Effects of ocean acidification on red king crab larval survival and development

Abstract

Ocean acidification, a decrease in oceanic pH resulting from the uptake of anthropogenic CO2, can be a significant stressor for marine organisms. In this study, we reared red king crab larvae from hatching to the first crab stage in four different pH treatments: current surface ambient, diel fluctuation to mimic larval migration between the surface and mixed layer under current ambient conditions, pH 7.8, and pH 7.5. Larvae were monitored throughout development and the average length of each stage was determined. At each of the zoeal stages, the glaucothoe stage, and the first crab stage, we measured survival, morphometry, dry mass, and carbon, nitrogen, calcium, and magnesium content. Red king crab larvae were highly resilient to ocean acidification. There were no differences among treatments in survival or in average stage length. Although there were clear ontogenetic trends in size, weight, and elemental composition, most of these did not vary with pH treatment. Zoeal morphology did not vary among treatments, although glaucothoe and C1 crabs were slightly smaller in pH 7.8 than in the ambient treatment. Ambient larvae also had a slightly higher mass than pH 7.8 larvae but not pH 7.5. Ambient larvae had higher magnesium contents than pH 7.8 and pH 7.5, but calcium levels were the same. Ambient larvae also had slightly lower carbon and nitrogen content than pH 7.8 and pH 7.5 larvae but only in the 4th zoeal stage. Overall this study suggests that red king crab larvae are well adapted to a wide range of pH conditions and are unlikely to be significantly affected by ocean acidification levels projected for the next two centuries.

Narrowed gene functions and enhanced transposon activity are associated with high tolerance to ocean acidification in a juvenile subarctic crustacean

“…Survival, growth, and development results were reported in Long et al [55]. Briefly, survival, developmental time, calcification, and mass did not differ among treatments at any stage, nor did survival or developmental time cumulatively from hatch to the C1 juvenile stage differ.…”

“…As with many rearing experiments, the cumulative survival rate to the C1 juvenile stage was low, averaging 1.9% across all replicate tanks (for details see Long et al [55]). While survival rates did not differ among treatments in this experiment [55], there could have been treatment-specific survival rates among the ~20 families, possibly resulting in genotype-specific expression patterns. We therefore assessed whether there were genetic differences among treatments.…”

“…Glaucothoe continued to be monitored until they molted to the first crab stage. Survival, growth, and development metrics were captured at each of the four zoea, glaucothoe, and C1 stages (for details, see [55]).…”

“…One study to date has explored molecular changes in OA-exposed red king crab, and found no pronounced effects on the larval transcriptome (individuals were pooled) [54] which corresponded with decreased survival rates [52]; whereas in juveniles, expression of genes involved in cuticular processes were strongly affected by OA exposure [54] despite no changes in morphology (survival and growth were negatively affected) [51]. Interestingly, Long et al [55] recently found that when red king crabs are exposed to OA during multiple stages of development-from hatch through the early juvenile stage-they are surprisingly tolerant of moderate (pH 7.8) and severe (pH 7.5) acidification, with no change in survival, growth, or development [42]. Therefore, when OA-exposure is prolonged and begins at hatch, red king crab may effectively acclimate without negative physiological impacts.…”

“…In this study, we used functional genomics to examine the molecular response of OAexposed red king crab. We leveraged juveniles from Long et al [55] that were exposed to (and tolerated) three carbonate chemistry treatments from hatching to the first crab stage (C1), thus capturing transcriptional differences among crab that are reared in historically ambient conditions along the Bering Sea shelf (pH 8.0), and those acclimated to a moderately (pH 7.8) and severely (pH 7.5) acidified environments that are projected to occur in surface and bottom waters by the end of this century [15]. Using RNA-Seq, a high-throughput sequencing approach that measures gene-activity, our study provides a snap-shot of system-wide changes in energy allocation due to acidification exposure by identifying genes, their functions, and biological processes that differ in OA-reared crab [56].…”