Metabolic rates are significantly lower in abyssal Holothuroidea than in shallow-water Holothuroidea

Abstract

Recent analyses of metabolic rates in fishes, echinoderms, crustaceans and cephalopods have concluded that bathymetric declines in temperature- and mass-normalized metabolic rate do not result from resource-limitation (e.g. oxygen or food/chemical energy), decreasing temperature or increasing hydrostatic pressure. Instead, based on contrasting bathymetric patterns reported in the metabolic rates of visual and non-visual taxa, declining metabolic rate with depth is proposed to result from relaxation of selection for high locomotory capacity in visual predators as light diminishes. Here, we present metabolic rates of Holothuroidea, a non-visual benthic and benthopelagic echinoderm class, determined in situ at abyssal depths (greater than 4000 m depth). Mean temperature- and mass-normalized metabolic rate did not differ significantly between shallow-water (less than 200 m depth) and bathyal (200–4000 m depth) holothurians, but was significantly lower in abyssal (greater than 4000 m depth) holothurians than in shallow-water holothurians. These results support the dominance of the visual interactions hypothesis at bathyal depths, but indicate that ecological or evolutionary pressures other than biotic visual interactions contribute to bathymetric variation in holothurian metabolic rates. Multiple nonlinear regression assuming power or exponential models indicates that in situ hydrostatic pressure and/or food/chemical energy availability are responsible for variation in holothurian metabolic rates. Consequently, these results have implications for modelling deep-sea energetics and processes.

Slow crabs ‐ fast genomes: Locomotory capacity predicts skew magnitude in crustacean mitogenomes

“…Due to the intrinsic association between the metabolic rate and locomotory capacity, this implies that the relationship between metabolic rate and skew magnitude is negatively correlated in many crustaceans lineages. There are additional multiple lines of evidence that support our results: eurybathic organisms generally exhibit decreased metabolic rates (Brown et al, 2018;Seibel & Drazen, 2007), troglobitic isopods have a much lower metabolic rate than terrestrial isopods (Kleimenov & Alekseeva, 2002), and hypoxia negatively affects the metabolic rate in isopods (Stevens et al, 2010). Yet, we found that troglobitic and deep-sea (low oxygen environment) crustacean taxa exhibit elevated skew and ω magnitudes.…”

Morphology and genome of a snailfish from the Mariana Trench provide insights into deep-sea adaptation

“…Previous studies have suggested that mutation rates are sensitive to many factors, including environmental energy 14 , metabolic rate 15 , life-history traits 16 and, in particular, generation times 17 . Hadal species reportedly have comparatively low metabolic rates 18 , so the MHS may have a 'slow life'. Coincidentally, we observed that the female MHS produced fewer but larger eggs than females of other snailfish species, suggesting that they may have a specialized reproduction strategy (for example, epimeletic behaviour and/or eggs that hatch as juveniles rather than larvae), which could further increase the generation time.…”

Toward a reliable assessment of potential ecological impacts of deep‐sea polymetallic nodule mining on abyssal infauna

“…Direct in situ or ex situ respiration measurements on deep‐sea meiofauna have not yet been successfully done, as the animals do not survive the pressure difference when recovered to the surface, and no device has yet been built for in situ measurements. Recent in situ metabolic rates measured for the megafauna (Holothuroidea) revealed no differences between shallow‐water and bathyal individuals, but rates were considerably lower for abyssal organisms (Brown et al 2018). These results can give an indication of potentially lower metabolic rates for abyssal meio‐ and macrofauna, but currently these measurements are still lacking.…”