Surface microtopographies of tropical sea stars: lack of an efficient physical defence mechanism against fouling

The role of surface topography as a defence against fouling in tropical sea stars was investigated. The sea stars Linckia laevigata, Fromia indica, Cryptasterina pentagona and Archaster typicus are not fouled and have paxillae (modified ossicles with a median vertical pillar) on their aboral surfaces, which varied in diameter, height and distance depending on species and position on the aboral surface, providing unique and complex surface microtopographies for each species. The surfaces of the sea stars L. laevigata, F. indica and A. typicus were moderately wettable, with their mean seawater contact angles, calculated from captive bubble measurements, being 60.1 degrees, 70.3 degrees and 57.3 degrees, respectively. The seawater contact angle of C. pentagona could not be measured. To evaluate the effectiveness of the surface microtopographies in deterring the settlement of fouling organisms, field experiments with resin replicas of the four sea star species were conducted at three sites around Townsville, Australia, for 8 weeks during the dry and wet seasons. The fouling community and total fouling cover did not differ significantly between replicas of L. laevigata, F. indica, C. pentagona, A. typicus and control surfaces at any site during the dry season. Significant differences between fouling communities on the replicas of the sea stars and control surfaces were detected at two sites during the wet season. However, these differences were transitory, and the total fouling cover did not differ significantly between replicas of sea stars and control surfaces at two of the three sites. In contrast to recent literature on the effects of biofouling control by natural surfaces in the marine environment, the surface microtopographies of tropical sea stars alone were not effective in deterring the settlement and growth of fouling organisms.     

Fouling-resistant surfaces of tropical sea stars

Abstract

Qualitative evidence suggests sea stars are free of fouling organisms; however the presence of fouling-resistant surfaces of sea stars has not previously been documented. Field surveys were conducted in northern Queensland, Australia, during the wet and dry seasons and several tropical sea star species were examined for surface-associated micro- and macro-organisms. Mean bacterial abundances on seven sea star species were approximately 10⁴ to 10⁵ cells cm^?2 during both seasons. There were no consistent trends in bacterial abundances with season, species and aboral positions on sea star arms. No common generalist fouling organisms, such as algae, barnacles, serpulid polychaetes, bryozoans and ascidians, were found on any specimens of 12 sea star species. However, low numbers of parasitic and commensal macro-organisms were found on six sea star species. The gastropods Parvioris fulvescens, Asterolamia hians, Thyca (Granulithyca) nardoafrianti and Thyca crystallina were found exclusively on the sea stars Archaster typicus, Astropecten indicus, Nardoa pauciforis and Linckia laevigata, respectively. The shrimp Periclimenes soror was only found on Acanthaster planci, and the polychaete Ophiodromus sp. on A. typicus. The copepods Stellicola illgi and Paramolgus sp. were only found on L. laevigata and Echinaster luzonicus, respectively. As no common generalist fouling organisms were discovered, sea stars offer an excellent model to investigate the mechanisms driving fouling-resistant surfaces and the selective settlement of specialist invertebrates.     

Fouling-resistant surfaces of tropical sea stars

Qualitative evidence suggests sea stars are free of fouling organisms; however the presence of fouling-resistant surfaces of sea stars has not previously been documented. Field surveys were conducted in northern Queensland, Australia, during the wet and dry seasons and several tropical sea star species were examined for surface-associated micro- and macro-organisms. Mean bacterial abundances on seven sea star species were approximately 10(4) to 10(5) cells cm(-2) during both seasons. There were no consistent trends in bacterial abundances with season, species and aboral positions on sea star arms. No common generalist fouling organisms, such as algae, barnacles, serpulid polychaetes, bryozoans and ascidians, were found on any specimens of 12 sea star species. However, low numbers of parasitic and commensal macro-organisms were found on six sea star species. The gastropods Parvioris fulvescens, Asterolamia hians, Thyca (Granulithyca) nardoafrianti and Thyca crystallina were found exclusively on the sea stars Archaster typicus, Astropecten indicus, Nardoa pauciforis and Linckia laevigata, respectively. The shrimp Periclimenes soror was only found on Acanthaster planci, and the polychaete Ophiodromus sp. on A. typicus. The copepods Stellicola illgi and Paramolgus sp. were only found on L. laevigata and Echinaster luzonicus, respectively. As no common generalist fouling organisms were discovered, sea stars offer an excellent model to investigate the mechanisms driving fouling-resistant surfaces and the selective settlement of specialist invertebrates.     

