Feeding repellence of Antarctic and sub-Antarctic benthic invertebrates against the omnivorous sea star Odontaster validus

Antarctic and sub-Antarctic benthic invertebrates are subjected to intense predation by mobile macroinvertebrates. Accordingly, chemical protection as well as other defensive mechanisms are expected to be common in organisms inhabiting these ecosystems. In order to evaluate anti-predation activities and allocation of chemical defenses within the anatomy of marine benthic Antarctic and sub-Antarctic invertebrates, 55 species were tested for feeding repellence against the sea star Odontaster validus, a common eurybathic sympatric predator. The invertebrates tested were collected from the deep waters of two poorly surveyed areas in terms of chemical ecology studies: the eastern Weddell Sea (Antarctica) and the vicinities of Bouvet Island (sub-Antarctica). Experiments were conducted at the Spanish Antarctic Base in Deception Island. In the feeding deterrence experiments, shrimp pieces were treated with crude lipophilic fractions obtained from each species, and were offered to the sea stars. A total of 29 species (53 %) from 7 different phyla (Porifera, Cnidaria, Chordata, Bryozoa, Echinodermata, Mollusca, and Annelida) showed feeding repellence against O. validus, and are therefore chemically protected against this keystone predator. Furthermore, 25 species were dissected into parts to investigate the possible allocation of defensive compounds. Some of the results obtained from these analyses support the prediction that the most exposed/vulnerable tissues concentrate chemical defenses to avoid predation against the sea stars. In summary, the results obtained in our survey support the hypothesis that deep-water Antarctic and sub-Antarctic benthic invertebrates are well protected chemically against sympatric predators, similarly to what has been reported in previous studies investigating shallow-water Antarctic species.     

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.     

Effects of reduced seawater pH on fertilisation, embryogenesis and larval development in the Antarctic seastar Odontaster validus

The effects of ocean acidification will be pronounced in high-latitude marine communities, although little is known on how reproduction in free-spawning polar invertebrates will respond. Using the circum-Antarctic sea star Odontaster validus, we examined fertilisation, larval survival and development under a controlled seawater treatment (temperature = ?0.5 °C, pH 8.1, pCO₂(aq) = 326.6 μatm, TA = 2,274.2 μmol kg soln^?1), two near-future pH treatments (pH 7.8 and 7.6) and an extreme treatment (pH 7.0). At a sperm concentration of 3.5 × 10⁵ sperm ml^?1, percentage of fertilisation was 98–90 % across a pH 8.1–7.0 range. At near-future pH ranges (pH 7.8 and 7.6), fertilisation was not significantly lower than in the control pH 8.1 except at the lowest sperm concentration (2.2 × 10³ sperm ml^?1) where fertilisation was reduced to 60 and 61 % in pH 7.6 and 7.8, respectively. Larval survival was not significantly affected by a decrease in pH of 0.3 units, but at pH 7.6 survival was significantly reduced. This difference was apparent at 9 days, and at the end of the experiment at 58 days, survival was 55 % compared with 85 % in the ambient treatment. Near-future changes to pH yielded smaller larvae, a result of both subtle differences in their morphology and slowed development rates, while larvae at pH 7.0 showed evidence of abnormal development. O. validus fertilisation and larval success declines in seawater pH conditions expected in coastal Antarctica over the coming decades, although the responses observed are within the range observed in warmer-water echinoderms.     

Chemical Composition of the Antarctic Starfish Odontaster validus (Koehler 1911) and Its Reactions to Glutamic and Kynurenic Acids

The protein content in the dry body weight of the starfish Odontaster validus is 30%. The composition of amino acids is characterized by a very high level of glycine (27%). Glutamic acid (Glu) in a concentration of 10 mM/liter in seawater causes an increase in the metabolic rate of starved O. validus. As the period of starvation increases, this reaction is enhanced. A two-hour exposure to kynurenic acid (Kyn) in a concentration of 0.1 mM/liter blocks the reaction to glutamic acid.     

