DEPARTMENT OE MARINE BIOLOGY. 1 51 



COLONIES FROM PLANUL.^ SETTLING ON COLLECTORS. 



Sixty-one tiles were attached to stakes driven into the reefs off the north- 

 west face of Loggerhead Key in 1909. The upper surfaces of these tiles 

 were examined in June 1910 and June 1911, to discover any young colonies 

 that might be growing on them, but none were found. The aggregate area 

 of the upper surfaces of these tiles is about 24 square feet; as the tiles were 

 out for 2 years, the exposed surface would be equivalent to 48 square feet 

 for I year, or a square about 7 feet on each side, assuming conditions in the 

 two years to have been similar. These tiles were planted among corals, at 

 depths below the water-level of the lowest observed tides. This experiment 

 clearly shows that smooth, flat, horizontal surfaces on reefs are not favor- 

 able locations for the attachment of coral larvse. It was observed that adven- 

 titious planulae had attached to the upper surfaces of the tiles in the floating 

 live-car and to the upper surfaces of some of the tiles on stakes off the north- 

 west face of the Fort Jefferson moat-wall. The conclusion from these ob- 

 servations seems substantiated, that the strong forward and backward flow 

 of water over reefs, with the flood and ebb of the tides, together with the 

 exposure to storms and the consequent breakers, prevents planulae from set- 

 tling on smooth, open, horizontal surfaces, while they will settle on such 

 surfaces in more protected situations. 



The tiles planted on stakes off the northwest face of the Fort Jefferson 

 moat-wall bore numerous young colonies, less than one year old, on their 

 peripheries and under surfaces, as well as on their upper surfaces. This 

 observation led to the inspection of the peripheries and under surfaces of 19 

 tiles planted as collectors on Loggerhead Reef. Nine of these tiles bore a 

 total of 18 young colonies. These observations indicate that on the reefs 

 planulae effectively attach themselves in the more protected places. An ex- 

 amination of the natural surfaces of the Loggerhead reefs to find young 

 colonies revealed very few, some Favia fragum and some Pontes astreoides 

 growing in protected places. Although a more thorough inspection would 

 doubtless have yielded a larger number, the important factors controlling 

 effective attachment seem evident. 



Many of the colonies developed from naturally attached planulae were 

 photographed and measured, and incorporated in the series of studies in 

 growth-rate. Tile 15 is illustrated by plate 4, fig. 4. The table on page 152 

 presents the dimensions of these yearlings : 



Culture-tiles 13, 14, and 30, and tile 15, were inverted because of the large 

 number of colonies growing on the under surfaces, while there were no 

 living colonies on the upper surfaces. The following colonies were on the 

 peripheries of these tiles : 



Culture 13, c (Porifes astreoides from planula culture), g (Pontes astreoides). 

 Culture 14, a, d {Favia fragum), i (Porites clavaria). 



Culture 30, b (Favia fragum), c (Porites astreoides), f (Favia fragum), j (Pontes 

 astreoides) . 



These data show the great preponderance of attachments in nature to be 

 on the lower surfaces of the tiles. However, though the conditions are most 

 favorable for original attachment and initial growth on the free under surfaces 

 of objects immersed in the water, such a habitat is not the most favorable for 

 the ultimate survival of the young corals. On the lower surfaces of the tiles 

 algae of various species, sponges, and Bryozoa, that have a more rapid 

 growth-rate than the young corals, grow luxuriantly and frequently smother 

 more slowly growing organisms. In the competition between attached and 



