Conceived and designed the experiments: ST. Performed the experiments: AB ST. Analyzed the data: AB. Contributed reagents/materials/analysis tools: ST. Wrote the paper: AB ST.
The authors have declared that no competing interests exist.
Depth zonation of fauna on continental margins is well documented. Whilst increasing hydrostatic pressure with depth has long been considered a factor contributing significantly to this pattern, discussion of the relative significance of decreasing temperature with depth has continued. This study investigates the physiological tolerances of fed and starved specimens of the bathyal lysianassoid amphipod
The deep sea is one of the largest habitats on Earth. Phenotypic
Hydrostatic pressure (0.1 MPa = 10 m depth) effects on living systems initially result from thermodynamic shifts in chemical reaction rates
To the authors knowledge no organism-level study has extensively examined the interaction of hydrostatic pressure and temperature effects on a deep-sea species across and beyond the entire range experienced within the known natural distribution. This study tests the hypothesis that the bathymetric range of the necrophagous bathyal amphipod species
All experiments were conducted in accordance with the legal requirements of the United Kingdom. The use of Crustacea is unregulated in the United Kingdom and subsequently does not require ethics approval by a specific committee.
Adult specimens of the scavenging amphipod species
Temperature was sampled by ROV on 17th July 2009. Temperatures within the known bathymetric range of the lysianassoid amphipod
Oxygen consumption rates (MO2) of individual animals were used to assess acute respiratory response to pressure following a minimum of 3 hours exposure to experimental temperatures. Experimentation was conducted within 1 week of capture (unacclimated to atmospheric pressure and fed), after 2 months food deprivation (acclimated to atmospheric pressure and starved), and within 1 week of feeding (cod) subsequent to 2 months food deprivation (acclimated to atmospheric pressure and fed). Experimental pressures (0.1, 5, 10, 15, 20, 25 or 30 MPa) and temperatures (1, 3, 5.5 or 10°C) were selected to represent those found across and beyond the natural distribution of the species. Due to cruise time constraints experiments with unacclimated animals were restricted to the two temperatures closest to that of the sample site: i.e. 3 and 5.5°C. Five individuals were exposed to each experimental combination. Animals were sampled randomly and were not reused in the experiments; each specimen was exposed to a single combination of experimental conditions. A total of 70 unacclimated and fed animals, 140 acclimated and starved animals, and 140 acclimated and fed animals were used in experimental treatments.
Oxygen consumption rates were measured using an adaptation of previously described protocols
To eliminate any bias due to bacterial oxygen demand or calibration, individual respiration rates (MO2) were obtained by comparison with control chambers (no animals) exposed to the same experimental conditions. Respiration rates are therefore an average for the 10 minutes during which the organisms were exposed to experimental conditions. Oxygen saturation did not fall below 50% saturation under any treatment, minimising the potential for any hypoxic exposure effect
The absence of correlation between body size and weight-specific oxygen consumption has been reported for deep-sea amphipods and attributed to species-specific metabolic characteristics and adaptation to low food supply
Data were not normally distributed (Kolmogorov-Smirnov test,
Comparing mean MO2 of unacclimated and fed animals to mean MO2 of acclimated and fed animals (3 and 5.5°C only;
In the absence of an effect of acclimation to atmospheric pressure on the interaction of temperature and pressure effects, unacclimated and acclimated treatments were pooled. The effect of temperature on the relationship between pressure and mean (±1 s.e.) rate of oxygen consumption (MO2) of fed
Comparing mean MO2 of acclimated and starved animals to mean MO2 of acclimated and fed animals (
(
The effect of pressure was independent of starvation (
Measurement of acute respiratory response was both necessary as a result of technological constraints, and expedient in assessing the organism's ability to tolerate acute exposure to extreme environmental conditions. Long-term maintenance of organisms at high pressure is possible (reviewed by
Although respiratory rates measured in acute exposures may be higher than routine rates
Respiration rate of the deep-sea mysid
As expected
Effects of low temperatures and high pressures on physiological processes have previously been observed to be analogous
The combinations of temperature and hydrostatic pressure used during this study were chosen to represent the environmental conditions found in and around the natural distribution of this species. The levels at which physiological impairment occurs (hydrostatic pressure greater than 20 MPa at temperatures of 1°C and 3°C) are consistent with the limit of the natural distribution range reported for
Whilst temperature has long been regarded as the principal factor restricting the latitudinal distribution of marine invertebrates (for review see
Increases in depth range have been observed in North Sea fishes in response to climate change
The authors' thanks are due to the captain and crew of