BIOLOGICAL SURVEY OF WOODS HOLE AND VICINITY. 1 77 



number of species belonging to this category (though not these in particular) do repro- 

 duce sexually during the summer months. In few cases, if any, however, do we know 

 from local observations that their sexual period is confined to these months. We may 

 comment parenthetically upon the urgent need of determining the reproductive condi- 

 tion of local marine organisms throughout the entire year." 



In the case of one species among those which appear to be restricted to the warmer 

 waters of the region we have definite evidence that an actual destruction of adult organ- 

 isms may occur as a result of extreme cold in winter. We refer to the common sea urchin, 

 Arbacia punc tula ta, which, as our records show (see pp. 114, 1 15), was almost exterminated 

 in Vineyard Sound during the winter of 1 903-4. And it is well known to fishermen and 

 others that great numbers of dead fishes and mollusks of certain species are frequently 

 found after a particularly hard spell of cold weather.* This is sometimes attributed 

 to the action of "anchor ice" or "ground frost." Gould (1840) cites the case of an 

 extensive destruction of oysters which was believed to be due to this agency. That 

 anchor ice does form in salt water, even at the depth of a number of fathoms, and that 

 it may "freeze around fish caught in nets," is vouched for by Sir William Dawson and 

 others.*^ On the other hand, we are informed by Prof. Herdman that he has had personal 

 knowledge of the death from cold of fishes in aquaria, and even of burrowing mollusks 

 along shore, in cases where actual freezing was out of question. It seems difficult, indeed, 

 to believe in such a wholesale formation of anchor ice throughout Vineyard Sound as 

 would be necessary to account for the extermination of the sea urchins by this agency. 

 However, the extermination did occur during an exceptionally cold winter, and it seems 

 a legitimate inference that it resulted in some way from the cold. 



Now it is known that Arbacia finds in this region its northern limit of distribution 

 upon our coast. It would seem, therefore, that in this latitude it is adapted to withstand- 

 ing the average winter but not the exceptional one. On the other hand, no mere refer- 

 ence to winter temperatures can explain the absence of this species from the western end 

 of Vineyard Sound, or from Crab Ledge. For, although at these latter points the sum- 

 mer temperatures are considerably lower than they are nearer Woods Hole, the winter 

 temperatures are no lower, and possibly, indeed, not so low. Here, then, the law of Mer- 

 riam may have application. Arbacia may not be adapted to reproducing in these colder 

 waters. 



But Merriam's principle, in its completed form, really contains two wholly distinct 

 principles. The second is that animals are "restricted in southward distribution by the 

 mean temperature of a brief period covering the hottest part of the year" (1895, p. 234). 

 It is not stated whether this effect has to do with the ability of the adult organism itself 

 to withstand higher temperatures, or whether the reproductive power is curtailed. 



As regards the distribution of our local marine fauna, this phase of Merriam's law 

 can apply, if at all, only to those predominantly northern species which were found to be 

 restricted to the waters which were cooler during the summer months. And it does seem 

 likely, indeed, that some of these species are unable to endure the high temperatures 



a .\side from the case of certain fishes, our data for the winter months are derived almost wholly from an examination of 

 tow-net collections made by Mr. Edwards. 



/> The scraping action of ordinary- floating ice in removing the rock-weeds (Fucus and A scophyllum)iTom the boulders along 

 shore is pointed out in the botanical section of this report. This same agency doubtless restricts the distribution of such littoral 

 animals as inhabit these weeds, and may even affect certain other forms, e. g.. barnacles, which occur directly on the rocks. But 

 it can, of course, have no influence upon the benthos, with which we are especially concerned here. 



*Cf. Barnes, 1906, p. 210. 21^-22$. 



16269° — Bull. 31, pt I — 13 12 



