Barnacle Balanus Amphitrite Research Articles

Oxygen consumption and energy budget of the barnacle Balanus amphitrite amphitrite (Darwin, 1854) in an estuarine ecosystem, Basrah-Iraq

The annual O2 consumption, annual energy budget and the ecological efficiencies of a population of the barnacle Balanus amphitrite amphitrite were estimated in Garmat-Ali river, in the period October 1994-September 1995. The annual O2 consumption was 2156 kJ/ m2/yr, the rate of O2 consumption increased with increasing temperature and body weight, the barnacle consumes oxygen at a rate of 0.622 µlO2/mg/h at 15°C, 0.84 µlO2/mg/h at 23°C and 0.954 µlO2/mg/h at 30°C. The Q10 values increased with increasing size of barnacle. The food items provided were the alga, Chlorella sp. with a calorific contents of 3.2 kcal/g DW, and a flesh of the clam C. fluminea with 5.4 kcal/g DW. The barnacle assimilates the flesh of the clam about 7 times more than assimilating the Chlorella. The barnacle allocates 45-55% of the assimilated energy for net growth and 27-37% for metabolic energy expenditure, whereas 18% is channeled for faeces production. The respiratory coefficient (R/P) of this barnacle was 0.6. The assimilation efficiency for the plant and animal food were 88-91%. The annual energy budget equation for a population of barnacle at Garmat-Ali river is: Cp 16271.14 = Pp 11639.55 + Rp 2156 + Fp 2475.60.

Anatomy and Ultrastructure of the Cyprid Temporary Adhesive System in Two Species of Acorn Barnacle

Acorn barnacles are sessile as adults and select their settlement site as a cypris larva. Cyprids are well adapted to exploring surfaces in dynamic environments, using a temporary adhesive secreted from the antennules to adhere during this process. The temporary adhesive and the secretory structures are poorly characterized. This study used serial block-face scanning electron microscopy and three-dimensional modelling to elucidate the anatomy related to temporary adhesion. The temporary adhesive glands of two acorn barnacle species, Balanus amphitrite and Megabalanus coccopoma, were located in the proximal region of the first antennular segment, contrary to previous descriptions that placed them in the more distal second segment. The temporary adhesive systems of these acorn barnacles are therefore similar to that described for the stalked barnacle, Octolasmis angulata, although not identical. Knowledge of the true location of the temporary adhesive glands will underpin future studies of the production, composition and secretion of the adhesive.

Preparation and evaluation of fouling-release properties of amphiphilic perfluoropolyether-zwitterion cross-linked polymer films

The biofouling of marine structures presents a problem for maritime industries, including increasing fuel and operational costs. There has been much work developing and evaluating chemically ‘ambiguous’ amphiphilic coatings based upon hydrophobic fluoropolymer and hydrophilic poly(ethylene glycol) (PEG). Many of these coatings have shown good fouling-release performance against diatoms, which present a fouling challenge to commercially-available state-of-the-art silicone-based fouling-release coatings. However, PEG is prone to oxidation, which limits its practical use in the marine environment, and thus an alternative hydrophilic material would be desirable in the future development of amphiphilic coatings. In this regard, zwitterionic materials are emerging as a promising class of hydrophilic antifouling material, which we hypothesized would be a suitable alternative to PEG within amphiphilic coatings. To test this hypothesis, cross-linked amphiphilic films consisting of commercially available perfluoropolyethers and the zwitterionic monomer sulfobetaine methacrylate were developed and studied. The difficulty in formulating these chemically incompatible species was overcome by careful choice of solvents and a series of prototype cross-linked films were prepared in which increasing quantities of zwitterion were systematically incorporated. The fouling-release performance of these films was tested against the diatom Navicula incerta, a common microfouling organism responsible for the formation of so-called ‘slime’ layers, and antifouling performance with cypris larvae of two barnacle species, Balanus amphitrite, and Balanus improvisus. To expand the scope of the study, the clinically-relevant biofilm-forming pathogen Staphylococcus aureus, which is a major culprit in the infection and failure of millions of indwelling medical devices, was also evaluated. Results indicate that the incorporation of zwitterion into perfluoropolyethers leads to significant improvements in fouling-release performance and these amphiphilic coatings display potential in fouling-release applications.

