Effects of Reduced pH on Larval Settlement and
Survival of the Donkey’s Ear Abalone,
Haliotis asinina (Linnaeus 1758)


Abduraji S. Tahil1 and Danila T. Dy

Department of Biology, University of San Carlos,
Talamban Campus, Cebu City
1Mindanao State University Tawi-Tawi, Sanga-Sanga, Bongao, Tawi-Tawi

corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.



The potential effects of reduced pH as a result of an increased CO2 concentration on settlement and survival of Haliotis asinina larvae were investigated. The settlement frequency (%F) was significantly different with respect to pH levels. On day 5, 100% of the settlement plates contained postlarvae at ambient conditions (pH 7.98) and pH 7.76. Lower %F was obtained at pH 7.41 (12.5% - 37.5%) and pH 7.57 (25% - 62.5%). Hence, significantly higher number of larvae attached to plates at ambient conditions (16 postlarvae plate-1) and at pH 7.76 (10 postlarvae plate-1). On the other hand, the concentration of carbonate ion was lowest in the high-CO2 or reduced pH treatment and the larval settlement was also lower. Fewer larvae settled on plates exposed to pH 7.41 (3 postlarvae plate-1) and pH 7.57 (5 postlarvae plate-1). Post settlement survival (10 and 15 days after exposure) was significantly lower at reduced pH levels compared to ambient conditions. Settlement rate was also affected by the reduction in % cover of crustose coralline algae (CCA) of the plates and delayed morphological development of larvae at reduced pH. This study confirmed that reduction in pH of seawater to the levels predicted by the end of this century will have negative effect on the settlement and survival of H. asinina larvae, and by extension, the future economy of the abalone industry of the Philippines.



The planktonic larval phase in the life cycle of abalone ends with settlement onto the substratum and metamorphosis into the benthic adult form. Upon settlement, the larvae continue to creep for sometime before adhering firmly to a favorable substratum. After settlement, the larvae secrete mucus from the foot sole, adhere firmly to the substratum and start feeding on benthic diatoms (Singhagraiwan & Doi 1993) until they metamorphose into plantigrade juveniles.
Poor larval settlement and survival, and abnormal metamorphosis are among the major problems in seed production of H. asinina. This may be related to insufficient amount of effective settlement cue (i.e. crustose coralline algae) and morphological deformities under unfavorable. . . . . . read more


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