As osmoconformers with low metabolic rates, echinoderms are generally regarded as rather weak acid–base regulators. Accordingly, little attention has been placed on whether echinoderms have evolved mechanisms to regulate ionic homeostasis. In the last century, only few studies examined the acid–base physiology of echinoderms, mostly sea urchins. These studies were conducted in an environmental context as some species inhabit rock pools and experience periodic emersion from their marine environment that can cause a metabolic acidosis. Lately, acid–base physiology in marine invertebrates, especially calcifying species, has received considerable attention as these animals were considered as particularly vulnerable in the context of CO2-induced ocean acidification. A substantial extracellular pH regulatory ability has been hypothesized to determine the degree of sensitivity in marine taxa. The emerging field of ocean acidification research in the last decade also shed new light on the acid–base physiology in echinoderms. Therefore, most of the available literature on echinoderm acid–base physiology describes the effects of CO2-induced seawater acidification on the extracellular acid–base homeostasis of echinoderm adults and larvae. This book chapter will summarize the most recent advances of acid–base physiology and nitrogen excretion in echinoderms in the face of ocean acidification. It will cover adult pH regulation as far as mechanistic data is available and also echinoderm larval physiology in respect to intracellular and extracellular acid–base regulation. Finally, it will make a short excursion into the ocean acidification research field, since most of the conducted research started because of this.
Stumpp M. & Hu M. Y., 2017. pH regulation and excretion in echinoderms. In: Weihrauch D. & O’Donnell M. (Eds.), Acid-base balance and nitrogen excretion in invertebrates: mechanisms and strategies in various invertebrate groups with considerations of challenges caused by ocean acidification, pp. 261-273. Springer International Publishing. Book chapter (subscription required).