Celebrating 20 Years of NOAA Ocean Exploration

Sharks Happen: Swordfish Fall Attracts a Range of Predators

The objective of the seventh dive of Windows to the Deep 2019 was to explore a potential maritime heritage site thought to be the wreck of SS Bloody Marsh based on high-resolution mapping data. Instead of a shipwreck, however, we found a rocky outcrop. Not to be deterred, the team shifted from “maritime heritage” mode to “biology/geology” mode and continued exploring for sponges, corals, fish, and more. Near the end of the dive, we came upon a rare scene: at least 11 dogfish sharks feeding on a recently deceased Atlantic swordfish approximately 2.5 meters (8 feet) in length.

Large body animals that die and descend to the deep seafloor are called “food falls,” and they play an important role in the transfer of organic carbon within the ocean. Despite attempts to study these food falls, our understanding of them as well as the types and scope of species interactions that occur beyond the continental slope and into the deep sea remains limited.

In the words of fisheries biologist, Peter Auster, “Sometimes “sharks just happen.” You can’t plan on seeing [events like the swordfish fall], especially in the deep ocean. It is simply serendipity; by just spending enough time underwater and being prepared for the unexpected, you can stumble across scenes that will replay in your mind’s eye over and over for a lifetime.”

Deep-Sea Battle: Shrimp Versus Fish

“Wow” was a frequently uttered word when our science team witnessed a fierce deep-sea battle between a caridean shrimp (Heterocarpus sp.) and a type of midwater dragonfish, possibly a stareater, while exploring Ufiata Seamount within the Tokelau Seamount Chain as part of the Discovering the Deep: Exploring Remote Pacific Marine Protected Areas expedition. While scientists noted that they had seen squat lobsters pick midwater fish out of the water and eat them, they had never seen a shrimp consume a fish like this before. Adding to the gore factor, the fish was still alive as the shrimp slowly picked it apart and feasted on several pieces of its tissue and stomach contents.

This high drama in the deep sea was incredible to witness and left scientists wondering how the shrimp was able to capture the fish, as deep-sea shrimp are thought to be primarily scavengers. Sometimes new discoveries and observations lead to even more questions.

Calamari for Dinner: Brittle Stars Nab a Squid Meal

Our Mountains in the Deep: Exploring the Central Pacific Basin dive to explore a ridge off the southeast side of Jarvis Island was described as revealing a “trove of deep-sea treasures.” During the dive, we discovered not one or two but six high-density coral communities hosting a wide range of organisms. But perhaps the most surprising and action-packed portion of the dive happened when we watched a group of ophiuroid brittle stars capture, fight over, and then eat a squid (Abralia sp.) that was swimming by.

This was a deliberate predatory act that shocked our science team. Prior to this observation, it was thought that brittle stars were primarily scavengers, feeding on whatever they could get...but grabbing a squid right out of the water column? Totally unexpected. This “once in a lifetime” observation helps us to understand a bit more about bentho-pelagic (seafloor-water column) coupling and the dynamics of life in a region of the ocean that remains largely unexplored and unknown.

Caviar Dreams: Crab Feasts on Fish Eggs

During Windows to the Deep 2019, while exploring a canyon off of Roanoke, North Carolina, at a depth of 920 meters (3,018 feet), we came upon a Chaceon sp. crab perched above a cluster of hundreds of pallid sculpin eggs. By itself, this observation provided us with information about how and where these fish deposit their eggs and whether the eggs are defended or left unguarded. But that’s not it...

As we continued to watch, the crab began plucking eggs from the pile and eating them! A close zoom revealed dozens of amphipods crawling over the crab’s mouthparts, presumably scavenging and taking advantage of the sloppy feeding of the crab.

Crabs in the Chaceon genus are opportunistic feeders, meaning they will eat what they encounter, such as mollusks, polychaete worms, and even other crabs. With this observation, we can now safely add fish eggs to the menu as well!

Taking Its Time: Sea Star Predation on a Coral

Not all predation events that we are lucky enough to witness are action packed, but that doesn’t make them any less valuable to scientists. This sea star, likely Evoplosoma sp., was seen eating its way up a coral on a ridge at 2,006 meters (6,851 feet) depth during a 2017 Laulima O Ka Moana: Exploring Deep Monument Waters Around Johnston Atoll expedition dive. These sea stars are one of the most common predators of corals that we see, and, as predators, they play an important role in deep-sea ecosystem activity and diversity, impacting the deep ocean in the same way that wolves can shape a forest ecosystem. When sea stars devour coral tissue, the coral’s skeleton can become habitat for other organisms to live in, on, or around. Research suggests that sea stars can sometimes remain on deep-sea corals, feeding for over a year. As observations of the interactions between this deep-sea predator and its coral prey are rare, there is still much we don’t know about these extraordinary creatures.