Behavioural and metabolic responses of the Antarctic sea star Odontaster validus to food stimuli of different concentration

Experiments were carried out to study the behavioural and metabolic responses of the Antarctic sea star, Odontaster validus, to different concentration of food signals (glutamic acid, aspartic acid, glicyne, alanine, tyrosine and a mixture of 11 amino acids). Stimulus concentration increase caused a rise in both the percentage of reacting animals and in the reaction intensity. At low stimulus concentration, O. validus reaction consisted of tube foot waving, and only high concentrations elicited a complicated sequence of several types of behaviour. The metabolic rate of small O. validus was more sensitive to chemical stimuli than of large individuals, with small sea stars reacting even to low signal concentration. It can be speculated that small body size can be a factor restricting sea star capabilities and influencing its reaction to chemical signals.     

The effect of copper ions on behavior of larvae of the sea urchin Strongylocentrotus intermedius at different temperatures of sea water

We investigated the behavior of larvae of the sea urchin Strongylocentrotus intermedius at the blastula and early pluteus stages in the water column at a temperature of 20, 22, and 23.5°C and in the presence of copper in concentrations of 0.01 and 0.02 mg/l. In clean sea water, at all tested temperatures, sea urchin larvae preferred the subsurface layer to where they rose from the bottom of the vessel to form dense aggregations. In water supplemented with copper, the behavior of larvae at 20 and 22°C was not different from that in clean water. An increase in temperature to 23.5°C and the addition of copper altered the behavior of the larvae; they did not leave near-bottom water, did not rise to the surface, although they continued moving.     

The role of amino acids in phagostimulation in the shallow-water omnivorous Antarctic sea star Odontaster validus

Experiments were carried out to study the behavioural responses of the omnivorous Antarctic sea star Odontaster validus to natural food odour, several single amino acids and their mixtures. Starved sea stars responded to natural food stimulus by rapid rise of metabolic rate, locomotory activity directed towards signal source, cessation of movement after reaching it and initiation of feeding. All single amino acids that were tested were detected by experimental animals, although there were marked differences in the sea stars reaction to them. Amino acids with narrow and broad scope of influence were distinguished, with glutamic acid being the most potent sea star stimulant. It was also found that the same sea star reaction (e.g. metabolic rate increase or locomotory activity) can be caused by several different amino acids. The effects of amino acid mixtures were significantly stronger than that of single amino acids, with >80% of animals reaching signal source. O. validus seems well adapted to using both single and complicated food signals in its foraging behaviour.     

Changes in the electrical activity of the hippocampus during elaboration of an inhibitory reaction in the dog

A conditioned alimentary instrumental reflex was elaborated in three dogs with chronically implanted electrodes to a consecutive complex conditioned stimulus consisting of two equal acoustic stimuli separated by a pause. At first, the animals reacted with motor reactions during the whole action of the complex signal. Then inhibition of reaction was elaborated at first in pause and then in response to the preparatory stimulus. In the process of stabilization of inhibition, there was an increase of similarity of spectral composition of hippocampal theta-rhythm with the values obtained in the inter-signal period. Conclusion is made that the hippocampus is not a structure necessary for the elaboration of internal inhibition. The frequency of hippocampal theta-rhythm may serve as a characteristic of the property called in Pavlov's school mobility of the nervous system.     

Distribution of echinoderms and their larvae in the southwestern Peter the Great Bay, Sea of Japan

Based on results of processing planktonic and benthic samples collected in 1996 and 1997, a spatial distribution of echinoderms in the bottom and of their larvae in the plankton were collated for the water area of the Southern region of the Far Eastern State Biosphere Marine Reserve. Some correlation between distributions of the adult and larval sea star Asterias amurensis in July was revealed. At the same time, there was no correlation between distributions of larvae and adult individuals of the brittle star Ophiura sarsi and sea urchin Echinocardium cordatum, which are most abundant in the area. The size structure of bottom populations of the brittle stars O. sarsi and Amphiodia fissa in the studied area was assessed. The correlation coefficient between the distribution of young-of-the-year and the population density was 0.47 in O. sarsi and 0.74 in A. fissa respectively, which implied a selective settling of larvae of those species in areas inhabited by adult brittle stars. Recruitment of bottom populations from 1996 spawning was 5% in O. sarsi and 3.3% in A. fissa.     