Biofouling Community Structure in a Tropical Estuary of Goa on the West Coast of India

Biofouling community structure was studied in a tropical monsoon-influenced Mandovi estuary in Goa, west coast of India. Monthly, seasonal and yearly observations on biofouling on polyvinyl chloride (PVC) panels immersed at subsurface water level were recorded and photographed from May 2012 to September 2013. The barnacle Balanus amphitrite was the dominant fouling organism followed by calcareous polychaetes. The settlement and recruitment of barnacles took place year-round, with the exception of July 2012 and June 2013 (monsoon months). However, their peak abundance was observed during the later months of monsoon (August and September). Polychaetes were dominant during late post-monsoon and pre-monsoon months (December 2012 to April 2013). Silt and slime were observed throughout the observation period. Comparing the fouling pressure of barnacles in the two monsoon seasons (2012 and 2013), fouling was more intense during the monsoon of 2013, indicating an inter-annual variation in the fouling community.

Resistance of Zwitterionic Peptide Monolayers to Biofouling.

Self-assembled monolayers (SAMs) are widely used in science and engineering, and recent progress has demonstrated the utility of zwitterionic peptides with alternating lysine (K) and glutamic acid (E) residues for antifouling purposes. Aiming at developing a peptide-based fouling-resistant SAM suitable for presentation of surface-attached pheromones for barnacle larvae, we have investigated five different peptide SAMs, where four are based on the EK motif, and the fifth was designed based on general principles for fouling resistance. The SAMs were formed by self-assembly onto gold substrates via cysteine residues on the peptides, and formation of SAMs was verified via ellipsometry, wettability, infrared reflection-absorption spectroscopy and cyclic voltammetry. Settlement of cypris larvae of the barnacle Balanus (=Amphibalanus) amphitrite, the target of pheromone studies, was tested. SAMs were also subjected to fouling assays using protein solutions, blood serum, and the bacterium Mycobacterium marinum. The results confirm the favorable antifouling properties of EK-containing peptides in most of the assays, although this did not apply to the barnacle larvae settlement test, where settlement was low on only one of the peptide SAMs. The one peptide that had antifouling properties for barnacles did not contain a pheromone motif, and would not be susceptible to degredation by common serine proteases. We conclude that the otherwise broadly effective antifouling properties of EK-containing peptide SAMs is not directly applicable to barnacles, and that great care must be exercised in the design of peptide-based SAMs for presentation of barnacle-specific ligands.

Phylogenetic analysis and antifouling potentials of culturable fungi in mangrove sediments from Techeng Isle, China.

To search for more microbial resources for screening environment-friendly antifoulants, we investigated the phylogenetic diversity and antifouling potentials of culturable fungi in mangrove sediments from Techeng Isle, China. A total of 176 isolates belonging to 57 fungal taxa were recovered and identified. The high levels of diversity and abundance of mangrove fungi from Techeng Isle were in accordance with previous studies on fungi from other mangrove ecosystems. Fifteen of the 176 isolates demonstrated high divergence (87-93%) from the known fungal taxa in GenBank. Moreover, 26 isolates recorded in mangrove ecosystems for the first time. These results suggested that mangrove sediments from Techeng Isle harbored some new fungal communities compared with other mangrove ecosystems. The antifouling activity of 57 representative isolates (belonging to 57 different fungal taxa) was tested against three marine bacteria (Loktanella hongkongensis, Micrococcus luteus and Pseudoalteromonas piscida) and two marine macrofoulers (bryozoan Bugula neritina and barnacle Balanus amphitrite). Approximately 40% of the tested isolates displayed distinct antifouling activity. Furthermore, 17 fungal isolates were found to display strong or a wide spectrum of antifouling activity in this study, suggesting that these isolates deserve further study as potential sources of novel antifouling metabolites. To our knowledge, this is the first report on the investigation of the phylogenetic diversity and antifouling potential of culturable fungi in mangrove sediments from Techeng Isle, China. These results contribute to our knowledge of mangrove fungi and further increases the pool of fungi available for natural bioactive product screening.

