Tetraclita Japonica Research Articles

A study on the intertidal animal diversity of Xia-Sanheng Island by using morphological and DNA barcoding identification

Intertidal animals are an essential part of the ecosystem, and species diversity can reflect the state of the local ecological environment. However, traditional morphological identification is prone to corresponding classification errors or research limitations. With the development of molecular biology, many techniques and bioinformatics classification methods have been applied to identify species efficiently in recent years. This research aimed to examine the feasibility of DNA barcoding within the identification of intertidal animal species collected from the Xia-Sanheng Island. A total of 41 cox1 gene sequences were obtained by experimentalization or downloaded from the National Center for Biotechnology Information (NCBI) database. Then morphological classification, molecular identification, phylogenetic tree analysis, and Automatic Barcode Gap Discovery (ABGD) method were used to analyze the animal samples. We found that although the molecular classification of molluscs was not accurate enough, the collected specimens could be divided into 15 species, 12 families, and 4 phyla. Tetraclita japonica, Thais luteostoma, and Mytilus coruscus were the dominant species on the Xia-Sanheng Island. Additionally, there may be a new species, Platynereis sp., which needs further confirmation. We suggest that further identification of marine biodiversity should be carried out by combining morphological and molecular biological methods.

Biogeography of intertidal and subtidal native and invasive barnacles in Korea in relation to oceanographic current ecoregions and global climatic changes

AbstractThe coastline of the Korean Peninsula is influenced by three major oceanographic ecoregions, including the estuarine Yellow Sea ecoregion on the west coast, the warmer and saline East China Sea ecoregion on the south coast, and the cold East Sea ecoregion on the east coast. The influence of these marine ecoregions on the distribution of intertidal barnacles has not been extensively studied. The present study examines the biogeography of thoracican barnacles from intertidal and shallow subtidal zones, along the coasts of Korea. Twenty-one species in seven families were identified, including three species of coral-associated barnacles. Species composition varied significantly in the three marine ecoregions. Multivariate analysis showed barnacle assemblages were significant among the three ecoregions, although there are large overlaps of clusters between the Yellow Sea and East China Sea ecoregions. The estuarine species,Fistulobalanus albicostatus, occurred mainly in the Yellow Sea ecoregion; warm-water species,Tetraclita japonica, and sponge inhabiting barnaclesEuacasta dofleiniwere observed in the East China Sea ecoregion; and cold-water species,Balanus rostratusandPerforatus perforatus, were found in the East Sea ecoregion. Four invasive barnacle species were recorded and the European barnaclePerforatus perforatusexpanded its range northward from its recorded distribution nine years earlier. The cold-water species,Chthamalus dalliandSemibalanus cariosus, previously recorded in the East Sea ecoregion, were absent in the present survey. A trend of increasing seawater temperatures in Korean waters may have a significant impact on the distribution of cold-water species and enhance the northward invasion ofP.perforatus.

Evolution of Feeding Shapes Swimming Kinematics of Barnacle Naupliar Larvae: A Comparison between Trophic Modes.

SynopsisA central goal in evolutionary biology is connecting morphological features with ecological functions. For marine invertebrate larvae, appendage movement determines locomotion, feeding, and predator avoidance ability. Barnacle larvae are morphologically diverse, and the morphology of non-feeding lecithotrophic nauplii are distinct from those that are planktotrophic. Lecithotrophic larvae have a more globular body shape and simplified appendages when compared with planktotrophs. However, little is known about whether and how such morphological changes affect kinematics, hydrodynamics, and ecological functions. Here, we compared the nauplii kinematics and hydrodynamics of a lecithotrophic Rhizocephalan species, Polyascus planus, against that of the planktotrophic nauplii of an intertidal barnacle, Tetraclita japonica. High-speed, micro-particle image velocimetry analysis showed that the Polyascus nauplii swam faster and had higher amplitude and more synchronous appendage beating than the Tetraclita nauplii. This fast swimming was accompanied by a faster attenuation of induced flow with distance, suggesting reduced predation risk. Tetraclita nauplii had more efficient per beat cycles with less backward displacement during the recovery stroke. This “anchoring effect” resulted from the anti-phase beating of appendages. This movement, together with a high-drag body form, likely helps direct the suction flow toward the ventral food capturing area. In sum, the tradeoff between swimming speed and predation risks may have been an important factor in the evolution of the observed larval forms.

