The chromosomes of Trypetesa lampas (Cirripedia,Acrothoracica)

Observations were made of the chromosomes of the burrowing barnacle Trypetesa lampas (Hancock). A method of squash preparation was used, which incorporated staining the material in a solution of 2% orcein in 45% acetic acid. The diploid number of chromosomes of T. lampas was found to be 12 and the haploid number 6, in both males and females. No obvious chromosomal mechanism of sex determination was found. There was, therefore, no cytogenetic confirmation of Kühnert's view (1934) that the sex of the larva is predetermined genetically. During mitosis in the females and embryos of Trypetesa lateralis Tomlinson and Kochlorine floridana Wells and Tomlinson, the diploid number of chromosomes was found to be about 14. The numbers of chromosomes in the 3 species of Acrothoracica studied were approximately half those observed in all 12 species of Thoracica and all 5 species of Rhizocephala previously investigated.     

Gametogenesis of Pollicipes cornucopia (Cirripedia: Scalpellomorpha) in north-west Spain

The gametogenesis and gonad microanatomy of the stalked barnacle Pollicipes cornucopia (Leach) is described. An histological classification of gametogenic development is proposed for the firt time for a species of the Cirripedia. This species has an annual gametogenic cycle on the north-west Spanish coast. Spawning takes place mainly from March to September. Ovaries release gametes at least twice during the gametogenic cycle.     

Influence of occupant microhabitat on the composition of encrusting communities on gastropod shells

The exploitation of microhabitats is widely considered to increase biodiversity in marine ecosystems. Although intertidal hermit crabs and gastropods may inhabit the same shell type and shore level, their microhabitat may differ depending on the state of the tide. On the south coast of Wales the hermit crab Pagurus bernhardus mainly inhabits the shells of Nucella lapillus (84%). Hermit crab shells had a significantly different encrusting community compared with live N. lapillus shells. At low tide the live gastropods were found on exposed rock surfaces whereas hermit crabs were restricted to tidal pools. Communities encrusting live gastropod shells were characterised by lower species richness and abundance compared with shells inhabited by hermit crabs (12 species found in total). A greater abundance and richness of epibionts was recorded from both shell types during the summer compared with winter. Differences in community composition between shell occupant types were attributed to microhabitats used by gastropods and hermit crabs and the associated desiccation pressures, rather than competitive interactions or shell characteristics. This contradicts earlier studies of subtidal shells where biological processes were considered more important than physical factors in controlling species abundance and richness patterns. The use of rockpool microhabitats by hermit crabs increases the biodiversity of rocky shores, as some species commonly found on hermit-crab-inhabited shells were rare in other local habitats.Communicated by J.P. Thorpe, Port Erin     

Size regulation in larvae of the crustacean Balanus eburneus (Cirripedia: Thoracica)

We tested the hypothesis that larval size in the acorn barnacle Balanus eburneus Gould (Cirripedia Thoracica) varies in relation to food availability. In March–November 1980, and March–July 1981, larvae were obtained from adult Balanus eburneus collected in the Newport River, North Carolina, USA. Carapace length and width of larvae reared at three different food concentrations were measured. Mean naupliar instar size was independent of food concentration. Mean size of the cypris instar increased with increasing food level. Greater cypris size could be attributed to increased food reserves in the preceding naupliar stage, and was coinciden with inmarked increase in metamorphic success. Variation in instar size remained constant or declined during naupliar development, but increased sharply at the molt to the cyprid. Naupliar size regulation involved: (1) conservation of a molt increment specific for each naupliar-naupliar molt, (2) an inverse relationship between premolt size and the molt increment during the first five naupliar instars, and (3) an increase in the precision of the molt increment at the molt to the sixth naupliar instar. Experimental evidence implies that size regulation in Balanus eburneus limits variation about a fixed final naupliar size (e.g. volume). Measurement of naupliar size, accumulated energy reserves, survival and development time, and cypris metamorphic success indicated that naupliar cuticular growth is the most conservative feature of larval development. The data suggest that maximum naupliar size is limited by escalating metabolic costs during development, while minimum naupliar size is limited by size-related feeding effectiveness.     