HAMA MANGROVE DI KECAMATAN BATU AMPAR, KABUPATEN KUBU RAYA, KALIMANTAN BARAT Mangrove Pests at Batu Ampar, Kubu Raya, West Kalimantan

Mangrove ecosystem is a complex tropical forest ecosystem that is able to live and to adapt in coastal environments.Unfortunatelly, its existence is vulnerable to the environmental change. Unless utilization of mangrove forest is notfollowed by enrichment and rehabilitation, it will lead to degradation of logged-over land such as pest and diseaseinfestation. The pest study was conducted in mangrove stands in PT. Bina Ovivipari Semesta (BIOS), Kubu Raya, WestKalimantan. The result of study consisted of three sample plots obtained from the average of mangrove pest on thecutting area of 2017 (93.33%), attack intensity (28%). Additionally, the average of cutting area of 2012 were at 91.95%and attack intensity (29%) while the protection forest obtained the average of attack at 79.23% and attack intensity(21.87%). The results of pest identification of mangrove arboretum were 9 pests, including pagoda bagworm (Pagodiellaspp.), bagworm (Acanthopsyche sp.), krama / tree climbing crab (Episesarma spp.), nacerdes beetle (Xanthochroa sp.),aphid (Prociphilus tessellatus), barnacles (Balanus amphitrite), snails (Gastropoda Class), cobwebs, leatherleaf slugs(Vaginula bleekeri).Key words: Kubu Raya, Mangrove, Pagodiella spp., PT. BIOS

Comparison of mixed Ultrasound waves with the extracts of Nerium oleander L. on the growth of cyprid barnacles Balanus amphitrite Amphitrite

This study was conducted to demonstrate the effect of plant extracts from the Nerium oleander L. plant and ultrasound waves of different frequencies (10-50) (20-45) (50-60) (30-65) KHz on the barnacle larvae cyprid of barnacle Balanus amphitrite amphitrite obtained from Nasiriya Thermal Power Station inlet water. Samples were collected bimonthly three replicates. The results of the Oleandrin 1 and 2.5 mg/500 ml showed a an effect of losing the larvae cyprid, 2.5 mg showed an increasing effect on the seventh day. A maximum losing of larvae cyprid was attained when using ultrasonic with conjunction of 2.5 mg Oleandrin extract reached 100% on the tenth day

Nitric Oxide-Serotonin interplay in the cyprid metamorphosis of Balanus amphitrite (Cirripedia, Thoracica)

Nitric Oxide (NO) signaling is known to govern the cyprid metamorphosis of barnacle Balanus amphitrite, a potential biofouling organism. This signaling cascade is mainly driven by two important enzymes, Nitric Oxide Synthase (NOS) and cyclic Guanosine monophosphate (cGMP)-specific Phosphodiesterase (PDE), which exist in multiple isoforms. But, involvement of the exact isoform of these enzymes was unknown, and the same was addressed in the present study using pharmacological compounds, targeting the specific isoforms of NOS and PDE. When the cyprids were treated with specific NOS inhibitors (7-Nitroindazole for NOS I and S-methylisothiourea hemisulphate for NOS II), the metamorphosis was promoted indicating the involvement of both NOS I and NOS II. However, when cyprids were exposed to PDE inhibitors (Sildenafil, Dipyridamole and Bay 73–6691 targeting PDE5, PDE6 and PDE9 respectively), metamorphosis was significantly inhibited only in case of Sildenafil, indicating the involvement of PDE5. The expression of PDE5 in the cyprid was demonstrated using immunofluorescence technique. Further, it was also demonstrated that the interplay between NO and Serotonin signaling plays a vital role in the pelago-benthic transition of B. amphitrite. Targeting these signaling pathways in the future could provide an antifouling solution against barnacles.

Environmentally benign antifouling activity and toxic properties of bioactive metabolites from mangrove Excoecaria agallocha L.

This study was aimed to investigate the antifouling (AF) potentials and toxic properties of methanol extract from leaves of mangrove Excoecaria agallocha. Antimicrofouling activity results inferred that this extract strongly inhibited fouling bacterial and microalgal growth. This extract had also inhibited the settlement of brown mussel Perna indica and larvae of barnacle Balanus amphitrite. Further, EC50 < LC50 and therapeutic ratio >1 together propagated non-toxic nature of the extract. Mollusk foot adherence assay result showed complete inhibition of foot spreading and loss of attachment of common rocky fouler Patella vulgata to the substrata. Field assay results affirmed that this extract effectively deterred settlement of biofoulers. Purification and GC-MS analysis of bioassay-guided active spot evidenced presence of three major compounds (>85%) responsible for the promising AF activity. The identified lead compounds subjected to an estimation (BIOWIN™) program developed by United States Environmental Protection Agency (USEPA) predicts that they are biodegradable in nature. Graphical abstract.

