Observations upon the Growth-rate and Oecology of Gorgonians. 85 



limits of the crack over the bottom, so that its apparent height is not 

 measured from its original point of attachment. 



On the shallow reefs, where the gorgonians are most abundant, the 

 amount of algse, bryozoons, and other incrusting organisms appears to vary 

 only slightly during the different seasons of the year. In no observed 

 instance did these organisms seem to form a mass dense enough to exclude 

 a sufficient amount of water for the well-being of the young gorgonian 

 colony. Frequently the fronds of algje extend beyond the free ends of the 

 gorgonian colony, but the specimens found in such locations appear, to 

 judge from comparative measurements, to have suffered no harm from being 

 so closely surrounded. 



In comparison with the young coral polyp the gorgonian colony has an 

 obvious advantage in that its most rapid growth is perpendicular to the 

 surface of the substratum, which would keep the most rapidly growing 

 part in a position favorable for the securing of food and oxygen. 



On the sea-bottom, away from the shallow reefs, gorgonians are gener- 

 ally found as scattered specimens or in groups of at most only a few indi- 

 viduals. These colonies will almost invariably be found to be attached to 

 some irregular mass of rock which affords the protecting cavity necessary 

 for the permanent attachment of the young gorgonian. 



DESTRUCTIVE AGENTS. 



Of the destructive agents to which the gorgonians are subjected the 

 wave-action during severe storms is apparently by far the most important. 

 The wave-action developed by the ordinary northeast trade-winds during 

 the winter months is of sufficient force to cause the destruction of many 

 colonies which have a comparatively weak attachment. The tendency for 

 any colony to be torn away will increase from year to year as its surface 

 area becomes increasingly larger. 



An opportunity to study wave-action at its maximum severity was 

 afforded the writer in January 191 1, and later, in July of the same year, 

 when the observations made during the first visit were confirmed and 

 extended to a much greater area. The hasty observation made in January 

 shows that, as the result of the hurricane of the previous October, there had 

 been a great destruction of gorgonians on the reefs about Tortugas. On the 

 east shore of Loggerhead Key, the only one visited at that time, many 

 specimens of some five or six species of gorgonians were found thrown up on 

 the beach along its entire length. At that time no estimate of the number 

 cast up was made nor was the area visited sufficient to give conclusive 

 evidence of the proportion of colonies carried from their natural location. 

 In July 191 1 the observations on these points were extended to cover a 

 large area of shore-line and submerged reef. 



At one point on the inside of the east reef, near Bush Key, the gorgonian 

 skeletons were counted over a strip of beach 112 yards in length, where 



