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KOHN 



face sediment, filamentous algae and the foraminiferan, 

 Calcarina: the triggerfish Rhinecanthus aculeatus (main 

 foods: algae, gastropods, isopods, crabs, shrimp, 

 polychaetes, fishes); and the damselfish Abudefduf sor- 

 didus (main foods: algae, crabs, fishes, polychaetes, 

 Calcarina) (Hiatt and Strasburg, 1960). 



Use of intertidal windward platforms by carnivorous 

 fishes at high tide is poorly documented. The black-tip reef 

 shark Carcharhinus melanopterus is frequently seen there 

 but constituted less than 0.5% of all fishes observed by 

 Miller (1983). This species is piscivorous (Hiatt and Stras- 

 burg, 1960). 



UTILIZATION OF INTERTIDAL 

 HABITATS BY BIRDS 



Shorebirds of several species fly to the windward inter- 

 tidal platform to feed at low tide. Johnson (1979) reported 

 that whimbrels fNumenius phaeopus), bristle-thighed cur- 

 lews (N. tahitiensis) and wandering tattlers (Heteroscelus 

 incanus) use intertidal habitats more intensively than the 

 other common Enewetak shorebirds, golden plovers (Pluui- 

 alis dominica fulva) and ruddy turnstones (Arenaha 

 interpresj. However, 1 have observed several occasions 

 when golden plovers were the only common birds on the 

 windward platform at Enewetak Island. 



Bristle-thighed curlews are known to eat the proso- 

 branch gastropod Nerita sp. by picking up the snail in the 

 tip of the beak, raising the head, swinging the bill laterally 

 and then across the back, and finally hurling the snail 

 downward against the rocks. This procedure may be 

 repeated several times until the shell is broken; the bird 

 then extracts the snail's body (Carpenter, Jackson, and 

 Fall, 1968). 



BEACH AND SUPRALITTORAL 

 FRINGE HABITAT 



The most conspicuous invertebrates of the uppermost 

 intertidal and supratidal beaches are ghost crabs of the 

 genus Oci^pode. Two species occur, O. cordimana extend- 

 ing from just below high-tide line to well up in the zone of 

 fringing beach vegetation, and O. ceratophthalma, 

 ranging downward from about high-tide line. The latter 

 species is more common, but both tend to occur on the 

 same beaches. Both live in burrows during the day and are 

 active nocturnally. Little is known of their ecology, but at 

 night O. cordimana usually sits near its burrow entrance, 

 retreating within at the slightest disturbance. Only 

 O. ceratophthalma wanders over the beach at night. In the 

 account from which the preceding information was taken, 

 Horch (1975) compared acoustic and other aspects of the 

 behavior of these species. 



In the wave-washed zone of sand beaches in Enewetak 

 Lagoon, the predatory anomuran crustacean Hippa pacifica 

 is prominent nocturnally. Mysid crustaceans, caught with 

 hairs on the long first pereiopods, are its main food at 

 Enewetak (Wenner, 1977). 



Among the few meiofaunal taxa reported from 

 Enewetak are tardigrades of the genera Hypsibius and 

 Macrobiotus, found in supralittoral fringe beach sand 

 (Mehlen, 1972). 



EFFECTS OF ENVIRONMENTAL 

 DISTURBANCES ON INTERTIDAL BIOTA 



In recent years several cases of mass mortality of tropi- 

 cal intertidal organisms from severe storms or other 

 episodic catastrophes have been documented. These are 

 cited by Leviten and Kohn (1980), who described the 

 effects on gastropod populations of an unusually severe 

 rainstorm that coincided with a low tide that left the inner 

 40 m of the windward platform at Enewetak emcrsed for 

 several hours. On Sept. 3, 1972, 4.3 cm of rain fell dur- 

 ing a 6-hour period. A strong smell of rotting organisms 

 persisted for more than a week after the storm during low 

 tide periods, attesting to the death of many types of organ- 

 isms. Of 155 individuals of six species of Conus censused 

 in the area on Sept. 6, we found that 70% (83/119) of 

 C ebraeus and 92% (33/36) of the five other species 

 were killed. Thus the species whose distribution normally 

 extends farthest inshore, C ebraeus, had the highest sur- 

 vivorship. The nearly total mortality of all other species in 

 the affected area suggests that unpredictable catastrophes 

 such as rainstorms may prevent them from occupying 

 inshore areas of bench. Mortality of C ebraeus was also 

 size-selective: all individuals <15 mm long were killed, 

 while 38% of those >15 mm survived (not 15%, as 

 erroneously reported in Leviten and Kohn, 1980). Thus 

 the observed size-frequency distributions of Conus sp>ecies 

 noted above may also be determined by variations in 

 physical stress across the platform (Leviten and Kohn, 

 1980). 



It was also possible to assess the effects on inter- 

 tidal gastropods of another severe environmental distur- 

 bance, Typhoon Alice, which struck Enewetak Jan. 5, 

 1979. On the central portion of the Enewetak Island plat- 

 form, where thick algal turf had provided protected sites 

 for gastropods, the turf was much thinner and population 

 density of Conus species was much lower after the 

 typhoon. However, on the portion of the platform where 

 cracks, crevices, and rubble-filled depressions on otherwise 

 smooth, bare bench were the main refuges, there was no 

 significant reduction of Conus abundance or species rich- 

 ness. Predatory gastropods other than Conus species, 

 predominantly (94%) Muricidae, were not significantly 

 reduced in number of individuals or species in the latter 

 area and were reduced less than Conus species in areas 

 with algal turf, probably due to the greater tenacity of 

 muricids as described above (Kohn, 1980). Predatory gas- 

 tropods on the windward reef platform are thus 

 behaviorally adapted to use refuges that shelter them ade- 

 quately from the most severe storm conditions likely to be 

 encountered there. In six of 10 comparisons involving 

 C. ebraeus. C. chaldaeus, and C. sponsalis at several sites, 



