Nutrient regeneration also occurs in lagoon sediments (Entch, et al., 1983) where 

 nutrients are utilized by extensive macroalgae and turtle grass beds. These beds are heavily 

 grazed upon by reef fish. Many of these fish exhibit diel migration patterns, whereby they 

 graze on the backreef and in the lagoons by day but shelter in the deeper forereef by night. 

 Material that they transport in their guts at dusk is defecated over the forereef or in their 

 nocturnal shelters. This form of transport may be an important means of upstream nutrient 

 recycling on coral reefs. The reverse cycle of migration (nocturnal feeding, daytime 

 sheltering) by juvenile grunts has been shown to have measureable impact on nutrient 

 concentrations around coral heads (Meyer, et al., 1983). 



PATHWAYS OF NUTRIENT TRANSFER 



DIRECT TRANSFER 

 PARTICULATE ' 

 DISSOLVED 



DETRITUS 

 » FEEDERS 



Figure 1. Diagramatic representation of nutrient pathways on a coral reef. 



FUNCTIONAL GROUPS 



The various processes and functional groups involved in coral reef nutrient dynamics are 

 diagramatically represented in Figure 1. 



New nutrients enter the system in both dissolved and particulate form, or are generated 

 in situ by N2 fixation. Dissolved nutrients and some particulates are taken up by the 

 organisms included in the "fine-pore concentrators" group made up of algae and 

 zooxanthellae. Other particulates are trapped by the reef framework and by filter-feeding 

 organisms, which I call the "coarse-pore concentrators". Planktivorous fish also concentrate 

 particulates and have been shown to excrete and defecate significant amounts of NH4 and 

 organic material in their nocturnal shelters (Bray, 1982). Herbivores graze on the algae and 

 corals, and carnivores, in turn, feed on the herbivores. The fecal material from both of 

 these groups, many of which spend about one-half of their time sheltering in reef crevices, 



137 



