STUDIES IN MARINE ECOLOGY. 1 89 



On the earlier lists, fifteen species were recorded from some 

 place in each of the four main types of habitats: wharf pilings, 

 rocks, flats, and dredging. In 1920 this list had increased to 54. 

 These results mean, as has already been suggested, that as 

 collecting has proceeded, animals have been picked up in habitats 

 in which they are not abundant. The scarcity of many of these 

 is shown by the number of single specimen records on the lists. 

 There is little doubt but that if the present type of collecting 

 were continued long enough, there would finally be stray records 

 of many of the animals found in the region from each type of 

 habitat. Even dredging, which we have usually carried on in 

 deep water in Vineyard Sound, yields a different type of animals 

 and becomes more closely related to other habitats as a result 

 of dredging records taken in Great Harbor. In some one or 

 more of their dredging operations, the Biological Survey found 

 most of the animals we have taken from inshore digging. This 

 result might be expected from the fact that some of their dredgings 

 are recorded from less than 10 feet of water. If made at high 

 tide, these would be almost as close inshore as our deepest col- 

 lecting on wading and digging expeditions when we often collect 

 out to four feet of water at low spring tides. 



In other words, in such a small region as we are now con- 

 sidering, provided with strong tidal currents which aid in distri- 

 bution, the animals tend to become widely distributed and 

 occasional specimens will be found that can tolerate for a time 

 conditions that are essentially unfavorable. Under these condi- 

 tions the mere record of the presence of a species in a given 

 habitat means very little unless there is due consideration of its 

 abundance and duration in that locality. One is thus driven 

 again to the conclusion of the last section, that quantitative 

 work is necessary before final judgment can be passed in the 

 matter of the constitution of animal associations. 



We have found no evidence that the long continued collecting 

 over the same grounds by the Invertebrate Class, nor the com- 

 mercial collecting of the Supply Department of the M. B. L. 

 has affected the number of animals present within the past nine 

 years sufficiently for the effect to be noticeable by the collecting 

 methods we have used. With growing experience in collecting 