Genetic diversity and metapopulation structures of two intertidal species along the coast of Zhejiang, China: implications for conservation

To priority areas for conservation in the coast of Zhejiang, this study attempts to map the spatial patterns of the intra-specific genetic diversity of two intertidal species, Septifer virgatus and Tetraclita japonica, using the sequences of mitochondrial DNA cytochrome oxidase subunit I (COI) and large subunit ribosomal RNA (16S rRNA) genes. In total, 129 and 112 specimens were collected from 12 and 11 populations for S. virgatus and T. japonica, respectively. These two species revealed congruent population historical signals, including (1) high levels of haplotype diversity and low values of nucleotide diversity, (2) post-LGM expansion, (3) the lack of population genetic structure, sharing haplotypes over all sampling populations, (4) gene flow connections, and (5) migration directions. Largely, all results supported that all sampling populations could be divided into two main metapopulations, exhibiting a northern and southern distribution. The north metapopulation could be considered as a marine protected area. The genetic patterns of the two species should be considered in the management and conservation in the islands along the Zhejiang, China.

Mitochondrial genome of Tesseropora rosea: molecular evidence for non-monophyly of the genus Tetraclita

The complete mitochondrial genome of Tesseropora rosea (Tetraclitidae) was presented. The genome is a circular molecule of 15,330 bp, which encodes 13 PCGs, two rRNA genes, and 22 tRNA genes. The length of all non-coding regions is 768 bp, with the longest one speculated as the control region (255 bp), which is located between 12S rRNA and trnK. Phylogenetic analysis based on mitochondrial PCGs shows that T. rosea is nested within the genus Tetraclita, more closely related to Tetraclita japonica than to Tetraclita rufotincta or Tetraclita serrata. Thus, the monophyly of the genus Tetraclita is not supported.

A unique duplication of gene cluster (S2–C–Y) in Epopella plicata (Crustacea) mitochondrial genome and phylogeny within Cirripedia

Barnacles (Crustacea: Cirripedia) are important model species in invertebrate larval biology, intertidal ecology, and anti-fouling researches. The complete mitochondrial genome of the intertidal barnacle Epopella plicata Gray, 1843 (Cirripedia: Sessilia: Tetraclitidae) is presented. The mitochondrial genome of E. plicata of 15 296 bp in length encodes 13 PCGs, 2 rRNA genes, and 25 tRNA genes. The genome of E. plicata has a duplicate gene cluster (trnS2–trnC–trnY) that is unique in the infraclass Cirripedia. The two copies of trnC share identical sequences, but nucleotide substitutions are observed in the other two pairs of tRNAs. Comparison of the two trnS2 indicates that DHU arm and acceptor stem have nucleotide variation. In the two trnY, nucleotide variations are found in the acceptor stem, TψC arm, DHU arm, and variable loop. However, there is no nucleotide variation in the anticodon arm of the three tRNAs. Epopella plicata mitochondrial genome shares seven gene rearrangements with that of Tetraclita japonica (Tetraclitidae), including trnK, trnA, trnE/trnS1, trnP/trnT, trnI/trnQ, trnY and trnC. Comparison of gene orders in the two tetraclitid barnacles and the pancrustacean ground pattern suggests that the arrangement of E. plicata mitochondrial genome is a derived character in this species within the family Tetraclitidae. Sequence analysis of all available barnacle mitochondrial genomes shows that within the order Sessilia, E. plicata and Tetraclita japonica cluster together, resulting in monophyly of Tetraclitidae. Notochthamalus scabrosus (Chthamalidae) is at the basal position of the order Sessilia. Monophyly of the family Balanidae was questioned based on both gene order comparison and sequence analyses, and its phylogenetic status needs to be elucidated further.

Functional phenotypic plasticity of the endolithic mytilid Leiosolenus curtus (Lischke, 1874) (Bivalvia: Mytilidae)

In Sagami Bay, Japan, Leiosolenus curtus (Lischke, 1874) bores into dead shells of rock barnacles (Tetraclita japonica) in Manazuru, calcareous sand-rock in Oiso, weathered tuff in Miura and agglomerates formed by the tubes of clam worms (Spirobranchus kraussii) in Kanaya. In order to understand the relationships between morphology and environment, the shell morphologies and genetic characteristics of L. curtus, together with the calcium content of the different bored substrata, were analysed. Individuals from Kanaya and Manazuru were characterised by a chalk-like encrustation and a more rounded and inflated shell shape, while those from Oiso and Miura had a striated encrustation. The molecular phylogenetic tree and haplotype network showed that the genetic sequences of the individuals from all investigated localities were very similar, and implied that they belong to the same species. The striated encrustation of the individuals from Oiso and Miura presumably enables them to scrape those residues not dissolved by the mucus secreted by the mantle gland, and thereby to bore into non-calcareous substrata. The more rounded and inflated shell shape of the individuals from Manazuru is thought to be advantageous for boring into thin substrata.

