190 BULLETIN OF THE BUREAU OF FISHERIES. 



7. CHANGES IN THE COMPOSITION OF THE LOCAL FAUNA. 



Every area of land or sea doubtless undergoes more or less frequent changes in the 

 composition of its fauna and flora, due to the immigration or artificial introduction of 

 exotic species or the extinction of indigenous ones. For the Woods Hole region we 

 have certain well-known and highly authentic instances of this phenomenon, together 

 with some others which seem probable, if only inferential. 



The best-known local instances of the sort are those of the European periwinkle, 

 Littorina litorea, and of the small sea anemone, Sagartia lucice. Rather full accounts of 

 the history of both of these immigrants are fortunately extant. (See Verrill, 1880; 

 Ganong, 1886; Verrill, 1898; Parker, 1902. These accounts are summarized in our own 

 catalogue.) It may be here remarked that the periwinkle reached Woods Hole from 

 the north about 1876; while the anemone seems to have come from the south, 

 arriving about 1898. Within about 30 years, and perhaps much less, Littorina litorea 

 has become the most abundant and generally distributed of our littoral (intertidal) 

 mollusks, while Sagartia lucics in a considerably shorter time has become by far the 

 commonest local actinian. It would be interesting to know what effects, if any, these 

 immigrants have had in limiting the abundance or restricting the distribution of species 

 already present. Unfortunately few observations, if any, have been made to test this 

 point. 



Concerning certain other species, we have some reasons for believing either that 

 they are, in local waters, far more abundant now than formerly, or that they have actu- 

 ally migrated hither within recent years. The only other alternative seems to be that 

 they were overlooked or confused with quite distinct species by a number of competent 

 naturalists. For example, of our four local species of hermit crabs, Pagurus annulipes 

 is second in abundance only to the ubiquitous P. lonqicarpus. Its distribution in local 

 waters is almost universal, as will be seen from a glance at the distribution chart for 

 this species. Yet this hermit crab was not mentioned by Verrill and Smith in 1873," 

 nor, so 'far as we are aware, has it been recorded for local waters in any work prior to 

 Miss Rathbun's catalogue of the Crustacea of New England (1905"). We have, it is true, 

 learned from Miss Rathbun that specimens of this crustacean were recently found 

 among the earlier material dredged by Verrill and Smith. But the fact that it was 

 overlooked, or at least not mentioned by these writers, raises strong doubts as to whether 

 it occurred then in its present abundance. 



Another problematic case is that of one of the shore barnacles, Chthamalus stellatus, b 

 which at present is extremely abundant upon stones and boulders between tides every- 

 where. This well-known European species is, in our waters, at least, quite distinct 

 in appearance from the other common shore barnacle (Balanus balanoides) . Yet it 

 has not been mentioned in any catalogue of New England fauna, although several far 

 less common cirripedes have been listed. It is hard to believe that this species has 

 been habitually confused with Balanus balanoides by the long succession of field natu- 

 ralists and systematic zoologists who have exploited the shores of New England for 



o Allowance must be made for the fact that, in the words of one familiar with the circumstances, "the Vineyard Sound report 

 was prepared when the Fish Commission had spent but one summer at Woods Hole, and was rushed through expeditiously for 

 insertion in the Fish Commission Report for 1871-72. It did not list everything that had been discovered, but omitted much 

 that had not been sufficiently studied." 



For an account of this case, see Sumner, 1909. 



