STUDIES ON THE BIO-OPTICS OF CORAL REEFS 



Phil 1 ip Dustan 



Department of Biology 



College of Charleston 



Charleston, South Carolina 29401 



ABSTRACT 



This paper examines the possibility of using underwater light measurements 

 to study the primary productivity of coral reefs. This is a new technique that 

 may have wide ranging uses as man begins to use remote sensing to study the 

 processes taking place on the surface of the Earth. 



INTRODUCTION 



Sunlight is the primary source of energy for the coral reef ecosystem. 

 Photosynthetic reef organisms utilize light to liberate oxygen from water, fix 

 carbon, and enhance the rate of calcification. This paper will examine the 

 concept of using bio-optical techniques (Smith and Baker, 1978a_; Gordon, et 

 al . , 1980) to measure the input of light energy to coral reef ecosystems. The 

 simplicity of the technique, combined with nondestructive sampling, may enable 

 reef ecologists to study the productivity and flow of energy into coral reefs 

 at a higher level of ecosystem organization than is presently possible. In 

 addition, it is of interest to understand the entrance of energy into these 

 benthic ecosystems since many reef organisms may be termed polytrophic (Muscatine 

 and Porter, 1977), and because the structure and dynamics of the primary 

 production trophic level may have an influence on the structure and/or organization 

 of subsequent higher trophic levels. Understanding the optics of coral reefs 

 also holds the promise of one day being able to study these complex and remote 

 ecosystems from orbiting spacecraft and other remote sensing platforms. 



Investigators have long sought a technique that would quantify the primary 

 productivity of coral reefs. For the most part, estimates have been made using 

 respirometry and/or radiotracer experiments which have been extrapolated to the 

 areal extent of the reef (see part III in Stoddart and Johannes, 1978, for 

 review). While these techniques usually are precise, they are subject to errors 

 in scale which arise from extrapolating data from an experimental specimen to 

 the reef community. Another way to estimate primary production is to measure 

 the input of light energy to the system over a relatively large area of substrate. 

 Then, using known and theoretical estimates of the quantum efficiency for 

 photosynthesis, it should be possible to estimate primary production on a scale 

 commensurate with the scale of the reef ecosystem. 



The initial step in primary production is the harvesting of light by the 

 photosynthetic pigments of the primary producers (Rabinowich and Govingee, 

 1969). This process is a function of the available light, both spectral quality 

 and intensity, and the absorption characteristics of the algae. The absorption 

 and reflectance of light by phytoplankton also can be influenced by the 

 nutritional state and age of the alga (Kiefer, 1973; Kiefer, et aj^, 1979; 



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