AFSC/RACE/SAP/Long: Data from: Effects of Ocean Acidification on Juvenile Red King Crab (Paralithodes camtschaticus) and Tanner Crab (Chionoecetes bairdi) Growth, Condition, Cal...

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Kodiak Fisheries Research Center

Note: Dataset migrated by Dan Woodrich (AFSC data management coordinator) on 12/16/2021. Contact: Daniel.woodrich@noaa.gov

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For this experiment, we used filtered seawater pumped into the laboratory from Trident Basin (Kodiak, AK). The experimental setup used flow-through water at ambient temperature and salinity. As we did not control temperature, the conditions the crabs were exposed to mimicked the natural fluctuations to which crabs would naturally be exposed. We used seawater acidified with CO2 to pHs based on projected future levels of atmospheric CO2 and the predicted change in seawater pH associated with it: 1) ambient pH (about 8.0), 2) 7.8 pH c. 2100, and 3) 7.5 pH c. 2200. To obtain the desired treatment levels CO2 was bubbled in ambient local seawater to a pH of 5.5. This water was mixed with seawater to the treatment pHs using a peristaltic pump whose speed was controlled by a pH probe in a head tank similar. Water from the head tank was supplied to the experimental containers. When the measured pH in the experimental containers deviated from the nominal pH levels by more than 0.02 units the settings on the pH probe were adjusted accordingly.

Red king crabs were supplied by the Alutiiq Pride Shellfish Hatchery. Ovigerous red king crabs were captured in Bristol Bay, Alaska, in commercial pots during the winter of 2009. Larvae were reared to the first crab stage before being transported to the Kodiak lab in insulated shipping containers. Juvenile Tanner crabs were caught in a modified benthic sled with a 1 m mouth opening in local Kodiak waters. Throughout the experiment, the crabs were fed to excess on a gel diet of “Gelly Belly ” (Florida Aqua Farms, Inc., Dade City, Florida, USA) with Cyclop-eeze powder and pollock bone powder (United States Department of Agriculture, Agricultural Research Service, Kodiak, Alaska, USA). Crabs were fed three times a week and old food was removed just prior to feeding. The experiment was performed in three tanks (120 (L) x 60 (W) x 60 (H) cm), each of which was randomly assigned a treatment. Ninety crabs per species were randomly assigned to each of three treatments (30 crabs per species per treatment). Each crab was placed in an individual holding cell made of a piece of PVC pipe (diameter 5.1 cm) with mesh glued on the bottom. Flow-through water from the head tanks was provided to each cell. The Tanner crab experiment was started on June 4, 2010, and the red king crab experiment on June 10, 2010. Daily, five randomly selected cells per treatment were monitored for pH and temperature. pH was measured using a Ross Combination glass bulb pH electrode (Thermo Electron Corporation, Beverly, MA) calibrated with Tris buffer on the pHF scale. Weekly water samples were taken from the head tanks, poisoned with mercuric chloride, and sent to an analytical laboratory for salinity, dissolved inorganic carbon (DIC), and alkalinity analysis. DIC was determined using a CM5014 Coulometer with a CM5130 Acidification Module (UIC Inc., Joliet, IL) using Certified Reference Material from the Dickson Laboratory (Scripps Institute, San Diego, CA). Alkalinity was measured via open cell titration. Crabs were checked daily for molting or death. Dead crabs and exuvia were removed from the tanks for morphometric analysis. The carapace from each exuvia and dead crab was carefully removed and photographed under a stereomicroscope. Partway through the experiment, we noted that it had become difficult to remove the carapace off dead crabs, particularly in the low pH treatments, so we started photographing dead crabs before attempting to remove the carapace. If successful, we photographed the carapace as well and used that for image analysis; otherwise, we used the image of the dead crab. Image analysis was performed using Image-Pro Plus v. 6.00.260 imaging software (Media Cybernetics, Inc., Bethesda, Maryland, USA) calibrated with a micrometer. On red king crab we measured carapace width, carapace length, rostrum base width, orbital spine width, and the first spine length. On Tanner crab, we measured carapace width CW), carapace length (CL), carapace length to the rostrum, carapace length to the eye orbit, rostrum base width, rostrum length, orbital spine width, and orbital spine length. The wet mass of each crab, after it was carefully blotted dry, was measured at the beginning of the experiment and 7 days after each molt. The experiments were ended on December 20, 2010, when temperatures had dropped low enough that the crabs were no longer molting frequently. At the end of the experiment, all crabs were sacrificed by freezing. The crabs were imaged for morphometric analysis as above. Each crab was dried to a constant mass at 60 C to obtain the dry mass. Calcium, magnesium, potassium, and sodium content in each crab was determined at an analytical laboratory using a Dionex Ion Chromatography system. The conditions of the crab at the end of the experiment were calculated as the condition index (also known as the body mass index) defined as the dry mass in grams divided by the CL^3 (red king crab) or CW^3 (Tanner crab) in millimeters.