Carbonic anhydrases are influenced by the size and symbiont identity of the aggregating sea anemone Anthopleura elegantissima.

Carbonic anhydrases (CA; EC 4.2.1.1) play a vital role in dissolved inorganic carbon (DIC) transport to photosynthetic microalgae residing in symbiotic cnidarians. The temperate sea anemone Anthopleura elegantissima can occur in three symbiotic states: hosting Breviolum muscatinei (brown), hosting Elliptochloris marina (green) or without algal symbionts (aposymbiotic). This provides a basis for A. elegantissima to be a model for detailed studies of the role of CA in DIC transport. This study investigated the effects of symbiosis, body size and light on CA activity and expression, and suggests that A. elegantissima has a heterotrophy-dominated trophic strategy. We identified putative A. elegantissima CA genes and performed phylogenetic analyses to infer subcellular localization in anemones. We performed experiments on field-collected anemones to compare: (1) CA activity and expression from anemones in different symbiotic states, (2) CA activity in brown anemones as a function of size, and (3) CA activity in anemones of different symbiotic states that were exposed to different light intensities. CA activity in brown anemones was highest, whereas activity in green and aposymbiotic anemones was low. Several CAs had expression patterns that mirrored activity, while another had expression that was inversely correlated with activity, suggesting that symbionts may induce different DIC transport pathways. Finally, CA activity was inversely correlated with anemone size. Our results suggest that the observed CA activity and expression patterns are affected not only by symbiosis, but also by other factors in the host physiology, including trophic strategy as it relates to body size and cellular pH homeostasis.