AFSC/RACE/SAP/Swiney: Effects of ocean acidification and increased temperatures on juvenile red king crab

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Alaskan waters

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

Seawater was acidified using the same methods described in Long et al. (2013a). Briefly, sand filtered seawater was pumped into the Alaska Fisheries Science Center’s Kodiak Laboratory seawater facility from 15 and 26 m depth intakes in Trident Basin. A tank of pH 5.5 was established by bubbling CO2 into ambient seawater. This pH 5.5 water was mixed with ambient seawater in the treatment head tanks via peristaltic pumps controlled by Honeywell controllers and Durafet III pH probes. The ambient head tank did not receive any pH 5.5 water. Waters from the treatment head tanks were then supplied to the treatment tubs. To heat the water, a 200W submersible heater was placed in each heated treatment tub. In the coldest months of the experiment, a 100W heater was added to the warmest treatments to maintain the correct temperatures. Temperature and pHF (free scale) were measured daily from three random inserts in each treatment tub (see below for experimental set-up details) using a Durafet III pH probe calibrated with a TRIS buffer, and when the pH deviated from the target pH by more than ±0.02 pH units, the Honeywell controller set points were adjusted to bring the pH back to the target value. Heater set points were changed manually based upon ambient temperature for each day to maintain target treatment temperatures.

Weekly water samples from the treatment head tanks were taken, fixed with mercuric chloride, and sent to an analytic laboratory for dissolved inorganic carbon (DIC) and total alkalinity (TA) analysis. Two laboratories which used similar, but slightly different, instruments were used during the course of the study. At the first laboratory, 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) (Dickson et al., 2007). The TA was measured via open cell titration according to the procedure in Dickson et al. (2007). At the second laboratory, DIC and TA were determined using a VINDTA 3C (Marianda, Kiel, Germany) coupled to a 5012 Coulometer (UIC Inc., Joliet, IL) using Certified Reference Material from the Dickson Laboratory (Scripps Institute, San Diego, CA) and the procedures in DOE (1994). Laboratory Study Ethical approval for this research was not required by any federal, state, or international laws because the study was conducted on invertebrates which are not covered under these laws.

Young-of-the-year were reared in the Kodiak Laboratory from an ovigerous female collected in Bristol Bay, Alaska, June 2011 and shipped live to the laboratory. Thirty young-of-the-year crab were randomly assigned to each of 6 treatments: 1) ambient pH, ambient temperature, 2) ambient pH, ambient +2ºC, 3) ambient pH, ambient +4ºC, 4) pH 7.8, ambient temperature, 5) pH 7.8, ambient +2ºC, and 6) pH 7.8, ambient +4ºC. Each treatment was contained in a 53 (L) x 38 (W) x 23 (H) cm tub. Each tub had a flow rate of 600 mL min-1 from the head tank. The young-of-the-year were reared in individual inserts constructed from 40 mm inner diameter PVC pipe with 750 µm mesh attached to the bottom and the inserts were placed inside the treatment tub. The area of this insert was determined to be optimal for individual rearing of juvenile red king crab of the size used in this study (Swiney et al., 2013b). Inserts were placed on plastic grating to raise them off the bottom of the tub. Water was delivered into each insert from above via a submersible pump connected to a manifold which recirculated water within each tub. A temperature logger that recorded data every 30 minutes was placed into each tub. To acclimate the crab to the treatment temperatures, each day the temperature in the tubs was increased by 1ºC until the desired temperature was obtained. Day 1 of the experiment (August 5, 2012) was marked when all of the treatments reached the correct temperature; the experiment ran for 184 d.

Throughout the duration of the experiment, crab were fed a gel diet of Gelly Belly (Florida Aqua Farms, Inc., Dade City, FL, USA) enhanced with Cyclop-eeze powder (Argent Laboratories, Redmond, WA, USA), pollock bone powder (US Department of Agriculture, Agricultural Research Service, Kodiak, AK, USA), and astaxanthin (Daly et al., 2012). Crab were fed to excess 3 times per week and old food was removed prior to each feeding. Each insert was checked daily for exuvia and mortalities which were removed for growth and morphometric analysis. Carapaces were carefully removed from all exuvia and mortalities and photographed under a dissecting microscope. Carapace width, carapace length, rostrum base width, orbital spine width, and the first spine length (Figure 1) were measured in mm using Image Pro Plus v. 6.00.260 imaging software (Media Cybernetics, Inc., Bethesda, MD, USA, Long et al., 2013b).