the Description and Ecology of the Motus section. Gilbertese 

 names are prefixed with motu. Any name not appearing on 

 Arundel's map ( Fig. 4) was given to the islets by us. They have 

 been sent to the British Admiralty and US Hydrographic Office 

 (along with corrections to the Pacific Pilot) for official 

 recognition. 



Structure and Topography 



General Account 



Caroline, one of the oceanic islands contributing to 

 Darwin's theory of atoll formation (Darwin. 1842), is a low 

 island derived entirely from coral reefs and mollusks, living 

 and dead. Although undoubtedly resting upon an ancient 

 basaltic base, today's atoll reveals no visible fragments of its 

 volcanic heritage. "The atoll consists of a chain of twenty-five 

 [sic] little islets, well covered with trees and shrubbery, the 

 whole forming a quiet scene of grove and lake, charmingly set 

 off by the contrasting ocean" (Holden & Qualtrough, 1884). 

 This description could apply equally well today. Caroline is 

 actually composed of a ring of 39 "permanent" and 3 incipient 

 islets whose total area is 398.94 ha. Most are well wooded, but 

 four tiny ones, less than 0. 1 ha in size, are scarcely more than 

 coral rubble piled on the reef, supporting sparse patches of 

 Tournefortia and Heliotropium. One islet. Noddy Rock 

 (PI. 19), is a vestige of a former reef segment. 



Our terminology is based on Tracey et al. (1955) as cited 

 by Wiens (1962), to which we have one addition. The name 

 motu, Polynesian for "islet" or "small island," is now a technical 

 term for detrital reef islands (Danielsson, 1954; Stoddart & 

 Gibbs, 1975). In this paper the terms motu and islet are used 

 interchangeably; however, as motu is now a bona fide English 

 word and not italicized, it may be pluralized by adding an "s" 

 (normally Polynesian words are not pluralized with "s"). 



Caroline's overall shape is like a flattened crescent. 9.7 km 

 long on its north-south axis. Its perimeter is 26.9 km. measured 

 along the outer reef. Its greatest breadth ( including both reefs), 

 2.3 km, lies centrally along an east-west transect that includes 

 Motu Mannikiba and lower Long Island. The longest islet. 

 Long, extends 4.23 km from north to south, while South Island, 

 extending 1.2 km from east to west, claims the widest stretch 

 of land. 



The motus, lying upon a wide, continuous reef flat which 

 encloses an elongated, relatively shallow lagoon, fall naturally 

 into groupings of 3 large islands (South, Nake, Long) and 

 4 groups of smaller islets! 13 Windwards, 5 Southern Leewards, 

 1 I Central Leewards, 7 South Nakes). There are four basic 

 motu shapes: 



/. long, linear, and parallel to the reef axis (e.g.. Long 

 Island); 



2. small, linear or oval, and perpendicular to the reel axis 

 (e g., Southern Leeward Islets i; 



3. triangularorcrescentic.withtheapex lacing the seaward 

 reel (e.g.. most of the Windward Islets); and 



4. large and quadrangular, occupying the ends of the atoll 

 (e.g.. South. Nake). 



All individual motus are discussed m detail in the 

 Description and Ecology of the Motus section. 



Reef Flats 



Caroline's peripheral reefs, which completely surround 

 the lagoon and upon which the motus rest, are consistently wide 

 (average 562 m, range 396-759 m, N = 100). The windward 

 and leeward reefs differ in structure and dimensions. Neither 

 are entirely dry, even at the lowest tides. They consist primarily 

 of barren calcareous rock, which on other atolls generally 

 represents the erosional surface of an older reef. Jagged 

 "mushrooms" of newer (but dead) reef dot the leeward reefs 

 (PI. 11 ). There are no passes from ocean to lagoon, a typical 

 feature of central Pacific atolls (Wiens, 1962). The combined 

 area of intertidal and subtidal marine environments that they 

 enclose is several times the areaoccupied by terrestrial habitats. 



In the Southern Hemisphere, reef flats tend to be widest in 

 the southwest sector and narrowest in the northeast (Wiens, 

 1962). Caroline's reefs are quite wide throughout the west 

 (PI. 12), and definitely narrowest in the northeast off Nake 

 (PI. 13). 



The reef rim. irregularly dentate and 26.9 km in 

 circumference, is surmounted by islets for 55% of its length. 

 On 72% of all Pacific atolls, less than half the reef circumference 

 is occupied by land (Wiens. 1962). Caroline lies within a 28% 

 minority in which one-half to two-thirds of the reef rim contains 

 land. Corresponding values for 2 Tuamotuan atolls. Rangiroa 

 and Raroia. are 33% and 35% (Stoddart & Sachet. 1969). 

 Where motus exist, the reef flat is divided into the seaward reef 

 flat (PI. 12), islet, and lagoon reef flat (PI. 14). 



At low tide all reef fiats are wadable. Black-tipped reef 

 sharks were a threat to our safety in most areas in 1988, but by 

 1 990 dozens had been killed. The reef segments that separated 

 the Southern and Central Leeward groups and the Leeward and 

 South Nake groups were particularly hazardous. Within these 

 islet clusters, names such as Blackfin, Shark, and Danger 

 reflected this ubiquitous feature of Caroline. 



The only tidal measurements taken were by the Solar 

 Eclipse Party (Holden & Qualtrough. 1884). who noted that in 

 May 1 883 the greatest daily fluctuation ranged from a maximum 

 of 475 mm (1' 7") to a minimum of 125 mm (0' 5"), similar to 

 that (around 2') in the Tuamotus (Stoddart & Sachet. 1969); 

 Arundel's map (Fig. 4) gives 0.5 m ( 1.5') for Caroline, which 

 we have tentatively used in the schematic profiles 

 (Figs. 34-36) as the difference between low and high spring 

 tidal levels. 



Windward Reef Flats : Constantly pounded by surf 

 (PI. 16). the windward reefs are typically narrower than those 

 to leeward, averaging 5 19 m ( range 396-759 in), though this is 

 less evident from a map than in the field. 



The windward reefs are 13.5 km long, surmounted by 16 

 motus that total 63% of its length. This is not surprising, as a 

 recurrent pattern on central Pacific and Tuamotuan atolls is that 

 motus are more frequent along windward reef rims (Thomas. 

 1961; Wiens. 1962). The longest islets are Nake ( 1.980 inland 

 Long (4.226 m), both formed from the coalescence of two or 

 more smaller islets (Figs. 37-39). The rest vary from 1 S m to 

 858 m in length. 



The character of these reef Hats differs, depending on the 

 presence or absence of land, interisland distances, lagoon 

 depth, and recent weather conditions. In February 1990. part 



10 



