Katherine M. Swiney

Effects of Ocean Acidification on Juvenile Red King Crab (Paralithodes camtschaticus) and Tanner Crab (Chionoecetes bairdi) Growth, Condition, Calcification, and Survival

Ocean acidification, a decrease in the pH in marine waters associated with rising atmospheric CO2 levels, is a serious threat to marine ecosystems. In this paper, we determine the effects of long-term exposure to near-future levels of ocean acidification on the growth, condition, calcification, and survival of juvenile red king crabs, Paralithodes camtschaticus, and Tanner crabs, Chionoecetes bairdi. Juveniles were reared in individual containers for nearly 200 days in flowing control (pH 8.0), pH 7.8, and pH 7.5 seawater at ambient temperatures (range 4.4–11.9 °C). In both species, survival decreased with pH, with 100% mortality of red king crabs occurring after 95 days in pH 7.5 water. Though the morphology of neither species was affected by acidification, both species grew slower in acidified water. At the end of the experiment, calcium concentration was measured in each crab and the dry mass and condition index of each crab were determined. Ocean acidification did not affect the calcium content of red king crab but did decrease the condition index, while it had the opposite effect on Tanner crabs, decreasing calcium content but leaving the condition index unchanged. This suggests that red king crab may be able to maintain calcification rates, but at a high energetic cost. The decrease in survival and growth of each species is likely to have a serious negative effect on their populations in the absence of evolutionary adaptation or acclimatization over the coming decades.

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.

HATCH TIMING, INCUBATION PERIOD, AND REPRODUCTIVE CYCLE FOR CAPTIVE PRIMIPAROUS AND MULTIPAROUS RED KING CRAB, PARALITHODES CAMTSCHATICUS

Abstract Adolescent and mature female red king crab Paralithodes camtschaticus were captured by scuba divers and held in seawater tanks at the Kodiak Fisheries Research Center at ambient temperatures. Over three separate years, we monitored dates of embryo extrusion, timing and length of the hatching period, duration of embryological developmental, total degree-days, and volume and number of larvae released on a daily basis. Primiparous females extruded their embryos on a mean date of 3 February, two months prior to extrusion by multiparous crab. Mean hatching date for primiparous females occurred 16 days prior to that of multiparous females in 2001, and 12 days earlier in 2003. Primiparous females required a mean of 365 days and 2601 degree-days for complete embryonic development, whereas multiparous females required significantly less time, with a mean of 328 d, and 2482 degree-days. Although multiparous females were significantly larger than primiparous females, there was no significant difference between reproductive types in the time required for complete hatching (mean 32 days), total volume (mean 308 mL) or number of larvae released (mean 106, 884). Multiparous female crabs held in filtered or unfiltered (raw) seawater showed no differences in hatch timing, hatching days, or volume released. Virtually all larvae (91-95%) were released in the 4 hour period between 1800 and 2200 hours, and 50% were released in the first half-hour of darkness. Extended hatching exhibited by red king crabs is not synchronous with the occurrence of planktonic food sources, but may be an adaptation to the uncertainty of food availability. Shorter development times for multiparous embryos are necessary to complete the reproductive cycle prior to obligatory molting before extruding the next batch of eggs. This information was incorporated into a conceptual model of the first 3 years of reproduction for red king crab.

Thermal Effects on Embryonic Development and Hatching for Blue King Crab Paralithodes platypus (Brandt, 1850) Held in the Laboratory, and a Method for Predicting Dates of Hatching

Abstract Climate change may affect crab populations via thermal effects on embryo development and hatching. To test this, we measured the duration of development and hatching for the embryos of 11 blue king crabs Paralithodes platypus held at 2.3 ± 0.45, 4.3 ± 0.31, and 6.1 ± 0.61°C. Embryo area, length, and width, eye length and width, and percent yolk were measured biweekly from digital images, and hatching larvae were collected daily from individual crabs. Data were compared between eggs of identical age (weeks since fertilization). Temperature did not have a significant effect on embryo measurements, but did affect development indices (percent yolk and eye size). Hatching was significantly delayed at colder temperatures with about a 46-day difference from 2.3°C to 6.1°C. Length of development was related to temperature via a power function, and ranged from 410 ± 8 days at 6.1°C to 434 ± 11 days at 2.3°C. Length of hatching increased from 40 ± 4.6 days at 2.3°C to 55 ± 6.2 days at 6.1°C. A model for predicting hatching dates from an eye index was developed using a quadratic equation. Embryo development at 4.3 and 6.1°C was arrested between weeks 35 and 50; this evidence, plus other behavioral observations, suggests that crabs may be able to adjust development rates to partially compensate for temperature changes.

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.

Survival, growth, and morphology of blue king crabs: effect of ocean acidification decreases with exposure time

&NA; Ocean acidification is an altering marine carbonate chemistry resulting in potential effects to marine life. In this study, we determine the effects of decreased pH on the morphology, growth, and survival of juvenile blue king crab, Paralithodes platypus. Crabs were reared at three pH levels: ambient (control, pH ˜8.1), pH 7.8, and pH 7.5, for 1 year and monitored for morphological changes, survival, and growth. Exposure to seawater at pH 7.8 had no effect on morphology or mortality and had only a minor effect on growth compared with the ambient treatment. However, exposure to seawater at pH 7.5 substantially increased mortality and decreased growth compared with the ambient treatment. The best fit model of mortality rate at pH 7.5 showed an initially high mortality rate, which dropped to become comparable to the mortality rate in the other treatments. This suggests phenotypic variability or plasticity in juveniles and may indicate acclimation by blue king crab to ocean acidification. As such, blue king crab may have scope for evolutionary adaptation in response to gradually changing pH levels. However, effects on other life‐history stages, sub‐lethal effects, carryover or transgenerational effects, and interactions with other stressors, such as increased temperature, still need to be investigated.

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.