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Ocean acidification, a decrease in ocean pH with increasing anthropogenic CO 2 concentrations, is expected to affect many marine animals. To examine the effects of decreased pH on snow crab ( Chionoecetes opilio ), a commercial species in Alaska, we reared ovigerous females in one of three treatments: Ambient pH (~8.1), pH 7.8, and pH 7.5, through two annual reproductive cycles. Morphometric changes during development and hatching success were measured for embryos both years and calcification was measured for the adult females at the end of the 2-year experiment. Embryos and larvae analyzed in year one were from oocytes developed, fertilized, and extruded in situ , whereas embryos and larvae in year two were from oocytes developed, fertilized, and extruded under acidified conditions in the laboratory. In both years, larvae were exposed to the same pH treatments in a fully crossed experimental design. Starvation-survival, morphology, condition, and calcium/magnesium content were assessed for larvae. Embryo morphology during development, hatching success, and fecundity were unaffected by pH during both years. Percent calcium in adult females’ carapaces did not differ among treatments at the end of the experiment. In the first year, starvation-survival of larvae reared at Ambient pH but hatched from embryos reared at reduced pH was lowered; however, the negative effect was eliminated when the larvae were reared at reduced pH. In the second year, there was no direct effect of either embryo or larval pH treatment, but larvae reared as embryos at reduced pH survived longer if reared at reduced pH. Treatment either did not affect other measured larval parameters, or effect sizes were small. The results from this two-year study suggest that snow crabs are well adapted to projected ocean pH levels within the next two centuries, although other life-history stages still need to be examined for sensitivity and potential interactive effects with increasing temperatures should be investigated.

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.

Structural and mechanical properties of the decapod exoskeleton affect foraging, defense, and locomotion. Ocean acidification (OA) poses a threat to marine biomes and their inhabitants, particularly calcifying organisms. Vulnerability of the snow crab, Chionecetes opilio, a commercially important, high-latitude species, to OA has not been explored. Although all oceans are experiencing acidification, abiotic factors in high-latitude areas increase the rate of acidification. We examined the effect of long-term (2 year) exposure to decreased seawater pH (7.8 and 7.5, PCO2 ~ 760 and 1550 µatm, respectively) on exoskeletal properties in post-terminal-molt female C. opilio. Since the effects of OA vary among body regions in decapods, exoskeletal properties (microhardness, thickness, and elemental composition) were measured in five body regions: the carapace, both claws, and both third walking legs. Overall, adult C. opilio exoskeletons were robust to OA in all body regions. Decreased pH had no effect on microhardness or thickness of the exoskeleton, despite a slight (~ 6%) reduction in calcium content in crabs held at pH 7.5. In contrast, exoskeletal properties varied dramatically among body regions regardless of pH. The exoskeleton of the claws was harder, thicker, and contained more calcium but less magnesium than that of other body regions. Exoskeleton of the legs was thinner than that of other body regions and contained significantly greater magnesium concentrations (~ 2.5 times higher than the claws). Maintenance of exoskeletal properties after long-term OA exposure, at least down to pH 7.5, in adult C. opilio suggests that wild populations may tolerate future ocean pH conditions.

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.

Detrital subsidies such as leaf litter, animal carcasses, and marine wrack can profoundly shape recipient habitats by influencing resiliency and productivity. Species introductions and climate‐driven range shifts alter the quantity and quality of these subsidies in donor habitats, thereby potentially influencing recipient communities. Such impacts might be particularly important when detrital shifts alter detritivore feeding and performance. Attempts to identify a general theory predicting the consequences of invasive species on detritivores have been challenging, in part because most theories have been based on the study of microbes or consumers of living prey. Further, two recent meta‐analyses disagree about the impacts of invasive plants on detritivore populations. Here, we examined the potential impact of a human‐mediated shift in macroalgal detrital subsidy from native giant kelp (Macrocystis pyrifera) to invasive devilweed (Sargassum horneri) on recipient rocky shores, with an emphasis on exploring species‐specific impacts. We assessed consumer performance on single species diets or on a mixture in no‐choice assays, and we assessed feeding preference in choice assays. Additionally, we examined the impacts of this shift on grazing of native benthic seaweeds by an intertidal consumer assemblage. Replacing native Macrocystis with invasive Sargassum had consumer‐specific impacts on performance—suppressing growth of red abalone (Haliotis rufescens) but enhancing growth of black turban snails (Tegula funebralis). The effect of mixed diets on consumer growth also displayed consumer specificity. Also, replacing Macrocystis with invasive Sargassum increased grazing of native benthic seaweeds by a realistic detritivore assemblage, but only on the habitat‐forming brown seaweed, Silvetia compressa. Thus, invasion‐mediated changes in detrital wrack composition had consumer‐ and seaweed‐specific impacts. Such species specificity could underlie disagreements about the impact of species invasions on detritivore populations and could impede our ability to identify a general theory about how species invasions will impact recipient communities via detrital pathways.