Scanning electron microscopy of metamorphosis in four species of barnacles (Cirripedia Thoracica Balanomorpha)

Metamorphosis and early juvenile development was followed in the laboratory in Balanus amphitrite and B. improvisus (family Balanidae) and in Semibalanus balanoides and Elminius modestus (family Archaeobalanidae) from cyprid settlement until 24 h after ecdysis. Stages of development were studied in vivo and with scanning electron microscopy. Events in metamorphosis and early juvenile development are very similar in all four species and can be interpreted in terms of a highly modified moult. Notably, there was no indication whatsoever of the amorphous decorticated settler previously described from metamorphosis of B. amphitrite. The shape of a juvenile barnacle with cirri and incipient shell plates is apparent immediately after the shedding of the cypris carapace, and rudimentary peduncle can be distinguished below the developing wall plates. A basal row of cuticular hairs encircles the peduncle in all species except S. balanoides. These hairs seem to serve a restraining function during early development, when the juvenile barnacle is only attached by the initially secreted cyprid cement. Similarly situated hairs are also present in very young juveniles of the lepadomorph Scalpellum scalpellum. In Semibalanus balanoides nothing indicates that the rostrum originates from the fusion of two latera as previously claimed, since this plate is single as soon as it can be distinguished.     

Combined sclerochronologic and oxygen isotope analysis of gastropod shells (Gibbula cineraria, North Sea): life-history traits and utility as a high-resolution environmental archive for kelp forests

The grey top-shell, Gibbula cineraria is a common member of temperate to cold water kelp forest communities, but its longevity and the age structure of its populations remains unresolved. Combined measurements of shell growth rates (sclerochronology) and oxygen isotope composition allow analysis of rate and timing of shell growth. Eight specimens were analyzed from the southern North Sea (near Helgoland, German Bight). Three age groups were identified but external measurements (width, height, ornamentation patterns and number of whorls) and shell weight are not adequate for ontogenetic age discrimination. Stable oxygen isotope data is consistent with shell growth during the interval from April to December in isotopic equilibrium with seawater, and growth increments exhibit strong tidal controls with fortnightly bundles well preserved. Reliable environmental proxy data (water temperature) can be extracted from the shell aragonite using conventional stable oxygen isotope analyses, with a temporal resolution of days attainable during intervals of maximum growth, but annual extremes are not always recorded in the shell. While demonstrating the utility of G. cineraria as a environmental and potential paleoenvironmental proxy for kelp forest habitats, its longevity has been significantly overestimated.     

Functional morphology of Lithotrya dorsalis (Cirripedia: Thoracica) in relation to its burrowing habit

Burrowing mechanisms of the scalpellid barnacle Lithotrya dorsalis collected from Indian Key, Florida, USA and Fort Point, Jamaica, West Indies, in the fall and spring of 1983 and 1984 were investigated. Calcite spicules covering the peduncule of this animal mechanically abrade carbonate substratum and are described by light and scanning electron microscopy. These spicules undergo a morphological transformation during the molt cycle. Initial observations on the burrowing habit of L. dorsalis indicate that it also employs a chemical agent during bioerosion. Characteristic etching patterns on both optically pure calcite (Iceland spar) and shell material lend further support to this contention. Possible sources of this chemical agent are discussed.     

Prolonged withdrawal: A possible predator evasion behavior in Balanus glandula (Crustacea: Cirripedia)

The duration of cirral withdrawal in Balanus glandula (Darwin) varies by a factor of three depending on the type of stimulus applied. Contact with potential predators including thaidid gastropods (Thais emarginata, T. lamellosa), and forcipulate asteroids (Leptasterias hexactis, Pycnopodia helianthoides) elicits significantly longer withdrawal durations than contact with an herbivorous gastropod (Tegula pulligo), a grazing, spinulosid asteroid (Henricia leviuscula) or a neutral, brown algal stimulus (Fucus distichus). By substantially attenuating the release of metabolites, prolonged withdrawal probably increases the likelihood of being bypassed by nonvisual predators relying on chemical cues to verify that barnacles are alive. The reduced response to the non-predatory species indicates that this is not a generalized response to gastropods or asteroids, but rather that it appears to be specific to potential predatory species.     

