Euechinoidea and Cidaroidea respond differently to ocean acidification.
The impact of the chemical changes in the ocean waters due to the increasing atmospheric CO₂ depends on the ability of an organism to control extracellular pH. Among sea urchins, this seems specific to the Euechinoidea, sea urchins except Cidaroidea. However, Cidaroidea survived two ocean acidification periods: the Permian-Trias and the Cretaceous-Tertiary crises. We investigated the response of these two sea urchin groups to reduced seawater pH with the tropical cidaroid Eucidaris tribuloides, the sympatric euechinoid Tripneustes ventricosus and the temperate euechinoid Paracentrotus lividus. Both euechinoid showed a compensation of the coelomic fluid pH due to increased buffer capacity. This was linked to an increased concentration of DIC in the coelomic fluid and thus of bicarbonate ions (most probably originating from the surrounding seawater as isotopic signature of the carbon - δ¹³C - was similar). On the other hand, the cidaroid showed no changes within the coelomic fluid. Moreover, the δ¹³C of the coelomic fluid did not match that of the seawater and was not significantly different between the urchins from the different treatments. Feeding rate was not affected in any species. While euechinoids are able to regulate their extracellular acid-base balance, many questions are still unanswered on the costs of this capacity. On the contrary, cidaroids do not seem affected by a reduced seawater pH. Further investigations need to be undertaken to cover more species and physiological and metabolic parameters in order to determine if energy trade-offs occur and how this mechanism of compensation is distributed among sea urchins.
Laboratoire de Biologie Marine, Université Libre de Bruxelles, 50 Avenue F.D. Roosevelt, B-1050 Brussels, Belgium; Analytical, Environmental and Geo-Chemistry, Earth Systems Science Research Group, Vrije Universiteit Brussel, Pleinlaan 2, 1050 Brussels, Belgium. Electronic address: marie.collard9@gmail.com.
Marie
M
Collard
Laboratoire de Biologie Marine, Université Libre de Bruxelles, 50 Avenue F.D. Roosevelt, B-1050 Brussels, Belgium.
Aurélie
A
Dery
Analytical, Environmental and Geo-Chemistry, Earth Systems Science Research Group, Vrije Universiteit Brussel, Pleinlaan 2, 1050 Brussels, Belgium.
Frank
F
Dehairs
Laboratoire de Biologie Marine, Université Libre de Bruxelles, 50 Avenue F.D. Roosevelt, B-1050 Brussels, Belgium.
Philippe
P
Dubois
D000136:Acid-Base Equilibrium; D000222:Adaptation, Physiological; D000818:Animals; D017756:Aquaculture; D001267:Atlantic Ocean; D001522:Behavior, Animal; D001826:Body Fluids / Q000737:chemistry; D002247:Carbon Isotopes; D057231:Climate Change; D004447:Echinodermata / Q000502:physiology*; D005247:Feeding Behavior; D005602:France; D006863:Hydrogen-Ion Concentration; D007563:Jamaica; D047328:Paracentrotus / Q000502:physiology; D015203:Reproducibility of Results; D012617:Sea Urchins / Q000502:physiology*; D012621:Seasons; D012623:Seawater / Q000737:chemistry*; D013045:Species Specificity
D002247:Carbon Isotopes
Acid–base regulation; Buffer capacity; Cidaroids; Echinoderms; Eucidaris tribuloides; Euechinoids; Ocean acidification; Paracentrotus lividus; Sea urchins; Tripneustes ventricosus