Ocean acidification, a reduction in the pH of the oceans caused by increasing CO2, can have negative physiological effects on marine species. In this study, we examined how CO2-driven acidification affected the growth and survival of juvenile golden king crab (Lithodes aequispinus), an important fishery species in Alaska. Juveniles were reared from larvae in surface ambient pH seawater at the Kodiak Laboratory. Newly molted early benthic instar crabs were randomly assigned to one of three pH treatments: (1) surface ambient pH ~ 8.2, (2) likely in situ ambient pH 7.8, and (3) pH 7.5. Thirty crabs were held in individual cells in each treatment for 127 days and checked daily for molting or death. Molts and dead crabs were photographed under a microscope and measured using image analysis to assess growth and morphology. Mortality was primarily associated with molting in all treatments, differed among all treatments, and was highest at pH 7.5 and lowest at ambient pH. Crabs at pH 7.5 were smaller than crabs at ambient pH at the end of the experiment, both in terms of carapace length and wet mass; had a smaller growth increment after molting; had a longer intermolt period. Carapace morphology was not affected by pH treatment. Decreased growth and increased mortality in laboratory experiments suggest that lower pH could affect golden king crab stocks and fisheries. Future work should examine if larval rearing conditions affect the juvenile response to low pH.

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.

Ocean warming and acidification are expected to influence the biology of the ecologically and economically important red king crab, Paralithodes camtschaticus . We investigated transcriptome responses of adult, larval and juvenile red king crab to assess sensitivity to reduced pH and elevated temperature. In adults, gill tissue (but not heart or cuticle) responded to reduced pH by differentially regulating many genes involved in metabolic, membrane and cuticular processes, but not ionic or acid/base regulation. In larval crabs, we found little evidence for a strong transcriptomic response to pH, but did observe large differences in the transcriptomes of newly hatched and one-week old larvae. In juvenile crabs, we found that there was a strong transcriptomic response to temperature across all pH conditions, but that only extreme low pH caused transcriptomic shifts. Most of the genes in juveniles that were differentially expressed were for cuticular and calcification processes. While inferences regarding the specific biological responses associated with changes in gene expression are likely to change as resources for red king crab genomics enabled studies continue to improve (i.e. better assemblies and annotation), our inferences about general sensitivities to temperature and pH across the life stages of red king crab are robust and unlikely to shift. Overall, our data suggest that red king crab are more sensitive to warming than acidification, and that responses to acidification at the transcriptomic level occur at different levels of pH across life stages, with juveniles being less pH sensitive than adults.

Abstract This study compares timing of egg extrusion, embryo development, timing and duration of eclosion, and incubation periods of Kodiak, Alaska, primiparous and multiparous Tanner crabs (Chionoecetes bairdi) reared in identical conditions to determine if and how these variables differ between reproductive states. Female reproductive state (primiparous or multiparous) and dates of egg extrusion were recorded, eggs were sampled monthly to determine egg stage and area, and larvae were collected daily during eclosion to determine timing and duration of eclosion. Primiparous Tanner crabs extruded eggs on average 103 days earlier than multiparous females and embryos developed similarly between groups. Both groups exhibited an embryonic developmental diapause at the gastrula stage, but the length of diapause was approximately 6 months for the primiparous group and 3 months for the multiparous group. This diapause appears to synchronize eclosion. The eggs of primiparous Tanner crabs were significantly smaller than the eggs of multiparous females for a few months after extrusion, but the differences may not be biologically significant. Eclosion was relatively synchronous between the two groups, however the mean eclosion date was 10 days earlier for primiparous females and on average, eclosion took 7 days for primiparous females and 12 days for multiparous females. Primiparous Tanner crabs have an average incubation period of 489 days which is 92 days longer than the average multiparous female incubation period of 397 days. Results of this study clearly illustrate that reproductive cycles differ between primiparous and multiparous Tanner crabs which may result in different reproductive potentials. Differences between primiparous and multiparous Tanner crabs must be understood and included in models for effective stock assessment, fishery management plans, and rebuilding plans.

Stock assessment of Alaskan red king crab, Paralithodes camtschaticus (Tilesius, 1815), can be improved by incorporating reproductive output, which requires an understanding of maternal size effects on embryo and larval quality. In June 2009 and 2010, we collected clutches of recently extruded red king crab embryos in Bristol Bay, Alaska, to assess embryo quality based on dry weight, carbon and nitrogen content. To assess larval quality, we collected ovigerous females from Bristol Bay in 2007 and reared them in the laboratory until larval hatching in 2008. Larval quality based on dry weight, carbon and nitrogen content, and times to 50% mortality under starvation conditions were assessed. All samples were collected in years that were colder than the 15-year average in the eastern Bering Sea. Among the measures of embryo quality, only nitrogen content was significantly different, increasing with maternal size. Carbon and nitrogen content were significantly higher for embryos in 2009 than in 2010, suggesting inter-annual differences in maternal investment. No effect of maternal size with larval quality was found. Our results indicate that maternal size does not have a biologically significant effect on embryo and larval quality in colder-than-average years, and therefore maternal size effects on embryo and larval quality does not need to be explicitly incorporated into reproductive output estimates in stock assessments under these conditions. We are, however, cautious to extrapolate our results to years with different environmental conditions. Further study is needed to fully resolve the possible interaction of environment with maternal size effects on embryo and larval quality for red king crab.