Mead (1970) conjectured: "The extent of the algal forest (but not 

 its diversity) increases poleward. The abundance of the advanced 

 percoid herbivores decreases poleward. Is there a causal correlation?" 

 There may well be, although other factors, such as respiration- 

 photosynthesis ratios, amount of dissolved oxygen, and available 

 nutrients in cold versus warm seas must be considered, 



Percoid fishes, which include most marine herbivorous fishes, 

 are believed to have evolved in the tropics, and radiated into temper- 

 ate, and to a lesser extent, polar seas (Mead, 1970). 



Most herbivorous marine fishes are recent, structurally advanced 

 and specialized, with striking morphological and physiological 

 adaptations to obtain and digest plant material (Hiatt and Strasburg, 

 1960; Mead, 1970; Suyehiro, 1942), This represents influence of 

 plants on the evolutionary history of fishes. It is tempting to 

 speculate (as had Mead, 1970) about the nature and extent of the algal 

 forest of tropical seas prior to the appearance of percoid herbivores, 

 and to wonder if morphology, distribution and general aspect of 

 tropical marine plants have developed in part in response to heavy 

 grazing, clearly a significant environmental factor. 



The Food Web 



Ecologists have puzzled over the apparent anomaly presented by coral 

 reefs that characteristically abound with animal consumers, but are 

 almost devoid of conspicuous plant producers, Odum and Odum (1955) 

 helped to solve the question at Eniwetok Atoll by finding that 

 zooxanthellae living within the tissues of coral and filamentous algae 

 in the coral skeletons may make coral heads more plant than animal 

 by a ratio of about 3:1, This, together with dense but inconspicuous 

 turfs of filamentous algae on rocks and sand provide food for many 

 reef species. At Eniwetok and in the Marshall Islands, corals and 

 associated algae apparently contributed substantially to the food 

 available to fishes (Odum and Odcrai, 1955; Hiatt and Strasburg, 1960), 

 But in the West Indies, corals are apparently not utilized much for 

 food by fishes of any kind (Randall, 1967), 



Randall found three families of West Indian Fishes to be almost 

 entirely dependent on benthic algae as primary food (Kyphosidae, the 

 sea chubs; Scaridae, the parrotfishes ; Acanthuridae, the surgeon- 

 fishes), and many species in other families to rely wholly or 

 partially on attached plants for sustenance. 



VI-170 



