Cardiac response of the hydrothermal vent crab Segonzacia mesatlantica to variable temperature and oxygen levels

Abstract

Segonzacia mesatlantica inhabits different hydrothermal vent sites of the Mid-Atlantic Ridge where it experiences chronic environmental hypoxia, and highly variable temperatures. Experimental animals in aquaria at in situ pressure were exposed to varying oxygen concentrations and temperature, and their cardiac response was studied. S. mesatlantica is well adapted to these challenging conditions and capable to regulate its oxygen uptake down to very low concentrations (7.3-14.2 µmol.l-1). In S. mesatlantica, this capacity most likely relies on an increased ventilation rate, while the heart rate remains stable down to this critical oxygen tension. When not exposed to temperature increase, hypoxia corresponds to metabolic hypoxia and the response likely only involves ventilation modulation, as in shallowwater relatives. For S. mesatlantica however, an environmental temperature increase is usually correlated with more pronounced hypoxia. Although the response to hypoxia is similar at 10 and 20˚C, temperature itself has a strong effect on the heart rate and EKG signal amplitude. As in shallow water species, the heart rate increases with temperature. Our study revealed that the range of thermal tolerance for S. mesatlantica ranges from 6 through 21˚C for specimens from the shallow site Menez Gwen (800 m), and from 3 through 19˚C for specimens from the deeper sites explored (2700-3000 m).

Currents and topography drive assemblage distribution on an active hydrothermal edifice

“…Bythograeid crabs are known for their affinity for hydrothermally active areas (Shank et al, 1998;Cuvelier et al, 2009;Podowski et al, 2010) and are well adapted to survive harsh environmental conditions (Mickel and Childress, 1982;Vetter et al, 1987). Although the sulfide tolerance of S. mesatlantica has not been characterized, shallow (800 m) Menez Gwen vent field specimens thrive at temperatures between 6 and 21°C (Hourdez, 2018). Given that most metazoans do not have such tolerances to harsh conditions, hydrothermally active areas likely constitute a predator-free zone for S. mesatlantica.…”

Oxygen consumption rates in deep-sea hydrothermal vent scale worms: Effect of life-style, oxygen concentration, and temperature sensitivity

“…In a first set of experiments, we aimed to study the capacity of different species to compensate a decrease of environmental oxygen concentrations to meet their metabolic demand (oxyregulation). Each experiment was performed on a single individual in a flow-through system at in situ pressure (provided by High Pressure Liquid Chromatography pumps, see Hourdez, 2018) and at a temperature of 10˚C. Once placed in the flow-through vessels, animals were allowed to recover for 10-12 hours before experimentation started.…”

“…Oxygen concentration was measured with an optode (NeoFox, Ocean Optics) placed in the outflow of the system (i.e. after the pressure relief valve), either after flowing through the aquarium containing the specimen or after flowing through a tubing that bypassed the aquarium (Hourdez, 2018).…”

“…For oxyregulation experiments, the curve described in Hourdez (2018) was used to fit to the datapoints and determine the oxygen concentration below which oxyregulation was no longer possible (critical oxygen concentration).…”

“…Crabs and shrimp from hydrothermal vents however possess greater ventilatory capacity (increased scaphognathite surface area) compared to shallow-water temperate relatives (Decelle et al, 2010). Studies on Bythograea thermydron (Gorodezky and Childress, 1994) and Segonzacia mesatlantica (Hourdez, 2018) have shown that these crabs can regulate their oxygen uptake to compensate for the decrease of environmental concentration down to very low levels compared to shallow-water relatives. This oxyregulation does not involve a modification of the heart rate but most likely relies on a modification of the ventilation rate (Hourdez, 2018).…”