Scopuquinolone B, a new monoterpenoid dihydroquinolin-2(1H)-one isolated from the coral-derived Scopulariopsis sp. fungus

Further chemical investigation of the secondary metabolites of the fungus Scopulariopsis sp. led to the discovery of a new alkaloid, scopuquinolone B (1). The structure of compound 1 was elucidated by extensive NMR spectroscopic data, CD spectrum and analysis of its Dess-Martin oxidation derivative. Compound 1 was evaluated for antilarval settlement activity of barnacle Balanus amphitrite and showed promising antifouling activity with an EC50 value of 0.103 μM and a high therapeutic ratio of 222.

Preparation, Structure, and Potent Antifouling Activity of Sclerotioramine Derivatives.

A series of 30 sclerotioramine derivatives (2-31) of the natural compound, (+)-sclerotiorin (1), has been successfully semi-synthesized by a one-step reaction with high yields (up to 80%). The structures of these new derivatives were established by extensive spectroscopic methods and single-crystal X-ray diffraction analysis for 3, 6, and 10. (+)-Sclerotiorin (1) and its semisynthetic derivatives (2-31) were evaluated for their antifouling activity. Most of them except 6, 7, 8, 12, and 28 showed potent antifouling activity against the larval settlement of the barnacle Balanus amphitrite. More interestingly, most of the aromatic amino-derivatives (13-17, 19-21, 23, 25-27, and 29-31) showed strong antifouling activity; however, only two aliphatic amino-derivatives (5 and 10) had the activity.

Thielavins W-Z₇, New Antifouling Thielavins from the Marine-Derived Fungus Thielavia sp. UST030930-004.

Eleven new depsides—thielavins W–Z (1–4) and thielavins Z1–Z7 (5–11)—and also four known thielavins—A, H, J, and K (12–15)—were isolated from the ethyl acetate extract of a marine-derived fungal strain Thielavia sp UST030930-004. All of these compounds were evaluated for antifouling activity against cyprids of the barnacle Balanus (=Amphibalanus) amphitrite. The results showed that compounds 1–3 and 6–13 were active, with EC50 values ranging from 2.95 ± 0.59 to 69.19 ± 9.51 μM, respectively. The inhibitive effect of compounds 1–3 and 7 was reversible. This is the first description of the antifouling activity of thielavins against barnacle cyprids.

Comparative Studies on the Biological Glue of Some Opportunistic Adult Marine Macro-Fouling After Dislodgement and Construction of Temporary Faunal Conglomerations

Comparative Studies on the Biological Glue of Some Opportunistic Adult Marine Macro-Fouling After Dislodgement and Construction of Temporary Faunal Conglomerations This study aimed to elucidate the composition of the biological glue of the sea anemone Metridium senile, the tubeworm Serpula vermicularis, the acorn barnacle Balanus amphitrite, the gastropod limpet Patella aspera and the sea squirt Styela plicata and to analyze these biological glue in the different seasons of the year. Furthermore, to propose antifouling strategies that can be developed from the present results. The sessile macro-fouling have the capability to dislodge and crawl searching for new suitable substrata for attachment. A total of 30 taxa representing five phyla were sampled every season across Northern Khobar estuarine beach of the Arabian Gulf. The proximate compositions of protein, lipid and carbohydrate in the basal discs or attachment integuments were measured using the Folin-Ciocalteu Phenol method of 66 Lowry et al., the chloroform-methanol method according to Folch et al. and the phenol-sulfuric acid method of Dubois et al. respectively. The total fat, protein, carbohydrate, and moisture contents ranged from 1 ± 0.57% -2 ± 0.98%, 23 ± 1.60 -23 ± 0.80, 0,2 ± 0,10 -1,98 ± 0,20 and 71 ± 0.61% -72 ± 2.07% by weight, respectively. The indispensable and conditional amino acids predominated in tissues were estimated. A high-pressure chromatographic separation was applied for amino acid analysis of biological glue. The most predominant amino acids were Aspartic acid (Asp D), Glutamine (Gln Q), Glycine (Gly G), Methionine (Met M), Phenylalanine (Phe F), Serine (Ser S) and Valine (Val V). Proteins in biological glue of the five species were resolved by SDS-PAGE and digested with trypsin. The majority of the resolved protein spots were within the molecular size ranging from 250 kDa to less than 30-kDa. The total lipid was estimated by chloroform-methanol method according to Folch et al. Capillary gas chromatography was applied to measure the fatty acid profiles of the biological glue. The lipid content of the biological glue of the five species studied were roughly similar but in different quantities. It was found that lipids of biological glue were predominant by C18:1 V-5, C18:2 V-6, C19:1 v- 8, C20:1 V-9, C24:1 V-6, C19:2 V-6. The estimation of total carbohydrate content of tissue in the basal discs or attachment integuments of the five macro-benthos ranged from 2.5 to 8.7 mg carbohydrates g-1 wet weight. The carbohydrate content of the biological glue was apparently dependent partly on species and partly on the season of settlement. All data obtained were statistically analyzed using One-way analysis of variance (ANOVA) of means with significance at P 0.05; Tukey's Multiple Comparison Test Mean Difference at P>0.05, P 0.05.

