e. Deep Ridge 



During the summer of 1973, an attempt was made to explore the deep 

 parts of several reefs in the Florida Reef Tract with the "Johnson-Sea-Link" 

 research submersible. At Looe Key, as well as at other reefs, a deep ridge 

 was discovered, separated from the end of the Deep Reef by an estimated 

 distance of at least 1 km of sand bottom (Antonius, 1974). 



This Deep Ridge runs parallel to the margin of the continental shelf. 

 It shows very little profile and is only a few meters wide, but is, neverthe- 

 less, an outcrop of living coral reef. It lies in about 45 m depth and is 

 formed mainly by plate-like colonies of Montastraea cavernosa and several 

 species of Agariciidae, which show considerable sedimentation damage. Also 

 present are deep water octocorals, such as Iciligorgia schrammi and Ellisella 

 barbadensis , with the latter much more abundant here than on the Deep Reef. 



One major significance of this deep ridge formation may lie in its 

 potential for elucidating the geological past of the area. Its biological 

 importance to the total Looe Key reef ecosystem has not been evaluated. 



2. Trophic Relationships 



Primary production generated by seagrasses and macro-algae on Looe Key 

 occurs mainly in two zones: the Patch Reefs and the Reef Flat. Many of the 

 herbivorous fish populations, as well as numerous invertebrates rely on 

 these seagrass beds both as their primary source of food and for protection. 

 The ecological significance of the interrelationships between patch reefs 

 and seagrass associations has been well documented (e.g., Ogden & Zieman, 1977), 



Numerous consumers utilize patch reefs as habitat, but feed directly on 

 seagrasses and their epiphytes, as well as on associated macro-algae. Thus, 

 the Patch Reef ecosystem provides the two most important requirements for 

 the mobile, herbivorous reef fauna: shelter from predators and an unlimited 

 supply of food. The high productivity of areas like this is harvested in 

 the Florida Keys in the form of finfish, lobster, and other shellfish by 

 both the commercial and sport fishing industry. 



With regard to feeding relationships, the importance of the coral reef 

 areas proper, (i.e., the reefs in the Patch Reef, the Fore Reef, and the 

 Deep Reef zones), lies mainly in their production of plankton, and, to an 

 unknown extent, excretion of non-living organic material, i.e, mucous. 



Transport of planktonic larvae, eggs, spores, and other reproductive 

 entities between the various zones and subzones is probably considerable. 

 Dissolved organics, exocrines and a wide array of other metabolic excretions, 

 originating in any of these natural communities, are distributed throughout 

 the reef by tide and wind-driven currents. In situ primary production fixes 

 a certain percentage of the energy requirement of the reef ecosystem. However, 

 imports of energy from adjacent seagrass beds and phytoplankton populations 

 are probably of great importance to the reef's consumers. 



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