The Influence of Natural Surface Microtopographies on Fouling

Multiple antifouling strategies of marine organisms may consist of combinations of physical, chemical and mechanical mechanisms. In this study, the role of surface microtopography (?<?500?μm) of different marine organisms, such as Cancer pagurus, Mytilus edulis, Ophiura texturata and the eggcase of Scyliorhinus canicula, has been investigated as a possible component of their defence systems. High resolution resin replicates of these natural surface structures were exposed to natural fouling in field experiments. Abundances of recruits were determined and compared to those on untextured, but otherwise identical, control surfaces to quantify the influence of the different microtopographies on fouling rates. Antifouling effects of microtopographies varied with type of microtopography and coloniser species. The surface microtopography of C. pagurus significantly rejected macrofoulers. The surface structures of the eggcase and O. texturata had repellent effects on microfoulers. Barnacle settlement was temporarily reduced on surface microtopographies of M. edulis and the eggcase. These results emphasise the promising non-toxic antifouling properties of microtextured surfaces.     

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.     

The influence of natural surface microtopographies on fouling

Multiple antifouling strategies of marine organisms may consist of combinations of physical, chemical and mechanical mechanisms. In this study, the role of surface microtopography (< 500 microns) of different marine organisms, such as Cancer pagurus, Mytilus edulis, Ophiura texturata and the eggcase of Scyliorhinus canicula, has been investigated as a possible component of their defence systems. High resolution resin replicates of these natural surface structures were exposed to natural fouling in field experiments. Abundances of recruits were determined and compared to those on untextured, but otherwise identical, control surfaces to quantify the influence of the different microtopographies on fouling rates. Antifouling effects of microtopographies varied with type of microtopography and coloniser species. The surface microtopography of C. pagurus significantly rejected macrofoulers. The surface structures of the eggcase and O. texturata had repellent effects on microfoulers. Barnacle settlement was temporarily reduced on surface microtopographies of M. edulis and the eggcase. These results emphasise the promising nontoxic antifouling properties of microtextured surfaces.     

Form and Function of the Primary Spines of Two Bathyal Echinothuriid Sea Urchins

The appearance, in situ activity and structure of the primary spines of the two deep sea echinothuriid sea urchins Phormosoma placenta and Araeosoma belli are described with particular reference to the unusual, fleshy, aboral spines. Oral primary spines of both species are clearly but differently adapted for movement over soft substrata. The aboral spines of both species bear fleshy extensions which are composed of gelatinous material in both species and are not poison sacs. Field experiments showed that the fleshy parts of the aboral spines of P. placenta are palatable to shallow-water fish. However, the aboral spines are shown to have stored within the hollow ossicle of the spine secretory material likely to be irritant in function. The structure of the tip of the spine ossicle of both species suggests that they may act like hypodermic needles. We conclude that the aboral spines of both species are probably defensive in function but remain equivocal over the exact role of the massive fleshy extensions found in P. placenta. Other possible non-defensive functions are briefly discussed.     

Effects of adsorbed organic and primary fouling films on bryozoan settlement

Marine primary fouling films, which consist of molecular organic and microbial components, have been reported to facilitate colonization of immersed surfaces by marine fouling organisms. Larvae of the cosmopolitan fouling bryozoan Bugula neritina (Linnaeus) were offered various substrata for attachment and metamorphosis. The materials were offered (a) after detergent washing, (b) after sorption of dissolved organic molecular films, and (c) after formation of primary films consisting of both microbial and adsorbed organic material. Wettability of the substrata by sea water was determined by contact angle measurements for each substratum. On washed substrata, attachment was favored with contact angles greater than ≈45° (cos contact angle <0.7). Adsorbed surface films had no effect on the low settlement of larvae on glass and high settlement on plastics. Microbial primary films, however, made glass attractive and plastics unattractive. These settlement preference changes did not correlate with the changes in wettability observed on these substrata. Dispersion of larvae over the settlement surface was random except on wettable surfaces coated with bacterial films, where settlement was strongly clustered (contagious).     

