Odontaster Validus Research Articles

The abundance and distribution of echinoderms in nearshore hard-bottom habitats near Anvers Island, western Antarctic Peninsula

AbstractEchinoderms are well represented in nearshore hard-bottom (< 100 m depth) habitats along the Antarctic Peninsula where they are presumably important contributors to benthic production, carbon flow, and determinants of community structure. The present study assesses the densities of echinoderms at shallow depths (2–15 m) at five sampling sites within three kilometres of Anvers Island on the central western Antarctic Peninsula. The asteroids Odontaster validus, Granaster nutrix, Lysasterias perrieri and Adelasterias papillosa, two ophiuroids in the Amphiuridae, the holothuroids Psolicrux coatsi and Psolus carolineae and one representative of the Cucumaridae, and the regular echinoid Sterechinus neumayeri were enumerated. Mean total echinoderm densities were high (34.9 individuals m-2) and ranged from 21.9 individuals m-2 for asteroids to 2.7 individuals m-2 for holothuroids. With the exception of a positive relationship between the abundance of the regular echinoid Sterechinus neumayeri and the biomass of the brown alga Himanthothallus grandifolius, no significant relationships were found between the abundance of asteroids, ophiuroids, or holothuroids and two species of brown algae or three algal ecotypes. The present study indicates nearshore hard-bottom echinoderms are important in the carbon cycle and their inherent vulnerability to ocean acidification may have community-level impacts.

Spatial and temporal variation in the heat tolerance limits of two abundant Southern Ocean invertebrates

While, in lower latitudes, population-level differences in heat tolerance are linked to temperature variability, in the Southern Ocean remarkably stable year-round temperatures prevail. Temporal variation in the physiology of Antarctic ectotherms is therefore thought to be driven by the intense seasonality in primary productivity. Here we tested for differences in the acute upper temperature limits (lethal and activity) of 2 Antarctic marine invertebrates (the omnivorous starfish Odontaster validus and the filter-feeding clam Laternula elliptica) across latitude, seasons and years. Acute thermal responses in the starfish (righting and feeding) and clam (burrowing) differed between populations collected at 77°S (McMurdo Sound) and 67°S (Marguerite Bay). Both species displayed significantly higher temperature performance at 67°S, where seawater can reach a maximum of +1.8°C in summer versus ?0.5°C at 77°S, showing that even the narrow spatial and temporal variation in environmental temperature in Antarctica is biologically meaningful to these stenothermal invertebrates. Temporal comparisons of heat tolerance also demonstrated seasonal differences in acute upper limits for survival that were consistent with physiological acclimatisation: lethal limits were lower in winter than summer and higher in warm years than cool years. However, clams had greater inter-annual variation of temperature limits than was observed for starfish, suggesting that variation in food availability is also an important factor, particularly for primary consumers. Teasing out the interaction of multiple factors on thermal tolerance will be important for refining species-specific predictions of climate change impacts.

Chemo-ecological studies on hexactinellid sponges from the Southern Ocean

Hexactinellids (glass sponges) are an understudied class with syncytial organization and poor procariotic associations, thought to lack defensive secondary metabolites. Poriferans, though, are outstanding sources of bioactive compounds; nonetheless, a growing suspicion suggests that many of these chemicals could be symbiont-derived. In Polar latitudes, sponges are readily invaded by diatoms, which could provide natural products. Hexactinellids are typical of deep waters; but in Antarctica, they dominate the upper shelf providing shelter and food supply to many opportunistic mesograzers and macroinvertebrates, which exert strong ecological pressures on them. Aiming to examine the incidence of defensive activities of hexactinellids against consumption, feeding experiments were conducted using their lipophilic fractions. Antarctic hexactinellid and demosponge extracts were tested against the asteroid Odontaster validus and the amphipod Cheirimedon femoratus as putative sympatric, omnivorous consumers. Hexactinellids yielded greater unpalatable activities towards the amphipod, while no apparent allocation of lipophilic defenses was noted. After chemical analyses on the lipophilic fractions from these Antarctic glass sponges, quite similar profiles were revealed, and no peculiar secondary metabolites, comparable to those characterizing other poriferans, were found. Instead, the lipidic compounds 5α(H)-cholestan-3-one and two glycoceramides were isolated for their particular outspread presence in our samples. The isolated compounds were further assessed in asteroid feeding assays, and their occurrence was evaluated for chemotaxonomical purposes in all the Antarctic samples as well as in glass sponges from other latitudes by NMR and MS. Characteristic sphingolipids are proposed as chemical markers in Hexactinellida, with possible contributions to the classification of this unsettled class.

