6 Papers from the Marine biological Laboratory at Tortugas. 



of biological significance. Thus on July 21-22, 191 1, at Tortugas, Florida, 

 after several hot, calm days, the shallow water over Bird Key Reef rose to 

 33 to 38 C. and Dr. L. R. Gary observed that large numbers of Diadema, 

 Octopus, Fissurella, and other mollusks and small fishes were killed in 

 considerable numbers over extensive areas, and corals were injured even 

 when not exposed to the air. 



In order that a marine animal may live throughout the year in the 

 shallow or surface waters of the tropics, it must be capable of surviving at 

 29 C. Similarly, the animals of the Arctic Ocean must survive at and, 

 indeed, Cyanea arctica continues to pulsate even when half its bell is frozen 

 into the ice, and after being embedded solidly for several hours it revives at 

 once, apparently uninjured, when the ice has melted. 



It is easy to see why such forms as the rhizostomous scyphomedusa 

 Cassiopea and the sea-urchin Diadema setosum are confined to the tropics, 

 for they lose all power of movement at from 10 to 12 C. Also the floating 

 barnacles, Lepas fascicidaris , can not survive in arctic waters, for they are 

 unable to move if cooled to 4.6 C, and, conversely, Cyanea arctica can not 

 enter the tropics, for it dies at 27 C. 



On the other hand, even the tropical Limjilus polyphemus, from the 

 Marquesas, Florida, survives being frozen into the ice, and near the northern 

 limit of its range, off the northern coast of Massachusetts, it continues to 

 move until heated to at least 40. Judging from its marked adaptability 

 to extremes of temperatures, one would expect this animal to be of world- 

 wide distribution, yet it ranges only from Maine to Yucatan and is unknown 

 from European coasts. 



When a boreal or arctic animal such as Aurellia becomes acclimated to 

 the tropics, its upper death-temperature is raised, and conversely it becomes 

 unable to withstand a degree of cold in which its northern relatives may 

 thrive. Its optimum temperature is, however, raised even more con- 

 spicuously than its death-points and thus its factor of safety against ab- 

 normally high temperatures is reduced. 



These facts are illustrated in fig. 8, page 18, wherein the ordinates of the 

 curve ABC represent the average rates of pulsation of Aurellia at Halifax, 

 Nova Scotia, the abscissas representing the respective temperatures in 

 degrees centigrade. The curve DEF shows the same factors for the Aurellia 

 from Tortugas, Florida, and it is evident that at Halifax a wide range of 

 temperature, from 2 to 19 C, produces but little change in the rate of 

 the medusa, whereas at Tortug a the medusa lives constantly at the temper- 

 ature of its maximum activity and any further elevation of temperature 

 causes a marked decline in its rate of pulsation. 



The case of the brittle-stars Ophioderma brevispina and 0. appressa is 

 unlike that of Aurellia, for at Montego Bay, Jamaica, they both have the 

 same temperature-range, their movements ceasing at 7 to 8 C. in cooled 

 and 37.3 to 38 C. in heated sea -water; yet the former species ranges from 

 Woods Hole, Massachusetts, to the West Indies, and the latter is restricted 

 to the tropics. 



