How brachyuran crabs survive in highly acidic areas near shallow-water hydrothermal vents

by Bob Yirka , Phys.org

Landscape and physiochemical features of the hydrothermal vent system study area.

 (a) Picture of the surface seawater around the upper sublittoral hydrothermal vent region 

of the study site at Kueishan Island (24°50′N, 121°57′E). Kueishan Island lies at the 

southern rifting end of the Okinawa Trough (inserted panel). A large area of the sea 

surface has a white appearance because of sulfur particles from the volcanic vent 

discharge. (b) Underwater photographs of the vent system demonstrate the low 

abundance of metazoans in these sub-tropical waters. (c) A high density of X. testudinatus 

crabs which are endemic to sulfide-rich hydrothermal vent systems can be found in 

sulfide-rich crevices in the immediate vicinity of the vents. Active feeding behavior can be

 observed where crabs scavenge sulfide-rich sediments and dead zooplankton that were 

killed by the toxic vent discharge. (d) sulfide concentrations were measured along two 

transects in the hydrothermal vent area of Kueishan Island. 

The schematic illustration shows the seafloor properties at the two sampling transects. 

The first transect included sampling sites 1–5 and was oriented in the north–south direction

 at 17 m depth. The second transect included sampling sites 6–9 with an east–west 

orientation and descended from 8 m to 20 m depth. Values are presented as mean ± s.d.

 (n = 4). (e) Content of sulfur compounds was measured in the seawater (SW) near 

Kueishan island (open bars) and the haemolymph of the native X. testudinatus (filled bars)

. Values represent the means ± s.d. (n = 3–7). (f) Sulfide tolerance as a function of 

exposure time of X. testudinatus (determined in the present study) compared to other 

marine species. Credit: Proceedings of the Royal Society B: Biological Sciences (2023).

 DOI: 10.1098/rspb.2022.1973

A team of researchers affiliated with multiple institutions in Taiwan and one in Germany has discovered the means by which brachyuran crabs are able to survive in highly acidic waters near shallow-water hydrothermal vents. In their paper published in Proceedings of the Royal Society B, the group describes how they studied crab specimens and the environment in which they live to solve the puzzle of their existence.

Hydrothermal vents are hot springs that exist on the sea floor. In most instances, they occur along mid-ocean ridges. Such vents spew heated water, along with other materials, into the surrounding water creating a mix. In this new effort, the researchers were curious about a species of crab that lives in a shallow-water hydrothermal vent field off the southeast coast of Kueishantao Island, near Taiwan. They noted that the crab is the only metazoan creature living in the area due to the large amount of sulfide emitted by the hydrothermal vent.

To find out how the crab survives in such a hostile environment (hydrogen sulfide is toxic to most animals) the researchers collected samples of the water in which they lived and conducted experiments on the crabs they found living there. They also captured some of the crabs and brought them back to their lab for closer inspection.

In looking at the crabs, the researchers found that they had unique gills (located under the carapace)—they were able to oxidize the sulfide to thiosulfate and to bind it to hypotaurine which led to the generation of thiotaurine, which is much less toxic than hydrogen sulfide. And then, bacteria living in the gills absorbed the thiotaurine—they used it as an energy source and in so doing made it even less toxic.

The net result was that the crab was able to get the oxygen it needed from the water without succumbing to the hydrogen sulfide from the hydrothermal vent. The researchers suspect that the detoxification allows the crab to gain energy from the thiotaurine as well. They note that the arrangement with the bacteria makes the crab a holobiont—a species able to survive in an environment inhospitable to virtually all other creatures.

More information: Pei-Hsuan Chou et al, Cellular mechanisms underlying extraordinary sulfide tolerance in a crustacean holobiont from hydrothermal vents, Proceedings of the Royal Society B: Biological Sciences (2023). DOI: 10.1098/rspb.2022.1973

Journal information: Proceedings of the Royal Society B 

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