Dataset: LT50 Copepod Pressure Vessel Experiment Fkt230627
Deployment: FKt230629

Specimens were collected with ROV SuBastian at 9°N 50’N and 104°W along the East Pacific Rise in the Tica vent area and sites Bio9 and Biovent (~2500 m depth) during expedition FKt230627 in July 2023 aboard R/V Falkor(too). 

Deep-sea hydrothermal vent copepods were sampled from two different habitats: diffuse flow habitats dominated by Riftia pachyptila tubeworms and Bathymodiolus thermophilus mussels, and focused flow habitats dominated by Alvinella pompejana pompeii worms. A suction sampler and/or ROV manipulator grabs were used to sample detritus and megafauna respectively. These samples were then sorted for copepods and subsampled to be used for a total of 118 LT50/LD50 exposure incubations performed on board the research vessel. Each incubation contained 3 replicate vials with 10 copepods each, for a total of 3540 copepods.

Diverse exposure times, temperatures, pressures, and oxic/anoxic conditions were selected to explore the tolerance of deep-sea hydrothermal vent copepods in relation to habitat, temperature, oxygen concentration and pressure. Exposure times were the following: 2h, 4h, 8h, 10h. Temperature ranges for each incubation were established based on the ROV’s temperature probe readings. A control temperature of 4°C was always included to represent similar thermal conditions to the ambient bottom water around hydrothermal vents. The other temperatures (12, 22, 25, 28, 31, 34, 37, 40, 43°C) were selected to obtain a complete survival curve that ranged from ~100% survival at the lowest temperature to ~0% at the highest temperature for each habitat/time/oxygen/pressure treatment combination. Two oxygen concentration conditions were tested: oxic (163.88 ± 5.82 µM before and 95.63 ± 9.14 µM after incubations) and anoxic (0.24 ± 0.11 µM before and 1.76 ± 0.38 µM after incubations). Concentrations were monitored before and after incubations using self-adhesive Oxygen Sensor Spots mounted on the inside of the incubation vials (SP-PSt3-SA) and a fiber-optic oxygen meter (Fibox 4).

Ten live copepods were transferred using a pipette to each seawater-filled 5.9 ml glass vial (Exetainer 719W) equipped with an airtight pressure relief cap. The glass vials were placed into pressure vessels and pressurized up to 200 bar (3000 psi) using a Waters 515 HPLC Pump, and then placed in a water bath (ARGOLAB WB 12 Lt) to keep a constant temperature. At the end of each incubation the vessel was depressurized, and the content of each vial was examined under a Leica EZ4 W stereomicroscope to record the number of living/dead copepods. After the experiment, dead copepod specimens were not disposed, but instead were fixed in 95% Ethanol for preservation.

The data was used to estimate the median lethal temperature (LD50) corresponding to each exposure time (LT50) by fitting a survival curve to the temperature and respective copepod survival data using Nonlinear Least Squares regression and isolating the theoretical 50% survival temperature.