Balanus amphitrite (Cirripedia: Thoracica) — A potential indicator of fluoride,copper, lead,chromium and mercury in North Adriatic lagoons

The capacity of the barnacle Balanus amphitrite Darwin to accumulate pollutants above ambient levels was examined in two North Adriatic lagoons with respect to fluoride, copper, lead, chromium and mercury. Levels in soft tissues ranged from 138 to 312 ppm (dry weight) for fluoride, 41 to 109 ppm for copper, 7.1 to 11.7 ppm for lead, 2.10 to 3.89 ppm for chromium, and from 0.96 to 1.35 ppm for mercury. The concentration factor was of the order of 10² for fluoride, 10³ for copper, and possibly higher than 10³ for lead, chromium and mercury. The differences of about 2:1 in the fluoride and copper concentrations in the waters of the two lagoons were clearly reflected by the levels in the barnacles. B. amphitrite that had set on experimental panels had levels similar to those found in specimens collected from long-term natural populations as early as 42 days after immersion of the panels. Compared with literature data, the accumulation levels found in B. amphitrite for fluoride were among the highest known for invertebrates; the values for copper and lead were considerable, but exceeded by others published for B. balanoides; the results for chromium and mercury were one order of magnitude lower than values reported for other suspension-feeders or indicator organisms. B. amphitrite appears to possess most of the properties considered essential for a biological indicator. Eventual determination of the response time of the barnacle to changes in environmental level could profitably be carried out utilizing experimental panels.     

Reproduction in Balanus amphitrite Darwin (Cirripedia: Thoracica): influence of temperature and food concentration

Balanus amphitrite, an acorn barnacle, is distinctly euryhaline, eurythermal and a dominant fouling organism found in warm and temperate waters throughout the world. In this study, the influence of temperature and food concentration on the reproductive biology of this species collected from a tropical habitat was evaluated. Adult barnacles were maintained at 20, 25 and 30°C temperatures at different concentrations of food (50, 100, 150 and 200 Artemia ind⁻¹ day⁻¹). In this previously believed obligatory cross-fertilizing hermaphrodite, self-fertilization was observed. The rise in temperature from 20 to 30°C resulted in a longer interbreeding interval (6–7 days, 200 Artemia ind⁻¹ day⁻¹; 11–13 days, 50 Artemia ind⁻¹ day⁻¹). Computed carbon gained through feeding during the interbreeding interval indicated an inverse relationship to the temperature. At 20°C, although a greater amount of carbon was gained through feeding, the numbers of larvae produced were fivefold less when compared to those raised at 30°C. At 20°C, 2.3 μg C was required to produce a single larva, whereas at 30°C it was 0.4 μg C. A rise in rearing temperature also influenced the molting rate positively. Observations on temporal variation in the gonad development of this species in a tropical coastal environment influenced by the monsoons indicated gonad development to be positively related to chlorophyll a concentration.     

Effects of various temperature cycles on the larval development of the gastropod molluscCrepidula fornicata

Veligers ofCrepidula fornicata (L.) were reared for 12 days at constant temperatures of 15°, 20°, 25°, 30° and 35°C, and at 5 C° daily cycles of equal periodicity (COEP) over the temperature ranges 15° to 20°C, 20° to 25°C, 25° to 30°C and 30° to 35°C. COEP consisted of equal periods (6 h) of maximum temperature, minimum temperature, and uniformly increasing and decreasing temperature each 24 h period. Survival was high and not influenced by cyclic or constant temperature from 15° to 30°C. At 35°C and COEP 30° to 35°C, all larvae died before Day 6. Shell growth rate increased markedly over the range 15° to 25°C, and growth rates at cyclic temperatures in this range were intermediate between growth rates at the corresponding constant temperatures. Larvae reared at COEP 15° to 20°C and COEP 30° to 35°C had discontinuities in their shells due to inhibition of shell secretion during the adverse part of each temperature cycle. Groups ofc. fornicata veligers were exposed for 2 days to daily temperature cycles of equal and unequal periodicity in the critical 30° to 35°C range. [Cycles of unequal periodicity (COUP) consisted of unequal periods (varying between 3 and 15 h) of maximum and minimum temperature and uniformly increasing and decreasing temperature each 24 h period.] These veligers showed shell growth although their body tissue declined, as indicated by decreasing carbon content per larva. Least shell growth and most body tissue loss occurred in those cycles with the longest exposure to higher temperature. Larvae exposed for arious days to the mildest 30° to 35°C COUP (15 h at 30°C, 3 h increasing temperature, 3 h at 35°C and 3 h decreasing temperature) recovered and resumed normal growth when transferred to constant 30°C, but their growth was retarded in proportion to the number of days in the temperature cycle. Rates of shell growth of veligers in temperature cycles show an immediate effect of environmental temperature, while changes in carbon content per larva better reflect the effects of temperature on general metabolism and survival.     