Physiological responses of two acorn barnacles, Tetraclita japonica and Megabalanus volcano, to summer heat stress on a tropical shore

Species living on rocky shores are subject to periodic tidal emersions and can experience intense thermal stress during daytime low tides. Tetraclita japonica and Megabalanus volcano are common intertidal barnacles in Hong Kong, with T. japonica occupying the high to mid-intertidal zone where its lower limits overlap with the upper limits of M. volcano, which is found in the lower intertidal to subtidal zone. In this study, daily profiles of body temperature and hemolymph osmolality on the shore, and responses to thermal challenge under laboratory conditions were compared between the two species to investigate their behavioral and physiological responses to heat and desiccation stress. On-shore measurements of body temperature revealed contrasting thermal profiles, with T. japonica from the upper shore experiencing greater thermal stress than T. japonica and M. volcano from the lower shore. Aerial exposure of the barnacles was associated with an increase in hemolymph osmolality. M. volcano, however, showed a greater increase in hemolymph osmolality than T. japonica at similar shore levels. When the two species were exposed to rock temperatures of 40°C for 5h, more individuals (94%) of T. japonica entered a coma state, and at an earlier time than M. volcano (36%). All T. japonica individuals resumed activity when re-immersed in water, whereas in contrast, all M. volcano that went into a coma state did not recover and died within 24h. Quiescence and reversible coma during the early stages of acute heat stress, as observed in T. japonica, could therefore be adaptive responses to cope with thermal stress in the upper rocky shore.

The complete mitochondrial genome of the fire coral-inhabiting barnacle Megabalanus ajax (Sessilia: Balanidae): gene rearrangements and atypical gene content

The complete mitochondrial genome of Megabalanus ajax Darwin, 1854 (Sessilia: Balanidae) is reported. Compared to typical gene content of metazoan mitochondrial genomes, duplication of one tRNA gene (trnL2) and absence of another tRNA gene (trnS1) are identified in M. ajax mitochondrial genome. There is a replacement of one tRNA (trnS1) by another tRNA (trnL2) in M. ajax mitochondrial genome compared to Megabalanus volcano mitochondrial genome. Inversion of a six-gene block (trnP-nd4L-nd4-trnH-nd5-trnF) is found between M. ajax/M. volcano and Tetraclita japonica mitochondrial genomes. With reference to the pancrustacean mitochondrial ground pattern, there is an inversion of a large gene block from the light strand to heavy strand in the two Megabalanus mitochondrial genomes, including three PCGs and two tRNAs (nd4L-nd4-trnH-nd5-trnF). Furthermore, four tRNAs (trnA, trnE, trnQ and trnC) exhibit translocation, while translocation and inversion occur in three tRNAs (trnP, trnY and trnK).

How hot for how long? The potential role of heat intensity and duration in moderating the beneficial effects of an ecosystem engineer on rocky shores

Studies of the importance of ecosystem engineers have focused on their benefit to biodiversity through ameliorating environmental stress, without understanding the exact benefits gained by associated organisms. On monsoonal tropical shores, species experience strong seasonality in environmental conditions from almost temperate winters to tropical summers when mass mortalities can occur during daytime emersion. The limpet, Cellana grata, associates with an ecosystem engineer, the barnacle Tetraclita japonica, in summer, but not in winter. To understand the benefits of this association, physiological responses (heart rates and osmotic responses) of the limpet either amongst Tetraclita or on open rock surfaces were investigated under three environmental conditions in a laboratory mesocosm: awash (non-stressed), low (30 °C) and high thermal stress (40 °C) of varying durations (3 or 6 h). In general, at 30 °C, limpets showed similar physiological responses under all conditions for both exposure durations. After 6 h at 40 °C, however, all limpets on open rock surfaces died, whereas those associated with barnacles survived. The surviving limpets experienced similar levels of stress as those exposed to 40 °C on open rock surfaces for half the time (3 h), showing that both the level and duration of stress were important. Limpets, therefore, gain benefits from engineering species when conditions are extreme or stress is prolonged. Under low temperatures or for short durations (e.g. winter), associating with barnacles does not provide physiological benefits. Understanding how, and to what extent, associates benefit from ecosystem engineers highlights how close the margin between survival and mortality can be when conditions are extreme.

