Zoological Studies

Vol. 62, 2023

(update: 2023.3.20)

Effect of pH on the Early Development of the Biofouling Ascidian Ciona robusta

Bailey S.C.L. Jones1,2,, Lauren A. Holt1,, and Kit Yu Karen Chan1,*

1Biology Department, Swarthmore College, 500 College Ave., Swarthmore, Pennsylvania, PA 19081, USA. *Correspondence: E-mail: kchan1@swarthmore.edu (Chan).
E-mail: baileycenlu@gmail.com (Jones); lholt2399@gmail.com (Holt)
2Department of Ophthalmology & Visual Science, Yale University School of Medicine, 300 George St., New Haven, CT 06511, USA

BJ and LH contributed equally to this work.
(Received 30 May 2022 / Accepted 6 November 2022 / Published 20 March 2023)
Communicated by Benny K.K. Chan

Ocean acidification (OA) impacts the survival, fertilization, and community structure of marine organisms across the world. However, some populations or species are considered more resilient than others, such as those that are invasive, globally distributed, or biofouling. Here, we tested this assumption by investigating the effect of pH on the larval development of one such tunicate, Ciona robusta, which is currently exposed to a wide range of pH levels. Consistent with our hypothesis, C. robusta larvae developed and metamorphosed at a rate comparable to control (pH 8.0) at modest near-future conditions (pH 7.7) over a 58-hour period. However, development was stunted at the extreme low pH of 6.8 such that no embryo progressed beyond late cleavage after 58 hours. Interestingly, piecewise regression of the proportion of embryos at the most advanced stage at a given time point against pH identified a breakpoint with the highest pH (~pH 7.6) at around hatching. The variation in breakpoint pH throughout ontogeny highlighted that the sensitivity to decreasing pH differs significantly between developmental stages. More broadly, our results show that even a cosmopolitan, biofouling, invasive species could be negatively impacted by decreasing pH.

Key words: Tunicates, Tadpole, Larvae, Global climate change, Ocean acidification.

Citation: Jones BSCL, Holt LA, Chan KYK. 2023. Effect of pH on the early development of the biofouling ascidian Ciona robusta. Zool Stud 62:04. doi:10.6620/ZS.2023.62-04.