Archival electronic tagging of a predatory sea star — Testing a new technique to study movement at the individual level

Sea stars are important marine predators, and their feeding often controls the distribution of associated species. Therefore, quantifying their activity at an individual level is important in further understanding how they structure marine communities. Sea stars are difficult to tag, so there is little information on activity of sea stars in their natural environment over extended periods of days to weeks. We tagged the New Zealand sea star Coscinasteriasmuricata with small archival electronic tags that recorded water temperate and depth every 5 min for up to 2 weeks. The tagging was undertaken to test the viability of using electronic tags in research on the ecology of the sea stars in a New Zealand fiord, where their vertical distribution is influenced by the presence of low-salinity layers. The effects of the tagging were tested in the laboratory and in the field, with tagging having no detectable influence on invitro survival, feeding rate, and righting time, or on their insitu movement and depth distribution. Laboratory experiments testing the salinity tolerance of C.muricata showed they could tolerate salinities as low as 25 PSU for at least a 20-day period. Tagging of sea stars in their natural environment provided information on depth distributions, vertical migrations and the influence of the physical environment on their behaviour. The tagging also revealed a large variation in activity at the individual level. This study represents one of the first to utilise electronic tagging to study the ecology of a mobile invertebrate such as a sea star. The success of this initial study suggests that we could gain valuable quantitative insight into the ecology of these animals in future tag deployments.     

Responses of the black sea urchin Tetrapygus niger to its sea-star predators Heliaster helianthus and Meyenaster gelatinosus under field conditions

We ran field experiments to examine the responses of the black sea urchin Tetrapygus niger to predatory sea stars. Trials involving simulated attacks (one or several arms of a sea star being placed on top of half the urchin) showed that the urchin differentiated between the predatory sea stars, Heliaster helianthus and Meyenaster gelatinosus, and a non-predatory sea star, Stichaster striatus, and showed almost no response to a sea star mimic. We further compared the responses of the urchin to different threat levels presented by the two predatory sea stars. The highest threat level was a simulated attack, then mere contact, and subsequently sea stars being placed at different distances from the urchin. All urchins responded to simulated attacks and contact with both sea stars. The proportion responding decreased with distance and more rapidly in trials with H. helianthus (0% at a distance of 30 cm) than with M. gelatinosus (33% at a distance of 50 cm). At each of the threat levels where there was a response to both sea stars, the urchins responded more rapidly to M. gelatinosus than to H. helianthus. In a third experiment where a predatory sea star was added to a circular area (1-m diameter) in which either 4-8 or 11-19 undisturbed urchins were present, the urchins fled the area more rapidly when the added sea star was M. gelatinosus, but the rate of fleeing did not vary with density, as might occur if there was communication among urchins using alarm signals. Our observations suggest that M. gelatinosus presents a stronger predatory threat than H. helianthus. This corresponds to field observations showing that the urchins are more frequently consumed by M. gelatinosus. These are the first field experiments demonstrating distance chemodetection by a marine invertebrate under back-and-forth water flow from wave activity.     

Beyond food: a foundation species facilitates its own predator

Facilitation by foundation species can play a critical role in structuring ecological communities. As environmental stress increases, generally more organisms become dependent on the stress buffering provided by foundation species. As such, foundation species may even facilitate their own predators, an interaction that can influence the functioning and structure of the foundation species population and thereby the facilitated organisms. This work presents a case study on the blue mussels and sea stars, where we tested to what extent a foundation species (i.e. blue mussels) may facilitate its own predator (sea star) when exposed to a gradient of environmental stress (hydrodynamic forces). Amelioration of hydrodynamic stress by mussels facilitated sea stars, allowing them to persist on a soft bottom in highly dynamic environment, which would not be possible in the absence of mussels. Moreover, sea stars continue preying on mussels when environmental stress increases. The results suggest that a foundation species may interact with its own predator beyond the role of food source, by ameliorating environmental stress, creating an additional dependence link between the foundation species and the predator, which potentially has major implications for ecosystem structure and stability.     

