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- Title
Diel fluctuations of mycosporine-like amino acids in shallow-water scleractinian corals.
- Authors
Yakovleva, I.; Hidaka, M.
- Abstract
Reports of bathymetric decrease in the total mycosporine-like amino acid (MAA) concentration of benthic invertebrates suggest that light gradients may be important determinants of MAA content. With the pronounced diel light changes, distinct temporal variations in MAA concentrations might also be expected. We examined the changes in the abundance of MAA in three shallow-water scleractinian corals,Pavona divaricata,Galaxea fascicularisandMontipora digitatafrom Okinawa, Japan, in relation to daily cycles in solar radiation and tested whether the species have different capabilities for protection against UVR depending on their MAA composition. The results show that symbiotic algae freshly isolated from the investigated coral species do not contain MAAs and that distribution of these compounds resided only within the animal tissue. Total MAA content in the tissue ofP.divaricata,G.fascicularisandM.digitatarose rapidly at midday and significantly dropped at night. The observed variations were by a factor of two and, thus, very dramatic. For all the investigated coral species, total MAA concentrations were significantly correlated with the diurnal cycle in solar radiation, during both winter and summer seasons. Seawater temperature was significantly correlated with MAA levels only in the June experiment, but represented no more than 20% of the MAA variation in all three coral species, whereas solar radiation explained 60-70% of the MAA fluctuations. This suggests that MAAs are an integral component of the hard coral’s biochemical defense system against high solar irradiance stress. The diurnal increase in total MAA concentrations was due to an increase in the concentration of imino-MAA species of up to 2-2.5-fold of their pre-dawn values. In contrast, the oxocarbonyl-MAA mycosporine-glycine (Myc-Gly) showed the lowest (Tukey-Kramer HSD test:P<0.05) values at midday, compared to afternoon and night hours. Analysis of diel changes in chlorophyll fluorescence and chlorophyllacontent of the investigated species revealed thatP.divaricataandG.fasciculariswere less sensitive to the high levels of ambient irradiance compared toM.digitata. InP.divaricataandG.fascicularis, Myc-Gly, an MAA with an antioxidant function, is the most abundant MAA, contributing about 70% to the total MAA pool, whereas the major MAA factions inM.digitatawere represented by oxidatively robust imino-MAAs. We speculate that MAAs furnish scleractinian corals with protection from biologically damaging ultraviolet radiation through both the direct sunscreening activity of imino-MAAs and the antioxidant properties of oxocarbonyl-MAAs and suggest that the predominance, in the host tissue, of MAA species with an antioxidant ability may render corals more tolerant to high photosynthetically active and ultraviolet radiation.
- Subjects
CIRCADIAN rhythms; MYCOSPORINE-like amino acids; AMINO acids; CORALS; MARINE biology; MARINE sciences; AQUATIC biology; BIOLOGY
- Publication
Marine Biology, 2004, Vol 145, Issue 5, p863
- ISSN
0025-3162
- Publication type
Article
- DOI
10.1007/s00227-004-1384-9