Assessment of a trap for measuring larval supply of intertidal barnacles on wave-swept, semi-exposed shores

Larval supply and settlement of Semibalanus balanoides (L.) on a semi-exposed wave-swept shore in E Scotland were assessed by means of a new larval trap design. Two midshore sites were utilised throughout the peak of the 2001 settlement season (May 11–June 3). Larval supply was quantified by 176 ml baffled cylinder traps filled with a 4-M killing solution of urea in seawater. Larval trap washout of urea typically ranged from 25% per day under minimal wave action to a maximum of 39% under heavy wave action during an onshore gale. The maximum capture for a single trap was 334 cyprids over one tide. Significant and consistent positional effects, both on urea retention and larval capture, were found for replicate traps separated by 9 cm. These indicated fine-scale variations in hydrodynamic flow and larval supply over the substratum which will have implications for the quantification of spatial heterogeneity of larval input to the benthos. The retention of urea and larval capture efficiency generally were not compromised by traps being serviced daily, as opposed to tidally, except perhaps for captures at very low larval densities. Larval supply measured on a tidal basis was strongly correlated between sites (r=0.975), but supply at Site C was 5× that at Site T: the reduction at Site T could not be explained by its slightly shorter immersion time and hence ‘availability’ of cyprids alone. At Site C settlement was quantified for 5×5 cm quadrats of natural substratum cleared daily. Settlement on these clearances (subject to possible grazing by limpets) was quantified only from May 20–June 3, after the peak of larval supply on May 17, and the variation in larval supply explained 65% of the variance in settlement. The larval supply/settlement relationship at Site T was quantified using grooved acrylic panels. A high correlation coefficient (0.961) was obtained for the daily supply/settlement relationship for these panels over the period May 15–June 3, which included the peak of supply. Larval supply varied up to 15-fold within a site on consecutive tides and up to 100-fold between sites on the same tide. Although further improvements to both the larval trap and the settlement panels can be made, this larval trap does appear capable of providing high-resolution data on tidal or daily larval supply over a wide range of wave conditions and larval concentrations.     

Temporal changes in the strength of density-dependent mortality and growth in intertidal barnacles

1. In demographically open marine systems, the extent to which density-dependent processes in the benthic adult phase are required for population persistence is unclear. At one extreme, represented by the recruitment limitation hypothesis, larval supply may be insufficient for the total population size to reach a carrying capacity and density-independent mortality predominates. At the opposite extreme, populations are saturated and density-dependent mortality is sufficiently strong to reshape patterns established at settlement. 2. We examined temporal variation in the way density-independent and density-dependent mortality interact in a typical sessile marine benthic invertebrate, the acorn barnacle Semibalanus balanoides (L.), over a 2-year period. 3. Recruitment was manipulated at two high recruitment sites in north Wales, UK to produce recruit densities covering the range naturally found in this species. Following manipulation, fixed quadrats were monitored using digital photography and temporal changes in mortality and growth rate were examined. 4. Over a 2-year period there was a clear, spatially consistent, over-compensatory relationship between the density of recruits and adult abundance indicating strong density-dependent mortality. The strength of density dependence intensified with increasing recruitment. 5. Density-dependent mortality did not operate consistently over the study period. It only operated in the early part of the benthic phase, but the pattern of adult abundance generated was maintained throughout the whole 2-year period. Thus, early life-history processes dictated adult population abundance and dynamics. 6. Examination of the natural recruitment regime in the area of study indicated that both positive and negative effects of recruitment will occur over scales varying from kilometres to metres.     

Predation on barnacles of intertidal and subtidal mussel beds in the Wadden Sea

Balanids are the numerically dominant epibionts on mussel beds in the Wadden Sea. Near the island of Sylt (German Bight, North Sea), Semibalanus balanoides dominated intertidally and Balanus crenatus subtidally. Field experiments were conducted to test the effects of predation on the density of barnacle recruits. Subtidally, predator exclusion resulted in significantly increased abundances of B. crenatus, while predator exclusion had no significant effects on the density of S. balanoides intertidally. It is suggested that recruitment of B. crenatus to subtidal mussel beds is strongly affected by adult shore crabs (Carcinus maenas) and juvenile starfish (Asterias rubens), whereas recruits of S. balanoides in the intertidal zone are mainly influenced by grazing and bulldozing of the very abundant periwinkle Littorina littorea, which is rare subtidally. Thus, not only do the barnacle species differ between intertidal and subtidal mussel beds, but the biotic control factors do so as well. Electronic Publication     