The phylogeny of echinoderm classes based on mitochondrial gene arrangements

Summary Previous analyses have demonstrated that, among the echinoderms, the sea star (class: Asteroidea) mitochondrial genome contains a large inversion in comparison to the mitochondrial DNA of sea urchins (class: Echinoidea). Polymerase chain reaction amplification, DNA cloning, and sequencing have been used to examine the relationships of the brittle stars (class: Ophiuroidea) and sea cucumbers (class: Holothuroidea) to the sea stars and sea urchins. The DNA sequence of the regions spanning potential inversion junctions in both brittle stars and sea cucumbers has been determined. This study has also revealed a highly modified tRNA cluster in the ophiuroid mitochondrial genome. Our data indicate mitochondrial gene arrangement patterns that group the sea cucumbers with sea urchins and sea stars with brittle stars. This use of molecular characters clarifies the relationships among these classes.     

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.     

The dynamics of forming an active defensive reflex in cats]

Active defensive reflexes were elaborated in cats with pain stimulations of the forepaw by means of an electrical pricking device with a target attached to it. The elaboration was carried out during action of a flickering light used for the convenience of the EEG analysis. Repeated pain stimulation led to elaboration of an aggressive attacking reaction, chiefly manifested in the paw striking the target. At the beginning of the elaboration, passive-defensive reactions were manifest, which did not completely disappear even after formation of a stable attacking reflex. Two types of active defensive reflexes were elaborated: A-type reflex which helped the animal to get rid of the pain stimulation at the very beginning; B-type reflex which prevented the pain stimulation. The difference beteween these two types is discussed.     

Reduction of attractiveness to the sea star Asterias forbesi (Desor) by the clam Mercenaria mercenaria (Linnaeus)

Both in field and laboratory choice tests, the sea star, Asterias forbesi (Desor), was attracted to distant upstream clams, Mercenaria mercenaria (Linnaeus). Clams exposed to upstream sea stars were chosen less frequently by downstream sea stars than clams without sea stars upstream. Sea stars neither attracted nor repelled downstream conspecifics.When clams were exposed to upstream sea stars, their oxygen consumption decreased, as did their pumping rate and activity (as measured by number of visible siphons). The former may result from one or both of the latter.It is concluded that clam and sea star sense each other over a distance by chemical cues. The response of the clam is a general lowering of activity which may result in decreased attractiveness to sea star predators. This response may serve as a defensive measure against distance detection by Asterias forbesi.     

Effects of substrate on interactions between juvenile sea scallops (Placopecten magellanicus Gmelin) and predatory sea stars (Asterias vulgaris Verrill) and rock crabs (Cancer irroratus Say)

We investigated the effect of substrate (glass bottom, sand, granule, pebble) on predation of juvenile sea scallops (Placopecten magellanicus) by sea stars (Asterias vulgaris) and rock crabs (Cancer irroratus) at two prey sizes (11-15 mm and 24-28 mm shell height), and two prey densities (10 and 30 scallops per aquarium) in laboratory experiments. Specifically, we quantified predation rate and underlying behaviours (proportion of time a predator spent searching for and handling prey, encounter rate between predators and prey, and various outcomes of encounters). We detected a significant gradual effect of particle size of natural substrates on sea star predation: specifically, predation rate on and encounter rate with small scallops tended to decrease with increasing particle size (being highest for sand, intermediate for granule, and lowest for pebble). Substrate type did not significantly affect predation rates or behaviours of sea stars preying on large scallops or of rock crabs preying on either scallop size classes. Other factors, such as prey size and density, were important in the scallop-sea star and scallop-rock crab systems. For example, predation rate by sea stars and crabs and certain sea star behaviours (e.g. probability of consuming scallops upon capture) were significantly higher with small scallops than with large scallops. As well, in interactions between small scallops and sea stars, predation rate and encounter rate increased with prey density, and the proportion of time sea stars spent searching was higher at low prey density than high prey density. Thus, substrate type may be a minor factor determining predation risk of seeded scallops during enhancement operations; prey size and prey density may play a more important role. However, substrate type still needs to be considered when choosing a site for scallop enhancement, as it may affect other scallop behaviours (such as movement).     

