FISHERY BULLETIN: VOL. 84, NO. 1 



dive F, for example (Fig. 1), a 0.2 kn (0.10 m/s) cur- 

 rent was observed at 125 m running south (i.e, 

 counterclockwise when viewed from above). There 

 was no current between 180 and 275 m. At 300 m, 

 however, a 0.1 kn (0.05 m/s) current was observed, 

 traveling in a northerly direction (i.e, clockwise). A 

 similar depth-related current reversal was observed 

 during dive C, although on this occasion the 

 shallower current (170 m) ran clockwise and the 

 deeper one (290 m) counterclockwise. In contrast, 

 a weak downslope current (0.1 kn or 0.05 m/s) was 

 observed but once (dive E at 305 m). No upwelling 

 currents were encountered. 



Geologically, the deep slope of Johnston Atoll was 

 grossly similar at all points visited. The low escarp- 

 ment at 130 m was most likely due to erosion of an 

 ancient limestone reef. This feature was character- 

 ized by mounds of coral rubble, boulders, small 

 undercut caves, and a profusion of fishes. Below it 

 the slope angle was remarkably uniform, with low 

 topographic relief. The bottom was still composed 

 of limestone and showed severe biological and chem- 

 ical weathering (i.e, dissolution) along the slope gra- 

 dient, being pitted and striated with numerous 

 shallow depressions. Few sediments or boulders were 

 observed. At a depth of 240 m topographic relief in- 

 creased, as large slab boulders became increasingly 

 prominent. Subaerial dissolution had produced low 

 shallow limestone caves, and fine sediments were 

 more common. Between 290 and 335 m the slope was 

 very steep, with a well-developed system of sharp 

 ridges and deep erosional channels. The substratum 

 had the superficial appearance of dark basalt but was 

 composed of thin manganese crusts overlying an- 

 cient limestone reef materials (Keating see footnote 

 6). Fine sediments spilled down the channels in the 

 slope and piled up at the base of the deep dropoff 

 (350 m). More limestone boulders were arrayed along 

 this deep terrace and fine sediments covered the 

 bottom. 



As expected, few fleshy macroalgae were seen. The 

 only algae encountered regularly were two coral- 

 lines, Halimeda sp. and an unidentified crustose 

 species. The former occurred in small scattered 

 clumps between 100 and 200 m, with loose remnant 

 exoskeletal "sands" found in sediment pockets as 

 deep as 290 m. The crustose form was abundant be- 

 tween 150 and 250 m where it covered much of the 

 slope face Otherwise, an unidentified species of 

 brown algae seen on dive H between 150 and 250 

 m was the only other algae seen. A more detailed 

 description of the algal biota at Johnston Atoll is in 

 preparation. 7 



In contrast to the depauperate flora, the inverte- 



brate fauna was rich. Listed here are those forms 

 seen often enough to constitute indicator species for 

 particular depth strata. In addition to these a great 

 many others were observed and photographed. 

 In the Cnidaria, three stoney corals were especially 

 plentiful: Leptoseris hawaiiensis (115-165 m), 

 Stylaster sp. (135-245 m), and Madracis sp. (140-200 

 m). Several species of black corals (Order An- 

 tipatharia) were also common. Of the crustaceans, 

 a single large Panulirus marginatum, previously 

 known only from one specimen (Brock 1973), was 

 observed in a small hole during dive A at 122 m, and 

 at least two types of galatheid crab were very 

 abundant in small holes pitting the reef slope 

 between 230 and 350 m. In deep water the remain- 

 ing attached valves of dead rock oysters were seen 

 in patches along the base of the deep dropoff 

 (350 m), as was an unidentified species of solitary 

 tunicate (335-365 m). Echinoids were particularly 

 abundant immediately below the shelf break; eg, 

 Diadema cf. savignyi (110-170 m), Chondrocidaris 

 gigantea (120-160 m), and heart urchins (Brissidae, 

 130-200 m). Other than galatheid crabs, the 220-310 

 m zone was largely barren and devoid of mega- 

 benthos. 



Ichthyofauna 



A total of 69 fish species in 29 families were ob- 

 served during Makalii dives (Table 2). Overall, the 

 proportional representation of different families was 

 similar to that of the shallow water community 

 (Gosline 1955; Randall et al. in press), although the 

 representation of genera was grossly different. Ser- 

 ranid species were most numerous with nine species 

 observed (eight in the anthiine subfamily). Lutjanids 

 were also abundant (eight species), but no members 

 of the ubiquitous genus Lutjanus were seen. Forty 

 of the species listed in Table 2 (58%) are new records 

 for Johnston Atoll (Randall et al. in press). Photo- 

 graphs of several fishes observed during dives are 

 presented in Figure 4. 



An indication of species' depth distributions is 

 given in Table 2. Because no observations were made 

 in <100 m, upper limits can be misleading. This is 

 particularly true of shallow-water species which 

 penetrated to the 135 m escarpment but not beyond, 

 including: Triaenodon obesus, Parapercis schau- 

 inslandi, Aphareus furcatus, Chromis verater, Paru- 

 peneus cyclostomus, P. multifasciatus, Forcipiger 

 flavissimus, Holacanthus arcuatus, Bodianus bilu- 



7 C. Agegian, University of Hawaii, Honolulu, HI 96822, pers. com- 

 mun. June 1984. 



146 



