Meta-analysis suggests variable, but pCO2-specific, effects of ocean acidification on crustacean biomaterials

Abstract

Crustaceans comprise an ecologically and morphologically diverse taxonomic group. They are typically considered resilient to many environmental perturbations found in marine and coastal environments, due to effective physiological regulation of ions and hemolymph pH, and a robust exoskeleton. Ocean acidification can affect the ability of marine calcifying organisms to build and maintain mineralized tissue and poses a threat for all marine calcifying taxa. Currently, there is no consensus on how ocean acidification will alter the ecologically-relevant exoskeletal properties of crustaceans. Here, we present a systematic review and meta-analysis on the effects of ocean acidification on the crustacean exoskeleton, assessing both exoskeletal ion content (calcium and magnesium) and functional properties (biomechanical resistance and cuticle thickness). Our results suggest that the effect of ocean acidification on crustacean exoskeletal properties varies based upon seawater pCO and species identity, with significant levels of heterogeneity for all analyses. Calcium and magnesium content were significantly lower in animals held at pCO levels of 1500-1999 μatm as compared to those under ambient pCO. At lower pCO levels, however, statistically significant relationships between changes in calcium and magnesium content within the same experiment were observed: a negative relationship between calcium and magnesium content at pCO of 500-999 μatm and a positive relationship at 1000-1499 μatm. Exoskeleton biomechanics, such as resistance to deformation (microhardness) and shell strength, also significantly decreased under pCO regimes of 500-999 μatm and 1500-1999 μatm, indicating functional exoskeletal change coincident with decreases in calcification. Overall, these results suggest that the crustacean exoskeleton can be susceptible to ocean acidification at the biomechanical level, potentially predicated on changes in ion content, when exposed to high influxes of CO. Future studies will need to accommodate the high variability of crustacean responses to ocean acidification, as well as ecologically-relevant ranges of pCO conditions, when designing experiments with conservation-level endpoints.

Exoskeletal predator defenses of juvenile California spiny lobsters (Panulirus interruptus) are affected by fluctuating ocean acidification-like conditions

“…In mantis shrimp, exoskeletal hardness and stiffness remained the same despite increases to Mg content (deVries et al, 2016). Altered mineralization, either through increases or decreases, has the potential to disrupt the material properties and mechanical efficiency of organism structures, but the thresholds for these effects are likely specific to structures and species (Siegel et al, 2022). As such, there is still much to learn about the relationship between changes to material composition and the degree to which the material is compromised.…”

“…A better understanding of potential impacts is especially needed for crustaceans, which have generally garnered less OA research attention than other marine calcifiers (Whiteley, 2011;Siegel et al, 2022), but have an exoskeleton that is complex, multifunctional, and highly variable within a single individual. The decapod crustacean exoskeleton is heterogenous and comprised of mineral, usually in the form of calcite, magnesian calcite, amorphous calcium carbonate, and sometimes calcium phosphate, that is embedded among lamellae of sugars and protein, which stack to form the distinct layers of the epicuticle, exocuticle, and endocuticle (Travis, 1963;Huner et al, 1979;Vigh and Dendinger, 1982;Addadi et al, 2003;Dillaman et al, 2005;Boßelmann et al, 2007;Kunkel et al, 2012).…”

“…Within the exocuticle and endocuticle, layer thickness, lamellae stacking density, and mineral composition can all be adjusted to produce a spectrum of material properties that support a range of exoskeleton functions (Raabe et al, 2005;Chen et al, 2008). Crustaceans can construct exoskeletal regions with specificity to meet functional demands (Melnick et al, 1996;Dutil et al, 2000;Chen et al, 2008) and likely have complex responses to OA-like conditions (Siegel et al, 2022).…”