the panels indicated the same progression, but generally was more 

 susceptible to silting. In some panels as much as 3/4 of the concave 

 side became covered -with a layer of silt 1/8 inch thick. 



The part of Figure 19 showing photographs of the 2-month panels 

 reveals in even more vivid fashion the biological sequence. The 

 April to June panel shows barnacles almost exclusively with a few 

 grasslike hydroids. On the June to August panel many tubeworms 

 and encrusting bryozoans overlie barnacles. A few hydroids also 

 appear on this panel. The August to October panel shows a thick 

 matlike growth of colonial hydroids together with encrusting bryozoans. 

 Barnacles occur beneath the hydroids and bryozoans. Only an occasional 

 tubeworm appears on this panel. The October to December panel 

 contains a few barnacles, hydroids, and bryozoans. Tubeworms do 

 not appear on this panel. The December to February and February to 

 April panels show no attachments; however, silt appears on these 

 panels, indicating the probable presence of an underlying substrate 

 of bacterial or protozoan slime which is thought to be the basic 

 stratum . upon which further attachment occurs. The 3-month panels 

 (Fig. 19) serve to confirm the biological attachment progression 

 displayed by the 1- and 2-month panels. With increased exposure 

 time (Figs. 19 and 20), the growth becomes more luxuriant, the gross 

 appearance of the panels becomes less dissimilar, and detailed size 

 and count analyses become much more difficult. 



Table I contains a complete list of the fouling organisms observed 

 on the test panels of this study. 



V. CONCLUSIONS 



The analysis of a 1-year fouling study in Thimble Shoal Channel 

 near Norfolk, Virginia has served to provide valuable preliminary data 

 on the type, seasons of attachment, and growth of attaching fouling 

 organisms in that area. 



Total wet weight of fouling accumulated at the rate of about 30 

 ounces per square foot per year for the period April 1956 to April 

 1957. For comparison, Ayers (1951) reports an accumulation of fouling 

 on the bottom in the approaches to New York Harbor of 19.2 to 76.8 

 ounces wet weight per square foot per year. 



Important foulers are jingle shells ( Anomia simplex ), barnacles 

 ( Balanus improvisus ), encrusting bryozoans, hydroids, and calcareous 

 tubeworms. Lesser components of the complex include oysters, algae, 

 amphipods, sponges, and tunicates. 



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