Effects of starvation, ammonium concentration, and photosynthesis on the UV-dependent accumulation of mycosporine-like amino acids (MAAs) in the coral Stylophora pistillata

Abstract

This study addresses several unresolved questions regarding the biosynthesis, metabolism, regulation, and diversity of MAAs in zooxanthellate scleractinian corals. Starved colonies of Stylophora pistillata accumulated the same concentrations of mycosporine-like amino acids (MAAs) as fed corals after 28 d of exposure to photosynthetically available radiation (PAR) and ultraviolet radiation (UVR), suggesting that dietary MAAs are of little quantitative importance in this phototrophic symbiosis. Starved corals continued to accumulate MAAs and conserved them disproportionally compared with declining protein and chlorophyll a, indicating the priority placed on maintaining this UV-sunscreen defense. In 2 different colonies (SP1 and SP2) exposed to enriched (10 µM) ammonium and PAR + UVR during starvation, the final concentrations of MAAs and chlorophyll a were identical. However, under ambient ammonium (< 0.4 µM), SP2 produced MAAs at the expense of chlorophyll a, whereas SP1 maintained chlorophyll a levels but synthesized less MAA. Ammonium consistently affected only the accumulation of primary, Symbiodinium-MAAs (mycosporine glycine, shinorine, porphyra-334, and mycosporine-2 glycine) and not secondary MAAs derived from the former, probably in the host's tissues. Mycosporine-2 glycine and palythine (a secondary MAA) were synthesized by SP1 but not SP2, suggesting (1) genotypic differences between the zooxanthellae in SP1 and SP2, and (2) a biosynthetic relationship between these 2 MAAs that we proposed previously. Exposure to UVR alone did not support large-scale biosynthesis of MAAs in S. pistillata, and accumulation of the full suite of MAAs required PAR + UVR; together with an inhibitory effect of DCMU, this indicates that photosynthesis is required for the UV-stimulated, de novo biosynthesis of MAAs. Cultures of zooxanthellae isolated from S. pistillata and exposed to PAR + UVR showed increased levels of shinorine, and some production of mycosporine-glycine. Host extract had no qualitative effect on the MAAs produced by these zooxanthellae.

Feeding sustains photosynthetic quantum yield of a scleractinian coral during thermal stress

“…Host starvation is thought to reduce ammonium assimilation in the zooxanthellae as well as photosynthetic rates, and has been shown to increase cell degradation and reduce cell division and numbers (Fitt and Cook 2001;Titlyanov et al 2000Titlyanov et al , 2001. Corals typically maintain high levels of lipids derived from excess photosynthetically Wxed carbon and receive substantial amounts of essential fatty acids (Harland et al 1993), amino acids (Wang and Douglas 1999) and mycosporine-like amino acids (Shick et al 2005) from their zooxanthellae. In addition, the coral host is believed to obtain essential nutrients for tissue synthesis from heterotrophic sources (Dubinsky and Jokiel 1994;Mueller-Parker et al 1994;Anthony et al 2002).…”

Experimental assessment of organic carbon fluxes in the scleractinian coral Stylophora pistillata during a thermal and photo stress event

“…Levels of inorganic and organic nutrients in supplied seawater were low (Ferrier-Pagès et al 2001). After healing, feeding was stopped and nubbins were first maintained 5 wk under controlled conditions before the start of the experiment, to cancel any feeding effect (Grover et al 2002, Shick et al 2005, Rodrigues & Grottoli 2007. The above papers indeed showed that 4 wk after the end of feeding, protein or lipid levels were significantly decreased in the coral tissue, cancelling the feeding effect.…”

Among-species variation in the energy budgets of reef-building corals: scaling from coral polyps to communities

“…A total of 36 small experimental colonies (nubbins, surface area 5 to 8 cm 2 ) per species, 6 nubbins from each parent colonies, were created prior to the experiment, evenly distributed into 6 glass aquaria (20 litre volume) and allowed to recover for 4 weeks. During the recovery period, nubbins were not provided with food in order to remove any previous feeding effect on their physiology (see Shick et al, 2005). During the experimental period (5 weeks), nubbins in three of the six tanks (18 per species) were provided with Artemia salina nauplii three times a week (feeding density of approximately 2000 prey per nubbin per feeding event) whereas nubbins in the remaining three tanks (18 per species) received no food at all.…”