Giant crustaceans inhabit most of Earth's deep ocean floors, according to a surprising study

Sometimes, scientists will label a creature as being “rare” simply because it’s hard to find. One such example is the supergiant amphipod Alicella gigantea , which can reach about 13.4 inches in length. After years of scattered sightings, A. gigantea is now confirmed to appear far more often than suspected. According to new findings presented by Dr. Paige J. Maroni from the University of Western Australia , this hefty crustacean, which looks like a giant white shrimp, seems to have been hiding in plain sight. “Historically, it has been sampled or observed infrequently relative to other deep-sea amphipods, which suggested low population densities,” Dr Maroni said. “And, because it was not often found, little was known about the demography, genetic variation and population dynamics with only seven studies published on DNA sequence data.” Amphipods in extreme environments Researchers have known for decades that amphipods are found in nearly every aquatic environment on Earth, including lakes, coral reefs, and ocean trenches. Many species occupy extreme depths, with the hadal zones extending well below 19,700 ft into waters under crushing pressure. Amphipods are a diverse group of crustaceans that share some traits with shrimp, yet many adapt in unexpected ways. A few can flourish in low temperatures and pitch-black conditions, which explains how they manage life in the deepest parts of our planet. Alicella gigantea is elusive The earliest camera evidence of A. gigantea emerged in the North Pacific at around 17,400 ft. For more than 20 years, this species remained elusive, and scientists suspected it was truly uncommon. Only a handful of physical samples turned up, making it look like these giant scavengers existed in scattered pockets. As field expeditions continued, a larger picture began to form, and that picture changed everything. Scientists compiled 195 records from multiple expeditions worldwide to piece together a sweeping view of Alicella gigantea . Genetic data from two mitochondrial genes and one nuclear gene showed minimal differences across populations, reinforcing the idea that this amphipod likely moves around the depths with few barriers. It appears that this species has a presence in a vast network of trenches and plains, spanning the Pacific, Atlantic, and Indian Oceans. “As exploration of the deep-sea increases to depths beyond most conventional sampling, there is an ever-growing body of evidence to show that the world’s largest deep-sea crustacean is far from rare,” Dr Maroni said. This discovery challenges old assumptions and expands our view of what we thought possible for an invertebrate in such an extreme environment . Single global species Despite appearing in distant waters, Alicella gigantea shows very little genetic change. Some marine specialists propose that lower temperatures and stable conditions in the deep sea slow down evolutionary divergence, keeping populations similar across large areas. Others suggest that shifting ocean currents and tectonic changes over millions of years opened pathways for these animals to spread. In either scenario, the evidence supports one widely distributed type, rather than many closely related variants. Spilhaus world projection showing the sample sites...

Preview: ~500 words