Erratum to: Multi-year observations on the gametogenic ecology of the Antarctic seastar Odontaster validus

Due to an unfortunate error, the original version of this article has been published with an error in the reference citation. It should be Brockington et al. (2007) instead of Brockington et al. (2006).

Chemical defenses of tunicates of the genus Aplidium from the Weddell Sea (Antarctica)

Predation and competition are important factors structuring Antarctic benthic communities and are expected to promote the production of chemical defenses. Tunicates are subject to little predation, and this is often attributed to chemical compounds, although their defensive activity has been poorly demonstrated against sympatric predators. In fact, these animals, particularly the genus Aplidium, are rich sources of bioactive metabolites. In this study, we report the natural products, distribution and ecological activity of two Aplidium ascidian species from the Weddell Sea (Antarctica). In our investigation, organic extracts obtained from external and internal tissues of specimens of A. falklandicum demonstrated to contain deterrent agents that caused repellency against the Antarctic omnivorous predator, the sea star Odontaster validus. Chemical analysis performed with Antarctic colonial ascidians Aplidium meridianum and Aplidium falklandicum allowed the purification of a group of known bioactive indole alkaloids, meridianins A-G. These isolated compounds proved to be responsible for the deterrent activity.

Overview of the Chemical Ecology of Benthic Marine Invertebrates along the Western Antarctic Peninsula

Thirteen years ago in a review that appeared in the American Zoologist, we presented the first survey of the chemical and ecological bioactivity of Antarctic shallow-water marine invertebrates. In essence, we reported that despite theoretical predictions to the contrary the incidence of chemical defenses among sessile and sluggish Antarctic marine invertebrates was widespread. Since that time we and others have significantly expanded upon the base of knowledge of Antarctic marine invertebrates' chemical ecology, both from the perspective of examining marine invertebrates in new, distinct geographic provinces, as well as broadening the evaluation of the ecological significance of secondary metabolites. Importantly, many of these studies have been framed within established theoretical constructs, particularly the Optimal Defense Theory. In the present article, we review the current knowledge of chemical ecology of benthic marine invertebrates comprising communities along the Western Antarctic Peninsula (WAP), a region of Antarctica that is both physically and biologically distinct from the rest of the continent. Our overview indicates that, similar to other regions of Antarctica, anti-predator chemical defenses are widespread among species occurring along the WAP. In some groups, such as the sponges, the incidence of chemical defenses against predation is comparable to, or even slightly higher than, that found in tropical marine systems. While there is substantial knowledge of the chemical defenses of benthic marine invertebrates against predators, much less is known about chemical anti-foulants. The sole survey conducted to date suggests that secondary metabolites in benthic sponges are likely to be important in the prevention of fouling by benthic diatoms, yet generally lack activity against marine bacteria. Our understanding of the sensory ecology of Antarctic benthic marine invertebrates, despite its great potential, remains in its infancy. For example, along the WAP, community-level non-consumptive effects occur when amphipods chemically sense fish predators and respond by seeking refuge in chemically-defended macroalgae. Such interactions may be important in releasing amphipods from predation pressure and facilitating their unusually high abundances along the WAP. Moreover, recent studies on the sensory biology of the Antarctic keystone sea star Odontaster validus indicate that chemotactile-mediated interactions between conspecifics and other sympatric predatory sea stars may have significant ramifications in structuring community dynamics. Finally, from a global environmental perspective, understanding how chemical ecology structures marine benthic communities along the WAP must increasingly be viewed in the context of the dramatic impacts of rapid climatic change now occurring in this biogeographic region.

