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.     

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

Abstract

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°, 70.3° and 57.3°, 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.     

Evidence of predation on Cretaceous sea stars from north-west Germany

Asteroids and asteroid ossicles of the Late Cretaceous White Chalk of north-west Germany were examined for evidence of predation. Bite marks of fishes were commonly found on larger ossicles and on one entirely preserved specimen of Recurvaster polyplacus. On ossicles of Pycinaster magnificus, tooth marks show evidence of serration, probably by the galeoid shark Squalicorax. Predation of durophagous fishes is obviously size-related, because regurgitated pellets contain exclusively ossicles of small asteroids.     

A non‐lethal method for estimation of gonad and pyloric caecum indices in sea stars

Abstract. Gonad and pyloric caecum indices are widely used indicators of reproductive effort and nutritional condition in asteroids. Current methods of quantification generally require sacrificing multiple animals and the resulting reduction in local sea star density could have an unintended impact on benthic communities. Using the intertidal sea star Pisaster ochraceus, we developed and tested a method for estimating organ indices through the non‐lethal sampling of single arms. Indices estimated via dissections of single arms accurately predicted the values obtained by sacrificing whole animals. In laboratory and field trials, we compared two methods of sampling single arms: (1) arm removal, and (2) organ extraction through an incision (without arm removal). Two years after these treatments, organs had regenerated in the affected arms of most sea stars, but were small relative to those in unmanipulated arms. The extent of organ recovery did not differ between the two treatments, but sea stars in the arm removal group were relocated in the field more frequently than those in the arm incision group. Our results suggest that sampling via the removal of single arms can be an effective, non‐lethal method for estimating gonad and pyloric caecum indices in asteroids.     

Strong character incongruence and character choice in phylogeny of sea stars of the Asterinidae

Abstract. Historically, characters from early animal development have been a potentially rich source of phylogenetic information, but many traits associated with the gametes and larval stages of animals with complex life cycles are widely suspected to have evolved frequent convergent similarities. Such convergences will confound true phylogenetic relationships. We compared phylogenetic inferences based on early life history traits with those from mitochondrial DNA sequences for sea stars in the genera Asterina, Cryptasterina , and Patiriella (Valvatida: Asterinidae). Analysis of these two character sets produced phylogenies that shared few clades. We quantified the degree of homoplasy in each character set when mapped onto the phylogeny inferred from the alternative characters. The incongruence between early life history and nucleotide characters implies more homoplasy in the life history character set. We suggest that the early life history traits in this case are most likely to be misleading as phylogenetic characters because simple adaptive models predict convergence in early life histories. We show that adding early life history characters may slightly improve a phylogeny based on nucleotide sequences, but adding nucleotide characters may be critically important to improving inferences from phylogenies based on early life history characters.     

In the footsteps of sea stars: deciphering the catalogue of proteins involved in underwater temporary adhesion

Sea stars adhere strongly but temporarily to underwater substrata via the secretion of a blend of proteins, forming an adhesive footprint that they leave on the surface after detachment. Their tube feet enclose a duo-gland adhesive system comprising two types of adhesive cells, contributing different layers of the footprint and de-adhesive cells. In this study, we characterized the catalogue of sea star footprint proteins (Sfps) in the species Asterias rubens to gain insights in their potential function. We identified 16 Sfps and mapped their expression to type 1 and/or type 2 adhesive cells or to de-adhesive cells by double fluorescent in situ hybridization. Based on their cellular expression pattern and their conserved functional domains, we propose that the identified Sfps serve different functions during attachment, with two Sfps coupling to the surface, six providing cohesive strength and the rest forming a binding matrix. Immunolabelling of footprints with antibodies directed against one protein of each category confirmed these roles. A de-adhesive gland cell-specific astacin-like proteinase presumably weakens the bond between the adhesive material and the tube foot surface during detachment. Overall, we provide a model for temporary adhesion in sea stars, including a comprehensive list of the proteins involved.     

