In brief: Life at the bottom

A new study co-authored by NIWA marine ecologist Dr Ashley Rowden has found the first evidence that the biochemistry of fish may constrain how deep they can venture.

The secret to survival is a protein called trimethylamine N-oxide (TMAO). The more TMAO a fish has, the deeper it can go. This study shows that there seems to be a tipping point where TMAO becomes ‘uneconomical’.

To test the idea, the scientists had to get hold of a hadal snailfish. It is capable of living at a depth of more than 7000m and none have been caught in 60 years. Rowden notes the find as an example of the unique biodiversity in a special part of New Zealand’s marine estate.

“We’re incredibly lucky to have a hadal-zone trench like the Kermadec Trench right in our backyard. And it’s collaborations with the likes of the University of Aberdeen that make studying these environments possible.”

Rowden illustrates the type of pressure that has to be withstood at these depths.

“It’s like having all the weight of a cow put on just your big toe. Without high levels of TMAO it is improbable that the snailfish would be able to survive unless it has another means of dealing with the effects of high pressure.”

In order for fish to live at greater depths they need high levels of TMAO. However, too much can have negative effects. As TMAO rises proportionally to the depth, there is a point at roughly 8200m where it seems the fish cannot physiologically moderate these effects.

It has long been suspected that the pressures of the world’s deepest trenches, which descend to nearly 11,000m, would be too great for a fish to withstand. This study, for the first time, offers a biochemical explanation based on empirical data for the observation that no fish have yet been recorded from a depth greater than 8370m.

Hadal snailfish. [University of Aberdeen]