AFSC/RACE/SAP/Foy: Effects of ocean acidification on larval Tanner crab: Kodiak Island, Alaska.

To study the effects of ocean acidification we examined the effects of ocean acidification on the larval stages of the economically important southern Tanner crab, Chionoecetes bairdi.

Ovigerous females were reared in one of 3 treatments: control (ambient pH ~8.1), pH 7.8, and pH 7.5 for 2 years. Larvae in year 1 were from oocytes developed in the field whereas larvae in year

2 were from oocytes developed under acidified conditions. Larvae hatched each year, were also exposed to 3 pH treatments to examine starvation-survival, morphology, condition, and calcium/magnesium

content. Approximately 300 larvae were stocked in multiple treatments for testing the effect of pH. Hatching success was measured as the total % of larval hatched from a full clutch while duration

was the number of days over which hatching occurred. Hatching success did not differ among treatments in 2012 but varied between 46 to 87% in 2013 dependent on pH treatment. Larval mass was highest

in pH 7.8 in 2012 and lowest in the control, however in 2013 the highest larval mass was in the control water. There were only small (not significant) changes in magnesium or calcium content among

treatments in 2012 however, the reduction in both minerals at higher pH was greater in 2013. There was higher percent carbon and nitrogen contents in pH 7.5 larvae in 2013. The morphology of Tanner

crab larval was assessed from 200 larvae stocked in multiple 2 L beakers. There was no effect of treatment on larval morphometrics. In 2012 and 2013, we examined if embryos developed under acidified

conditions affected larval morphology by assessing 15 newly hatched larvae from each treatment. There was again no effect of treatment on larval morphometrics. Starvation survival experiments

were performed in 1 L sized PVC inserts. In both years larvae from embryos that developed in pH 7.5 water survived about 3 days longer than those that developed in control water. However, in 2012

larvae from embryos that had developed in pH 7.8 water were similar to control larvae whereas in 2013 they were intermediate between the control and pH 7.5 larvae. The overall effects of treatment

at the larval stage appeared to be better condition and initial survival at lower pH, however multiple years of treatment led to lower survival.

The purpose of the larval studies was to test the effects of lower pH on larval hatching success, condition, and survival.

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The accuracy of the hatching success and duration data is high (100%) due to the type of data (counts) and due to the frequency of observations

during the experiment. The accuracy of the larval experimental data is high (less than 1% difference from actual). The instruments used for mass,

Ca and Mg had low measurement error. The accuracy of the Larval Morphology data is high due to consistency during morphological measurement from experienced

scientists with replicate readings when appropriate. In addition, the frequency of observations was high during the experiment to ensure that the temporal

changes were captured. The accuracy of the Larval Survival data is high (100%) due to the type of data (i.e. counts).

The larval experimental datasets are complete (i.e. not filtered).

Hatching success and duration, larval morphology, and Ca and Mg information were broadly compared to previous studies on Tanner crab mineral content and

to similar measurements made on similar crab species and statistically compared to a control (alpha=0.05). Larval mass and survival information was compared

broadly to known values and statistically compared to a control (alpha=0.05); replicate response was also considered.

For example, for comparing we used the study described in Mathis, Jeremy T., Jessica N. Cross,

and Nicholas R. Bates. "Coupling primary production and terrestrial runoff to ocean acidification and carbonate

mineral suppression in the eastern Bering Sea." Journal of Geophysical Research: Oceans (19782012) 116.C2 (2011).

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