84 Papers from the Marine Biological Laboratory at Tortugas. 



breeding season is over for any given year. On August 21, 1912, a young 

 specimen, probably of P. flexuosa, was found, the size of which (3 mm. in 

 height) was such that it would have been overlooked had it not been growing 

 in a location where its color was in striking contrast to the background of 

 white coral. 



To apply these facts to the observed scarcity of yearling specimens in 

 191 1, which was a general occurrence over all of the reefs visited in the 

 regions about Tortugas, it is necessary to take into account a severe hurri- 

 cane which occurred on October 16, 1910. The destruction of adult gor- 

 gonians by this storm is known to have been very severe upon certain 

 reefs and the amount of debris moved over the bottom in shallow water 

 was very great, which in itself would account for the destruction of the 

 very young specimens at that time. In July 191 1 there would be no easily 

 recognizable young which had set during the same season, and only very 

 rarely had any of those from the set of the year before been able to survive 

 the destructive effects of the hurricane. In August 1912, on the other hand, 

 young specimens of several gorgonians, besides the two above discussed, 

 were found upon every considerable reef examined. This would seem to 

 show that the setting of a considerable nuniber of young was the usual 

 occurrence. That the number of young found during the past season on the 

 reefs, which had been carefully examined each season for three years, may 

 be greater than would ordinarily be found might be inferred from the 

 breeding habits of some other sedentary invertebrates, especially the 

 Mollusca, where after a season, when for any cause the set is below normal, 

 an especially hea\y set is to be expected the following year. 



ATTACHMENT OF PLANUL^. 



Vaughan's observations on the attachment of coral planulae^ show that 

 for effective attachment they must settle in a place protected from too rapid 

 currents and wave-action, where the bottom is rough, and where other more 

 rapidly growing organisms are least likely to obtain a foothold. 



For the effective attachment of the planulffi of the gorgonians studied 

 the roughness of the bottom, i. e., the presence of small depressions or 

 cracks into which the planulae could settle, appears to be the most important 

 factor. In every instance the one-year old specimen had its base in a 

 depression. Frequently the depth of the point of attachment below the 

 surface of the rock was more than half the length of the colony. The single 

 (very small) specim.en found, when it consisted of only one or two calyces, 

 was entirely below the level of the surface of the coral head to which it was 

 attached. Many of the adult colonies have their point of attachment at 

 the bottom of a crack of considerable depth, so that, on the basis of the 

 observed growth for a year, they must have remained below the general 

 level of the bottom until more than one year old. In the later growth of 

 the gorgonian colony its non-polyp-bearing basal portion spreads beyond the 



« Carnegie Institution of Washington Year Book No. lo, pp. 151-152. 



