DEPARTMENT OF MARINE BIOLOGY. 221 



The collecting of daily water samples at Fowey Rock, off Miami, Florida^ 

 throughout one year is now nearly finished. Mr. R. B. Dole, of the U. S. 

 Geological Survey, has titrated the samples for salinity as they were received 

 and has made twelve composite samples, one for each month, composed of an 

 equal amount of water from each daily sample. He is quantitatively deter- 

 mining the amount of calcium in each composite, and will make a complete 

 quantitative analysis of a composite composed of all the monthly composites. 



Last year Dr. Mayer put on the rocks, under the landing for the laboratory 

 pump wharf, the corals used in the light-exclusion experiment. Seven of the 

 specimens were recovered,^ and the following records were made on July 21^ 

 1915: 



Orbicella annularis: 1 specimen, part of which is pale, with no zoanthoxellae, but in other 



places the colony has resumed its normal color. 

 Orbicella cavernosa: 2 specimens, both aHve, somewhat damaged apparently by rolling; still 



a Uttle paler than usual. 

 Moeandra clivosa: 2 specimens, (1) color gray, otherwise normal; (2) pale, but part of the 



specimen is brown. 

 Siderastrea radians: 2 specimens, (1) most of it of normal, brownish color; (2) has some 



Ught patches. 

 Siderastrea siderea: 2 specimens, of normal, brownish color, have grown appreciably. 



These specimens not only survived being in the dark for 43 days, but before the 

 end of a year were again very nearly or quite normal. The fact that the corals 

 are not normal in the dark, although they will endure the exclusion of light for a 

 considerable period, and the fact that corals are absent on the central piers 

 under Fort Jefferson wharf, where it is dark, while they are abundant on the 

 peripheral piers, is strong evidence in favor of light being one of the ecologic 

 factors determining the locus of species of corals. 



Three additions were made during the season to the list of the Tortugas 

 coral fauna, as follows: 



Madracis decactis (Lyman) and Agaricia nobilis Verrill were dredged at a 

 depth of 18 fathoms south of Tortugas BuoJ^ Phyllangia americana M.-Ed. 

 & H. and Stephanoccenia inter septa (Esper) were dredged in 16 fathoms (these 

 are not new records for the Tortugas, but it was interesting to find the species) . 

 A fine specimen of Mycetophyllia lamarckana M.-Ed. & H. was collected by 

 Mr. George Matthai on the piers of Fort Jefferson wharf. 



Growth-rate of the Floridian and Bahaman Shoal-Water Corals. 



Except to allude to the continuation of the experiments and observations, 

 no specific report on the results of the study of the growth-rate of corals has 

 been published since the one in Year Book No. 10, pp. 148-156, plates 4-6, 

 where all data then available on the size of year-old corals were presented. 

 The technique for rearing and planting corals and that for measuring corals 

 growing under natural conditions are described in Year Book No. 10 and in 

 Year Book No. 9, pp. 136-144, plate 1 . The descriptions there given need not 

 be repeated here. It was stated in the last Year Book, p. 225, that the investi- 

 gations of growth-rate, except the remeasurement of colonies reared from plan- 

 ulae or of known age, were terminated. The colonies on which additional 

 records were desired were remeasured in July 1915, and they also have now 

 been taken up and shipped to Washington. 



During the past winter I had all records on growth-rate copied on appropri- 

 ate schedules, and since my return from Tortugas I have added the records 

 made during July of this year and have had the average annual rate for the 



^For records made in 1914, see Year Book 13, p. 223. 



