Action spectrum for the effects of UV radiation on photosynthesis in the hermatypic coral Pocillopora damicornis

Abstract

Colonies of the hermatypic coral Pocillopora damcornis were collected from the shallow reefs of Kaneohe Bay, Hawaii, to assess the wavelength-dependent effects of ultraviolet (UV) radiation on photosynthesis. Measurements of photosynthesis and respiration were made while corals were exposed to different UV irradiances, keeping visible radiation constant, using long-band pass filters. A differential action spectrum (biological weighting function) for the inhibition of photosynthesis by UV radiation was then determined for P darnicornis The action spectrum revealed an increase in the wavelength-dependent effects of UV radiation on photosynthesis between 290 and 310 nm that is greater than those increases reported for action spectra on natural assemblages and unialgal cultures of marine microalgae. The greater effect at these wavelengths is a result of the high biologically effective doses of UV radiation experienced by these corals on shallow reefs, and the decrease in the absorbance of UV radiation by UV absorbing compounds found in the host tissues and algal symbionts between 290 and 310 nm. The irradiances of wavelengths in the region between 290 and 310 nm are those which will increase in the event of any decrease in stratosphenc ozone over equatonal regions. If the observed sensitivity of P. damicorn~s in this spectral region is common in other species, it may have important consequences for growth, reproduction, and occurrence of the bleaching phenomenon for shallow water corals.

MODIS-derived spatiotemporal water clarity patterns in optically shallow Florida Keys waters: A new approach to remove bottom contamination

“…Under extreme stress, corals will expel the zooxanthellae from their tissues, resulting in a 'bleached' condition, often leading to mortality of the coral polyp (see reviews by Brown, 1997;Hoegh-Guldberg, 1999;Douglas, 2003, and others). The relationship between incident radiation and stress response in corals is also wavelength dependent (Lesser & Lewis, 1996;Zepp et al, 2008), highlighting the necessity for multispectral characterization of the light field reaching coral reefs. In a more general sense, decreases in water clarity are often associated with increased nutrient loading and subsequent increases in water column chlorophyll concentrations (Riley, 1956;Rodhe, 1948).…”

UV‐absorbing compounds in the coral Pocillopora damicornis: Interactive effects of UV radiation, photosynthetically active radiation, and water flow

“…Total photosynthetically active radiation (PAR, 400-700 nm) and the integrated spectral irradiance of UV (300-400 nm) and UVB (300-320 nm) radiation calculated from the underwater spectral scans at the Point Reef (Hawaii Institute of Marine Biology). The weighted UV radiation irradiances were calculated using the biological weighing function for the inhibition of photosynthesis by UV radiation in Pocilloporu dumicomis (Lesser and Lewis 1996) dards from Palythoa turberculosa. MAAs were normalized to total coral protein that was measured by the procedure of Bradford (1976) with bovine gamma globulin as a standard.…”

Ultra-Violet Radiation Has a Limited Impact on Seasonal Differences in the Acropora Muricata Holobiont

“…UVR levels actually show depth and seasonal variations (Smith and Baker, 1981;Torres et al, 2007;Zepp et al, 2008), which may contribute to the seasonal changes that have been observed in coral physiology. For example, variations in tissue content of mycosporine-like amino acids (MAAs), which protect corals from the deleterious effects of UVR (Shick et al, 1996;Shick and Dunlap, 2002) has been attributed to changes in UV exposure (Lesser and Lewis, 1996;Lesser, 2000), and severe bleaching has been linked to the concomitant increase in seawater temperature and UVR levels (Lesser et al, 1990). Despite these few studies, the seasonal changes in UVR levels on Symbiodinium functioning, coral calcification, organic matter release and coral microbiota need to be further studied.…”