Uncovering Mysteries of the Deep

West Hawai‘i Project

Fangtooth fish

Much of the focus and attention of Hawaii’s marine ecosystem is on the beautiful coral reefs and majestic marine mammals. However, as you make your way further from shore and deeper into the water, there exists a seemingly alien yet highly productive biological environment. The mesopelagic, sometimes referred to as the twilight zone, encompasses a depth range from about 200-1000 meters (640-3,330 feet). This oceanic zone is home to an extraordinary number of strange deep-sea animals. Despite the estimation that up to 90% of the planets fish live in this depth zone surprisingly little is known about it and what kinds of animals make up the community in this environment. What we do know is that these deep dwellers are likely a key component to a healthy marine ecosystem.

 

The Mesopelagic Boundary Layer Community

The majority of the mid-water community, called the Mesopelagic Boundary Layer (MBL) community, is comprised of fishes, crustaceans, and cephalopods. Using active acoustics, we can visualize a daily vertical migration of these animals, concentrating in high numbers at shallower depths during the night. This migration results in a peak in nighttime biomass at 400 – 600 m. Most animals in this migration are considered micronekton, a size class of intermediately sized animals of 2 – 20 cm.

The MBL community likely fills an important trophic role in Hawaii’s marine food-web. For example, much larger squid, the preferred meal for most deep-diving marine mammals, rely on micronekton for food. In addition, large pelagic fisheries also need the reliable food source that the MBL community provides. The MBL community may also play 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 as a consequence of their diel migration.

Ocean layers

Ecological Hotspot Off West Hawai‘i

Previous research lead by the West Hawai‘i IEA has identified an anomalously high concentration of MBL organisms close to shore compared to surrounding waters. Current research is focused on quantifying the abundance and diversity of organisms at this ecological hotspot in order to understand why a greater density of these deep-sea dwellers is found closer to shore. These findings could potentially support the theory that there is an increased primary productivity near islands (i.e. Island Mass Effect), and that this enhancement 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.