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Shellfish Assessment Program - Ocean Acidification & Climate: Past Research


Effects of Ocean Acidification on Southern Tanner Crab Reproduction and Early Life History

Photo of measurements made on southern Tanner crab embryos.
Measurements made on southern Tanner crab embryos.

Ocean acidification, a decrease in ocean pH due to absorption of anthropogenic atmospheric CO2, has variable effects on different species. To examine the effects of long-term exposure on Tanner crab embryonic development, hatching success, calcification, and larvae, ovigerous females were reared in one of three treatments: ambient pH (~8.1), pH 7.8, and pH 7.5 for 2 years.

Embryos and larvae in year 1 were from oocytes developed in the field and appear to be resilient to ocean acidification. Likewise, wild-brooded larvae also appear to not be sensitive to ocean acidification. Embryos and larvae in year 2 were from oocytes developed under acidified conditions.

Oocyte development appears to be sensitive to ocean acidification and effects carryover and altered embryonic development, reduced hatching success, and affected larval morphology, size, and metabolic rate.

Percent calcium was reduced among females exposed to pH 7.5 waters and their carapaces were noticeably more pliable than the carapaces in the other treatments. Softer carapaces may result in reduced defenses against predators and a reduction in the ability to feed on prey with hard parts such as shells.

The results from this long-term study suggest that projected ocean pH levels within the next two centuries will likely have a pronounced impact on Tanner crab populations unless the crab are able to acclimatize or adapt to changing conditions.

        Photo of newly hatched Tanner crab larvae             Photo of experimental set-up for Tanner crab larval experiment
        Newly hatched southern Tanner crab larvae.             Experimental set-up for southern Tanner crab larval experiment.

Ocean Acidification and Increased Temperature Effects on Young of the Year

Photo of experimental set-up for young-of-the-year red king crab experiment. Each insert contains 
			one red king crab
Experimental set-up for young-of-the-year red king crab experiment. Each insert contains one red king crab.

Multiple stressor studies are needed to better understand the effects of oceanic changes on marine organisms.

To determine the effects of near-future ocean acidification and warming temperature on young of the year red king crab survival, growth, and morphology, we conducted a long-term (184 d) fully crossed experiment with two pHs and three temperatures: ambient pH (~7.99), pH 7.8, ambient temperature, ambient +2°C, and ambient +4°C, for a total of 6 treatments.

Mortality rate increased with both reduced pH and by higher temperatures, but interpretation of the multistressor effects is not straightforward as a clear trend was not observed.

Photo of young-of-the-year red king crab 
			carapace measurements. OW = orbital spine width, SL = first spine length, RW = rostrum length, 
			CW = carapace width, CL = carapace length. Click image to enlarge.
Young-of-the-year red king crab carapace measurements. OW = orbital spine width, SL = first spine length, RW = rostrum length, CW = carapace width, CL = carapace length. Click image to enlarge.


A synergetic effect was observed; the pH 7.8 and ambient +4°C temperature treatment had the lowest survival, with only 3% surviving to the end of the experiment. However, antagonistic effects were observed in the pH 7.8 ambient +2°C temperature treatment; the mortality rate in this treatment was less than the mortality rate of each of the stressors individually.

Despite the effects on mortality, neither decreased pH nor increased temperature had an effect on growth or morphology. The results of this study combined with other studies suggest that ocean acidification and warming may have profound negative effects on red king crab populations in the upcoming decades unless the species is able to quickly adapt or acclimate to changing conditions.







Effects of Ocean Acidification on Juvenile Golden King Crab

Most, if not all, life stages of golden king crab (Lithodes aequispinus) are likely living in acidified waters.

Carbon chemistry data is typically limited to surface, shallow, and shelf waters, not the deep-waters that golden king crab inhabitant. However, the current calcite saturation horizon is reported to be approximately 250 m in the eastern Bering Sea and in September 2008 in the Gulf of Alaska waters deeper than approximately 175 to 225 m were undersaturated with regards to aragonite.

These calcite and aragonite saturation horizons are shallower than where golden king crab of all life stages are generally thought to inhabit.

In this study we reared young of the year golden king crab in local ambient pH (~8.2), pH 7.8 and pH 7.5 waters for 127 days to study the effects of ocean acidification on survival, growth, and morphology.

            Photo of a juvenile golden king crab in a 
			holding container. Click image to enlarge             Photo of juvenile golden king crab carapace 
			measurements. OW = orbital spine width, SL = first spine length, RW = rostrum length, 
			CW = carapace width, CL = carapace length. Click image to enlarge.
            Photo of juvenile golden king crab holding container. Click image to enlarge.             Juvenile golden king crab carapace measurements. OW = orbital spine width, SL = first spine length, RW = rostrum length, CW = carapace width, CL = carapace length. Click image to enlarge.


