by rivers out to sea. So far, plastics — in pieces 

 sufficiently large and buoyant to support goose 

 barnacles — evidently constitute a substrate of 

 only minor importance for this kind of animal. 



Tar (Figures IF, 2K, L) 



The 57 pieces of barnacle-bearing tar, presuma- 

 bly originating from natural seepage or oil bun- 

 kers, were mostly flattened 2-3 mm thick, 10-60 

 mm in diameter. This substrate, unlike those de- 

 scribed hitherto, appeared to be preferred by 

 Lepas. More than 42% of the lumps collected bore 

 only this species, and many of the pieces had more 

 than 10 animals attached. About 65% of the bar- 

 nacles found on tar were of this species. Some were 

 more than 15 mm long. They were generally not 

 clumped, but occurred scattered over the surface of 

 the substrate, often on both upper and under sur- 

 faces, suggesting that the lump had repeatedly 

 turned over while afloat on the ocean. Compara- 

 tively fewer of the tar lumps bore only specimens 

 ofDosima, and only 10 of these had more than 10 

 animals each. Per unit of surface area, the indi- 

 viduals of Dosima appeared to be more sparsely 

 distributed on tar than on feathers or grass leaves. 



Discussion 



Lepas (Dosima) fascicularis is the most 

 specialized pleustonic goose barnacle, with an al- 

 most uncalcified shell and a gas-filled bubble float. 

 The larval stages were described on the basis of 

 material collected and reared during the Chal- 

 lenger Expedition (Willemoes-Suhm 1876). Since 

 there were several errors and omissions in that 

 paper, all the stages were redescribed by Bain- 

 bridge and Roskell (1966). 



Boetius (1952-53) reported that all of the speci- 

 mens of Dosima, which he found on the Danish 

 North Sea coast in September 1952, had floats 

 roughly proportional in diameter to the length of 

 the animal. These barnacles are able to support 

 themselves in the adult stage by their own float, 

 but the cyprid larvae must settle on some sub- 

 strate before they can metamorphose. The larvae 

 of Dosima have been shown to settle preferen- 

 tially on small floating objects; only later do they 

 produce a bubble float which enables them to stay 

 at the sea surface even when detached from such a 

 support (Boetius 1952-53; Newman 1974). In our 

 collections, all of the Dosima specimens, but none 

 of the Lepas specimens, were attached to bubble 



floats of their own making. Some 27 individuals of 

 Lepas (1-10 mm), the smaller of the two species, 

 were found attached to larger specimens of 

 Dosima, but, despite their larger absolute num- 

 bers, only 8 Dosima specimens (1-14 mm) were 

 found on other animals of this species. Evidently 

 floating barnacle colonies do not normally grow by 

 accretion in this way. 



The blue pigment of Dosima was studied by Fox 

 et al. (1967), who reported that it is a conjugated 

 carotenoid. Although many of the blue barnacles 

 which they studied (washed ashore in the same 

 location) were found attached to the floats of Ve- 

 lella, and although we have found large numbers of 

 these siphonophores stranded at various other 

 times in recent years, we found no Velella floats 

 among the barnacle substrates in this study. In 

 fact, although hundreds of pleustonic barnacles 

 were stranded on our beach during the period 

 studied, we found no specimen of Physalia, Velella , 

 or lanthina, which are all common components of 

 the pleuston community in the open ocean. We 

 found only one Glaucus (a pelagic nudibranch), a 

 few specimens of Fiona (another nudibranch, 

 normally associated with Macrocystis), and sev- 

 eral polychaete worms. This probably indicates 

 the relatively nearshore rather than oceanic ori- 

 gin of the barnacle colonies. Although, when 

 brought back to a laboratory aquarium and given 

 fresh running seawater, many of the specimens 

 remained alive and apparently healthy for more 

 than 1 wk, such stranded animals are normally 

 unable to return to the sea. When exposed to the 

 sun on the beach they would probably be eaten by 

 gulls or dry up within a few hours. 



We have not attempted to study the gut contents 

 of our animals but assume that, like other barna- 

 cles in nature, they probably feed mainly on 

 microorganisms and small zooplankton (Howard 

 and Scott 1959; Crisp and Southward 1961). We 

 noted that in the laboratory, when supplied with a 

 suspension of the unicellular alga Platymonas , 

 many individuals of Dosima extended their cirri, 

 apparently moving them towards the food source, 

 directing it towards the mouth. 



Goose barnacles are hermaphrodites. Adults 

 develop both male and female organs at the same 

 time and can cross-fertilize each other. The eggs 

 are brooded in the mantle cavities, and hatch as 

 larvae which live in the plankton before settling. 

 They attach themselves to a solid substrate by an 

 adhesive secreted by the cement glands; the com- 

 position of the cement of Lepas fascicularis has 



216 



