They’re small, with soft flabby bodies, over-sized heads and thin, weakly developed bones. Aliens? That’s one thought, but they’re more likely a group of freaky fish that have evolved to the point that they can live in the oxygen-depleted dead zones of the ocean. Are they the eventual survivors of whatever it is we eventually do to destroy the rest of life on Earth?
“I could hardly believe my eyes. We observed cusk eels, grenadiers, and lollipop sharks actively swimming around in areas where the oxygen concentration was less than one percent of typical surface oxygen concentrations. We were in a suboxic habitat, which should exclude fish, but instead there were hundreds of fish. I immediately knew this was something special that challenged our existing understanding of the limits of hypoxia [low-oxygen] tolerance.”
In a paper published in the journal Ecology, Natalya Gallo, graduate student at the Scripps Institution of Oceanography, described what she and a research team from the Monterey Bay Aquarium Research Institute (MBARI) found on a cruise and dive trip to some deep basins in the Gulf of California that are known to be suboxic – so-called dead zones where oxygen levels are so low that few if any animals or plants can live there. The remotely operated Doc Ricketts underwater robot (developed by MBARI) was sent to explore the Cerralvo Trough at depths between 600–900 meter (1,969–2,953 ft) and unexpectedly found the freaky-looking fish, not just surviving but thriving in schools numbering in the hundreds.
“Many other types of fish are considered tolerant of low-oxygen conditions. But the fish in these parts of the Gulf are like the winners among a group of elite Olympic athletes.”
These Michael Phelps of the dead zone were predominantly cusk eels (Cherublemma emmelas) and lollipop cat sharks (Cephalurus cephalus). Both are bottom feeders with large heads and slender soft bodies (hence the name ‘lollipop’) which are good for living at great depths, and large gills which may help them take in enough of the suboxic water to get sufficient oxygen to live.
Obviously, these ‘Olympian’ fish don’t have Phelps-like Olympic bodies. It turns out they don’t have Phelpsian appetites either. What and how much these cull eels and cat sharks eat is still a mystery because they live in a dead zone which is, as its name suggests, dead. No fish, no plants, no worms, no Big Macs. It could be that their small, flabby, almost gelatinous bodies have low metabolisms but Gallo – whose Ph.D. thesis focuses on animals living in very low-oxygen environments – wants more data, which requires more dives into the Cerralvo Trough and the Gulf of California.
This level of oxygen-deprived living is so unprecedented, the MBARI team believes these particular fish need a new name or classification. Their suggestion is ‘ligooxyphile’, which is Greek for ‘little oxygen lover’.
Little oxygen lovers. Is that the future of the rest of the creatures in our oceans … and possibly for us landlubber creatures as well? Team member and biological oceanographer Lisa Levin thinks it may be too late.
“Continued warming of the ocean may challenge even the most hypoxia-tolerant fishes. Elevated temperature will lower the solubility of oxygen in the water while increasing the amount of oxygen the fish need to survive.”
Do we all need to evolve into small, flabby, big-headed mouth-breathers? Or are we already?