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 pCO2 and
species identity, with significant levels of heterogeneity for all
analyses. Calcium and magnesium content were significantly lower in
animals held at pCO2 levels of 1500-1999 μatm as
compared to those under ambient pCO2. At lower
pCO2 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 pCO2 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
pCO2 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 CO2. Future studies
will need to accommodate the high variability of crustacean responses to
ocean acidification, as well as ecologically-relevant ranges of
pCO2 conditions, when designing experiments with
conservation-level endpoints.