Some events in the ocean happen all the time but are very rarely seen by humans. So, when a manta ray researcher saw scarlet excrement streaming from a manta ray’s behind, she was surprised.
“I've been filming this [New Zealand] population of oceanic manta rays for four years and have only seen two mantas poo,” says Lydia Green, founder and project director of Manta Watch Aotearoa New Zealand who had been filming the female manta as she cruised calmly through the water.
The ray rolled up her cephalic fins (the horn-like projections on her head) – this “is usually an indication of a 'change in mode',” explains Green – and two remoras (suckerfish) that were swimming with the manta moved to her rear end.
Then, the manta released an enormous, red poo. “The poop is bright red due to the manta's primary prey, krill,” she explains. “Krill have tiny red exoskeletons that are indigestible, and mantas eat upward of 20kg of krill per day!”
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This excrement wasn’t just special because of how rare it is to see – this manta was cruising at the surface so she could see the red poop in all its glory. “The vibrant colour contrast of the poop against the water was awesome to film,” she says, adding that “the poop trails looked white” in her previous sightings.
The bowel movement seemed to come out of nowhere, although there were clues. “The manta didn't show any signs that it was about to do a massive poop!” says Green. “I had a hunch something was about to happen when the remoras enthusiastically made their way to the base of the manta ray's tail.”
Even more astoundingly, the remoras then started feeding on the faeces. “You can see the remoras get into a bit of a feeding frenzy,” says Green, who describes them “opening their mouths to try and eat as much poop as possible within this 'fast food' window of opportunity!”
This might all sound gross but poo plays an important role in fertilising the ocean and supporting the food chain.
Analysing this excrement can also help researchers learn more about the lives of these gentle creatures, says Green: “Knowing the poop's composition enables researchers to understand what food sources and habitats are important for this specific manta population.”
Image and video credit: Lydia Green, Manta Watch NZ
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