The role of nano-roughness in antifouling

Nano-engineered superhydrophobic surfaces have been investigated for potential fouling resistance properties. Integrating hydrophobic materials with nanoscale roughness generates surfaces with superhydrophobicity that have water contact angles (θ) >150° and concomitant low hysteresis (<10°). Three superhydrophobic coatings (SHCs) differing in their chemical composition and architecture were tested against major fouling species (Amphora sp., Ulva rigida, Polysiphonia sphaerocarpa, Bugula neritina, Amphibalanus amphitrite) in settlement assays. The SHC which had nanoscale roughness alone (SHC 3) deterred the settlement of all the tested fouling organisms, compared to selective settlement on the SHCs with nano- and micro-scale architectures. The presence of air incursions or nanobubbles at the interface of the SHCs when immersed was characterized using small angle X-ray scattering, a technique sensitive to local changes in electron density contrast resulting from partial or complete wetting of a rough interface. The coating with broad spectrum antifouling properties (SHC 3) had a noticeably larger amount of unwetted interface when immersed, likely due to the comparatively high work of adhesion (60.77 mJ m^?2 for SHC 3 compared to 5.78 mJ m^?2 for the other two SHCs) required for creating solid/liquid interface from the solid/vapour interface. This is the first example of a non-toxic, fouling resistant surface against a broad spectrum of fouling organisms ranging from plant cells and non-motile spores, to complex invertebrate larvae with highly selective sensory mechanisms. The only physical property differentiating the immersed surfaces is the nano-architectured roughness which supports longer standing air incursions providing a novel non-toxic broad spectrum mechanism for the prevention of biofouling.     

Impact of wastewater fouling on contact angle

Capillary dependent systems are highly influenced by surface fouling and may degrade as material surface properties change. In anticipation of a spacecraft microgravity fluids management system exposed to highly variable wetting conditions, the impact of urine wastewater fouling on capillary contact angle was examined. The results indicate that, in general, surface fouling can decrease the contact angle when crystalline structures or biofilms form. Small crystalline growth on the order of 10 μm can lower advancing contact angles θ_adv by approximately 30°, while biofilm growth can lower it by approximately 15°. Vacuum drying of fouled surfaces increased θ_adv by about 8°, and defects greater in height than 5% of the capillary length increased θ_adv by approximately 30°. These trends may indicate that promotion of wastewater fouling may improve the performance of capillary dependent fluids management systems. These results may also influence terrestrial technologies, including medical catheters and sustainable wastewater treatment systems exposed to wastewater fouling.     

Lefty acts as an essential modulator of Nodal activity during sea urchin oral-aboral axis formation

Nodal is a key player in the process regulating oral–aboral axis formation in the sea urchin embryo. Expressed early within an oral organizing centre, it is required to specify both the oral and aboral ectoderm territories by driving an oral–aboral gene regulatory network. A model for oral–aboral axis specification has been proposed relying on the self activation of Nodal and the diffusion of the long-range antagonist Lefty resulting in a sharp restriction of Nodal activity within the oral field. Here, we describe the expression pattern of lefty and analyse its function in the process of secondary axis formation. lefty expression starts at the 128-cell stage immediately after that of nodal, is rapidly restricted to the presumptive oral ectoderm then shifted toward the right side after gastrulation. Consistently with previous work, neither the oral nor the aboral ectoderm are specified in embryos in which Lefty is overexpressed. Conversely, when Lefty's function is blocked, most of the ectoderm is converted into oral ectoderm through ectopic expression of nodal. Reintroducing lefty mRNA in a restricted territory of Lefty depleted embryos caused a dose-dependent effect on nodal expression. Remarkably, injection of lefty mRNA into one blastomere at the 8-cell stage in Lefty depleted embryos blocked nodal expression in the whole ectoderm consistent with the highly diffusible character of Lefty in other models. Taken together, these results demonstrate that Lefty is essential for oral–aboral axis formation and suggest that Lefty acts as a long-range inhibitor of Nodal signalling in the sea urchin embryo.     

