400 



500 600 



WavQlQngth (nm. ) 



700 



Figure 2. --Calculated upwelling and downwelling spectral irradiance at the 

 substrate surface of a sandy area 7 m deep on Molasses Reef, Key Largo. The 

 difference between upwelling and downwelling irradiance equals the light 

 absorbed by the substrate (1 x 10^ q/cm^/s). Scans were calculated from 

 sets of spectral irradiance data as described in the text. 



This fraction is somewhat higher than the earlier data from Jamaica but is 

 within a range that could be considered acceptable, since the technique is in 

 an early stage of development. 



Similar measurements made over a nearby grove of living coral on Molasses 

 Reef revealed somewhat different and unexpected results. The values for 



193 



