FOOD OF THE SEA-UROHIN 



53 



SESSIONAL PAPER No. 22a 



abundant in the Bay of Fundy, from low water to 109 fathoms, ......... Fossil in 



the Post-pliocene of Portland, Maine, U.S. ; Kew Brunswick, Canada ; and Labrador.' 

 These records show that sea-urchins have been abundant on our coast for many years, 

 and if they are such enemies of seaweed, the seaweed would, in all likelihood have dis- 

 appeared before man came to this continent. 



In the next place there are only a few districts in which the seaweed is said to be 

 decreasing. There are now localities where sea-urchins are so numerous that it would 

 be hard to imagine them more abundant — where they are massed in heaps often obscur- 

 ing the bottom — and yet in these very places seaweed is equally plentiful, great bunches 

 being found in all suitable places. I have seen boulders covered with seaweed, and yet 

 in the interspaces between the boulders the bottom was literally carpeted with urchins 

 whose intestines contained seaweed alone. In case it might be suggested that the 

 seaweed would soon begin to decrease in these localities, it may be remembered that from 

 Dr. Stimpson's description sea-urchins were very abundant on Grand Manan in 1851 — 

 a half century ago — and although they have continued to be so until the preseni/ time, 

 Grand Manan is not one of those places where seaweed is said to be decreasing. 



In the third place, the sea-urchins do not live on exactly the same zone of the 

 beach as the seaweed. The ordinary seaweed is most plentiful between tide-marks, 

 beginning about half-tide and extending a little below the low tide mark. The sea- 

 urchins, however, are not found above the low tide mark and are abundant in about half 

 a fathom. As shown before a sea-urchin might move a considerable distance in the 

 course of a tide, but as a rule they do not move very far. They certainly do not move 

 up the beach as far as the seaweed extends, and thus a large part of the seaweed is 

 really inaccessible to the urchins. 



In the last place it must not be forgotten that there are probably nearly as many 

 urchins living on surface sand as on seaweed. It is quite surprising the difference a few 

 feet may make in the character of the food of these animals. In one case urchins living 

 15 feet from boulders covered with seaweed had not eaten any of it. At the same 

 time other urchins within a yard of the same boulders hid plenty of seaweed in their 

 intestines. As a general statement I would say that any urchin, which at low water is 

 10 or 15 yards away from seaweed, will be found to have eaten very little of it. 



In conclusion it may again be pointed out that sea-urchins can live without the 

 large fucoid or laminarian seaweeds ; that there are localities now in which sea-urchins 

 and large seaweeds are both abundant and have been so for years ; and that a great 

 proportion of the seaweed on our coast is really inaccessible to the sea-urchins owing to 

 their limited means of locomotion. There is no doubt that the myriads of sea-urchins 

 on our coast do consume an immense quantity of seaweed in a year, but seaweed grows 

 rapidly and thus its consumption by the urchins has been going on for ages. From the 

 above considerations we may conclude that there is no danger of sea-urchins denuding 

 our coast. Although my studies were not made in one of the districts where the seaweed 

 is said to be decreasing, it seems to me, that if the seaweed really is diminishing we 

 must look for other causes rather than the sea-urchins for its devastation. 



REFERENCES. 



^ Ganong, W. F., ' The Echinodermata of New Brunswick,' Bulletin of the Natural 

 History Society of New Brunswick, No. VII., p. 12, 1888. 



^ Sharpey, W. ' Echinodermata.' Todd's Cyclopaedia of Anatomy and Physiology, 

 Vol. II., p. 39, London, 1838. 



^ Butler, F. H., ' Echinodermata.' Encyclopaedia Britannica, ninth edition, Vol- 

 Vir., p. 631, Edinburgh, 1877. 



* Schmidt, Oscar, Brehm's Thierleben, zweite Auflage, p. 430, Leipzig, 1878. 



^ Dawson, J. W., 'The Food of the Common Sea-Urchin.' The American Naturalist, 

 Vol. L, p. 124, 1867. 