Starvation and chemoreception in antarctic benthic invertebrates

Sensitivity (chemoreception) to different amino acids was studied in six invertebrate species: Serolis polita, Glyptonotus antarcticus, Abyssochromene plebs, Waldeckia obesa, Odontaster validus, and Sterechinus neumayeri. The sensitivity was estimated by the changes in basic metabolism (respiration rate). Starvation increased the sensitivity in all the species. The metabolism rates increased in the presence of L-glutamic acid in G. antarcticus, A. plebs, O. validus, and S. neumayeri. The serine and arginine amino acids had a significant impact on the metabolism of the necrophagous species S. polita and W. obesa. The chemical information may be mediated by means of L-glutamic acid via glutamate receptors, which can be blocked by kynurenic acid, as occurs in the experiments with G. antarcticus and A. plebs.

The effects of temperature on the behaviour of the Antarctic sea star Odontaster validus

The effects of temperature on the behaviour of the Antarctic sea starOdontaster validusMany Antarctic marine benthic invertebrates are adapted to specific environmental conditions (e.g.low stable temperatures, high salinity and oxygen content). Changes caused by global climatic shifts can be expected to have significant impact on their physiology and distribution.Odontaster validus, an ubiquitous, omnivorous sea star is one of the "keystone species" in the Antarctic benthic communities. Laboratory experiments were carried out to study the effect of temperature rise (from 0 to 5°C) on some vital biological functions that sea stars must perform in order to survive in their environment. Parameters such as behavioural reaction of sea stars to food and food odour, locomotory performance and ability to right were measured. Temperature increase significantly impaired the ability ofO. validusto perform these functions (e.g.lowering the number of sea stars able to right, increasing time-to-right, reducing locomotory activity, weakening chemosensory reaction to food and food odour). At temperatures of 4 and 5°C a loss of motor coordination was observed, although at all tested temperatures up to 5°C there were single individuals performing successfully.

Field studies on deterrent properties of phlorotannins in Antarctic brown algae

Abstract Antiherbivore effects of phlorotannins from eight common Antarctic brown algae were tested with three omnivorous sympatric grazers, the fish Notothenia coriiceps, the sea star Odontaster validus, and the amphipod Gondogeneia antarctica. Incidence of grazing deterrence overall was relatively low, with only a few algal species deterring each of the grazers, and with phlorotannins from different algae active against different grazers. Most activity was found in Desmarestia menziesii and Cysto-sphaera jacquinotii, which deterred two out of the three grazers, while D. anceps and Himantothallus grandifolius deterred only one grazer type each. Only weak antimicrobial effects were detected in all phlorotannin extracts against four Antarctic bacterial strains, with phlorotannins of D. anceps and Phaeurus antarcticus having the strongest effects. Phlorotannin extracts of all brown algal species tested caused strong in vitro mortality in a fouling diatom. The ecological significance of this activity remains to be tested. While the bulk tissue phlorotannin concentrations likely overestimate naturally occurring surface concentrations encountered by foulers in situ, fouler settlement may be deterred at much lower concentrations than those eliciting mortality. Overall, Antarctic phlorotannin deterrent properties were specific both to the algal species as well as the grazer, bacteria and diatom taxa tested. For grazer deterrence, we propose that, for each of the tested grazers, complex interactions between phlorotannin chemical properties and grazer digestive characteristics may determine the effectiveness of specific phlorotannins. Larger generalizations of phlorotannin-grazer patterns such as distinction between meso- and macrograzers may not be valid, at least not for Antarctic brown algal phlorotannins.

Palatability and chemical defenses of sponges from the western Antarctic Peninsula

The present study surveyed the palatability of all sponge species that could be collected in sufficient quantities in a shallow-water area along the western Antarctic Peninsula. Of 27 species assayed, 78% had outermost tissues that were significantly unpalatable to the sympatric, omnivorous sea star Odontaster validus. Of those species with unpalatable outer tissues, 62% had inner tissues that were also unpalatable to the sea stars. Sea stars have often been considered as the primary predators of sponges in other regions of Antarctica, and their extra-oral mode of feeding threatens only the outermost sponge tissues. The observation that many of the sponges allocate defenses to inner tissues suggests the possibility that biting predators such as mesograzers, which could access inner sponge layers, may also be important in communities along the Antarctic Peninsula. In feeding bioassays with extracts from 12 of the unpalatable species in artificial foods, either lipophilic or hydrophilic extracts were deterrent in each species. These data indicate an overall level of chemical defenses in these Antarctic sponges that is comparable to, and slightly greater than, that found in a previous survey of tropical species.

