ECOLOGY AND TAXONOMY OF Halimeda 33 



provided about as extensive a world coverage as then existed, and 

 formed a good basis for the investigation which led to a revision of 

 Halimeda taxonomy (Hillis, 1959), with the recognition of 21 species 

 (Table I). 



A weakness of the Hillis monograph is that important regions of the 

 world, particularly the Indian Ocean, are poorly represented. This is 

 because little collecting had been done in these regions up to the 1950s. 

 Where phycologists had collected, their specimens provided little 

 ecological information, so that the treatment of the data had to be 

 without detail. In addition some type specimens and important 

 collections could not be examined. 



In the years since 1957 it has been possible to extend the work 

 considerably in both traditional and new ways. The International 

 Indian Ocean Expedition yielded good collections obtained by phycolo- 

 gists from new as well as familiar sites, and the new tool of scuba 

 provided the opportunity of exploring and collecting in sites that 

 grapple and dredge could not probe or penetrate. This led to the 

 discovery of new species, including the first species of Halimeda with 

 but a single medullary filament passing through the node (Fig. 15; 

 Colinvaux and Graham, 1964), which represents a fifth nodal medullary 

 filament pattern (Table III). 



Scuba diving, supplemented with skin diving and submersibles, 

 actually enable us, at last, to see these organisms in their communities 

 down to the limits of their depth range of approximately 100 m, and 

 also to investigate and eventually to understand their role in the 

 complex reef system. There have now been studies on the productivity 

 of Halimeda in culture and on the reef, on the processes of calcification, 

 on reef building, on ultrastructure and on ecology. This modern work is 

 reviewed here and is added to with many unpublished data. 



F. Summary: the evolution o/ Halimeda studies 



Halimeda was first known from the single species H. tuna that lives 

 in the Mediterranean Sea, and this species continued to be the only one 

 known for more than a century. The second, the familiar H. opuntia, 

 was found by Sloane (1707) in Jamaica. Only 8 of the species now 

 accepted were known by the turn of this century, and most of the 30 

 species now accepted are discoveries of the last three decades. Halimeda, 

 like so many other genera, was too easily split into many species on the 

 basis of superficial surface features during the nineteenth century. The 

 taxonomist who brought order to the genus was Barton (1901), and 



