. Advances in marine biology: volume 17. Coral fisheries. 262 li. HILLIS-COLnsrVAUX both the amounts of Halimeda segments shed and the types of currents may have seasonal components. At the Enewetak sites I visited, the commonest species were Tnacrophysa, opuntia, cylindracea, gigas, distorta, copiosa and lacunalis f. lata. These, then, are the species, about half the total number found on the atoll reef, which would contribute most of the Halimeda sediments (Hillis-Colinvaux, 1977), but it is likely that two or three from this short list produce the bulk of the Enewetak sediments. Tydemania e
. Advances in marine biology: volume 17. Coral fisheries. 262 li. HILLIS-COLnsrVAUX both the amounts of Halimeda segments shed and the types of currents may have seasonal components. At the Enewetak sites I visited, the commonest species were Tnacrophysa, opuntia, cylindracea, gigas, distorta, copiosa and lacunalis f. lata. These, then, are the species, about half the total number found on the atoll reef, which would contribute most of the Halimeda sediments (Hillis-Colinvaux, 1977), but it is likely that two or three from this short list produce the bulk of the Enewetak sediments. Tydemania expeditionis, the only other calcareous green alga present at Enewetak in sizeable populations (Gilmartin, 1960, 1966; 0 DEPTH r- 15-55 % Grain Composition 10 20 30 40 157 209 249 295 308. Fig. 86. Composition of sand-sized sediment from the fore-reef slope (— 15 m to — 55 m) and island slope ( — 123 m to —308 m) of Discovery Bay, Jamaica. Graph bars from top to bottoin represent Halimeda, calcareous red algae, corals, molluscs, foraminifera and "other". (Data from Moore et al., 1976.) Hillis-Colinvaux, 1977), also contributes to the sediments but not in an easily recognizable form. In Jamaica most of the Halimeda sediments derived from the shallower parts of the reef, that is, from the back-reef, reef crest and fore-reef to about — 55 m, are dammed by sill reefs at the base of the fore-reef slope (Goreau and Goreau, 1973; Goreau and Land, 1974; Moore et al., 1976). The contribution of the genus to identifiable sedi- ments of the island slope (depth approximately — 122 m to — 305 m) is at least as great (Fig. 86). In the suite of samples available for analysis. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Hillis-Colinvaux, Liewellya. London : Academic Press ; Toronto
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