Deep-Sea Habitats of the Marshall Islands

Pictured is a fragmented lava suspended in lithified sediment. When exposed to UV light, the sediment phosphoresces, glowing green for several seconds. This brief "glow in the dark" effect tells us that the sediment is made out of calcite and/or a phosphate mineral.
 

During the NA174 expedition, co-lead scientist Dr. Annette Govindarajan from Woods Hole Oceanographic Institution is sampling for environmental DNA (eDNA) to explore the deep-sea biodiversity in the Marshall Islands region. She will be using the Multipuffer eDNA sampler built by Aquatic Labs, which can filter large volumes of water, enabling greater #biodiversity detection than conventional Niskin bottle sampling. The sampler will be integrated onto the ROV Hercules for use during surveys. 

Today's Instagram Takeover comes from NA174 Science Communication Fellow Matthew Holden. A science teacher at Fayetteville High School in Arkansas, Matt started his career as a conservation biologist and ecologist. 
 

The Marshall Islands are renowned for their biodiverse shallow-water ecosystems, which host roughly 300 species of hard corals, 250 species of algae, 1,000 species of fish, 1,600 species of mollusks, and 700 species of crustaceans. However, these numbers likely underestimate the true marine diversity of the region, as many deep sea and offshore species remain undocumented. The surrounding offshore pelagic environments serve as important habitats and migration corridors for commercially important tuna species, as well as host some of the largest nesting populations of sea turtles. On the NA174 expedition, we're excited to explore some of the never-before-seen deeper ocean areas of the region and share that exploration with the world!

During NA174, co-lead scientist Dr. Fanny Girard from the University of Hawaii at Manoa will lead efforts to study the biology and ecology of deep sea coral communities on never-before-explored seamounts. She will specifically use ROV video footage to characterize the distribution and diversity patterns of these communities across the Marshall Islands, answering critical questions such as who is there and why. Dr. Girard plans to bring back samples collected during the expedition to the lab to study the reproductive biology of deep-sea corals.
 

Some evidence from the Ratak Chain suggests that its volcanoes are Cretaceous in age and are related to the Rurutu-Arago Hotspot, which is currently located near Arago (also known as Tinomana) Seamount in the Southern Pacific Cook-Austral Islands. The Ralik Chain also formed during the Cretaceous, but it has remained sparsely sampled to date, and its origins are not yet firmly identified.

During NA174, co-lead scientist Dr. Val Finlayson from the University of Maryland will oversee geology efforts, including surveying two parallel volcanic chains within the greater Marshall Islands region, often referred to as “Ralik” and “Ratak”. A small number of volcanoes from these areas have been geochemically characterized, but overall, little remains known about the origins of these volcanoes.

"Lava samples that we aim to recover during NA174 preserve chemical signatures of where and when these volcanoes formed. We can use that information to gain new insights into the geologic history of the Marshall Islands and fill one of the many gaps in our knowledge about Cretaceous volcanic activity in the Western Pacific," she says.

Located midway between Hawaiʻi and the Philippines, the Republic of the Marshall Islands is an island nation in the Central Pacific region of Micronesia. As one of only four atoll-nations in the world, the Republic of the Marshall Islands consists of 29 low-lying atolls and five main islands that are surrounded by over 2.13 million square kilometers of mostly unexplored seafloor. The islands are oriented into two parallel island chains: Ratak in the east and Ralik to the west, which means sunrise and sunset in the Marshallese language, respectively. Each of the 29 atolls consists of a number of islets separating a central lagoon from the surrounding barrier reef, together totaling more than 1,200 individual islets. With a total land area of only 181 square kilometers, 98.9% of the Marshall Islands' territory is underwater - the largest proportion of water to land of any sovereign state.