Dosima 



FEATHERS 



Lepos 



° lOOn 

 a. 



SEA GRASS LEAVES 



[l 



20 



MACROCYSTIS 



Figure 2. — Size-frequency distributions of Lepas (Dosima) 

 fascicularis and Lepas (Lepas) pacifica on various substrates 

 as indicated. 



were 34 for Dosima and 15 for Lepas. Thirty-six of 

 the Dosima clusters consisted of more than 10 

 individuals, whereas only six of the Lepas clumps 

 on feathers comprised more than 10 animals. 

 From these data it appears that on feathers 

 Dosima is much commoner than Lepas and can 

 occur more densely and in larger clumps, presum- 

 ably because of its ability to produce its own float. 



Sea Grass Leaves (Figure 2C, D) 



Many of the Phyllospadix and Zostera leaves 

 bearing barnacles had been completely bleached; 



possibly they had become detached from the par- 

 ent plants and had drifted out to sea before being 

 colonized. The majority of the leaf sections col- 

 lected were found to carry one or more specimens 

 of Dosima. Almost 809^ carried only Dostma; only 

 3% bore Lepas alone; the rest had both. As in the 

 case of the feathers, the Dosima specimens at- 

 tached to leaves had produced their own floats, as 

 many as 23 individuals being found in one cluster. 

 The largest specimens of Dosima found on Phyl- 

 lospadix andZostera were 22 mm and 19 mm long, 

 respectively. In contrast, on these substrates the 

 Lepas individuals generally occurred either singly 

 or in pairs, and the majority of these animals did 

 not measure more than 5-6 mm in length, though a 

 few of those which occurred together with Z)ostma 

 exceeded 10 mm. Presumably, larger specimens of 

 Lepas cannot be supported by a floating leaf sec- 

 tion unless additional buoyancy is supplied by 

 floats of Dosima. 



Brown Algae (Figures IC, E, 2E-H) 



It is significant that the only algae found bear- 

 ing barnacles are parts of brown algae 

 (Phaeophyta), which either produce well- 

 differentiated gas-filled floats or, as in the cases of 

 Colpomenia and Scytosiphon, have hollow thalli 

 usually filled with air. The majority of the barna- 

 cles were found on float-bearing segments of Mac- 

 rocystis, and in Tables 1 and 2 the data for this alga, 

 which occurs in offshore waters, are presented 

 separately from those of other brown algae, which 

 are more or less intertidal. Since none of these 

 algae normally carry goose barnacles while grow- 

 ing in their natural habitats, it appears probable 

 that the pieces of thallus were colonized by barna- 

 cles after they had been detached. They must have 

 floated for some time, however, since the barnacles 

 had reached appreciable sizes: up to 21 mm in 

 length for Dosima and up to 12 mm in length for 

 Lepas. With the exception of one piece of Egregia 

 bearing a small 2-mm Lepas, the littoral brown 

 algae bore only Dosima (83 specimens in all), 

 whereas a large proportion of the Macrocystis 

 pieces bore mixed populations. 



Terrestrial Debris (Figure 21, J) 



The majority of the fragments grouped in this 

 category were pieces of wood, which may be con- 

 sidered a "natural" substrate since fallen branches 

 are a normal component of the flotsam carried 



215 