Illudalane Sesquiterpenoids of the Alcyopterosin Series from the Antarctic Marine Soft Coral Alcyonium grandis

Chemical investigation of the lipophilic extract of the Antarctic soft coral Alcyonium grandis led us to the finding of nine unreported sesquiterpenoids, 2-10. These molecules are members of the illudalane class and in particular belong to the group of alcyopterosins, illudalanes isolated from marine organisms. The structures of 2-10 were determined by interpretation of spectroscopic data. Repellency experiments conducted using the omnivorous Antarctic sea star Odontaster validus revealed a strong activity in the lipophilic extract of A. grandis against predation.

Intraspecific agonistic arm-fencing behavior in the Antarctic keystone sea star Odontaster validus influences prey acquisition

The importance of intraspecific social behaviors in mediating foraging behaviors of marine invertebrate keystone predators has received little attention. In laboratory investigations employing time-lapse video, we observed that the keystone Antarctic sea star Odontaster validus dis- plays frequent agonistic arm-fencing bouts with conspecifics when near prey (injured sea urchin). Arm-fencing bouts consisted of 2 individuals elevating the distal portion of an arm until positioned arm tip to arm tip. This was followed by intermittent or continuous arm to arm contact, carried out in attempts to place an arm onto the aboral (upper) surface of the opponent. Fifteen (79%) of the 19 bouts observed occurred near prey (mean ± 1 SE, 13 ± 1.6 cm distance to prey; n = 13). These bouts lasted 21.05 ± 2.53 min (n = 15). In all 5 bouts that involved a large individual (radius, R: distance from the tip of an arm to the center of the oral disk; 45 to 53 mm) competing with either a medium (R = 35 to 42 mm) or small (R = 25 to 32 mm) individual, the large sea star prevailed. The only exception occurred in 2 instances where a medium-sized sea star had settled onto prey and was subsequently challenged by a larger individual. Here, the outcomes were reversed in favor of the medium-sized individuals. These complex social behaviors mediating intraspecific competition for the acquisition of prey by a keystone predator are likely to have significant ramifications in terms of individual fitness, population structure, and community composition.

Ecological stoichiometry in six species of Antarctic marine benthos

Elemental (C, N, P) composition was examined in 6 benthic marine invertebrates from Antarctica: 2 suspension feeders (the holothurian Heterocucumis steineni and the polychaete Thele- pus cincinnatus), 1 epifaunal grazer (the limpet Nacella concinna), 1 deposit feeder (the polychaete Flabelligera mundata), 1 predator (the nemertean Parborlasia corrugatus) and an omnivore (the asteroid Odontaster validus). Correction for inorganic carbon was necessary only for O. validus, where skeletal carbonate produces a high mineral ash content. Elemental composition of tissue was 49 to 60% C, 10 to 14% N and 0.7 to 1.3% P (all on an organic mass basis); these are all within the normal range of values for aquatic invertebrates. The most variable component was P, though vari- ability was much lower than in stream insects. Stoichiometric molar ratios (C:P, C:N, N:P) were all typical of consumers, with a strong inverse relationship across species between %C and %N in tis- sue. Stoichiometry varied strongly between phyla, with less variation between species within phyla. There were also indications of variations in elemental composition (C:N ratio and %P) with feeding mode, but the limited range of taxa studied constrains this conclusion. Despite differences in nutrient status, the elemental composition of marine and freshwater benthos were, with the exception of insects, closely similar. Despite the very slow growth rates that characterise polar marine benthos, P contents were relatively high, suggesting that the predictions of the growth rate hypothesis are not upheld at low temperatures.