Fouling Deterrence on the Bivalve Shell Mytilus galloprovincialis: A Physical Phenomenon?

The physical nature of fouling deterrence by the mussel Mytilus galloprovincialis was investigated using high-resolution biomimics of the bivalve surface. The homogeneous microtextured surface of M. galloprovincialis (1.94 ± 0.03 μm), the smooth surface of the bivalve Amusium balloti (0 μm), and moulds of these surfaces (biomimics) were compared with controls of smooth (0 μm) and sanded moulds, (55.4 ± 2.7 μm) and PVC strips (0 μm) in a 12-week field trial. The shell and mould of M. galloprovincialis were fouled by significantly fewer species and had significantly less total fouling cover than the shell and mould of A. balloti over a 12-week period. However, the major effects were between surfaces with and without microtopography. Surface microtopography, be it structured as in the case of M. galloprovincialis shell and mould, or random as in the case of the sanded mould, had a lower cover of fouling organisms than treatments without microtopography after 6 weeks. There was also no difference between the effect of the M. galloprovincialis mould and the sanded mould. The strong fouling deterrent effects of both these surfaces diminished rapidly after 6 to 8 weeks while that of M. galloprovincialis shell remained intact for the duration of the experiment suggesting factors in addition to surface microtopography contribute to fouling deterrence.     

A comparative study of the anti-settlement properties of mytilid shells

Marine organisms have evolved defence mechanisms to prevent epibiosis. This study investigated the anti-settlement properties of natural periostracal microtopographies of two mytilid species, Mytilus edulis (from North, Baltic and White Seas) and Perna perna (from the SW Atlantic). Resin replicas of shells were exposed to cyprids of the barnacle Semibalanus balanoides. Replicas with intact isotropic microtopographies and smooth controls were much less fouled than roughened anisotropic surfaces. This indicates that in both M. edulis and P. perna the periostracum possesses a generic anti-settlement property, at least against S. balanoides cyprids, which is not regionally adapted. Such a potential globally effective anti-settlement mechanism possibly contributes to the invasive success of Mytilidae.     

Comparative microanatomy of the branchial sieve in three sympatric cyprinid species,related to filter-feeding mechanisms

The chimaeroid holocephalian fishes are distinguished among extant chondrichthyans by the possession of three pairs of tooth plates, evergrowing and partially hypermineralized, that are not shed and replaced like the teeth of living elasmobranchs. Although derivation of the chimaeroid tooth plate from the fusion of members of a plesiomorphic chondrichthyan tooth family has been proposed, evidence for this hypothesis has been lacking. A new analysis of the development and structure of the tooth plates in Callorhinchus milii (Holocephali, Chimaeriformes) reveals the compound nature of the tooth plates in a chimaeroid fish. Each tooth plate consists of an oral and aboral territory that form independently in the embryo and maintain separate growth surfaces through life. The descending lamina on the aboral surface of the tooth plate demarcates the growth surface of the aboral territory. Comparison with the tooth plates of Chimaera monstrosa indicates that compound tooth plates may be a feature of all chimaeroids in which a descending lamina is present. The tooth plates in these fishes represent the fusion of two members of a reduced tooth family. The condition of the tooth plates in C. milii is plesiomorphic for chimaeroids and is of evolutionary significance in that it provides further evidence to support a lyodont dentition in chimaeroid fishes similar to that found in other chondrichthyans. © 1994 Wiley-Liss, Inc.     

