Deep-sea habitats seem harsh from our perspective, with cold temperatures and a complete lack of sunlight. Pressures are high, reaching up to 15,000 psi at the ocean’s greatest depths. Yet, for many incredible organisms, the deep sea is simply home. On Alvin Dive 5097, we have the opportunity to explore Cayman waters and to understand what adaptations allow animals to live under these conditions.
After a gorgeous display of bioluminescence and a peaceful descent to the abyss, we arrive at the seafloor. The spectacular geology is immediately apparent, and Dr. Ken Rubin explains how the glassy black features indicate that these rocks formed recently, as lava flowed and cooled into round pillow-shaped rocks and long tendrils.
We see life right away here at 6079 meters. Amidst the pillow lavas, glass sponges have built their silica mesh vases. These sponges are living animals, exceptionally well adapted for filter feeding on small particles in the water column at these great depths.
A large red shrimp (called a decapod) glides into view. Ken spots the shrimp first, enthusiastically noting its large size. With the excitement of the dive, it can be easy to overestimate the size of organisms and features through the sub’s windows. We’ve heard many observers talk about fish that appear eight feet long or shrimp the length of an arm.
Two red lasers shining from the sub allow us to gauge the shrimp’s actual size, about 14 centimeters in body length. We observe the decapod’s elegant swimming gait as legs called pleopods paddle in perfectly synced waves. One of the long antennae of the shrimp brushes against Alvin’s manipulator arm and the shrimp quickly reacts and swims away.
At 6023 meters, we see a small brown fish up ahead. Pilot Danik Forsman deftly follows the fish, which swims a few feet above the pillow lavas. For me, this fish is the highlight of the dive. It is a cusk eel, in the family Ophidiidae, which are elusive, not often collected by common deep-sea research methods such as baited traps. Yet, we are beginning to understand that these fishes form an important part of the ecosystem here in the abyss. We will use video that Alvin has collected throughout the expedition to better understand how these cusk eels are distributed and how they interact with their environment.
We see a swimming isopod, likely in the genus Bathyopsurus, a beautiful white crustacean about 8 centimeters long. This isopod swims upside down and backwards, gracefully dancing by with four paddle-like arms that cross back and forth. Some of these carry algae called Sargassum that has sunk through almost four miles of water here to the seafloor.
These isopods have been a highlight of the expedition – we’ve seen several in both Puerto Rican and Cayman abyssal waters. The collections made by Alvin’s suction sampler will help us to better understand the physiology and distribution of these isopods and the role they play in the ecosystem.
Diving in Alvin has given me a new perspective on the deep seafloor. It is easier now to picture the three dimensionality and complexity of abyssal and hadal habitats. New technologies like Alvin 6500 will continue to inform new understanding of deep-sea ecosystems and the incredible organisms that call the deep oceans home.