202 



BULLETIN OF THE BUREAU OF FISHERIES 



that after attachment, in the case of these organisms as well as of the barnacle, they 

 are completely resistant to any ingredients of a paint film. The problem of pre- 

 vention of fouling accordingly resolves itself into one of prevention of attachment 

 of these forms. 



Bryozoa are a group of organisms abundantly present on all marine coasts but 

 much less abundant now than in prehistoric times. The great majority of them form 

 colonies of thousands of relatively small individuals, each of which is surrounded by 

 a more or less chitinous or calcareous shell. They may be either aborescent in their 

 form of growth, as Bugula (fig. 8 A), or more commonly they form an encrusting 

 lamellar growth, as in the case of Membranipora. (Figs. 8 B and G.) These 

 growths frequently vary greatly in their form and may produce "sea mats" and 

 coraline structures, which may form growths 6 to 8 inches in height and 12 inches in 

 diameter. Each colony originates from a single minute larva, which has a free- 

 swimming period persisting from one to many hours. 



In the case of mollusks, such forms as oysters and anomia attach directly to the 

 surface of the vessel and may grow to considerable size. Thus, oysters have been 

 collected fully 5 inches in length and 3 inches in width. (Fig. 9.) Such forms as 

 Mytilis, on the other hand, attach by means of byssal threads, and although they 

 grow to a very considerable size (fig. 9), upon the death of the organisms the shell 

 drops off, although the byssal threads may still persist for many years, leaving a 

 telltale story of their former presence. These forms, also, at the time they attach, 

 are minute, free-swimming larvse, which in several cases are known to be sensitive 

 to light. 



Of the annelids, only one type occurs at all abundantly, this being the serpulids, 

 which form calcareous, tube-shaped shells. (Fig. 10 B.) Hydroides tubes have been 

 found fully 3 inches long, and on a few ships in large numbers. This is the only type 

 of this group that has been found attaching directly to the hull, the other forms listed 

 being only casual inhabitants of the rich growths, both faunal and floral, that are 

 found on some ships. 



The Protozoa, unicellular forms, are indicative of the environment in which 

 the ship has been. The Vorticellidse, in particular, indicate a putrid environment 

 and on some ships were very abundant. 



The tunicates, or sea squirts, are both solitary and colonial in type. The former 

 were found more often and frequently grew to large size. (Fig. 10 A.) The colonial 

 forms are incrusting types and do not produce as large an amount of growth as the 

 other forms. These, too, are free-swimming organisms at the time of attachment. 



The alga? were the most ever-present form, with the possible exception of the 

 barnacles. They frequently formed heavy mats of growth, extending from the water 

 line to from 1 to 8 feet below. Although individual growths might be of little conse- 

 quence, the large numbers frequently made the mass appear much like a beautiful 

 lawn. In many cases the growths of alg<e, especially the Enteromorpha, would attain 

 a length of 7 to 10 inches. It is interesting to note that both the Enteromorpha and 

 Cladophora are remarkable for the fact that many of their species are found indif- 

 ferently in both salt and fresh water, and that they are characteristic plants of the 

 littoral zone, rarely, if ever, extending into the sublittoral. 