Development of the initial diatom microfouling layer on antifouling and fouling-release surfaces in temperate and tropical Australia

Diatoms are a major component of the slime layers that form on artificial surfaces in marine environments. In this article, the role played by diatoms during the pioneering stages of colonization of three marine antifouling (AF) coatings, viz Intersmooth 360®, Super Yacht 800® and a fouling-release (FR) coating Intersleek 700®, was investigated. The study was conducted over three distinct seasons in two very different marine environments in Australia, ie temperate Williamstown, Victoria and tropical Cairns, Queensland. Diatom fouling occurred more rapidly on the FR coating Intersleek 700, compared to both biocidal AF paints. However, colonization by diatoms on all three coatings was generally slow during the 16-day study. Benthic diatoms do not subsist by floating around in the water column, rather they only gain the opportunity to colonize new surfaces when they either voluntarily release or are displaced from their benthic habitat, thereafter entering the water column where the opportunity to adhere to a new surface presents itself. However, once settled, fouling diatoms grow exponentially from the site of attachment, spreading out until they populate large areas of the surface. This mode of surface colonization correlates more with an ‘infection’ type, epidemiology model, a mechanism that accounts for the colonization of significant regions of the coating surface from a single fouling diatom cell, forming ‘clonal patches’. This is in comparison to the bacterial colonization of the surface, which exhibits far more rapid recruitment and growth of cells on the substratum surface. Therefore, it is hypothesized that fouling diatoms may be characterized more by their ability to adhere and grow on surfaces already modified by bacterial biofilms, rather than on their strength of adhesion. Cell morphology and the ability to avoid shear may also be an important factor.     

Evolution of larval form in the sea star genus Patiriella: conservation and change in the larval nervous system

The organization of the peptidergic system in the larvae of Patiriella species with divergent ontogenies was compared to determine which aspects of neurogenesis are conserved and which are altered in the evolution of development in these sea stars. P. regularis has ancestral-type feeding bipinnaria and brachiolaria larvae and the organization of the nervous system, in association with feeding structures, paralleled the bilateral larval body plan. P. calcar and P. exigua have non-feeding planktonic and benthic brachiolariae, respectively, and there was no trace of the neuronal architecture involved with feeding. The nervous system in the attachment stage brachiolaria was similar in all three species and neuronal organization reflected larval symmetry. Delayed expression of peptidergic lineages to the brachiolaria stage in the lecithotrophs indicates heterochronic change in the timing of neurogenesis or deletion of the ancestral early neurogenic program. The bipinnarial program is suggested to be a developmental module autonomous from the brachiolar one. With a divergence time of less than 10 Ma, the evolution of development in Patiriella has resulted in extensive reduction in the complexity of the larval nervous system in parallel with simplification in larval form. There is, however, strong conservation in the morphology and neuronal architecture of structures involved with settlement.     

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.     

Photoperiodic regulation of feeding and reproduction in a brooding sea star from central California

Summary

Individuals of the sea star genus Leptasterias from the Monterey Peninsula, California, were maintained for 34 months under two contrasting regimes of seasonally changing photoperiod. In one regime the lights turned on and off in phase with local sunrise and sunset; in the other the daily photoperiod was kept 6 months out of phase with ambient photoperiods. Annual cycles of feeding, gametogenesis, and embryo brooding of the out-of-phase animals were all shifted out of phase with respect to those of the in-phase animals. These small, relatively hardy sea stars appear well suited for more detailed analyses of photoperiodism in asteroids.     

An analysis of the reproductive pattern in the sea star Astropecten irregularis (Pennant) from the Bristol Channel

Summary

The reproductive cycle in Astropecten irregularis is described, making use of a range of statistical techniques detailed previously. Analysis of gonad weights proved more satisfactory than the use of gonad indices, as the latter are not independent of animal size. When examining the course of oogenesis, standardised residuals in an (R × C) contingency table are much easier to interpret than size/frequency polygons.

The species has an annual cycle with spawning in June or July, but the gonads are small even when the animals are gravid, and the annual cycle in gonad weights is more marked in males. Proliferation of oogonia may apparently occur at any time of year, and the ripe ovary contains many small, previtellogenic oocytes. There is an annual cycle of small magnitude in the size of the pyloric caecum, with a peak in December.     

Adaptive strategy of the Porcellanasterid sea stars

Morphological–functional analysis suggests that the adaptations of sea stars of the family Porcellanasteridae to burrowing and deposit feeding are related to morphological simplification. This simplification led to reduction of the morphological structures responsible for respiration (papulae and paxillae), decrease in the number of cribriform organs, reduction of body size, and retention of juvenile characters by adults. The forced-circulation water system inside the burrow also changes. The water generated by the cribriform organs becomes upwardly directed. The adaptive strategy in the family is characterized by intensification of nonselective deposit feeding by means of active moving within the muddy sediment and removal of fecal materials from the burrow.     

