysteries of mesopelagic and why these deep ocean dwellers are important to all of us.


Alien? This amphipod, Phronima, is rumored to be the inspiration for the alien queen in the 1986 movie “Aliens.” These small parasitoid crustaceans hollow out salps (barrel-shaped invertebrates) to lay eggs inside. To the left is a Phronima in its natural form and to the right is a female Phronima inhabiting a salp. The small specs are her hatched eggs, protected by the salp (Photo: Bangor University/Beth Francis).

I began my PhD in October 2016, based at Bangor University in North Wales, UK. My PhD is funded by the Envision Doctoral Training Program, through the UK Government Natural Environment Research Council, but my main focus is studying gradients in productivity near to islands in Hawai‘i. In the six months since beginning my project, I have been privileged to join NOAA researchers twice on the Integrated Ecosystem Assessment (IEA) expeditions to West Hawai‘i, to learn more about the mesopelagic community there.


Mesopelagic Marvels: A tiny nautilus, a type of shelled deep-sea cephalopod, similar to an octopus or squid (Photo: Bangor University, Beth Francis).

The middle or mesopelagic depths, also known as the “twilight zone” of the ocean (between 200-1000 meters or 650-3300 feet) may seem like another world, but it is much closer to home than you may think. This region plays a crucial role in our planet’s ecosystem. An estimated 90% of the world’s fish live in this zone, and while most aren’t commercially important species, they form a key part of the food web. These deeper dwellers, such as shrimp and squid, are prey for dolphins, whales, and for the fish we eat. The mesopelagic also plays an important role in removing billions of tons of carbon dioxide from the atmosphere each year, pumping carbon from the surface water deeper into the ocean (Siegel et al., 2014).


Deploying the Cobb trawl net to target mesopelagic organisms (Photo: University of Hawai‘i/Jana Phipps).

Despite the importance of this layer of the ocean, relatively little is known or understood about species distribution and interaction in Hawai‘i—and these are a few of the mysteries we are researching through the West Hawai‘i IEA project. The West Hawai‘i IEA is an on-going project, collecting information on the oceanic communities in the region. Back in September 2016, and for part of this recent IEA expedition, we collected deep-sea organisms both nearshore and offshore of a known biological “hotspot” site. The goal is to quantify the abundance and diversity of organisms at both sites in order to understand why a greater density of these deep-sea dwellers is found closer to shore.

In order to sample the mesopelagic, we use a giant mid-water trawling net called the Cobb trawl. During Cobb trawls, we collect an array of weird and wonderful creatures of the deep, ranging from tiny to huge, cute and familiar, to very strange-looking! And most importantly, we have been able to collect a lot more information on the mesopelagic populations than ever before.


A free-swimming sea snail colloquially known as a sea butterfly because of its wing-like foot (Photo: Bangor University/Beth Francis).

So, what have we learned so far? Initial results collected last September have given us some really interesting information, suggesting that there are significantly more (roughly three times as many) organisms close to shore compared to offshore. And during the most recent expedition, the same pattern seems to be holding up. These findings potentially support the theory that there is an increased primary productivity near islands, and that this extends down into the deeper layers of the ocean. Hotspots in biological productivity, such as the one we are researching in West Hawai’i, could prove to be crucial in the longevity of the human interaction with the ocean, and act as a crucial natural refuge for changes to the climate in the future. We are hoping that the data we collect will help us to uncover some of these mysteries of the mesopelagic, and better understand the ocean in West Hawai’i and beyond.

Reference: Siegel, David A., et al., “Global assessment of ocean carbon export by combining satellite observations and food‐web models.” Global Biogeochemical Cycles 28.3 (2014): 181-196.

An Ocean of Life

By Rebecca Ingram

Living on an island, it is easy to see how intertwined our lives are with the ocean. We benefit daily from the ocean’s many resources, whether it be going fishing, diving, or simply walking along the shoreline. But if you live far away from the ocean, you may not realize that the ocean also influences your life in significant ways. The ocean affects weather patterns, the atmosphere, and contributes to global food supplies. Simply put, no matter how near or far, the ocean contributes to all life on Earth.

Scientists boarded the NOAA ship Oscar Elton Sette on April 17th to continue researching biological and oceanographic aspects of the West Hawai‘i marine environment. This research is fueled by the need to develop a better understanding of why this particular island region is so ecologically dynamic and productive. Specifically, we are researching fish larval habitats, species distribution in the water column, and productivity hot spots. (You can read more about our expedition here.) However, this important ship-based research does not tell the whole story.

Off the ship, scientists are investigating another important aspect of this ecosystem. There is a need to understand more about the connections between these biophysical ecosystems and the humans who live near them. People do not simply live in or near an ecosystem, but are an integral participant and rely on resources produced. So the question remains, in what ways does the West Hawai‘i community impact and rely on the marine ecosystem?

Answering this question leads to the primary strategy of Ecosystem Based Management (EBM), a holistic resource management approach that West Hawai‘i has been shifting towards in recent years. EBM recognizes that an ecosystem cannot be teased apart into neatly manageable pieces, but must be viewed through a unifying lens. EBM also specifically integrates humans, both our impacts and our reliance on resources, into management plans. (Read more about the shift toward EBM on the Big Island in a previous blog post.)

The West Hawai‘i Integrated Ecosystem Assessment helps pull both sides of the social-ecological story together and facilitate this fairly new style of resource management. It is a NOAA program focused on merging biophysical and ecological data with human dimensions. Essentially, this is a program that wants to provide managers with the means not only to conserve a species or place, but also conserve the resources valuable to the community. This includes activities like the opportunity to fish, dive, or appreciate the inherent value of being at a place. It also includes resources that stretch far beyond the island, since the health and productivity of West Hawai‘i coral reefs can be traced worldwide.

Kealakekua Bay

Kealakekua Bay: Looking down at popular tourist location, Kealakekua Bay, Hawai‘i, with surface slicks visible offshore. Photo credit: Rebecca Ingram, NOAA.


Kona Coast Sunrise

Kona Coast Sunrise: Looking at the Big Island from the ocean. Photo credit: Jamison Gove, NOAA.


Sette Scientist

NOAA Scientist: Jon Whitney (PIFSC/UH), aboard a small boat operation launched from the Sette. Photo credit: Don Kobayashi, NOAA.