W. Christopher Long

Effects of ocean acidification on the embryos and larvae of red king crab, Paralithodes camtschaticus

The effects of the decline in ocean pH, known as ocean acidification, on marine species are not well understood. To test the effects on embryos and larvae of red king crab, Paralithodes camtschaticus, ovigerous crab and their larvae were held in CO2-acidified (pH 7.7) and control (ambient; pH 8.0) seawater during development. Morphometrics, hatch duration, fecundity, survival, mineral content, and condition were measured. Acidified embryos had 4% larger eyes and 5% smaller yolks, while mean hatch duration was 33% longer and female fecundity was unaffected. Acidified embryos also resulted in 4% longer larvae while acidified larvae had lower survival. Calcium content of both larvae and female carapaces after molting increased by 5% and 19%, respectively. Although ocean acidification may increase larval size and calcium content, the implications of this are unclear and decreased survival is likely to harm red king crab populations.

Red King Crab, Paralithodes camtschaticus, Size-Fecundity Relationship, and Interannual and Seasonal Variability in Fecundity

ABSTRACT Stock assessment of Alaska red king crab, Paralithodes camtschaticus, can be improved by incorporating embryo production, which requires an understanding of the size-fecundity relationship and an understanding of interannual and seasonal variability in fecundity. We collected red king crab egg clutches from Bristol Bay, AK, during summer 2007 to 2010 and autumn 2007 to 2009 and estimated individual fecundity using dry weight methods. Fecundity increased with female size up to 138 mm carapace length (CL), at which point the slope decreased by 40%, suggesting senescence. Fecundity varied significantly but slightly (maximum, 5%) among years. Fecundity was consistently lower in autumn than spring, suggesting brood loss, with a 6% decrease between seasons in females smaller than 138 mm CL and a 10% decrease in larger females. When incorporating embryo production in stock assessments, differences in the size-fecundity relationship should be accounted for and rates of brood loss can be used to predict larval output more effectively if fecundity cannot be measured shortly before hatching. To include potential environmental effects on the relationship, time series of fecundity and female size should be extended over a wider range of future temperature conditions.

Ocean Acidification Affects Hemocyte Physiology in the Tanner Crab (Chionoecetes bairdi).

We used flow cytometry to determine if there would be a difference in hematology, selected immune functions, and hemocyte pH (pHi), under two different, future ocean acidification scenarios (pH = 7.50, 7.80) compared to current conditions (pH = 8.09) for Chionoecetes bairdi, Tanner crab. Hemocytes were analyzed after adult Tanner crabs were held for two years under continuous exposure to acidified ocean water. Total counts of hemocytes did not vary among control and experimental treatments; however, there were significantly greater number of dead, circulating hemocytes in crabs held at the lowest pH treatment. Phagocytosis of fluorescent microbeads by hemocytes was greatest at the lowest pH treatment. These results suggest that hemocytes were dying, likely by apoptosis, at a rate faster than upregulated phagocytosis was able to remove moribund cells from circulation at the lowest pH. Crab hemolymph pH (pHe) averaged 8.09 and did not vary among pH treatments. There was no significant difference in internal pH (pHi) within hyalinocytes among pH treatments and the mean pHi (7.26) was lower than the mean pHe. In contrast, there were significant differences among treatments in pHi of the semi-granular+granular cells. Control crabs had the highest mean semi-granular+granular pHi compared to the lowest pH treatment. As physiological hemocyte functions changed from ambient conditions, interactions with the number of eggs in the second clutch, percentage of viable eggs, and calcium concentration in the adult crab shell was observed. This suggested that the energetic costs of responding to ocean acidification and maintaining defense mechanisms in Tanner crab may divert energy from other physiological processes, such as reproduction.

Primiparous Red King Crab Paralithodes camtschaticus are Less Fecund than Multiparous Crab

ABSTRACT Incorporating fecundity into stock assessment models may improve stock assessment and management of Bristol Bay red king crab Paralithodes camtschaticus. To do this, the size—fecundity relationship for the population must be established, including variability due to female reproductive state. In 2012, egg clutches were collected from red king crab in Bristol Bay, AK, and individual fecundity was estimated. Best evidence suggests small females were primiparous (brooding first egg clutch), which provided the opportunity to compare estimated fecundity of primiparous and multiparous (brooding second or subsequent egg clutch) females. In the best-fit model, fecundity increased with female size and below 108.8 mm carapace length (CL) the slope of the size—fecundity relationship decreased by 27%.Multiparous females were 28%–30% more fecund than primiparous females of the same size. If managers incorporate fecundity into stock assessment models, the differences in fecundity between primiparous and multiparous females should be considered, otherwise population fecundity will be overestimated if the size—fecundity relationship of only multiparous females is used in the calculations because of the differences in fecundity between primiparous and multiparous females of the same size.