A laboratory study of behavioral interactions of the Antarctic keystone sea star Odontaster validus with three sympatric predatory sea stars

The circumpolar sea star Odontaster validus is ubiquitous in the nearshore marine benthos of Antarctica. Despite its ecological importance, little is known of its behavioral interactions with other common sympatric sea stars. To examine these interactions we employed time-lapse video analyses conducted in a large laboratory tank (1.8 m diameter circular tank, 1,629 L). In each experimental trial, 34 adult O. validus were placed in a tight circular grouping on one side of the tank, and one adult individual of one of three common sympatric species of predatory sea star (Labidiaster annulatus, Diplasterias brandti, or Perknaster aurorae) was placed on the opposite side of the tank. Digital images of sea star movements were then captured at one min intervals over a 24 h period and aspects of sea star movements subsequently analyzed. Each 24 h treatment was replicated three times, as was a control treatment consisting only of O. validus. O. validus had significantly elevated levels of activity in the presence of P. aurorae when compared with the other two sea stars (potential chemically mediated response), and displayed a distinct “flight response” (change in direction and twofold to sixfold increase of speed) upon tactile contact with this species. Moreover, an “alarm response” was detected when individuals of O. validus that encountered a fleeing conspecific also fled the vicinity. In contrast, our results indicated that O. validus displays virtually no chemical or tactile behavioral responses to the large multi-armed L. annulatus and only weak tactile responses to D. brandti.

Temperature limits to activity, feeding and metabolism in the Antarctic starfish Odontaster validus

Cold-blooded Antarctic marine species are highly stenothermal and possibly the most temperature-sensitive group on Earth. Studies to date have produced upper lethal temperatures in the range of 4 to 10 degrees C. Although invertebrates have not been acclimated to temperatures above 3 degrees C, some Antarctic fish have been acclimated to 4 degrees C. Activity competence has been evaluated in several Antarctic marine invertebrates and shown to be very sensitive to temperature, with 50% failures in the range of 1 to 3 degrees C for clams, limpets and scallops. The starfish Odontaster validus is much more capable of coping with elevated temperatures than any of these species. Turning speed increased with temperature, reaching a maximum at 7.5 degrees C. Temperature increase led to a clear hierarchy of response loss in the starfish, with lethal limits occurring at a higher temperature (15 degrees C) than loss of activity (9 degrees C) and loss of feeding competence (Specific Dynamic Action, or SDA) and coelomic oxygen level collapse both occurring at 6 degrees C. The higher temperature limit for activity than coelomic oxygen level could be explained by body design or taxonomic factors, which may also explain the markedly enhanced ability to cope with elevated temperature over other Antarctic marine species. Long-term acclimation and survival up to 6 degrees C should be possible for this species, which is important for species living on the west coast of the Antarctic Peninsula, possibly the fastest warming marine environment on Earth. The markedly higher resistance to elevated temperature and maintenance of function in a common Antarctic predator compared to the abilities of several of its prey species suggests that a warming environment could have dramatic consequences on the community-level ecological balance for large areas of the Antarctic benthos.

Lack of an HSP70 heat shock response in two Antarctic marine invertebrates

Members of the HSP70 gene family comprising the inducible (HSP70) genes and GRP78 (glucose-regulated protein 78 kDa) were identified in an Antarctic sea star (Odontaster validus) and an Antarctic gammarid (Paraceradocus gibber). These genes were surveyed for expression levels via Q-PCR after an acute 2-hour heat shock experiment in both animals and a time course assay in O. validus. No significant up-regulation was detected for any of the genes in either of the animals during the acute heat shock. The time course experiment in O. validus produced slightly different results with an initial down regulation in these genes at 2°C, but no significant up-regulation of the genes either at 2 or 6°C. Therefore, the classical heat shock response is absent in both species. The data is discussed in the context of the organisms’ thermal tolerance and the applicability of HSP70 to monitor thermal stress in Antarctic marine organisms.

Natural variability and distribution of trace elements in marine organisms from Antarctic coastal environments

AbstractIn an attempt to improve the understanding of the natural variability and distribution of trace elements in Antarctic organisms, the concentrations of arsenic, cadmium, cobalt, chromium, copper, manganese, nickel, vanadium and zinc in representative benthic species from two pristine coastal environments were measured and compared with literature data for other uncontaminated coastal ecosystems. Correlations between the elements, differences between the species and between the sampling sites were examined by principal component analysis. Metal accumulation was particularly evident in the tissues of the sea star Odontaster validus, the bivalve mollusc Laternula elliptica and in the red alga Phyllophora antarctica. However, metal accumulation was not the same for all the analytes, but, rather, depended on the organism characteristics. In particular, the soft tissues of Odontaster validus were characterized by high concentrations of cadmium, zinc and copper, those of Phyllophora antarctica by high concentrations of manganese and nickel, and the tissues of Laternula elliptica by high concentrations of all measured elements, particularly in its digestive gland. The Antarctic data as well as those reported for other pristine coastal ecosystems showed remarkably high natural variability in metal content, which must be taken into account when interpreting results from biomonitoring programmes.

