150 



KOHN 



m&nt a day. Webb et al. (1977) estimated that they dis- 

 solve about 1% of the ingested CaC03, equal to 2 5 g m^ 

 d~', or to about 25% of the net calcification rate on the 

 reef flat. 



Planktivores 



(1955) estimated dry biomass of 

 ^ in the coral-algal zone and of 



Odum and Odum 

 corals at about 100 g m "^ in the coral-alga 

 corals and anemones in the encrusting zone at about 50 g. 

 They classified them as herbivores because of their utiliza- 

 tion of zooxanthellae, but the predominant intertidal coral, 

 Pontes lutea (Highsmith, 1980, 1981), probably also feeds 

 on zooplankton at night. 



Inshore, the hydroid Di/namena crisioides is pre- 

 sumably a planktivore. 



Herbivores 



Herbivory by invertebrates on the windward reef plat- 

 forms has been most thoroughly studied in crabs of the 



family Xanthidae. Of the eight common species studied by 

 Havens (1974), seven are primarily herbivorous. In these, 

 78% to 100% of all individuals examined contained algal 

 food in their stomachs. Table 7 summarizes their feeding 

 habits and food based on Havens' findings. Predominantly 

 herbivorous nereid and eunicid polychaetes (author's obser- 

 vations) also occur in the outer zones, but they are much 

 less abundant than particle-feeding polychaetes (Bailey- 

 Brock, White, and Ward, 1980). Centrally on the reef plat- 

 form, the cowry C\;praea moneta eats primarily Jania capil- 

 lacea, to which it is preferentially attracted by distance 

 chemoreception (Rcnaud, 1976). Inshore, small but 

 numerous herbivores include the pulmonale limpjet 

 Siphonaha normalis, a grazer on microscopic algae (Menge, 

 1973; Cook and Cook, 1978, 1981), and cerithiid 

 prosobranch gastropods. 



Odum and Odum (1955) estimated herbivore biomass 

 at about 23% and 8% of plant biomass on the coral-algal 

 ridge and encrusting zones, respectively, of the interisland 

 reef. They considered corals and the sea urchin 



TABLE 7 

 Feeding Habits and Food of the Predominant Intertidal Xanthid Crabs of Enewetak* 



•Data from Havens, 1974. 



Key to plant foods: 1, blue-green algae; 2, Jania; 3, Polvsiphonia; 4, Laurencia + similar forms; 5, Ceratocentrum. 

 Key to animal foods: 1, Foraminifera; 2, polychaetes; 3, sipunculans; 4, Siphonaria; 5, small Crustacea; 6, crabs; 7, insects; 

 8, mites. 



