THE LARVAL STAGES OF THE OCEANIC, PEDUNCULATE BARNACLE AURITUM (L.) (CIRRIPEDIA, )

BY

RICHARD DALLEY N.E.R.C Unit, Marine Science Laboratories, Menai Bridge, Gwynedd LL59 5EH, United Kingdom

INTRODUCTION

Descriptions of the larvae of oceanic, pedunculate barnacles are few, and where available generally incomplete. Dohrn (1870) recognized several distinc- tive larvae, found in plankton hauls from the coast of Chile, as being the ad- vanced nauplii of an oceanic, pedunculate barnacle. Unable to determine the species to which the nauplii belonged, Dorhn gave them the pseudonym Ar- chizoé'a gigas. This method of naming unidentified larvae was followed by later workers. Several descriptions of isolated specimens found in plankton samples, and belonging generally to later stage nauplii., have been made using the generic names Metanauplius and Nauplius (Chun, 1896; Hansen, 1899; Gruvel, 1909, 1920; Rose, 1929; Kolosvary, 1940; Stubbings, 1940; Sandison, 1950). Willemoes-Suhm (1876) obtained a complete series of naupliar stages from the plankton in the North Pacific, which he was able to assign to fascicularis Ellis & Solander, because the larvae were collected amongst great numbers of the adults of this species. This material was re-examined by Bain- bridge & Roskell (1966), and their description remains the only complete ac- count of the larval stages of a known lepadid barnacle. Early workers had little success in rearing the larvae of lepadid barnacles in the laboratory. Thompson (1835), with L., L., and Conchoderma airgatum (Spengler); Willem6es-Suhm (1876) with L. fascicularis and Groom ( 1894) with L. anatifera, Lepas pectinata Spengler, and C. virgatum, all failed to rear larvae past the second naupliar stage. More reccntly Moyse (1963; pers. comm.) reared the larvae of L. anatifera and L. pectinata from hatching to the cyprid stage, but has not yet published any descriptions. Lang (1979) reared the larvae of'L. anserifera and L. pectinata to the third and fifth naupliar stages respectively, and provided incomplete descriptions for both species. (L.) is a lepadid barnacle (Thoracica: Lepadidae) found on whales, and occasionally on other large marine mammals (Clarke, 1966; 40

Best, 1971). In recent years it has posed a fouling problem. Large numbers may settle on the 'Very Large Crude Oil Carriers' plying between the Arabian Gulf? and Northern Europe. As part of a study of this problem, lar- vae of C. aMn/M/7?have been reared in the laboratory, from hatching through thcir complete series of naupliar stages.

MATERIALS AND NIETH()DS Adult C. auritum were removed from the hulls of fouled VLCCs which were discharging their cargoes at UK oil terminals. In the laboratory the adults were reattached to a plastic substratum using cyanoacrylate cement, and maintain- ed in tanks with fast-llowing, filtered seawater at 20°C. Nauplii of the brine shrimp Artemia spp. and homogenised mantle tissue of the mussel Mytilus edulis L. were given as food. Under these conditions adult C. auritum remained healthy for up to three months. Newly hatchcd nauplii were got both from which were already carrying ovigerous lamellae when brought into the laboratory, and from animals which conceived in the laboratory. Many attempts were made to rear the nauplii using variations of the same basic technique. Nauplii were held in 3 litres of gently aerated, filtered seawater in silica-glass jars, at densities of 100 to 500 animals lv , and at ternperatures of 15, 20 or 25°C. The diatoms Chaetocero.s calcitrans (Paulsen) and Skeletonema costatum ((,r(-v.); the flagellates Isochrysis galbana (Parke), Pavlova lutheri (Droop), Tetraselmis .suecica (Kylin), Micromonas squamata Manton & Parke, Rhodomonas baltica Karsten and Prorocentrum micans Ehrenb., and the coc- colithophore Coccolith us pelagic us (Wallich) were given as food at concentrations between 1 and 100 cells p,1-1. Every third day the contents of each rearing jar were poured through a fine filter, and the larvae resuspended in clean seawater with fresh algae. In later expcriments, nauplii were held in larger vessels (12 1), and at densities as low as 3 animals 1-1. Representatives of each naupliar stage were removed at intervals, and preserved in 4% neutral formaldehyde in seawater, or 70% ethanol in distilled water. Measurements wcre made on preserved, unflattened larvae using a dissecting microscope fitted with a calibrated eyepiece graticule. Descriptions were based on dissections of nauplii mounted and stained in Cotton Blue- lactophenol (Hopkins and Williams Ltd.).

RESULTS AND DISCUSSION Larval rearing The survival of larvae in culture was poor. Specimens of the sixth and final naupliar stage were produced in only a single culture, and no cyprids were ob- tained. High mortality was particularly associated with the moult from the second to the third stage nauplius. The best results were found in cultures at 25°C, where larval densities were low and where the larger flagellates Rhodomonas and Prorocentrum were given as food at approximately 5 cells p,1-1.