New Discovery: David Hoffman of the Deep
With crushing pressure, little to no light and ice cold temperatures, it was previously thought that life could not occur in the deep oceans of our planet. Even more extreme are hydrothermal vents: deep sea hotspots that release geothermally super-heated water laced with sulphides. Here, the pressure allows water to erupt at temperatures well above normal boiling point, whilst still remaining as a liquid. Far from being a biological wasteland, these vents are actually teaming with life, and are even thought to be the origins of life on our planet. Without any plant matter to kickstart a food chain, many animals here rely upon sulfide-feeding bacteria to sustain them. One such species is the newly discovered Kiwa tyleri. A type of squat lobster, K. tyleri is the third species of the Yeti Crab group to be discovered, all of which are deep sea species. It’s common name, however, is less of the deep seas and more of the stars: the Hoff Crab, after the popular 90’s actor, David Hasselhoff.
A paper in PloS One journal presented a detailed view of this particular squat lobster and it’s habitat. The Hoff Crab can be found on hydrothermal vents on the East Scotia Ridge (ESR), in the Southern Ocean, making it the only member of its genus to be found outside the Pacific Ocean. Hydrothermal vents on the ESR are surrounded by extremely cold waters, sometimes less than 0°C. Thanks to this, the Hoff Crab and it’s neighbouring animals are thought to be tightly constrained to their chosen vent sites. K. tyleri is found to be living, and indeed, dominating, two vent sites on the ESR, on the northern and southern branches.
Normally, Reptantia decapod crustaceans (crabs and lobsters) are not found south of the polar front that marks the Antarctic, but heating from the vents allows Hoff Crabs to survive in the Southern Ocean. However, the steep gradient in temperatures, from 0°C to 400°C forces the squat lobster to remain within a narrow range determined by temperature and need for chemosynthetic nutrition, via it’s symbiotic bacteria.
To utilise the sulphide-feeding bacteria, the Hoff Crab’s white exoskeleton is covered in setae, upon which filamentous bacteria attach. It is this hairy appearance that give’s the Hoff Crab it’s name, as comparisons were drawn between it and David Hasselhoff’s famously hairy chest, seen in Baywatch series. Bacteria are highly specialised to their environment: those found on K. tyleri are distinct from those found in bacterial mats on the vents themselves, and are closely related to other symbiotic groups. Similarly, regional variation occurs. At one vent site, E2, the bacteria Gammaproteobacteria dominated K. tyleri setae by up to 75%, whereas at vent site E9, almost 100% of epibionts were Epsilonproteobacteria.
With such a niche habitat, competition for space is fierce. Hoff Crabs are found in high densities close to hot water emission sites. However, females must leave the sites when brooding and laying eggs, as the chemically harsh environment is too extreme for the developing larvae. Unusually for crustaceans, K. tyleri heavily invests in it’s young, producing only a few, large eggs. Another unusual evolutionary strategy of the Hoff Crab is that the larvae fully develop, feeding off a yolk, rather than being released early and feeding upon plankton during development. This guaranteed food source, alongside the slow development dictated by the cold water benefits the larvae in that they have ample time to disperse and find new vents upon which to mature. The cost though, it that the mother must expose herself to cold conditions close to, or beyond her physiological boundary.
The discovery of the Hoff Crab, alongside similar species gives further evidence to the richness of species found around hydrothermal vents. Despite it’s amusing name, further studies on this species, and it’s relationship with sulphide-feeding bacteria could help to redefine our understanding of food webs and even the origins of life.