Investigation of the Influence of Hypercapnia on the Physiology of Ovigerous West Coast Rock Lobsters, Jasus lalandii, and Their Embryonic Development.

The West Coast rock lobster, Jasus lalandii, is a key ecological species and provides an important fishery resource in South Africa and Namibia. It is found along the west coast of southern Africa in the dynamic Benguela Current upwelling system. The low seawater pH of this system is expected to decline further due to ocean acidification and increase in upwelling in terms of frequency and severity. The lobster has therefore to respond to frequent and rapid changes in pH and other environmental impacts that are predicted to become more adverse in future. Although responses to such conditions are known for mature male and juvenile lobsters, there is a lack of information on mature females and later embryonic development. We addressed this by analysing the sensitivity of ovigerous ("berried") female WCRLs and their eggs/embryos to hypercapnia (high pCO₂, low pH) and formulated the following research questions: (1) Can berried female WCRLs respond swiftly to large changes in pH? (2) What physiological mechanisms facilitate a potential response to a rapidly declining pH, i.e., acute hypercapnia? (3) Does a potential response persist during prolonged hypercapnia? (4) Are eggs/embryos impacted by hypercapnia? To investigate this, we exposed berried WCRLs to acute (pH 7.5) and chronic (up to 60 days at pH 7.5 and 7.8) hypercapnia. We applied extracellular acid-base analysis, microscopic examination of egg growth and development, and SEM of female exoskeleton structure and egg membranes. The results revealed that berried females efficiently respond to acute and chronic hypercapnia by means of increasing bicarbonate concentrations in the haemolymph. Moreover, embryo growth and development are not impacted by chronic hypercapnia, but growth shows geographical area-specific differences. We conclude that females and embryos of J. lalandii are as resilient to hypercapnia as previously shown for males and juveniles.