Precisely proportioned: intertidal barnacles alter penis form to suit coastal wave action

For their size, barnacles possess the longest penis of any animal (up to eight times their body length). However, as one of few sessile animals to copulate, they face a trade-off between reaching more mates and controlling ever-longer penises in turbulent flow. We observed that penises of an intertidal barnacle (Balanus glandula) from wave-exposed shores were shorter than, stouter than, and more than twice as massive for their length as, those from nearby protected bays. In addition, penis shape variation was tightly correlated with maximum velocity of breaking waves, and, on all shores, larger barnacles had disproportionately stouter penises. Finally, field experiments confirmed that most of this variation was due to phenotypic plasticity: barnacles transplanted to a wave-exposed outer coast produced dramatically shorter and wider penises than counterparts moved to a protected harbour. Owing to the probable trade-off between penis length and ability to function in flow, and owing to the ever-changing wave conditions on rocky shores, intertidal barnacles appear to have acquired the capacity to change the size and shape of their penises to suit local hydrodynamic conditions. This dramatic plasticity in genital form is a valuable reminder that factors other than the usual drivers of genital diversification--female choice, sexual conflict and male-male competition--can influence genital form.     

Colonization by barnacles on fossil Clypeaster: an exceptional example of larval settlement

The presence of c. 1450 individuals of the balanid barnacle Balanus crenatus Bruguière encrusting the test of a clypeasteroid sea urchin from the Late Miocene of the Guadalquivir Basin (southwestern Spain) allows proposing a settlement pattern linked to the growth of the encrusting organism. The possible influence of dip angle was controlled by dividing the test into four concentric zones ranging from lowest margin to apex (0–15°, 15–30°, 30–50° and 0°). Contour diagrams were prepared to identify areas of highest barnacle density as well as size categories distribution in relationship to the pitch of the sea urchin test. The orientation of balanid tests was recorded and plotted on rose diagrams from 0° to 180°. Four size categories of barnacles were distinguished: (1) < 1 mm, (2) 1–2 mm, (3) 2–3 mm and (4) 3–4 mm; these correspond to a growth sequence ranging from post‐larval forms to juveniles. Two areas of maximum settlement density are situated on the posterior margin of the test, on aboral as well as oral surfaces. The aboral surface shows the maximum number of barnacles. Two groups of individuals are defined on the basis of their location, that is, those encrusting the posterior medium part of the urchin, and those located on the anterior half. The results suggest that larval settlement was initially controlled by the availability of free space and afterwards by an intensification effect. Orientation and dip of the test may have played a secondary role in the settlement of the larvae. Substrate colonization seems to have been closely related to the biostratinomic history of the sea urchin test and although several scenarios are possible, our data are congruent with a synchronous settlement of both surfaces (aboral and oral) by one spat or several.     

Testing adaptive hypotheses on the evolution of larval life history in acorn and stalked barnacles

Despite strong selective pressure to optimize larval life history in marine environments, there is a wide diversity with regard to developmental mode, size, and time larvae spend in the plankton. In the present study, we assessed if adaptive hypotheses explain the distribution of the larval life history of thoracican barnacles within a strict phylogenetic framework. We collected environmental and larval trait data for 170 species from the literature, and utilized a complete thoracican synthesis tree to account for phylogenetic nonindependence. In accordance with Thorson's rule, the fraction of species with planktonic‐feeding larvae declined with water depth and increased with water temperature, while the fraction of brooding species exhibited the reverse pattern. Species with planktonic‐nonfeeding larvae were overall rare, following no apparent trend. In agreement with the “size advantage” hypothesis proposed by Strathmann in 1977, egg and larval size were closely correlated. Settlement‐competent cypris larvae were larger in cold water, indicative of advantages for large juveniles when growth is slowed. Planktonic larval duration, on the other hand, was uncorrelated to environmental variables. We conclude that different selective pressures appear to shape the evolution of larval life history in barnacles.     