Complete mitochondrial genome of the acorn barnacle Striatobalanus amaryllis (Crustacea: Maxillopoda): the first representative from Archaeobalanidae

The mitochondrial genome of the barnacle Striatobalanus amaryllis (Sessilia: family Archaeobalanidae) is 15,063 bp in length. All the 13 protein-coding genes (PCGs) initiate with ATD codon (ATG, ATA or ATT). Four PCGs (COX3, ND3, ND4 and ND4L) end with incomplete stop codon (T- -). Four PCGs (ND1, ND4, ND4L and ND5) are encoded on the light strand (underlined below). Refer to the pancrustacean ground pattern, there are not less than seven tRNAs rearranged in the S. amaryllis mitochondrial genome, including tRNAAla, tRNAGlu/tRNASer(AGY), tRNAPro/tRNAThr, tRNAPro/tRNAThr, tRNATyr, tRNALys, tRNAGln and tRNACys. Three tRNAs (tRNALys, tRNAGln and tRNACys) are rearranged between S. amaryllis and Tetraclita japonica (Sessilia: Tetraclitidae), meanwhile one tRNA (tRNACys) inverted from one strand to another. Compared with Megabalanus volcano (Sessilia: Balanidae), an inversion of one large gene block is identified (including three PCGs and three tRNAs) in S. amaryllis mitochondrial genome: tRNAPhe-ND5-tRNAHis-ND4-ND4L-tRNAPro.

Comparative study on the fauna composition of intertidal invertebrates between natural and artificial substrata in the northeastern coast of Jeju Island

This study was carried out to learn about differences in the sessile macrobenthic fauna communities between the artificial and natural habitats. There were some differences in terms of species composition and dominant species and community structure between two habitat types. The dominant species include Pollicipes mitella and Granuilittorina exigua in natural rocky intertidal zones; Monodonta labio confusa, Ligia exotica, Tetraclita japonica in the artificial rocky intertidal zones. Among all the species, L. exotica and T. japonica occurred only in the artificial rocky intertidal zone. The results of cluster analysis and nMDS analysis showed a distinct difference in community structure between artificial and natural rocky intertidal zones. The fauna in the natural rocky intertidal zones were similar to each other and the fauna in the artificial rocky intertidal zones were divided depending on the slope of the substratum. In the case of a sloping tetrapod, M. labio confusa and P. mitella were dominant, but at the vertical artificial seawall, Cellana nigrolineata, L. exotica T. japonica were dominant. The analysis of the species presented in natural and artificial rocky intertidal areas showed the exclusive presence of 10 species on natural rocks and 12 species on artificial rocks. The species in the natural rocky intertidal area included mobile gastropods and cnidarians (i.e. rock anemones), and the species in the artificial rocky intertidal area mostly included non-mobile attached animals. The artificial novel structure seems to contribute to increasing the heterogeneity of habitats for marine invertebrate species and an increase the species diversity in rocky coastal areas.

Seasonal variation in utilization of biogenic microhabitats by littorinid snails on tropical rocky shores

Mobile species may actively seek refuge from stressful conditions in biogenic habitats on rocky shores. In Hong Kong, the upper intertidal zone is extremely stressful, especially in summer when organisms are emersed for long periods in hot desiccating conditions. As a result, many species migrate downshore between winter and summer to reduce these stressful conditions. The littorinids Echinolittorina malaccana and E. vidua, for example, are found on open rock surfaces high on the shore in winter but the majority migrate downshore in summer to the same tidal height as a common barnacle, Tetraclita japonica. In the laboratory, where environmental conditions could be controlled to approximate those occurring on the shore, we tested whether the downshore migration allowed littorinids to select barnacles as biogenic habitats to reduce stress and if this behaviour varied between seasons. In summer, littorinids demonstrated a strong active preference for the barnacles, which was not observed in the cool winter conditions, when animals were found on open rock surfaces even when barnacles were present. Littorinids, therefore, only actively select biogenic habitats during the summer in Hong Kong when they migrate downshore, suggesting that such habitats may play an important, temporal, role in mitigating environmental stress on tropical shores.

