Declining pH levels caused by absorption of accumulating atmospheric CO2 in the ocean threaten the normal development of early life stages and particularly impair the ability of calcifying organisms to construct their shells. An experiment was conducted to determine the direct effects of reduced pH on % hatching of fertilized eggs, survival and developmental stages of trochophore larvae of the Donkey’s ear abalone, Haliotis asinina. The ambient pH (7.97 ± 0.02) of experimental seawater was reduced by bubbling food-grade CO2 to obtain the desired pH levels of 7.78 ± 0.03, 7.60 ± 0.03 and 7.40 ± 0.02 as treatments. There were increasing negative impacts of reduced pH on the mean % hatched trochophores (97.6 at ambient pH conditions, 83.9 at pH 7.78, 24.1 at pH 7.60, and 1.4 at pH 7.40). Significant impacts of reduced pH were also observed on mean % survival of trochophores (98.3 at ambient pH conditions, 84.9 at pH 7.78, 24.1 at pH 7.60, and 1.4 at pH 7.40). Of the surviving trochophores, 23.2 ± 3.2% (mean ± sd) of those exposed to pH 7.60 were morphologically deformed but in much lower pH treatment (pH 7.40), all the trochophores were deformed. At pH 7.78, only 63.3 ± 3.7% of the surviving trochophores developed normally compared to 96.7 ± 1.6% normal trochophores at ambient pH conditions. Normal trochophores have prototrochal cells and girdle fully developed and developing shell tissue. Malformed trochophores showed highly undefined morphological characters and cleavage failed to progress to further developmental stages. In conclusion, the early larval development of H. asinina was found to be highly sensitive to reduced pH levels projected for the end of the present century. Therefore, future rise in CO2 concentration in tropical marine waters will likely pose a significant threat to the natural population densities of this species.
Tahil A. S. & Dy D. T., in press. Effects of reduced pH on the early larval development of hatchery-reared Donkey’s ear abalone, Haliotis asinina (Linnaeus 1758). Aquaculture. Article (subscription required).