First immunocytochemical study of echinoderm smooth muscle: the Antarctic cushionstar Odontaster validus Koehler (Echinodermata,Asteroidea)

Summary.  Our immunocytochemical observations reveal that the muscle present in the tips of the arms of the Antarctic cushionstar Odontaster validus contains caldesmon and calponin but not troponin. Thus, the muscle clearly belongs to the smooth muscle category. Distributions of contractile proteins such as actin, myosin (the latter a typical vertebrate muscle filament protein), paramyosin, and miniparamyosin (the latter two being characteristic of thick invertebrate muscle filaments) were also determined immunocytochemically. The results suggest that the thin filaments of the starfish smooth muscle are similar to those of the vertebrate muscle, but that the thick filaments differ from those of vertebrates and possess traits that are also seen in the muscle organization of invertebrates. The absence from the O. validus muscle of titin and nebulin, proteins so far known almost exclusively from the striated vertebrate muscle, comes as no surprise, but immunoreactivity to mini-titin (a protein of the same family as titin and its replacement in invertebrates) was strong and unambiguously recognizable between filaments. Odontaster validus' histochemical characteristics may be a reflection of the phylogenetic position of the echinoderms as deuterostome invertebrates or they may express an adaptation of the muscle to the harsh environmental conditions under which it has to function in the Antarctic water. Received June 6, 2002; accepted September 17, 2002; published online March 11, 2003     

Parameter Estimations of Dynamic Energy Budget (DEB) Model over the Life History of a Key Antarctic Species: The Antarctic Sea Star Odontaster validus Koehler, 1906

Marine organisms in Antarctica are adapted to an extreme ecosystem including extremely stable temperatures and strong seasonality due to changes in day length. It is now largely accepted that Southern Ocean organisms are particularly vulnerable to global warming with some regions already being challenged by a rapid increase of temperature. Climate change affects both the physical and biotic components of marine ecosystems and will have an impact on the distribution and population dynamics of Antarctic marine organisms. To predict and assess the effect of climate change on marine ecosystems a more comprehensive knowledge of the life history and physiology of key species is urgently needed. In this study we estimate the Dynamic Energy Budget (DEB) model parameters for key benthic Antarctic species the sea star Odontaster validus using available information from literature and experiments. The DEB theory is unique in capturing the metabolic processes of an organism through its entire life cycle as a function of temperature and food availability. The DEB model allows for the inclusion of the different life history stages, and thus, becomes a tool that can be used to model lifetime feeding, growth, reproduction, and their responses to changes in biotic and abiotic conditions. The DEB model presented here includes the estimation of reproduction handling rules for the development of simultaneous oocyte cohorts within the gonad. Additionally it links the DEB model reserves to the pyloric caeca an organ whose function has long been ascribed to energy storage. Model parameters described a slowed down metabolism of long living animals that mature slowly. O. validus has a large reserve that—matching low maintenance costs- allow withstanding long periods of starvation. Gonad development is continuous and individual cohorts developed within the gonads grow in biomass following a power function of the age of the cohort. The DEB model developed here for O. validus allowed us to increase our knowledge on the ecophysiology of this species, providing new insights on the role of food availability and temperature on its life cycle and reproduction strategy.     

The role of sea ice in structuring Antarctic ecosystems

Summary This paper focusses on the links between growth, persistence and decay of sea ice and the structure of Antarctic marine ecosystems on different spatial and temporal scales. Sea-ice growth may divide an oceanic ecosystem into two dissimilar compartments: (1) the water column, with primary production controlled by the reduction of irradiative fluxes due to the snow-laden sea-ice cover and thermo-haline convection, and (2) the pore space within the ice with incorporated organisms switching from a planktonic to a kryohaline mode of life. In the ice, physical boundary conditions are set by (1) the irradiance which is controlled by the optical properties of snow and ice and (2) the ambient temperature which controls salinity and brine volume. Partly due to the high levels of biomass within the sea-ice system, interaction between different groups of organisms concentrates on the planar environment predefined by the ice cover. As a result of regional structuring of ecosystems, four sea-ice regimes may be recognized: seasonal pack ice, coastal zone, perennial pack ice, and marginal ice zone. These regimes are interwoven through the temporal structuring of ecosystems brought about by ice-cover seasonality and ice drift. In comparison with open-water pelagic ecosystems, sea ice appears of particular importance as it partly inverts the ecosystem structure and enhances the degree of ecological variability.Data presented here were collected during the European Polarstern Study (EPOS) sponsored by the European Science Foundation     

Mycosporine-like amino acids in Antarctic sea ice algae,and their response to UVB radiation