Lower critical solubility temperature materials as biofouling release agents

Poly(N-isopropylacrylamide) (PNIPAAM) exhibits a lower critical solubility temperature (LCST) of 32°C. Using thin films of this compound as a model system, the potential of ‘smart polymers’ as biofouling-release agents was examined. PNIPAAM-coated glass slides were incubated in artificial sea water containing the marine bacterium Halomonas marina or in natural bay water at a temperature above the LCST. Upon rinsing of the biofouled samples with artificial sea water below the LCST, the dissolution of the coating released over 90% of the attached fouling material, a significant increase over the release obtained for glass controls. These experiments demonstrate the potential of PNIPAAM and similar polymers as possible fouling-release agents, and suggest that tethered PNIPAAM (or similar polymers) may be useful as regenerable fouling-release surfaces. Received 26 September 1997/ Accepted in revised form 29 November 1997     

PHYSIOLOGICAL PERFORMANCE OF FLOATING GIANT KELP MACROCYSTIS PYRIFERA (PHAEOPHYCEAE): LATITUDINAL VARIABILITY IN THE EFFECTS OF TEMPERATURE AND GRAZING1

Rafts of Macrocystis pyrifera (L.) C. Agardh can act as an important dispersal vehicle for a multitude of organisms, but this mechanism requires prolonged persistence of floating kelps at the sea surface. When detached, kelps become transferred into higher temperature and irradiance regimes at the sea surface, which may negatively affect kelp physiology and thus their ability to persist for long periods after detachment. To examine the effect of water temperature and herbivory on the photosynthetic performance, pigment composition, carbonic anhydrase (CA) activity, and the nitrogen (N) and carbon (C) content of floating M. pyrifera, experiments were conducted at three sites (20° S, 30° S, 40° S) along the Chilean Pacific coast. Sporophytes of M. pyrifera were maintained at three different temperatures (ambient, ambient ? 4°C, ambient + 4°C) and in presence or absence of the amphipod Peramphithoe femorata for 14 d. CA activity decreased at 20° S and 30° S, where water temperatures and irradiances were highest. At both sites, pigment contents were substantially lower in the experimental algae than in the initial algae, an effect that was enhanced by grazers. Floating kelps at 20° S could not withstand water temperatures >24°C and sank at day 5 of experimentation. Maximal quantum yield decreased at 20° S and 30° S but remained high at 40° S. It is concluded that environmental stress is low for kelps floating under moderate temperature and irradiance conditions (i.e., at 40° S), ensuring their physiological integrity at the sea surface and, consequently, a high dispersal potential for associated biota.     

Using textured PDMS to prevent settlement and enhance release of marine fouling organisms

The antifouling efficacy of a series of 18 textured (0.2–1000 μm) and non-textured (0 μm) polydimethylsiloxane surfaces with the profiles of round- and square-wave linear grating was tested by recording the settlement of fouling organisms in the laboratory and in the field by monitoring the recruitment of a multi-species fouling community. In laboratory assays, the diatoms Nitzschia closterium and Amphora sp. were deterred by all surface topographies regardless of texture type. Settlement of propagules of Ulva sp. was lower on texture sizes less than the propagule size, and settlement of larvae of Saccostrea glomerata and Bugula neritina was lower on texture sizes closest to, but less than, the sizes of larvae. After a six month field trial, all textured surfaces lost their deterrent effect; however, the foul-release capabilities of textures were still present. High initial attachment was correlated with most fouling remaining after removal trials, indicating that fouling organisms recruited in higher numbers to surfaces upon which they attached most strongly.     