Effects of Ocean Acidification on Juvenile Red King and Southern Tanner Crab

Photo of a juvenile southern Tanner crab in a
			holding container during 200 day experiment. Click image to enlarge.
Photo of a southern juvenile Tanner crab in a holding container during 200 day experiment. Click image to enlarge.

Ocean acidification, a decrease in the pH in marine waters caused rising atmospheric CO2 levels could affect Alaska crab species.

We conducted an experiment exposing juvenile red king crabs, Paralithodes camtschaticus, and southern Tanner crabs, Chionoecetes bairdi, to three pHs. Juveniles were held for nearly 200 days in ambient (pH 8.0), pH 7.8, and pH 7.5, seawater.

Survival was decreased by ocean acidification and 100% of red king crabs died after 95 days at pH 7.5. In addition, ocean acidification lowered the growth rate for each species.

Photo of interns measure and weighing baby crabs at beginning of experiment
Interns Kaitlyn Harris and Heather Page measure and weigh baby crabs at the beginning of experiment.

Examining the effects of ocean acidification on calcium levels (the substance that makes crab shells hard) and the condition index (a ratio between the size and mass of the crabs) showed some differences between the species.

In acidified water, red king crab had the same amount of calcium but lower condition index, while southern Tanner crabs had less calcium but the same condition index. It may be that red king crab put so much energy into maintaining the calcium levels of their shell that they don't have enough left over for growth.

In both cases, the lower survival and growth caused by ocean acidification is of concern because it suggest that the populations of these species, and the fisheries dependent on them, could be affected by future CO2 levels.




Effects of Ocean Acidification on the Embryos and Larvae of Red King Crab

Microscope photo of red king crab embryos
			close to hatching. Click image to enlarge
Red king crab embryos close to hatching. Photographed under a microscope. Click image to enlarge.

The anthropogenic release of CO2 into the atmosphere has resulted in increasing CO2 concentrations in both the atmosphere and the oceans and a reduction in the pH of the ocean known as ocean acidification. Marine life may be vulnerable to ocean acidification.

In this project, we determined the effects of ocean acidification on late-stage embryos and larvae of red king crab. Egg-bearing red king crab were held in either control (pH 8.0) or acidified (pH 7.7) treatments. Every month a sample of eggs were taken from each female and photographed under a microscope and measured.

When the larvae hatched they were used in a fully crossed experiment; larvae that had been exposed to control water as embryos were held in both acidified and control water, as were larvae that had been exposed to acidified water as embryos. We measured how acidification affected the calcification and mortality of the larvae.

Photo of newly hatched red king crab larvae
Newly hatched red king crab larvae.

Embryos reared in acidified water were larger, but had smaller yolks than those in control water.

Larval survived less well acidified water. Larvae held in acidified water were more calcified than those held in control water. A reduction in larval survival could reduce population and the fisheries dependent on it.

More research on the effects of ocean acidification detailing how it affects later stages and how it affects the physiology of the crabs is necessary to understand the overall effect it will have on red king crabs.










Shellfish Assessment Program - Ocean Acidification & Climate Research CURRENT RESEARCH


Related Publications

  • SWINEY, K. M., W. C. LONG, and R. J. FOY. 2016. Effects of high pCO2 on Tanner crab reproduction and early life history- Part I: long-term exposure reduces hatching success and female calcification, and alters embryonic development. ICES Journal of Marine Science 73(3):825-835.

  • LONG, W.C, K. M. SWINEY, and R. J. FOY. 2016. Effects of high pCO2 on Tanner crab reproduction and early life history, Part II: carryover effects on larvae from oogenesis and embryogenesis are stronger than direct effects. ICES Journal of Marine Science 73(3):836-848.

  • LONG, W. C., K. M. SWINEY, C. HARRIS, H. N. PAGE, and R. J. FOY. 2013. Effects of ocean acidification on juvenile red king crab (Paralithodes camtschaticus) and Tanner crab (Chionoecetes bairdi) growth, condition, calcification, and survival. PLoS ONE, 8(4):e60959. doi:10.1371/journal.pone.0060959. Online

  • LONG, W. C., K. M. SWINEY, and R. J. Foy. 2013. Effects of ocean acidification on the embryos and larvae of red king crab, Paralithodes camtschaticus. Marine Pollution Bulletin, 69:38-47.


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