<Emphasis Type="Italic">Engrailed</Emphasis> is expressed in larval development and in the radial nervous system of <Emphasis Type="Italic">Patiriella</Emphasis> sea stars

We documented expression of the pan-metazoan neurogenic gene engrailed in larval and juvenile Patiriella sea stars to determine if this gene patterns bilateral and radial echinoderm nervous systems. Engrailed homologues, containing conserved En protein domains, were cloned from the radial nerve cord. During development, engrailed was expressed in ectodermal (nervous system) and mesodermal (coeloms) derivatives. In larvae, engrailed was expressed in cells lining the larval and future adult coeloms. Engrailed was not expressed in the larval nervous system. As adult-specific developmental programs were switched on during metamorphosis, engrailed was expressed in the central nervous system and peripheral nervous system (PNS), paralleling the pattern of neuropeptide immunolocalisation. Engrailed was first seen in the developing nerve ring and appeared to be up-regulated as the nervous system developed. Expression of engrailed in the nerve plexus of the tube feet, the lobes of the hydrocoel along the adult arm axis, is similar to the reiterated pattern of expression seen in other animals. Engrailed expression in developing nervous tissue reflects its conserved role in neurogenesis, but its broad expression in the adult nervous system of Patiriella differs from the localised expression seen in other bilaterians. The role of engrailed in patterning repeated PNS structures indicates that it may be important in patterning the fivefold organisation of the ambulacrae, a defining feature of the Echinodermata.     

Comparative histological and immunohistochemical study of sea star tube feet (Echinodermata, Asteroidea)

Adhesion in sea stars is the function of specialized structures, the tube feet or podia, which are the external appendages of the water-vascular system. Adhesive secretions allow asteroid tube feet to perform multiple functions. Indeed, according to the sea star species considered, the tube feet may be involved in locomotion, fixation, or burrowing. Different tube foot shapes usually correspond to this variety of function. In this study, we investigated the variability of the morphology of sea star tube feet as well as the variability of the composition of their adhesive secretions. This second aspect was addressed by a comparative immunohistochemical study using antibodies raised against the adhesive material of the forcipulatid Asterias rubens. The tube feet from 14 sea star species representing five orders and 10 families of the Class Asteroidea were examined. The histological study revealed three main tube foot morphotypes, i.e., knob-ending, simple disc-ending, and reinforced disc-ending. Analysis of the results suggests that tube foot morphology is influenced by species habitat, but within limits imposed by the evolutionary lineage. In immunohistochemistry, on the other hand, the results were very homogeneous. In every species investigated there was a very strong immunolabeling of the adhesive cells, independently of the taxon considered, of the tube foot morphotype or function, or of the species habitat. This indicates that the adhesives in all the species considered are closely related, probably sharing many identical molecules or, at least, many identical epitopes on their constituents.     

Single copy DNA homology in sea stars

Summary The sequence homology in the single copy DNA of sea stars has been measured. Labeled single copy DNA fromPisaster ochraceus was reannealed with excess genomic DNA fromP. brevispinus, Evasterias troschelii, Pycnopodia helianthoides, Solaster stimpsoni, andDermasterias imbricata. Reassociation reactions were performed under two criteria of salt and temperature. The extent of reassociation and thermal denaturation characteristics of hybrid single copy DNA molecules follow classical taxonomic lines.P. brevispinus DNA contains essentially all of the sequences present inP. ochraceus single copy tracer whileEvasterias andPycnopodia DNAs contain 52% and 46% of such sequences respectively. Reciprocal reassociation reactions with labeledEvasterias single copy DNA confirm the amount and fidelity of the sequence homology. There is a small definite reaction of uncertain homology betweenP. ochraceus single copy DNA andSolaster orDermasterias DNA. SimilarlySolaster DNA contains sequences homologous to approximately 18% ofDermasterias unique DNA. The thermal denaturation temperatures of heteroduplexes indicate that the generaPisaster andEvasterias diverged shortly after the divergence of the subfamilies Pycnopodiinae and Asteriinae. The twoPisaster species diverged more recently, probably in the most recent quarter of the interval since the separation of the generaPisaster andEvasterias.     

Oxygen-depleted surfaces: a new antifouling technology

A novel, non-toxic strategy to combat marine biofouling is presented. The technology is paint with additions of up to 43% of industrial protein. Through microbial degradation of the protein component, an oxygen-depleted layer rapidly forms in a 0.2 mm layer close to the paint surface. With the present paint formulations, a stable, O₂-depleted layer can persist for 16 weeks. Barnacle larvae (cyprids) did not settle on panels where oxygen saturation was <20%, and cyprids were killed when exposed to O₂-free water for more than 1 h. It is also shown that the O₂-depleted layer will rapidly reform (within 15 min) after exposure to turbulent flow. Field exposure of panels for 16 weeks showed that paint with protein reduced fouling by barnacles and bryozoans by 80% and close to 100%, respectively. The results suggest that this novel technology may be developed into a non-toxic alternative to copper-based antifouling paints, especially for pleasure boats in sensitive environments. There is clearly potential for further development of the paint formulation, and a full-scale test on a boat-hull suggested that service-life under realistic operations needs to be improved.     