PDMS-based films containing surface-active amphiphilic block copolymers to combat fouling from barnacles B. amphitrite and B. improvisus

Surface-active amphiphilic diblock copolymers, Si-EFS14 and Si-EFS71, consisting of a poly(dimethyl siloxane) block (degree of polymerisation 11) and a poly(4-(triethyleneglycol monomethyl ether)-2,3,5,6-tetrafluorostyrene) block (average degree of polymerisation 14 and 71) were synthesised by ATRP. Films were prepared by incorporating each copolymer (4 wt%) into a PDMS matrix, which was then condensation cured. Bioassays were performed on the films using two barnacle species, Balanus amphitrite and Balanus improvisus, at different stages of their life cycles. The cyprids of B. improvisus settled on all test surfaces in higher numbers than those of B. amphitrite. However, the juveniles of B. improvisus were more easily removed from the films containing the copolymer Si-EFS14 than from those containing the copolymer Si-EFS71. An XPS analysis revealed that the near-surface region of copolymer Si-EFS71 was enriched in oxyethylenic chains and became even more populated by these hydrophilic chains after the films were immersed in water.

Anti-barnacle Activity of Isocyanides Derived from Amino Acids.

Creation of new potent antifouling active compounds is important for the development of environmentally friendly antifouling agents. Fifteen isocyanide congeners derived from proteinogenic amino acids were synthesized, and the antifouling activity and toxicity of these compounds against cypris larvae of the barnacle Balanus amphitrite were investigated. All synthesized amino acid-isocyanides exhibited potent anti-barnacle activity with EC50 values of 0.07 - 10.34 μg/ml after 120 h exposure without significant toxicity. In addition, seven compounds showed more than 95% settlement inhibition of the cypris larvae at 10 μg/ml after 120 h exposure without any mortality observed. Considering their structure, these amino acid-isocyanides would eventually be biodegraded to their original nontoxic amino acids. These should be useful for further research focused on the development of environmentally friendly antifoulants.

Charged hydrophilic polymer brushes and their relevance for understanding marine biofouling

The resistance of charged polymers to biofouling was investigated by subjecting cationic (PDMAEMA), anionic (PSPMA), neutral (PHEMA-co-PEG10MA), and zwitterionic (PSBMA) brushes to assays testing protein adsorption; attachment of the marine bacterium Cobetia marina; settlement and adhesion strength of zoospores of the green alga Ulva linza; settlement of barnacle (Balanus amphitrite and B. improvisus) cypris larvae; and field immersion tests. Several results go beyond the expected dependence on direct electrostatic attraction; PSPMA showed good resistance towards attachment of C. marina, low settlement and adhesion of U. linza zoospores, and significantly lower biofouling than on PHEMA-co-PEG10MA or PSBMA after a field test for one week. PDMAEMA showed potential as a contact-active anti-algal coating due to its capacity to damage attached spores. However, after field testing for eight weeks, there were no significant differences in biofouling coverage among the surfaces. While charged polymers are unsuitable as antifouling coatings in the natural environment, they provide valuable insights into fouling processes, and are relevant for studies due to charging of nominally neutral surfaces.

