Scientists have discovered that the planet’s largest amphipod – a ghostly crustacean the size of a loaf of bread – is far more common than previously thought.
Long considered rare due to infrequent sightings, new research now suggests that this elusive giant (Alicella gigantea, or A. gigantea) may be quietly thriving in 59% of the world’s oceans.
The study, led by Paige J. Maroni and published in the journal Royal Society Open Science, presents the "largest and most extensive dataset ever compiled on the world’s largest species of amphipod."
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Searching for 'supergiants'
Amphipods – a group of crustaceans known for their comma-shaped bodies – inhabit all aquatic environments around the world, including the deep ocean. They are among the most diverse crustacean orders, with over 10,000 living species.
Alongside the well-documented species, there many seemingly 'rare' ones. One of the best examples is A. gigantea, commonly known as the 'supergiant amphipod’. With a maximum body length of 34cm – roughly the size of a loaf of bread – this heavyweight of the animal kingdom is recognised as the world’s largest amphipod species.
The huge amphipod was first filmed in its natural environment in the 1970s – recorded at a depth of 5,304m in the North Pacific Ocean. Since then, the animal has only been collected in small numbers "signifying low population densities and providing a sense of rarity," Maroni explains.
However, Maroni adds, "there is an ever-growing body of evidence to show that A. gigantea should be considered far from rare.
"While their population density may be low relative to other deep-sea amphipods, they appear to inhabit an extraordinarily large geographical range."
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Keen to find out more, Maroni and colleagues analysed 195 A. gigantea records from 75 locations worldwide. Some of these records were based on newly sequenced specimens, which were "collected using autonomous lander systems that featured invertebrate and small vertebrate traps baited with whole mackerel."
With the aid of genetic data from DNA, the team mapped the amphipod’s global distribution.
"Despite the absence of records from the Arctic, Antarctic and Mediterranean, our global depth-based habitat suitability projection suggests that A. gigantea could inhabit approximately 59% of the world’s oceans and all six major ocean bodies," say the authors.
The Pacific Ocean was identified as the largest potential habitat for A. gigantea, spanning around 104.6 million km², followed by the Atlantic Ocean, which provides around 47.7 million km² of suitable habitat.
The Mediterranean Sea was found to have the smallest extent of suitable habitat, covering approximately 0.03 million km².
The authors point out that "of the 75 sites included in this analysis, 67 are from the Pacific Ocean, four are from the Indian Ocean and four are from the Atlantic Ocean, which may influence these results."
The paper concludes that "this finding confirms that the supergiant amphipod is far from 'rare' but instead represents a single, globally distributed species with an extraordinary and expansive range across the deep sea."
Main image: Alicella gigantea. Credit: Paige J. Maroni et al
Find out more about the study: The supergiant amphipod Alicella giganteamay inhabit over half of the world’s oceans
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