The spatial-temporal distribution and its biodiversity ofintertidal macro benthos in Dongtou Archipelago

In this paper,4 sections in Dongtou Archipelago were chosen to investigate the spatial-temporal distribution and the biodiversity of intertidal macrobenthos in autumn(Oct.) 2006 and spring(Apr.) 2007,respectively.The total number of macrobenthos in four sampling sites was 72,which included 44 species of mollusc,13 species of crustacean,11 species of macro algae,2 species of polychetes,1 species of echinoderm,and 1 species of the other group.Compared with the data in autumn and in spring,the number of species in the former(66 species) was slightly higher than that in latter(63 species),whereas the average biomass and abun-dance in the former(576.98 g/m2,461 ind/m2) were obviously lower than that in latter(1 129.23 g/m2,707 ind/m2).For all of the sections,Thais clavigera Kuster,Tetraclita japonica Pilsbry,Tectarius granularis Gray,were the dominant species and accounted for over 60% of the whole biomass and abundance.For the average index of biodiversity,the species biodiversity index was 1.73±0.47(0.83-2.10),the index of Margalef's species richness was 2.26±0.33(1.99-2.95),the Pielou's evenness was 0.62±0.19(0.29-0.85),and the index of Simpson's dominance was 0.70±0.18(0.36-0.87).The whole result indicated human activities were the main factor to lead to the extremely unstable community in the intertidal macrobenthos with the lower biodiversity in Dongtou Archipelago.And there was a trend of evolving into the secondary type community structure.

東京湾潮間帯におけるフジツボ類の分布

The distribution of intertidal barnacles was investigated at 558 sites in Tokyo Bay during 2004 and 2005. Ten species of barnacle were found in Tokyo Bay: Fistulobalanus albicostatus, Amphibalanus amphitrite, A. eburneus, A. improvisus, F. kondakovi, Balanus trigonus, Chthamalus challengeri, Tetraclita japonica, Megabalanus rosa, and M. volcano. Amphibalanus eburneus, A. improvisus, and F. kondakovi were found in the inner part of the bay, while T. japonica, M. rosa, and M. volcano appeared in the outer part of the bay. Fistulobalanus albicostatus, A. amphitrite, C. challengeri, and B. trigonus were found throughout the bay. Cluster analysis based on similarity of barnacle species composition classified the sites into two clusters, and Cluster 1 was further divided into three sub-groups. While Clusters 1 and 2 both consisted of sites in the outer part and inner part of the bay, Cluster 1 included sites exposed to open-shore conditions and Cluster 2 comprised sites on semi-sheltered shores. The distribution of the barnacles in the bay seems to depend on salinity at the macro scale, as between the inner bay and the outer part of the bay, but on wave exposure at the micro scale of less than several kilometers.

Genetic differentiation, hybridization and adaptive divergence in two subspecies of the acorn barnacle Tetraclita japonica in the northwestern Pacific

Two acorn barnacles, Tetraclita japonica japonica and Tetraclita japonica formosana, have been recently reclassified as two subspecies, because they are morphologically similar and genetically indistinguishable in mitochondrial DNA sequences. The two barnacles are distinguishable by parietes colour and exhibit parapatric distributions, coexisting in Japan, where T. j. formosana is very low in abundance. Here we investigated the genetic differentiation between the subspecies using 209 polymorphic amplified fragment length polymorphism markers and 341 individuals from 12 locations. The subspecies are genetically highly differentiated (phi(CT) = 0.267). Bayesian analysis and principal component analysis indicate the presence of hybrids in T. j.formosana samples from Japan. Strong differentiation between the northern and southern populations of T. j. japonica was revealed, and a break between Taiwan and Okinawa was also found in T. j. formosana. The differentiation between the two taxa at individual loci does not deviate from neutral expectation, suggesting that the oceanographic pattern which restricts larval dispersal is a more important factor than divergent selection in maintaining genetic and phenotypic differentiation. The T. j. formosana in Japan are probably recent migrants from Okinawa, and their presence in Japan may represent a poleward range shift driven by global warming. This promotes hybridization and might lead to a breakdown of the boundary between the subspecies. However, both local adaptation and larval dispersal are crucial in determining the population structure within each subspecies. Our study provides new insights into the interplay of local adaptation and dispersal in determining the distribution and genetic structure of intertidal biota and the biogeography of the northwestern Pacific.