Short-term testing of antifouling surfaces: the importance of colour

Abstract

Data from short-term biofouling assays are frequently used to evaluate the performance of antifouling (AF) coatings. There are a large number of factors, however, that may influence community development. One such factor is colour. The hypothesis was that differences in colour may impact the short-term development of a biofouling community and therefore bias the results. An experiment was designed to investigate the effect of black and white substrata on settlement of fouling organisms in the field. Both Ulva sp. and Spirorbis sp. had significantly higher settlement on black surfaces. This result emphasises the importance of considering colour and other factors when undertaking short-term testing of AF coatings.     

Origin and development of the germ line in sea stars

This review summarizes and integrates our current understanding of how sea stars make gametes. Although little is known of the mechanism of germ line formation in these animals, recent results point to specific cells and to cohorts of molecules in the embryos and larvae that may lay the ground work for future research efforts. A coelomic outpocketing forms in the posterior of the gut in larvae, referred to as the posterior enterocoel (PE), that when removed, significantly reduces the number of germ cell later in larval growth. This same PE structure also selectively accumulates several germ‐line associated factors—vasa, nanos, piwi—and excludes factors involved in somatic cell fate. Since its formation is relatively late in development, these germ cells may form by inductive mechanisms. When integrated into the morphological observations of germ cells and gonad development in larvae, juveniles, and adults, the field of germ line determination appears to have a good model system to study inductive germ line determination to complement the recent work on the molecular mechanisms in mice. We hope this review will also guide investigators interested in germ line determination and regulation of the germ line into how these animals can help in this research field. The review is not intended to be comprehensive—sea star reproduction has been studied for over 100 years and many reviews are comprehensive in their coverage of, for example, seasonal growth of the gonads in response to light, nutrient, and temperature. Rather the intent of this review is to help the reader focus on new experimental results attached to the historical underpinnings of how the germ cell functions in sea stars with particular emphasis to clarify the important areas of priority for future research. genesis 52:367–377, 2014. © 2014 Wiley Periodicals, Inc.     

Discovery and cross-amplification of microsatellite polymorphisms in asterinid sea stars

Variation in tandem repeats of two- to six-base nucleotide motifs (microsatellites) can be used to obtain inexpensive and highly informative multi-locus data on population genetics.We developed and tested a large set of cross-amplifiable sea star (Asterinidae) microsatellite markers from a mixed pool of genomic DNA from eight species. We describe cloned sequences, primers, and PCR conditions, and characterize population-level variation for some species and markers. A few clones containing microsatellites showed considerable similarity to sequences (including genes of known function) in other sea stars and in sea urchins (from the Strongylocentrotus purpuratus complete genome). The pooled genomic DNA method was an efficient way to sample microsatellites from many species: we cloned 2-10 microsatellites from each of eight species, and most could be cross-amplified in 1-7 other species. At 12 loci in two species, we found 1-10 alleles per microsatellite, with a broad range of inbreeding coefficients. Measures of polymorphism were negatively correlated with the extent of cross-amplification.     

The potential for translocation of marine species via small-scale disruptions to antifouling surfaces

Vessel hull fouling is a major vector for the translocation of nonindigenous species (NIS). Antifouling (AF) paints are the primary method for preventing the establishment and translocation of fouling species. However, factors such as paint age, condition and method of application can all reduce the effectiveness of these coatings. Areas of hull that escape AF treatment (through limited application or damage) constitute key areas that may be expected to receive high levels of fouling. The investigation focused on whether small-scale (mm² to cm²) areas of unprotected surface or experimental ‘scrapes’ provided sufficient area for the formation of fouling assemblages within otherwise undamaged AF surfaces. Recruitment of fouling taxa such as algae, spirorbids and hydroids was recorded on scrapes as narrow as 0.5 cm wide. The abundance and species richness of fouling assemblages developing on scrapes ≥1 cm often equalled or surpassed levels observed in reference assemblages totally unprotected by AF coatings. Experiments were conducted at three sites within the highly protected and isolated marine park surrounding Lady Elliott Island at the southernmost tip of the Great Barrier Reef, Australia. Several NIS were recorded on scrapes of AF coated surfaces at this location, with 1-cm scrapes showing the greatest species richness and abundance of NIS relative to all other treatments (including controls) at two of the three sites investigated. Slight disruptions to newly antifouled surfaces may be all that is necessary for the establishment of fouling organisms and the translocation of a wide range of invasive taxa to otherwise highly protected marine areas.