The northeastern side of South Island was washed by 

 strong oceanic surf throughout our stay at the atoll. The 

 prevailing wind in this area is easterly (see Kepler et <//.. 

 Subchapter 1.1. Appendix 2, this volume), an observation that 

 is consistent with the presence on the eastern side of South 

 Island of extensive coarsely fragmented coral limestone banks 

 2-2.5 in high, attributable to windstorms. These storm banks 

 contained large numbers of fresh bivalve mollusk (Asaphis cf. 

 violascens) shells, providing evidence fora large population of 

 these burrowing animals. The shallow islandward lagoon and 

 reef flat, with its extensive sand lenses, is inhabited by the 

 aforementioned bivalves, large numbers of gastropods of the 

 genera Cerithium, Drupa, Cyprae, et cetera, as well as by 

 predatory mollusks of the genus Conus, including unusually 

 large specimens of Conns ebreus (up to 55 mm long). 



The coral reef on the western side of South Island received 

 closer scrutiny. The distribution of organisms over the 

 hydrobiological section (I-I) is indicated in Fig. 2. 



The beach of the island showed many large red hermit land 

 crabs Coenobitaperlata, as well as Ocypode sp. crabs. Next to 

 the beach lay a zone of lifeless coral limestone remarkable for 

 its extreme lack of living organisms during the season of the 

 year when we visited. This zone became very narrow to the 

 south. The fact that the sea had until recently extended this far 

 was evidenced only by small numbers of Melarhaphe undulata 

 clinging to the underside of sun-baked coral slabs. It appears 

 that when the wind direction changes to westerly, powerful surf 

 inundates this area during high tide. During our visit, however, 

 surf continued to crash against the opposite side of the atoll. 

 The dry, lifeless zone ended with a ledge approximately 1 m in 

 height. The water reached this ledge during high tides. The 

 dominant fauna consisted of small hermit crabs, Grapsus sp. 

 crabs, holothuria. and the mollusks Nerita plicata and Thais 



armigera. Further seaward, the stones in the never-drying 

 pools of the islandward part of the lagoon harbored the following 

 fauna: Diadema sp. urchins; the mollusks Cypraea moneta, 

 Cerithium columna, Cerithium sp., Vasum tuhiferum. Conns 

 ebreus, and Conus sponsalis; the crabs Eriphia sp. and Actaea 

 sp.; three species of sea cucumbers (Holothuroidea); Linckia 

 sp. starfishes; and black and grey brittle stars (Ophiuroidea). 

 Part of the coral limestone in the same area was encrusted with 

 the calcareous algae Porolithon sp. and Lithothamnion sp. To 

 seaward, the littoral pools became deeperand somewhat larger, 

 interdigitating to form the islandward lagoon. The bottom in 

 this area consisted of coral limestone with small patches of 

 coral fragments and sand. The bottom was strewn with 

 limestone knolls that resulted from the intense buildup of 

 calcareous algae and corals of the genera Porites, Pocillopora, 

 Aeropora, and Montipora. These limestone knolls were 

 cavernous and often caved in under the weight of an adult 

 human. The fissures and caverns contained numerous small 

 crabs and other crustaceans, as well as sponges. Also prevalent 

 were algae bushes (Halimeda sp.). 



The bottom sloped upward towards the tidal strip, where 

 it was succeeded by a highly tenacious, firmly attached fauna 

 of a very particular kind. Unfortunately, because our 

 examination was confined to the upper portion of the reef flat, 

 the richly populated interior portion remained unstudied. The 

 cavities and fissures of the top portion of the reef flat revealed 

 an abundance of corals of the aforementioned genera. Dead 

 coral colonies, as well as all of the old coral limestone formations, 

 were densely encrusted with calcareous algae that cemented 

 the reef-flat surface together. There were many gastropods 

 (large Turbo argyrostomus and the smaller Drupa ricina, 

 D. morum, D. grossularia, etc. ) as well as large orange-colored 

 hermit crabs. The perpetually surf-washed tidal areas at the 



Q«fe f(3 



Mollusks: 



- Malarhaphe undulata y^ 



© - Nerita plicata \U/a, 



• Cerithium spp. 



ff - Nassa sp. 



(2) - Turbo argyrostromus 



<Q - Vasum tuhiferum 



- Conus spp. 



(S - Cypraea spp. 



Q - Thais armisera, and Drupa spp. 



Echinodermata: 

 ■ Heterocentrotus sp. 



Diadema sp. 



"7a[ - Lichia sp. 



< y%, - Ophiuroidea 

 ^^ - Holothuroidea 



Fig. 2. Distribution of organisms on the reef on the western side of South Island of Caroline Atoll (Section I-I). 



167 



