Amphipods Hitch Rides on Giant Sea Spiders in Deep Pacific
Researchers observed shrimp-like amphipods clinging to giant sea spiders in the deep Chilean Margin. The behavior was recorded at two sites, suggesting it may be a common interaction in this deep-sea environment.
Scientists have documented tiny crustaceans hitching rides on giant sea spiders in the deep southeastern Pacific Ocean. The discovery was made by a team led by Jorge Pérez-Schultheiss of Chile's National Museum of Natural History using the robotic submersible SuBastian.
Researchers observed the shrimp-like amphipods, identified as Mesopleustes abyssorum, clinging tightly to the much larger sea spiders, Colossendeis colossea. The amphipods used a long, claw-like structure at the end of their limbs to maintain a firm grip on their hosts. This unusual association was recorded during the Fkt241011 expedition onboard the research vessel Falkor(too).
Observations Across Two Sites
The team first spotted the behavior in a steep, rocky underwater canyon at a depth of 3,155 meters. According to their paper published in Ecology, two larger amphipods were attached to the sea spider's sensory and reproductive appendages, while a smaller female was on one of its walking legs.
Just four days later, the same hitchhiking was seen again roughly 225 kilometers away at a depth of 2,698 meters. There, a pair of large amphipods was attached to another giant sea spider. The researchers noted in their paper that "the association may be common and widespread in the area."
The details of the two observations are summarized in the table below.
| Location | Depth (meters) | Distance from First Site | Number of Amphipods Observed |
|---|---|---|---|
| Underwater Canyon | 3,155 | N/A | 3 (2 large, 1 small female) |
| Second Site | 2,698 | ~225 km | 2 (both large) |
Potential Reasons for the Behavior
The scientists do not yet know why this hitchhiking occurs. The fact it was observed multiple times suggests it is more than a random encounter. The team presented several possible explanations in their study.
The amphipods could be using the sea spiders for transport across vast distances, as they are poor swimmers. These giant hosts may also serve as mobile meeting spots for finding mates or avoiding predators. Another possibility is accessing food particles in an environment where resources are scarce.
An Environment Full of Mysteries
The deep sea remains largely unexplored compared to shallow waters. This leaves plenty of room for surprising discoveries like this one. The researchers conclude that more work is needed to understand the interaction fully.
Whether this interaction is accidental, a dispersal capacity for a nonmobile species, or a form of adaptation to seafloor environments with scarce food resources could be revealed with studies that involve more in situ observations, population genetic studies and trophic ecology, the team wrote. The findings were published in the journal Ecology on September 17, 2026.