Roles of larval supply and behavior in determining settlement of barnacles in a temperate mangrove forest

Recruitment is often a major influence on the spatial distribution of populations of benthic marine invertebrates, but the contributions of different components of recruitment are not well known, with the added complication that the relative importance of various life-history processes may be scale-dependent. Previously, we have shown that over a large scale across a mangrove (Avicennia marina) forest in southeastern Australia, settlement of the barnacle Elminius covertus explained its patterns of recruitment, which in turn explained the distribution of adults on mangrove pneumatophores. Post-settlement mortality had little influence on this pattern. In contrast, small-scale vertical distributions of adult barnacles along individual pneumatophores were determined by the pattern of recruitment, which differed from the pattern of settlement, so post-settlement mortality determined the vertical patterns of adults.

In this study, we tested whether larval supply and/or settlement behavior influence the observed settlement patterns of E. covertus across a forest (from seaward to landward zones). We also tested whether larval supply could explain the vertical settlement patterns along the pneumatophores. A pumping system was used to collect cypris larvae from seaward, mid and landward zones of a mangrove forest and an adjacent, unvegetated shore and from three heights above the sediment surface. We also used transplantation of wooden stakes bearing microbial films and barnacle recruits between horizontal zones of the forest to determine whether settlement was influenced by these films or recruits.

Both cyprid supply and cyprid behavior were important factors in determining the patterns of settlement of E. covertus across the forest. Cyprid supply was a result of three-fold differences in immersion times of different (landward, mid and seaward) zones across the forest and a decrease in density of cyprids in the water column from the seaward zone of the forest to the landward sections. In the absence of mangroves immediately adjacent to the forest, there was no temporally consistent difference in cyprid density across the shore and even the differences in immersion time did not produce consistent differences in cyprid supply across the shore. Wooden substrata that had been immersed at seaward sections of the forest attracted consistently more settlers than substrata immersed initially at other sections of the forest and settlement could be induced beyond the normal distribution of adults of E. covertus by stakes transplanted from the seaward zone.

The vertical settlement pattern could not be explained by the supply of cyprids, suggesting that larval behavior must determine the vertical settlement pattern.     

Linking stages of life history: How larval quality translates into juvenile performance for an intertidal barnacle (Balanus glandula)

Many marine invertebrates with complex life cycles produce planktoniclarvae that experience environmental conditions different fromthose encountered by adults. Factors such as temperature andfood, known to impact the larval period, can also affect larvalsize and consequently the size of newly settled juveniles. Afterdocumenting natural variation in the size of cyprids (the finallarval stage) of the barnacle Balanus glandula, we experimentallymanipulated temperature and food given to larvae to producecyprids of differing sizes but within the size range of cypridsfound in the field. In a set of trials in which larvae of B.glandula were raised on full or reduced rations in the laboratoryand subsequently outplanted into the field as newly metamorphosedjuveniles, we explored the effects of larval nutrition and sizeon juvenile performance. Larvae that received full rations throughouttheir feeding period produced larger cyprids (with more lipidand protein). These larger cyprids grew faster as juvenilesand sometimes survived better in the field than juveniles fromlarvae that had their food ration reduced in the last feedinginstar. For naturally settling barnacles brought into the laboratorywithin 2 days of settlement and fed, we found that initial juvenilesize was a good predictor of juvenile size even after 2 weeksof growth. By manipulating food given to juveniles that werederived from larvae fed either full or reduced rations, we foundthat larval nutritional effects persisted in juveniles for 2–3times the period that larvae experienced altered food rations.     

Ivermectin against larval stages of Dirofilaria repens in dogs

The prophylactic efficacy of ivermectin against Dirofilaria repens infections in dogs was investigated. A first trial was carried out on 15 dogs exposed to four inoculations of L3 larvae at 15-day intervals and treated, in groups of five, with 0, 6 or 12 micrograms/kg body weight of ivermectin given per os 30 and 60 days after the first inoculation. Necropsy, performed about 9 months later, revealed that worm burdens were reduced by 86.6 and 92.8% for the 6 and 12 micrograms/kg dose levels, respectively. In a second trial with an otherwise identical protocol, a dose rate of 24 micrograms/kg of ivermectin was tested in 12 dogs. Only one of the six treated dogs was found worm free at necropsy. The worm burden was reduced by 87.9% in treated animals as opposed to controls. A lengthening of the prepatent periods, which might be considered dose related, was apparent in all treated groups. Ivermectin was not completely effective in preventing establishment of experimental infections with D. repens in dogs.     