Development of the gooseneck barnacle Pollicipes polymerus (Cirripedia: Lepadomorpha): Fertilization through settlement

Pollicipes polymerus (Sowerby, 1833) is a common barnacle in rocky intertidal zones of the West Coast of North America whose development has been previously undescribed in detail. In the present study, certain aspects of the development of P. polymerus are recorded from fertilization through settlement. In vitro fertilization has been accomplished using already-implanted sperm plus ovulating eggs and oviducal gland fluid. The eggs are small (about 100 μ diameter at fertilization; 90 x 140 μ at first cleavage) and somewhat yolky. Embryos obtained from brooding adults and from in vitro fertilization were reared in glass dishes until hatching. Cleavage was total, asynchronous and unequal. Division of the D macromere lagged behind division of the other blastomeres, and gastrulation occurred by epiboly so that blastoderm surrounded the macromeres. The nauplii hatched an average of 25.4 days (range was 20.3 to 30.1 days) after fertilization, and molted within 1 day to Stage II nauplii. From Stages II through VI the nauplii required food. As they grew from stage to stage, the number of setae per appendage increased. Nauplii have feathery and hispid-type setae, previously described only in Chthamalus aestuarii. In contrast to other pedunculate larvae which have been described, P. polymerus nauplii are small and have specialized feathery setae. Cypris-larva settlement was stimulated only when healthy adult peduncles were available, thus showing an affinity for its own species.     

Stable carbon isotope ratios in Red Sea barnacles (Cirripedia) as an indicator of their food source

The stable isotope ratio ¹²C/¹³C was used to investigate the source of carbon in free-living barnacles and in coral-inhabiting barnacles from the Red Sea. The δ¹³C of most of the barnacles collected on the open shore ranges between −17.5 and −19.7‰, indicating relative enrichment of light carbon originating from the open-sea phytoplankton. Those collected in closed habitats showed heavier isotopic composition. The δ¹³C of the coral-inhabiting barnacles ranges from −14.1 to −16.7‰, suggesting that the carbon contribution of open-sea plankton to these barnacles is less important than it is to free-living barnacles. We hypothesize that coral organic matter and zooxanthellae expelled by the host coral contribute carbon to the barnacle, and that a mixture of this relatively heavy carbon with carbon from other sources is responsible for the high values of δ¹³C in coral barnacles. Received: 28 February 1997 / Accepted: 16 September 1997     

Settlement behavior and antennulary biomechanics in cypris larvae of Balanus amphitrite (Crustacea: Thecostraca: Cirripedia)

The settlement behavior, antennulary biomechanics and morphology were investigated in the intertidal cypris larvae Balanus amphitrite. The very maneuverable antennule of the cyprid consists of four jointed segments, and it is the prime appendage for substratum exploration and final settlement. We recorded several previously undescribed settling behaviors, such as the "tight direction change", for this intertidal species and discovered that the antennulary morphology is modified to facilitate such behaviors. Segment 2 has a modified lateral cuticle, which gives the segment an additional higher degree of maneuverability compared to non-intertidal cirripede species of Rhizocephala. Additional supporting muscle groups were also found in the antennule of our species, which were not found in the investigated rhizocephalan larvae. The results could very well be associated with the higher needs of substratum recognition in intertidal species, due to more heterogeneous habitats such as intertidal rock flats.     

Some observations of factors affecting embryonic and larval growth of Pollicipes polymerus (Cirripedia: Lepadomorpha) in vitro

Observations on the effects of several environmental conditions in embryonic and larval cultures are reported for the gooseneck barnacle Pollicipes polymerus (Sowerby, 1833). When the growth rates of control embryos kept in finger bowls at ambient-temperature sea water (ca. 12°–15°C) were compared to those of embryos grown under variously modified circumstances, it was found that growth rates were faster under conditions closely simulating the adult barnacle mantle-cavity (e.g. darkness and aeration). Addition of antimicrobial drugs and reduction of egg-mass size also promoted fast growth and development. Nauplii were fed several species of algae; only three species promoted growth to Stage V or older. Naupliar growth was fastest in larvae fed the combination of Prorocentrum micans/Platymonas sp. Larvae fed Prococentrum micans/pennate diatom grew slowest, and most larvae died at Naupliar Stage III. Interactions between algal species may have affected their nutritional value for Pollicipes polymerus nauplii. Less larval activity, slower growth rates, and higher mortality rates were observed in individuals given small amounts of food. The development of embryos and larvae in culture depends greatly on the culture conditions. These conditions should be described if comparison of timetables and envents are to be made between studies.     

