The impact of coral bleaching on the pigment profile of the symbiotic alga, Symbiodinium

Abstract

Bleaching of corals by loss of symbiotic dinoflagellate algae and/or photosynthetic pigments is commonly triggered by elevated temperatures coupled with high irradiance, and is a first-order threat to coral reef communities. In this study, a high-resolution high-performance liquid chromatography method integrated with mass spectrometry was applied to obtain the first definitive identification of chlorophyll and carotenoid pigments of three clades of symbiotic dinoflagellate algae ( Symbiodinium ) in corals, and their response to experimentally elevated temperature and irradiance. The carotenoids peridinin, dinoxanthin, diadinoxanthin (Dn), diatoxanthin (Dt) and b -carotene were detected, together with chlorophylls a and c 2 , and phaeophytin a , in all three algal clades in unstressed corals. On exposure to elevated temperature and irradiance, three coral species ( Montastrea franksi and Favia fragum with clade B algae, and Montastrea cavernosa with clade C) bleached by loss of 50-80% of their algal cells, with no significant impact to chlorophyll a or c 2 , or peridinin in retained algal cells. One species ( Agaricia sp. with clade C) showed no significant reduction in algal cells at elevated temperature and irradiance, but lost substantial amounts of chlorophyll a and carotenoid pigments, presumably through photo-oxidative processes. Two coral species ( Porites astreoides and Porites porites both bearing clade A algae) did not bleach. The impact of elevated temperature and irradiance on the levels of the photoprotective xanthophylls (Dn + Dt) and b -carotene varied among the corals, both in pool size and xanthophyll cycling, and was not correlated to coral bleaching resistance.

Modeling photoinhibition‐driven bleaching in Scleractinian coral as a function of light, temperature, and heterotrophy

“…However, oxidative stress only occurs when the production of ROS exceeds the ability of the organisms to eliminate the ROS using cellular products such as antioxidants (Lesser 2006). Accumulated ROS may cause damage to the photosystem, as well as to both symbiont and host tissues (Asada 2006;Venn et al 2008). The presence of highly ROS such as 1 O Ã 2 , with an average lifetime of 3.7 ms, commonly results in specific damage to protein in close association with the site where the ROS was formed (Lesser 2006).…”

“…A physical trigger of photoinhibition is the temperature-induced breakdown of the Ribulose bisphosphate carboxylase oygenase (Rubisco) enzyme (Lilley et al 2010). Rubisco is essential for the fixation of CO 2 for photosynthesis; if inactive, it causes a blockage of the electron transport chain (ETC) that leads to a build-up of electrons, which can react with O 2 to form superoxide (O { 2 ) at the site of photosystem I (PSI; Venn et al 2008). Superoxide dismutase catalyzes the reaction turning O { 2 of hydrogen peroxide (H 2 O 2 ), whereas the detoxifying enzymes ascorbate peroxidases can reduce the H 2 O 2 to water (Asada 2006).…”

“…The presence of highly ROS such as 1 O Ã 2 , with an average lifetime of 3.7 ms, commonly results in specific damage to protein in close association with the site where the ROS was formed (Lesser 2006). As 1 O Ã 2 forms at PSII, it can prompt the degradation of the D1 protein (Asada 1996), as well as cause damage and bleaching of pigments in the light-harvesting complex (Venn et al 2006). Other ROS such as H 2 O 2 , which is uncharged, have longer lifetimes and can therefore move across cell membranes to other parts of the algal cell or even into the host (Saragosti et al 2010).…”

“…When the coral is exposed to elevated light and temperature, the photosystem of the symbiotic algae may become photoinhibited (Hoegh-Guldberg and Jones 1999;Venn et al 2008). Photoinhibition may lead to damage to the photosystem and eventually bleaching due to oxidative stress, involving the production and accumulation of reactive oxygen species (ROS [Lesser 2006;Venn et al 2008]).…”

“…Photoinhibition may lead to damage to the photosystem and eventually bleaching due to oxidative stress, involving the production and accumulation of reactive oxygen species (ROS [Lesser 2006;Venn et al 2008]). A physical trigger of photoinhibition is the temperature-induced breakdown of the Ribulose bisphosphate carboxylase oygenase (Rubisco) enzyme (Lilley et al 2010).…”