24. November 2017 Larval sensitivity to ocean acidification



Regulation of stomach pH may represent an “Achilles heel” in marine larvae to ocean acidification

A recent study conducted by IMAP-Members Marian Hu and Meike Stumpp from Kiel University in collaboration with partners from the Academia Sinica in Taiwan and the University of Gothenburg, Sweden could demonstrate that the regulation of gastro-intestinal pH may represent an "Achilles heel" in larval stages of the marine superphylum Ambulacraria (echinoderms and hemichordates) to the global phenomenon of ocean acidification (OA). This collaborative project was recently published in Proceedings of the Royal Society B and the image of a sea star larva from the Kiel Fjord had been selected as cover image for this issue.

 

Near future ocean acidification simulations have been demonstrated to differentially affect marine organisms. A special focus has been dedicated to marine larval stages that are often the weakest ontogenetic link in the lifecycle of a species. In order to make large scale predictions regarding species´ sensitivity to OA large efforts were dedicated to the identification of unifying physiological systems that set the tolerance limits to changes in seawater pH. Many marine invertebrate larvae produce calcareous shells or skeletons, and a less alkaline marine environment with decreased pH may impede proper calcification. As a consequence, the majority of the current literature has focused on marine calcifiers, as they were hypothesized to represent the most sensitive group to ocean acidification. However, a growing number of studies reported mixed responses in different species of both, calcifying, and non-calcifying types exposed to simulated ocean acidification raising the suspicion, that there are more processes concerned than merely calcification.

This study demonstrated that the differential sensitivity of ambulacraria (echinoderms and hemichordates) larvae towards simulated ocean acidification independent from their ability to calcify but is rather dictated by the physiology of their digestive systems. Interestingly, in contrast to most vertebrates and humans, all ambulacraria larvae tested have moderate to highly alkaline digestive systems up to pH 10.5. Gastric pH regulation upon experimental OA was compared in six species of the marine superphylum ambulacraria. A strong correlation between sensitivity to OA and the ability to regulate gut pH was observed. Surprisingly, species with tightly regulated gastric pH were demonstrated to be more sensitive to ocean acidification.

This study provides a first evidence that regulation of highly alkaline conditions in the larval gut of the marine superphylum Ambulacraria (>7.000 species) may dictate their sensitivity to decreases in seawater pH. These findings highlight the importance of physiological approaches to better understand the basic physiological systems in marine larval stages that can fundamentally contribute to species´ resilience to near-future ocean acidification.

Original Source:
Hu, M.Y.; Tseng, Y-C.; Su, Y-H.; Lein, E.; Lee, H-Y.; Lee, J-R.; Dupont, S.; Stumpp, M. (2017) Variability in larval gut pH regulation defines sensitivity to ocean acidification in six species of the Ambulacraria superphylum. Proceedings of the Royal Society of London
B 284:20171066