One species of deep-sea fish has chosen to incubate its eggs in a seemingly impossible place: the baking hot rocks of hydrothermal vents. Such vents are openings in the seabed that spew sulphurous gases and fluids from the bowels of the Earth out into the ocean.
鈥淭his is the first time this egg-incubating behaviour, using heat from active hydrothermal vents, has been recorded in the marine environment,鈥� says study leader of the Charles Darwin Foundation on Santa Cruz Island in the Gal谩pagos. He suspects the fish do it 鈥渢o speed up egg incubation time鈥�.
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Salinas de Le贸n and his colleagues were exploring the , 45 kilometres north of Darwin Island and three kilometres under the sea. They were using a remotely operated vehicle called Hercules.
A few metres from a 鈥�black smoker鈥� vent, the team spotted 157 eggs. Each was about the size of a mobile phone and looked like a hot water bottle with fingers at each corner.
They used one of Hercules鈥檚 arms to collect聽a handful of egg cases. 鈥淲e found they were at a very early developmental stage,鈥� says Salinas de Le贸n.
Closer examination revealed that the eggs belonged to a deep-sea fish called the ().
Hercules wasn鈥檛 able to take the temperature of the rocks on which the eggs were deposited. However, the water 3.5 metres above the surface averaged 2.7掳C, a degree or so warmer than water away from the vents. This suggests the vents provide a warm refuge for marine life, as 鈥渢emperatures on the [vent surface] are likely to be considerably higher,鈥� says Salinas de Le贸n.
鈥淭his is the first time ray eggs have been documented from a vent site,鈥� says of the University of Oxford. 鈥淯sually, these sites are viewed as being too toxic for young life stages of animals to tolerate, but the tough cases of the eggs may offer some protection, and clearly the warmer temperatures will allow more rapid development compared to colder temperatures of the surrounding sea.鈥�
Little is known about the lifestyles of Pacific white skates. 鈥淲e have no information about what babies do when they hatch, where they spend their early days, [or] how long before they leave the site,鈥� says Salinas de Le贸n.
However, better-studied relatives like the (B. parmifera) incubate their eggs for three-and-a-half years at temperatures of 4.4掳C. Based on that, Salinas聽de Le贸n estimates that, at 2.7掳C, Pacific white skate eggs would take four years to hatch.
Many other creatures live on hydrothermal vents, such as giant tubeworms and yeti crabs. The skates spend most of their time elsewhere, but the vents may be a crucial site for them nevertheless. 鈥淧erhaps this offers a window on how some vent-endemic taxa began their evolution towards life around these hostile environments,鈥� says Rogers.
Scientific Reports
