DEPARTMENT OF MARINE BIOLOGY. I35 



The chief aim of the work in 1910 was the acquisition of material for a 

 study of nuclear activities in eggs whose potencies had been determined by 

 OH ion concentration. An abundance of material was obtained, but no re- 

 port can be made until the cytological study is completed. 



The Recent Madreporaria of Southern Florida, by Thomas Wayland 

 Vaughan, U. S. Geological Survey. 



SURVEY OE THE CORAE FIELDS. 



The survey of the coral fields of the Tortugas was continued in 1910 and 

 three additions to the list of the shallow-water madreporarian fauna were 

 made, viz : Astrangia solitaria, which grows on calcareous blocks on the reefs 

 off Loggerhead Key ; Cladocora arbuscula, which is attached to the outer 

 face of the northwest side of the Fort Jefferson moat-wall; and Acropora 

 palmata, which was observed by Dr. Mayer in the Five-Foot Channel, off 

 Bush Key reef, in water about 5 feet deep. 



Acropora ccrvicornis and A. prolifera covered acres or even square miles 

 of the shallow-water flats around the Tortugas previous to the "Black Water" 

 period of 1879, when they were nearly all killed. For many years subsequent 

 to this general destruction only occasional specimens of them could be found, 

 the principal locality being off the northwest face of Loggerhead Key in 

 water about 20 feet deep. Now, however, they are rapidly reestablishing 

 themselves, and have become fairly common on the flats west of Garden Key 

 off Fort Jefferson, and on the flat north of Bird Key, in water 4 or 5 feet 

 deep. The present tentative list of Tortugas Madreporaria comprises 27 

 species and forms,* including most of the common reef and flat corals of the 

 Antillean and Floridian regions. 



The annual surveys of the piers of the Fort Jefferson dock and of the Fort 

 Jefferson moat were continued. In both localities young corals were dis- 

 covered and measurements to determine growth-rate initiated. Especially 

 noteworthy among the young corals are single-caliced specimens of Busmilia 

 and small Mccandra clivosa on the piers of the dock, and a young Oculinu 

 in the moat. 



The continued observations on the piers of the dock seem to show that 

 strong light is essential for the growth of shallow-water corals, as the piers 

 in the permanently shaded area under the dock are devoid of corals, while 

 they are abundant wherever the light is strong. Skeletal texture and strength 

 of basal attachment are other factors determining habitat. Corals with 

 fragile skeletons, such as Busmilia and Oculina, can not live in the region of 

 breakers, while that kind of environment is favorable for massive species, 

 such as Orbicella annularis and Porites astreoides. Species with narrow 

 bases of attachment, as Mceandra areolata, are necessarily limited to rather 

 quiet water. 



The annual examinations of the moat show gradual changes in the biologic 

 associations. Certain algae, both non-calcareous and the calcareous Hali- 

 meda, are becoming more abundant, while ramose bryozoa are verj' prolific. 

 In some instances these organisms are overgrowing the corals, and probably 

 killing them. Evidently here is an opportunity not only to study the adapta- 

 bility of the corals to moat conditions, but also to observe the struggle for 

 supremacy between different groups of organisms. 



Effect of exposure between tides on corals. — Between June 6 and 8 was a 

 period of unusually low tide, accompanied by very calm weather, causing the 

 exposure of the tops of many colonies and in other instances exposing entire 



* Variations and forms are treated as species in this report. 