RESPOSTA IMUNE INESPECÍFICA DE ANIMAIS ECTOTÉRMICOS ANTÁRTICOS SOB TEMPERATURAS POLARES

Normal 0 21 false false false MicrosoftInternetExplorer4 /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Tabela normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-parent:""; mso-padding-alt:0cm 5.4pt 0cm 5.4pt; mso-para-margin:0cm; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:"Times New Roman"; mso-ansi-language:#0400; mso-fareast-language:#0400; mso-bidi-language:#0400;} This review presents data on nonspecific immune system of Antarctic metazoans poekiloterms. The phagocytosis, inflammation and wound repair were analysed in Antarctic animals, the big head fish ( Notothenia coriiceps = N. neglecta ), Antarctic starfish ( Odontaster validus ) and in Antarctic sea urchin (Sterechinus neumayeri ).

Fish blood as a chemical signal for Antarctic marine invertebrates

Chemical cues released from dead or injured organisms constitute important signals informing nearby animals about a feeding possibility. The ability to detect the signal, evaluate its meaning and locate its source can help organisms to exploit food resources efficiently, which is especially important to animals living in environments with limited food supply. Experiments were carried out to study the behavioral responses of several Antarctic benthic invertebrates to fish (Notothenia corriceps) blood. Necrophagous species such as sea stars Odontaster validus and Lysasterias sp., amphipod Waldeckia obesa and nemertean Parborlasia corrugatus responded to fish blood with changes in their behavior. The behavior common to all these species was locomotion directed towards the stimulus source. Behavioral components consistent with food consumption were observed in O. validus and P. corrugatus. The reaction of herbivorous limpets Nacella concinna to fish blood depended on the animal size. Large (>10 mm) limpets showed no behavioral response, whereas small ones (<10 mm) reacted to the stimulus by moving a short distance away. These results indicate that blood released from the tissues of injured or dead animals may be an important chemical signal for organisms belonging to different taxa.

Multi-year observations on the gametogenic ecology of the Antarctic seastar Odontaster validus

This study reports the first multi-year observations on the reproductive patterns for an Antarctic predator/scavenger, Odontaster validus (Koehler 1912). Seastars were collected monthly from a shallow site (15–20 m depth) near the British Antarctic Survey (BAS) Rothera Research Station (Adelaide Island, 67°34′S 68°08′W) from July 1997 to January 2001. Reproductive condition, oocyte size frequencies and spermatogenesis were examined in at least ten seastars each month using histological and image analysis techniques. Gonad indices (GI) and pyloric caeca indices (PI) were also examined in the same samples. Female and male GIs varied seasonally, in parallel with a reduction in the proportion of large oocytes and mature sperm in the gonad in August to mid-October following winter spawning. Despite there being remarkable consistency in the timing of spawning from year to year, differences in the reproductive condition of individuals were apparent. Patterns in the digestive tissues also varied with season, peaking in December and reaching a minimum in February in two of the three study years. This weaker annual pattern may partly reflect the varied diet of this predator/scavenger species, which is not directly dependant on the timing and magnitude of the annual phytoplankton bloom. Pooled oocyte size distributions and residual analysis suggested that oogenesis progressed over 18–24 months, with the largest of the two size classes (maximum diameter = 183 μm) being spawned annually. This pattern of oocyte growth and spawning was previously reported in the early 1960s for an O. validus population from McMurdo Sound, which lies south of Rothera by 10° latitude. The extremely catholic diet of this predator/scavenger suggests the reproductive patterns of the seastar will be less susceptible to changes in food supply compared to polar suspension feeders or deposit feeders.