212 
ZOOLOGY: A. G. MAYER 
Distance^ 
Living^ 
Species^ 
400 
3 
2 
525 
110 
11 
625 
126 
9 
825 
413 
13 
1025 
529 
15 
1225 
962 
9 
1425 
1838 
18 
1650 
1512 
27 
1750 
201 
15 
1 Distance in feet of the center of the square from shore. 
2 Number of living coral heads growing within each square (2500 square feet). 
' Number of diflFerent species of corals on each square. 
About 40 different species of corals are found growing within these 
squares. Of the 22 genera of corals found on these squares, four con- 
stitute 91% of the living coral heads. Thus: Porites 38%, Seriatopora 
25%, Acropora 18%, and Pocillopora 10%. 
Seriatopora is the most successful coral of the calm waters of the 
middle zone of the reef fiat 1100 feet from shore where it covers 40% 
of the area of the bottom, and constitutes 70% of the entire num- 
ber of Kving coral heads. In this region where Seriatopora is domi- 
nant all other species of corals are reduced in number. Yet Seriatopora 
cannot live within 500 feet of the shore, owing to the high temperature 
of the water in this region, nor can it survive in places more than 1650 
feet from shore due to the destructive action of the breakers upon its 
fragile stems. 
The coral heads are most densely clustered in a region about 200 
feet inward from the usual inner ^wash' of the breakers, but an even 
greater variety of species of corals are found to the seaward of this place 
where the water is strongly agitated by the surges. Thus in the place 
where coral growth is most dense there are only 18 species, but 200 feet 
to seaward of this zone there are 27 species, although owing to the rough 
water the coral stocks are much broken and are either large massive 
heads capable of resisting the waves or small ones protected within 
crevices. 
Of the 22 genera from the squares over this reef fiat 13, or more than 
half, are confined to the seaward parts of the flat and do not commonly 
appear within 1200 feet of the shore. In fact only two species, Bernard's 
'Porites No. 12' and a form allied to * Siderastrea ' sphaeroidalis 
Ortmann are practically confined to the shore fiats within 1100 feet of 
the beach. 
Temperature is the dominant factor, and is even more important 
than silt in determining the habitat of corals. The most sensitive 
