In the eerie silence and profound darkness of the Arctic night, a silent war rages beneath the icy surfaces. Amidst temperatures that would freeze most life forms in their tracks, tiny crustaceans have adapted to thrive.
These amphipods, discovered in Kongsfjorden, Svalbard, are not just surviving; they are preying on live jellyfish-a behavior previously unseen and undocumented.
A Hidden Battle Beneath the Ice
FRED TANNEAU/AFP via Getty Images
Scientists have long known that food resources become scarce during these prolonged nights. Many marine organisms enter a metabolic resting state to conserve energy.
However, these amphipods have developed a different strategy; they shift from specialized diets to become omnivorous predators.
"They are opportunistic feeders that can switch from being herbivores or detritivores to being carnivores depending on the availability of food," explains Dr. Charlotte Havermans, a researcher at the Alfred Wegener Institute in Germany and the lead author of the study that revealed this phenomenon.
Dr. Havermans and her colleagues were conducting a routine sampling of the marine fauna in Kongsfjorden, a fjord on the west coast of Spitsbergen, the largest island of the Svalbard archipelago.
They were using a device called a light-frame on-sight key species investigation system (LOKI), which is essentially a camera attached to a net that captures images and specimens of the planktonic organisms in the water column.
As they examined the images and the samples, they noticed something unusual: several amphipods of different species were attached to or close by the jellyfish, and some of them had visible bite marks or missing parts.
They also observed that the jellyfish were still alive and moving, indicating that they were not scavenged after death.
The researchers were astonished by this discovery. These crustaceans have evolved a mechanism to profit from potentially less rewarding foods available throughout the harsh winter months. It's not just about survival but an intricate dance of adaptation and evolution.
The amphipods belong to a group of crustaceans called hyperiid amphipods, which are widely distributed in the world's oceans and play an important role in the marine food web.
They are usually found in the mesopelagic zone, which is the layer of water between 200 and 1000 meters deep, where light is scarce and pressure is high.
Hyperiid amphipods have a remarkable diversity of shapes, sizes, and colors. Some of them have large eyes, antennae, or appendages that help them detect and capture their prey.
Others have transparent or reflective bodies that help them camouflage or avoid predators. Some of them even have bioluminescent organs that produce light for communication or attraction.
These adaptations are the result of millions of years of evolution in response to the environmental conditions and the ecological interactions of these animals.
However, the amphipods in Kongsfjorden have shown a more recent and rapid adaptation to the extreme seasonal changes in the Arctic.
The Arctic is characterized by a dramatic contrast between the long days of summer and the long nights of winter. During the summer, the sun never sets and the water is rich in phytoplankton, which are microscopic algae that form the base of the marine food chain.
During the winter, the sun never rises and the water is covered by a thick layer of ice, which blocks the light and reduces the primary production.
This means that the food resources for the amphipods and other marine organisms vary greatly throughout the year. During the summer, the amphipods can feed on the abundant phytoplankton or other herbivorous zooplankton, which are small animals that graze on the algae.
During the winter, however, the amphipods have to rely on other sources of food, such as detritus, which are organic particles that sink from the surface, or other animals that are still active in the dark.
The researchers hypothesize that the amphipods have learned to exploit the jellyfish as an alternative food source during the winter. Jellyfish are cnidarians, which are invertebrates that have stinging cells called nematocysts.
They use these cells to capture and paralyze their prey, which are usually small fish or zooplankton. However, the amphipods seem to have developed a way to avoid or resist the nematocysts and feed on the jellyfish without being harmed.
The researchers suspect that the amphipods use their sharp mandibles, which are mouthparts used for biting and chewing, to pierce the jellyfish and suck out their fluids and tissues.
They also suggest that the amphipods may have some chemical or physical protection against the nematocysts, such as a thick cuticle, which is the outer layer of their exoskeleton, or a coating of mucus, which is a slimy substance that covers their body.
The researchers also note that the amphipods may benefit from the symbiotic relationship that some jellyfish have with algae. Some jellyfish, such as the ones found in Kongsfjorden, harbor algae inside their cells, which provide them with oxygen and nutrients through photosynthesis.
The amphipods may be able to access these algae and obtain some of the energy and carbon that they produce.
This revelation underscores an essential aspect of Arctic ecology-life is resilient, adaptive, and far more complex than previously understood.
Every discovery like this brings scientists one step closer to unraveling the mysteries encapsulated within this frozen world.