The unusual floatation collar around nauplii of certain parasitic barnacles (Crustacea: Cirripedia: Rhizocephala)

Nauplii of the rhizocephalan families Peltogastridae and Lernaeodiscidae carry a torus-shaped collar around the body. It consists of an exceedingly thin cuticle connected to the general body cuticle along a continuous narrow ridge. In nauplii of some species, the collar is very large and its surface ornamented by a very conspicuous reticulated pattern of ridges. In other species the collar is smaller and with a smooth surface that impedes its detection when using a light microscope. The collar is absent from nauplii of all investigated species of the Sacculinidae. Transmission electron microscopy shows that the collar of the succeeding nauplius instar is formed in an unexpanded state beneath the old cuticle and it must therefore be inflated at or immediately after ecdysis. At ecdysis the collar of the old instar breaks along the attachment ridge, leaving the empty collar and the exuvium of the general body as separate objects. The collar must have a profound influence on the hydrodynamic properties of the nauplius, both when swimming and passively sinking. We therefore consider it as a floatation device, a view supported by the absence of the collar in the rapidly swimming cypris larvae. There is no obvious homology to the collar outside the Rhizocephala, and it therefore appears to have evolved only once.Communicated by L. Hagerman, Helsingør     

Interactions between shear rates and biofilms affecting exploratory behaviour by cyprids ofElminius modestus (Cirripedia)

The behaviour ofElrninius modestur Darwin cyprids suggests interaction between surface bacterial films acclimated to contrasting shear regimes and the range of shear rates over which observations were made. Exploratory behaviour is encouraged by filmed surfaces rather than biologically clean surfaces. Increasing shear rates encourage attachment to all surfaces, but cyprids detach from high-shear-acclimated films less often than from either low-shear-acclimated films, or clean surfaces. Furthermore, numbers of attaching cyprids are consistently lower on low-shear-acclimated films than on high-shear films.     

An energy budget for the free-swimming and metamorphosing larvae of Balanus balanoides (Crustacea: Cirripedia)

Analysis of biochemical components and measurements of oxygen consumption rates of cypris larvae of Balanus balanoides (L.) maintained in the laboratory at 10°C for up to 5 weeks after capture shows that lipid is the primary energy reserve, although later protein is utilised. Initially, the cyprids swim freely with an oxygen consumption rate of ca. 37×10^-3 l O₂ h^-1 cyprid^-1, but within a few days the rate falls to ca. 21×10^-3 l O₂ h^-1 cyprid^-1 when they cease swimming and explore the substratum. The cost of metamorphosis was calculated both from the loss of biochemical components and oxygen consumption rates during metamorphosis; the values were 2.8×10^-2 and 3.2×10^-2 cal cyprid^-1, respectively. A budget was collated from the data on respiration and biochemical composition, whereby the energy per cyprid was partitioned into that required for essential structural components (6.8×10^-2 cal), that needed for metamorphosis (3.0×10^-2 cal) and an excess available for swimming and exploring, which in the batches studied was about 5.0×10^-2 cal. This excess is mainly derived from the utilisation of lipid reserves and is used up usually 2 1/2 to 4 weeks after capture. During these measurements, samples of cyprids were taken at weekly intervals to test the rate of settlement and success of metamorphosis. The results showed that they lose their competence to metamorphose successfully approximately at the same time (3 to 4 weeks) that the energy supply for swimming and exploration is used up.     

Genetic structure of populations of two species of Chthamalus (Crustacea: Cirripedia) in the north-east Atlantic and Mediterranean

Protein electrophoresis on starch gels was used to investigate population genetic structure of the barnacles Chthamalus montagui Southward and C. stellatus (Poli) over their north-east Atlantic and Mediterranean ranges. In each species, a single locus exhibited marked differentiation of allele frequencies between Atlantic and Mediterranean localities; in C. stellatus, genetic differentiation between the two basins had not previously been noted. In both species, mean heterozygosity per locus appeared higher in the Mediterranean samples than in the Atlantic, and Mediterranean populations had more alleles at the loci studied. Possible explanations for the differentiation between the Atlantic and the Mediterranean populations are discussed. Received: 30 May 1996 / Accepted: 17 September 1996