Epibiotic community on the acorn barnacle (Balanus amphitrite ) from a monsoon-influenced tropical estuary

The epibiotic communities (diatoms and metazoans) on the outer surfaces of the shell of the barnacle Balanus amphitrite (BSh) and its opercular valves (the scutum and tergum; BST) were investigated on a monthly basis for 1 year in a tropical monsoon-influenced estuary and compared with that of the surrounding rock biofilm. BSh and BST were rich in the diatoms Achnanthes longipes and Melosira nummuloides and amongst the invertebrates, nematodes and tardigrades were abundant. To the best of our knowledge, this is the first report of epibiosis on the acorn barnacle. Diatom abundance was at its maximum during the monsoon season on all the inter-tidal substrata i.e. BSh, BST and rock. A significant correlation was found between the density of diatoms and invertebrates associated with the BSh and BST, possibly because of the trophic relationship between them or the suitability of the physical environment. The possible role of these epibionts on the settlement of this barnacle species is currently unknown and needs further investigation.

Combined effects of low pH and low oxygen on the early-life stages of the barnacle Balanus amphitrite

Abstract Ocean acidification (OA) is anticipated to interact with the more frequently occurring hypoxic conditions in shallow coastal environments. These could exert extreme stress on the barnacle-dominated fouling communities. However, the interactive effect of these two emerging stressors on early-life stages of fouling organisms remains poorly studied. We investigated both the independent and interactive effect of low pH (7.6 vs. ambient 8.2) and low oxygen (LO; 3 mg l−1 vs. ambient 5 mg l−1) from larval development through settlement (attachment and metamorphosis) and juvenile growth of the widespread fouling barnacle, Balanus amphitrite. In particular, we focused on the critical transition between planktonic and benthic phases to examine potential limiting factors (i.e. larval energy storage and the ability to perceive cues) that may restrain barnacle recruitment under the interactive stressors. LO significantly slowed naupliar development, while the interaction with low pH (LO–LP) seemed to alleviate the negative effect. However, 20–50% of the larvae became cyprid within 4 d post-hatching, regardless of treatment. Under the two stressors interaction (LO–LP), the barnacle larvae increased their feeding rate, which may explain why their energy reserves at competency were not different from any other treatment. In the absence of a settlement-inducing cue, a significantly lower percentage of cyprids (∼15% lower) settled in LO and LO–LP. The presence of an inducing cue, however, elevated attachment up to 50–70% equally across all treatments. Post-metamorphic growth was not altered, although the condition index was different between LO and LO–LP treatments, potentially indicating that less and/or weaker calcified structures were developed when the two stressors were experienced simultaneously. LO was the major driver for the responses observed and its interaction with low pH should be considered in future studies to avoid underestimating the sensitivity of biofouling species to OA and associated climate change stressors.

Transcriptome and proteome dynamics in larvae of the barnacle Balanus Amphitrite from the Red Sea.

BackgroundThe barnacle Balanus amphitrite is widely distributed in marine shallow and tidal waters, and has significant economic and ecological importance. Nauplii, the first larval stage of most crustaceans, are extremely abundant in the marine zooplankton. However, a lack of genome information has hindered elucidation of the molecular mechanisms of development, settlement and survival strategies in extreme marine environments. We sequenced and constructed the genome dataset for nauplii to obtain comprehensive larval genetic information. We also investigated iTRAQ-based protein expression patterns to reveal the molecular basis of nauplii development, and to gain information on larval survival strategies in the Red Sea marine environment.ResultsA nauplii larval transcript dataset, containing 92,117 predicted open reading frames (ORFs), was constructed and used as a reference for the proteome analysis. Genes related to translation, oxidative phosphorylation and cytoskeletal development were highly abundant. We observed remarkable plasticity in the proteome of Red Sea larvae. The proteins associated with development, stress responses and osmoregulation showed the most significant differences between the two larval populations studied. The synergistic overexpression of heat shock and osmoregulatory proteins may facilitate larval survival in intertidal habitats or in extreme environments.ConclusionsWe presented, for the first time, comprehensive transcriptome and proteome datasets for Red Sea nauplii. The datasets provide a foundation for future investigations focused on the survival mechanisms of other crustaceans in extreme marine environments.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-015-2262-1) contains supplementary material, which is available to authorized users.