Summer mortality: effects on the distribution and abundance of the acorn barnacle Tetraclita japonica on tropical shores

In the Hong Kong rocky intertidal, the demography of the acorn barnacle Tetraclita japonica is largely determined by regular, intense mortality events in the summer and subsequent pulses of recruitment in late summer. During 2 consecutive summers from 2000 to 2001, 34 to 52 and 98 to 99% of T. japonica were killed on the mid- and high shore, respectively, with younger cohorts suffering higher mortality in the mid-shore. Recruitment of T. japonica occurs in late summer; as a result, the population in the high shore consists of a single cohort of new recruits, while the mid-shore supports 2 cohorts (new recruits and adult survivors). To investigate how thermal stress affects acorn barnacle populations, air and rock temperatures and sub-lethal physiological measures (body tem- perature, sinus pulsation rate and haemolymph osmolality) of T. japonica were taken on the mid- and high shore during daytime, low spring tides in June-July 2001. Mean body temperature increased gradually after emersion, reaching a maximum of ~48°C at noon, 6 to 8°C higher than the adjacent rock surface. T. japonica entered a heat-induced coma when body temperatures reached 45°C. Osmolality of the haemolymph and sinus pulsation rate increased with body temperature as a result of water loss and possibly altered haemolymph pressure; both were greater in high than in mid-shore individuals, with barnacles on horizontal surfaces being hotter than those on vertical surfaces. Body temperature and sinus pulsation rate differed between shore levels, but were similar at spatial scales of 1 to 20 m at the same tidal height. Haemolymph osmolality, however, varied over this distance, probably due to individual variation in the amount of mantle water trapped before emersion and pos- sible micro-habitat differences. Heat and desiccation stress, therefore, play an important role in determining the life history of T. japonica by limiting their distribution and abundance and influenc- ing the demography of the population at different spatial scales.

Lack of mtDNA and morphological differentiation between two acorn barnacles Tetraclita japonica and T. formosana differing in parietes colours and geographical distribution

Tetraclita japonica and T. formosana are common intertidal barnacles with similar morphology, which leads to uncertainty in their species status. In the present study, we try to elucidate the taxonomic status of the two taxa using morphology and mitochondrial control region and cytochrome c oxidase subunit I (COI) sequences of the barnacles in their distribution range. The two taxa were found to be morphologically similar; a diagnostic difference between them was only observed in the colour of the parietes and opercular plates. Little genetic differentiation was detected in the control region and COI (ΦCT < 0.025 for both markers) between two taxa, but differentiation was found between the southern (Taiwan and Hong Kong) and northern (Japan) populations of T. japonica/T. formosana, which might be the result of isolation by distance and upwelling in summer. Our data suggest that the two presently recognized species probably represent two colour morphotypes of the same species exhibiting different geographical distribution. T. japonica is abundant in Japan and southeast coast of China, whereas T. formosana is only abundant in Taiwan. The heterogeneous environment might exert a divergent selection pressure leading to asymmetric distribution of the two colour morphotypes. The different colours might be a result of either phenotypic plasticity adaptive to environmental variables or genetic hitchhiking of local adaptive genotypes.

Cirral Length of the Acorn Barnacle Tetraclita Japonica (Cirripedia: Balanomorpha) in Hong Kong: Effect of Wave Exposure and Tidal Height

Abstract Tetraclita japonica is a common barnacle in Hong Kong, occupying a wide vertical zonation on exposed to semi-exposed shores. The length of the exopodite of cirri IV–VI of T. japonica varied with different degrees of wave exposure and tidal levels. Barnacles on exposed shores had shorter cirri than those on semi-exposed ones. Barnacles at the low intertidal also had shorter cirri than those at the high intertidal zone. Differences in desiccation and heat stress, the length of the immersion period for feeding, and predation pressure along the tidal gradient may be additional factors affecting the cirral length of T. japonica. Compared with Balanus glandula in temperate waters, the proportional difference in the cirral length of T. japonica between wave-extreme locations is much smaller (4%) than that of B. glandula (80%). Differing from B. glandula, which actively beat their cirri to feed, T. japonica exhibits prolonged extension of the cirri for feeding, which may not favour long cirri even on sem...

Population dynamics of the acorn barnacles, Tetraclita squamosa and Tetraclita japonica (Cirripedia: Balanomorpha), in Hong Kong

Tetraclita squamosa and Tetraclita japonica are common, intertidal barnacles. In Hong Kong, the population dynamics of the two species exhibited spatial and temporal variation on two semi-exposed shores. T. squamosa produced egg masses from May–June and annual settlement and recruitment occurred from June–July. In contrast, settlement and recruitment of T. japonica was sparse from March–May, but intensified in July–October. Mature gonads and egg masses were, however, only present from September–November, suggesting the larvae from the two settlement pulses originated from other locations as well as Hong Kong populations. Settlement intensity and post-recruitment mortality of the two species varied between sites, possibly due to spatial variation in free rock space, physical transport of larvae and abundance of food in the water column.