TRANSPORT AND DEFENSIVE ROLE OF ELATOL AT THE SURFACE OF THE RED SEAWEED LAURENCIA OBTUSA (CERAMIALES,RHODOPHYTA)1

Natural within‐thallus concentrations of elatol produced by Laurencia obtusa (Huds.) J. V. Lamour. inhibit herbivory and prevent fouling. However, elatol occurs in larger amounts within the thallus compared with the quantities from the surface of this alga. We evaluated whether the surface elatol concentrations inhibit both herbivory and fouling and whether the content of corps en cerise can be transferred to the external cell walls. Surface elatol concentrations did not inhibit herbivory by sea urchins, settlement of barnacle larvae, or mussel attachment. Evidence of a connection between the corps en cerise, where elatol is probably stored, and the cell wall of L. obtusa was based on channel‐like membranous connections that transport vesicles from the corps to the cell wall region. Therefore, L. obtusa presents a specific process of chemical transport between the cell storage structures and the plant surface. We hypothesized that if high amounts of elatol are capable of inhibiting herbivory and fouling, if the tested organisms are ecologically relevant, and if elatol really occurs on the surface of L. obtusa and this seaweed can transport this compound to its surface, the low natural concentration of defensive chemicals on the surface of L. obtusa is probably not absolute but may be variable according to environmental conditions. We also hypothesized that herbivory and fouling would not exert the same selective force for the production of defensive chemicals on L. obtusa’s surface since the low concentrations of elatol were inefficient to inhibit either processes or distinguish selective pressures.     

Assemblages of sea stars (Echinodermata: Asteroidea) and brittle stars (Echinodermata: Ophiuroidea) in the Weddell Sea (Antarctica) and off Northeast Greenland (Arctic): a comparison of diversity and abundance

Composition and distribution of asteroid and ophiuroid assemblages were investigated by means of Agassiz trawl catches at 34 stations in 220- to 1,200-m depth in the Weddell Sea and at 17 stations in 90- and 830-m depth off Northeast Greenland. A total of 86 species (48 sea stars, 38 brittle stars) were identified in the Weddell Sea whereas off Northeast Greenland a total of 26 species (16 sea stars, 10 brittle stars) were recorded. In both study areas, brittle stars were numerically more important than sea stars, and abundances generally decreased with water depths. Multivariate analyses revealed a conspicuous depth zonation of sea and brittle stars off Greenland. Very high abundances of Ophiocten sericeum and Ophiura robusta characterized the assemblages on shallow shelf banks whereas in greater depths Ophiopleura borealis, Ophioscolex glacialis and Ophiacantha bidentata became dominant, albeit at significantly lower densities. Mass occurrences of brittle stars, such as those recorded on Greenlandic shelf banks, have not been discovered in the Weddell Sea, where distinct assemblages were discriminated in deep shelf trenches as well as on the eastern and southern shelf. Ophioplocus incipiens, Ophiurolepis martensi and Ophiurolepis brevirima were the most prominent species on the eastern shelf. Ophiacantha antarctica, Ophiurolepis gelida and Ophionotus victoriae on the southern shelf, and Ophiosparte gigas as well as the asteriod Hymenaster sp., in the shelf trenches. Overall, the Weddell Sea housed conspicuously more asterozoan species than the waters off Greenland. Higher species diversity was also evident at both a regional and local scale, especially for the eastern Weddell Sea shelf. However, because many species from the Weddell Sea are closely related, the Weddell Sea assemblages were not significantly different from the Greenland ones in terms of taxonomic diversity and distinctness. Received: 29 April 1996/Accepted: 10 June 1996     

The green alga Dicytosphaeria ocellata and its organic extracts alter natural bacterial biofilm communities

Surfaces immersed in the marine environment are under intense fouling pressure by a number of invertebrates and algae. The regulation of this fouling can often be attributed to the bacterial biofilm that quickly develops on the surface of any available substratum in the ocean. The bacterial community composition on the surface of the green alga Dictyosphaeria ocellata was investigated and compared to those found on two other green algae, Batophora oerstedii and Cladophoropsis macromeres, and on a reference surface from three sites along the Florida Keys. Although the bacterial community composition of D. ocellata was not consistent across the sites, it was significantly different from the other algae and the reference surface at two of the three sites tested. Methanol extracts of D. ocellata significantly affected the abundance of bacteria and composition of the bacterial community on Phytagel? plates when compared to solvent controls, suggesting that the alga regulates the bacterial community by producing active metabolites.