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.     

Coelomocyte numbers and expression of HSP70 in wounded sea stars during hypoxia

Hypoxia, mainly caused by eutrophication, is a common and growing problem on marine soft bottoms. Echinoderms are known for their ability to regenerate tissue after wounding but hypoxia has a negative influence on regeneration and also on reproduction in echinoderms. We have investigated the cellular and molecular responses to wounding stress and hypoxia in the sea star Asterias rubens by using the total coelomocyte count (TCC) and the expression of heat shock proteins (HSPs). As early as 1 h after wounding, sea stars under hypoxic conditions show significantly increased TCC and, after 6 h, cell numbers increase approximately two-fold. After a 3-h hypoxia exposure of wounded animals, Western blot analysis reveals highly elevated coelomocyte cytoplasmic HSP70 expression. Non-wounded sea stars exposed to hypoxia and wounded animals kept in normoxia show enhanced HSP70 expression only after 24 h. Immunocytochemical analysis has not demonstrated any translocation of HSP70 from the cytoplasm to the nucleus. We conclude that both wounding and hypoxia elicit a stress response in sea stars and that the combined stress produces synergistic effects that may inhibit the initial processes of wound healing and regeneration.     

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.     

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.     

In-situ investigations on the echinodermAsterias rubens as a predator of soft-bottom communities in the western Baltic Sea

In-situ investigations on the life of the common sea star (Asterias rubens L.) were carried out in 1976, employing the Underwater Laboratory Helgoland in Lübeck Bay (Western Baltic Sea). The abundance ofA. rubens amounted to 2–31 m^–2 on sediment (fine sand), and to 324–809 m^–2 on mobile algal carpets drifting over the bottom. Actual population parameters (abundance, size class distribution) are influenced by both substrate quality and drifting. Stomach investigations revealed prey-size selectivity: Small sea stars feed mainly on the snailHydrobia ulvae when living on the sediment, but on mussel brood(Mytilus edulis) in the phytal. The principal food items of larger sea stars are the sand-dwelling clamMacoma baltica and the phytal-living isopodIdotea baltica respectively.A. rubens is very adaptive to the food available; the diversity of its diet corresponds to the species diversity found in its environment. A change of biotope during active or passive migrations causes switching. The sea star is able to catch motile animals and to dig out infaunal clams. It exhibits a diurnal feeding pattern related to light periodicity; the activity decreases at night. The average frequency of feeding is highly dependent on predator body size; it declines with growth. In-situ experiments indicate an exponential relationship between the feeding duration uponM. baltica and the quotient of clam size to logarithm of sea-star size. An approach is made toward a rough estimate of macrofauna consumption byA. rubens on sediment. The sea star seems to be an important predator and thus a competitor of demersal fishes on soft bottoms of the western Baltic Sea.     

Impacts of sea star predation on mussel bed restoration

Predation by sea stars has the potential to cause elevated levels of mortality in reestablished populations of bivalves relative to levels of recruitment. Recent efforts to restore beds of the nearly extirpated green‐lipped mussel within the Hauraki Gulf, New Zealand, resulted in high abundances of sea stars occupying those beds and it is unknown whether predation poses a potential limitation to the success of restoration in this bivalve species. The contribution of predation by sea stars to the mortality of mussels across four experimental mussel beds over a 2‐year period was estimated using data from regular assessments of sea star abundance and an experimentally determined consumption rate of sea stars upon mussels. In addition, the potential size selection of mussels by sea stars was assessed to determine if large sea stars selected for recent settlers. Sea stars' abundance within the mussel beds grew to an average of 0.57 sea stars/m² within 9 months, remaining at similar levels throughout the study. These predominantly large sea stars were estimated to have consumed 30.1% of the mussels over a 25‐month period, representing a contribution of 40.4% of the mussel mortality. Sea stars predominantly selected for larger mussels, and their predation likely contributes little to any lack in mussel recruitment. Sea star predation is clearly a limiting factor on the survival of transplanted adult mussels and the present study highlights the need to continually assess predation risk to determine if remediation is necessary for the persistence of the restored beds.