Meeting Abstract
Marine species that develop calcified structures during early development may be especially vulnerable to ocean acidification (OA). Although free spawning is common, species in several taxa undergo early development inside encapsulating structures. These structures could potentially buffer against effects of OA as they do against other environmental risks. On the other hand, embryos developing inside such structures may generate low internal pH as a byproduct of respiration. I used a microelectrode to measure pH gradients inside gelatinous egg masses of 11 species of gastropods. These species differed in egg mass design (strings, ribbons, and globose forms) and thickness (minimum dimension for diffusive exchange of gases and ions). Central pH in egg masses was highly variable across species, ranging from 7.77 to as low as 6.49 (for masses held at pH = 7.82). As expected, older embryos generated lower internal pH and steeper pH gradients, reflecting increased metabolism and CO2 production. Although globose masses were thicker and developed lower central pH, they had shallower pH gradients than ribbons, reflecting the effect of gel in spacing embryos and reducing pH stress in parallel with its effect on reducing oxygen stress. Egg masses held in acidified seawater (approx. pH = 7.42) exhibited slightly lower central pH but shallower pH gradients, suggesting that embryos were somewhat buffered from an external drop in pH. These results indicate that encapsulated embryos may experience chronically low pH and that egg mass design influences the degree of pH depression. As a result, encapsulation could lead embryos to evolve resilience to low pH and to future OA conditions. I will discuss this potential for pre-adaptation in light of the developmental performance of encapsulated embryos under elevated CO2 as presented in a separate poster.