Ontogenic development of the mouth and digestive tract in larval Malaysian mahseer,Tor tambroides Bleeker

This study analysed morphology and histology of the developing mouth and digestive tract of the Malaysian mahseer larvae to assess the best weaning time to a compound diet for the fry on the basis of their morphological features. The mouth development was monitored using light and scanning electron microscopy; the development of the alimentary canal was followed histologically using light microscopy after haematoxylin‐eosin staining. The larval mouth opened 1 day after hatching (1 DAH); the histological structures of oesophagus were completed by 5 DAH. At 2 DAH, differentiation of enterocytes began, and at 7 DAH the supranuclear protein inclusion appeared in the posterior intestine. The hepatopancreas was structurally completed at 4–5 DAH, coinciding with the start of exogenous feeding and the evidence of lipid storage in the liver. It was concluded that Malaysian mahseer larvae should certainly be able to ingest, and possibly digest and absorb, a formulated diet of 287 μm Ø from 7 DAH onward.     

Fatal errors in set as a cost of dispersal and the influence of intertidal flora on set of barnacles

Summary Cyprid larvae of Balanus cariosus settle preferentially on slate plates with a biota characteristic of the lower intertidal shore, and the cyprids also prefer plates with more algae. Cyprid larvae of Balanus glandula had the same preferences in two out of three experiments. We conclude that some component of the flora guides both species during settling and metamorphosis. Data on vertical distribution and fecundity of B. glandula show that the preference for the lower shore decreases fitness of B. glandula at the site of the settling experiments and at most other sites sampled in or near the San Juan Islands, though in some restricted habitats in the San Juans and extensive areas in the adjacent regions of Puget Sound a preference for the lower shore is appropriate. Extensive dispersal among sites is possible in the planktonic period of 2 to 4 weeks. This example supports the hypothesis that a cost to large scale dispersal is lower fitness at many sites within a species' range. In this case the cost is through poorer correlation between stimuli guiding choice of habitat and favorability of habitat.     

Parasitism of different larval stages of Cameraria ohridella

About 20 species of parasitic Hymenoptera havebeen reported from the horse chestnutleafminer, Cameraria ohridella Deschka & Dimic (Lepidoptera: Gracillariidae). Generally,parasitism is low compared to other closelyrelated leafminers and the parasitism levelvaries considerably. Among other reasons,parasitism rates depend on the developmentalstage of the moth and therefore vary with thesampling date. In the current study,investigations on the parasitism of the moth'sfirst generation were carried out in order todetermine which preimaginal stages areparasitized by the most abundant parasiticwasps. Minotetrastichus frontalis (Nees),Pnigalio agraules (Walker) and Chrysocharis nephereus (Walker) (allHymenoptera: Eulophidae) developed as larval orpupal parasitoids and preferred later larvalinstars of the moth. Egg parasitism did notoccur. Overall, the last two of the six larvalinstars (the spinning instars) of the leafminersuffered the heaviest attack. In concordancewith the fairly low parasitism rates, theeffect of the four most abundant chalcidoids onthe leafminer population was negligible, havingno significant influence on the mortality ofC. ohridella. Although the speciescomposition of the parasitoid complex of C. ohridella shows similarities with thesituation found in other closely relatedleafmining moths, it is unlikely that thenaturally occurring chalcidoids will be able toprevent the horse chestnut leafminer fromdeveloping epidemic population densities in thenear future.     

Lipophorin in the larval and adult stages of Musca domestica

The major Musca domestica hemolymph lipoprotein, lipophorin, was purified from larval and from adult animals. The housefly lipophorin is composed of two apoproteins, apolipophorin I (M_r ∽ 253,000) and apolipophorin II (M_r ∽ 85,000). The lipophorin contains about 3.9% carbohydrates and reacts positively with concanavalin A. The density of larval lipophorin is equal to 1.152 g/ml and of adult lipophorin to 1.106 g/ml. The amount of lipophorin per animal increases during the larval stage, is constant during pupal stage, and suffers a great reduction at the pharate adult stage. The amount of lipophorin remains stable during the whole first gonotrophic cycle of the housefly. Lipophorin is not detected in the eggs of this insect.     

Microheterogeneity of late histones in larval stages of sea urchin development

• 1.1. The total histone complement of early plutei were compared with that of intermediate and late larvae of the sea urchin Tetrapygus niger.
• 2.2. Electrophoretic comparison indicates that there are quantitative and qualitative shifts of the five classes throughout late larval development.
• 3.3. The strong similarity in the amino acid composition of total histones isolated from early, intermediate and late plutei indicates that the observed electrophoretic heterogeneity is due to post-translational modifications.