Differential effects of ocean acidification on growth and photosynthesis among phylotypes of Symbiodinium (Dinophyceae)

Abstract

We investigated the effect of elevated partial pressure of CO 2 (pCO 2 ) on the photosynthesis and growth of four phylotypes (ITS2 types A1, A13, A2, and B1) from the genus Symbiodinium, a diverse dinoflagellate group that is important, both free-living and in symbiosis, for the viability of cnidarians and is thus a potentially important model dinoflagellate group. The response of Symbiodinium to an elevated pCO 2 was phylotype-specific. Phylotypes A1 and B1 were largely unaffected by a doubling in pCO 2 ; in contrast, the growth rate of A13 and the photosynthetic capacity of A2 both increased by , 60%. In no case was there an effect of ocean acidification (OA) upon respiration (dark-or light-dependent) for any of the phylotypes examined. Our observations suggest that OA might preferentially select among free-living populations of Symbiodinium, with implications for future symbioses that rely on algal acquisition from the environment (i.e., horizontal transmission). Furthermore, the carbon environment within the host could differentially affect the physiology of different Symbiodinium phylotypes. The range of responses we observed also highlights that the choice of species is an important consideration in OA research and that further investigation across phylogenetic diversity, for both the direction of effect and the underlying mechanism(s) involved, is warranted.

Symbiodinium necroappetenssp. nov. (Dinophyceae): an opportunist ‘zooxanthella’ found in bleached and diseased tissues of Caribbean reef corals

“…The results are consistent with the interpretation that the three species adjust to changes in the light regime using different mechanisms (see also Iglesias-Prieto & Trench, 1994. Finally, Brading et al (2011) studied the effect of the elevated partial pressure of CO 2 (pCO 2 ) on growth and productivity of these species. The steady-state growth rate of S. necroappetens increased by approximately 60% when ambient partial pressure of CO 2 was doubled, whereas S. microadriaticum exhibited no significant change in growth rate ( Fig.…”

“…The steady-state growth rate of S. necroappetens increased by approximately 60% when ambient partial pressure of CO 2 was doubled, whereas S. microadriaticum exhibited no significant change in growth rate ( Fig. 28; reproduced from Brading et al, 2011). However, under this same treatment, the photosynthetic capacity (as assessed by gC•Chla −1 ) of S. microadriaticum increased significantly while the relative carbon to chlorophyll a of S. necroappetens remained unchanged (Fig.…”

“…Indeed, significant physiological differences in thermal tolerance, photo-acclimation and response to elevated CO 2 are described for S. necroappetens, S. microadriaticum and S. pilosum Hennige et al, 2009;Brading et al, 2011;Steinke et al, 2011). For example, the study of assessing photosystem II activity and electron transport, degradation of the D1 protein, and growth, in response to elevated temperature, demonstrated that S. necroappetens was more thermo-sensitive than S. microadriaticum (see also Steinke et al, 2011).…”

“…Asterisk indicates statistically significant differences between treatments for each species. The figures presented here were modified and redrawn from and Brading et al (2011).…”

Ocean acidification has no effect on thermal bleaching in the coral Seriatopora caliendrum

“…Anthony et al (2008) hypothesized that the mechanism of OAinduced bleaching involved the disruption of carbon-concentration mechanisms used by Symbiodinium (Weis et al 1989;Leggat et al 1999), or impaired photoprotective mechanisms, such as photorespiration (Crawley et al 2010) and nonphotochemical quenching (Hill et al 2005). Support for these hypotheses is limited; however, as effects of OA on the photophysiology of Symbiodinium in hospite have not been studied in detail, and where these effects have been investigated, the outcomes are equivocal (Godinot et al 2011;Iguchi et al 2011;Edmunds 2012) and may be specific to Symbiodinium phylotypes (Brading et al 2011).…”