ZOOLOGY: A. G. MAYOR 
391 
weight of stony substance per year in various coral heads of average size 
appears to be as follows: 
Knowing the number of coral heads of these genera upon a reef-flat, we 
have a means for ascertaining the weight of limestone added to the reef each 
year by the growth of coral upon its upper surface. 
By counting the numbers of coral heads and species of corals on squares 
of 24 feet on the side (576 square feet), the squares being staked out from 50 
to 100 feet apart from the shore to the seaward edge of the reef-flat, we are 
led to the following conclusions: 
On the upper surface of the Aua reef-flat between Breaker Point, Pago Pago 
Harbor, and the southern end of Aua Village, the area of the reef being 
2,550,000 square feet, the number of corals are approximately as follows: 
There are about 502,200 heads of Porites growing over 72% of the area of 
the upper surface of the reef-flat, and contributing (due to their growth) per 
annum 251,000 pounds of limestone. 
347,500 Acroporas distributed over 56% of the reef -flat contribute annually 
500,400 pounds of limestone. 
57,600 heads of Pocillopora scattered over the entire reef-flat contribute 
31,700 pounds of limestone. 
55,900 Psammocora distributed over 30% of the reef-flat contribute each 
year 11,000 pounds of limestone. 
15,500 Pavona found over 35% of the reef-flat area contribute each year 
about 11,600 pounds of limestone. 
Thus the growth of these corals appears to add about 805,000 pounds of 
limestone each year to the upper surface of the reef-flat and as these genera 
contribute 95% of the entire coral heads of the reef -flat, it is probable that 
about 840,000 pounds or 380,500 kilograms of limestone is added to the coral 
reef each year by the growth of the corals over its surface. 
There are, however, certain obvious losses which may be approximately 
determined. Among these the wash of the breakers due to the prevailing 
trade wind drives a current of about 40 feet per minute over the surface of 
the reef -flat from Breaker Point, northward to the jagged northern edge of 
the reef-flat over which the drifted limestone sand spills into deep water. 
In order to determine the annual loss of loose limestone sand lost to the 
reef-flat by being drifted off its northern edge, 6 barrels each 2 feet in diame- 
ter were weighted with volcanic rocks and sunk off the reef -flat close to the 
northern edge so that the water was about 1 foot deep over their open tops 
at lowest tide. 
Acropora 
Porites 
Pocillopora. . 
Pavona 
Psammocora, 
19 ounces avoirdupois, or 539 grams per annum 
8 ounces avoirdupois, or 227 grams per annum 
10 ounces avoirdupois, or 283 grams per annum 
12 ounces avoirdupois, or 340 grams per annum 
3 ounces avoirdupois, or 85 grams per annum 
t 