Mycosporine like amino acids (MAAs) were detected in low concentration in sea ice algae growing in situ at Cape Evans, Antarctica. Four areas of sea ice were covered with plastics of different UV absorption exposing the bottom- ice algal community to a range of UV doses for a period of 15 days. Algae were exposed to visible radiation only; visible + UV radiation; and visible + enhanced UV radiation. MAA content per cell at the start of the experiment was low in snow-covered plots but higher in samples from ice with no snow cover. During the study period, the MAA content per cell reduced in all treatments, but the rate of this decline was less under both ambient UV and visible radiation than under snow covered plots. While low doses of UVB radiation may have stimulated some MAA production (or at least slowed its loss), relatively high doses of UVB radiation resulted in almost complete loss of MAAs from ice algal cells. Despite this reduction in MAA content per cell, the diatoms in all samples grew well, and there was no discernible effect on viability. This suggests that MAAs may play a minor role as photoprotectants in sea ice algae. The unique structure of the bottom ice algal community may provide a self-shading effect such that algal cells closest to the surface of the ice contain more MAAs than those below them and confer a degree of protection on the community as a whole.     

Rapid microbial metabolism of non-protein amino acids in the sea

The non-protein amino acids, -alanine and -aminobutyric acid, frequently dominate the amino acid composition of deep-sea sediments. This accumulation is most likely due to the slower decomposition of non-protein amino acids by microorganisms or to the preferential adsorption of non-protein amino acids by clay minerals. We investigated relative rates of heterotrophic uptake of alanine, -ala, and -aba in sea water to see if there were different rates of microbial assimilation and respiration between these protein and non-protein amino acids. Heterotrophic uptake was rapid for all three amino acids with turnover times of hours in productive coastal waters and days in more oligotrophic open-ocean waters. Uptake of the non-protein amino acids was significantly slower than uptake of alanine, particularly in anoxic waters. However, the difference in uptake rates is probably not great enough to cause significant preferential accumulation of non-protein amino acids.     

The role of omnivorous crayfish in littoral communities

Large omnivorous predators may play particularly important roles determining the structure of communities because of their broad diets and simultaneous effects on multiple trophic levels. From June 2001 to June 2002 we quantified community structure and ecosystem attributes of six newly establishing freshwater ponds (660 m² each) after populations of omnivorous crayfish (Orconectes virilis) were introduced to three of the ponds. Crayfish preyed heavily on fish eggs in this experiment, which reduced recruitment of young-of-year fish. This effect indirectly enhanced zooplankton biomass in crayfish ponds. Phytoplankton abundance exhibited a more complex pattern and was probably influenced by non-trophic (e.g., bioturbation) effects of crayfish. Peak dissolved oxygen levels were lower in the crayfish ponds indicating that they had lower primary production: respiration ratios. Metaphytic algae were strongly affected by crayfish presence; filamentous greens quickly disappeared and the blue-green Gleotrichia (a less preferred food item) eventually dominated the composition in crayfish ponds. Chara vulgaris and vascular macrophytes established 34% cover in control ponds by June 2002, but were not able to establish in crayfish ponds. Two important periphyton herbivores (tadpoles and gastropods) were absent or significantly reduced in the crayfish ponds, but periphyton differences were temporally variable and not easily explained by a simple trophic cascade (i.e., crayfish—snails and tadpoles—periphyton). Our results indicate that crayfish can have dramatic direct and indirect impacts on littoral pond communities via feeding links with multiple trophic levels (i.e., fish, invertebrates, and plants) and non-trophic activities (bioturbation). Although the effects of omnivorous crayfish on littoral communities can be large, their complex effects do not fit neatly into current theories about trophic interactions or freshwater community structure.     

Modification in amino acids of dead sea scroll parchments

Fragments of Dead Sea Scroll Parchments were extracted for collagen and subjected to amino acid analysis. In modern parchment samples, 90% or more of the protein could be extracted in hot aqueous solution as collagen. In the ancient specimens, 70% or less was extractable. The hot-solution insoluble material was analyzed for collagen. In the soluble extract, the quantity of tyrosine, histidine, and methionine was reduces. Dityrosine was dected. The need to extend such studies is discussed.     

The role of excitatory amino acids in synaptic transmission in the hippocampus

We have highlighted some aspects of the action of excitatory amino acid transmission in the hippocampus. Fast epsps can be blocked by CNQX to reveal a component of synaptic transmission which is mediated by NMDA receptors. Extracellular recordings of ionic activities show that NMDA and non-NMDA ionophores are permeable to the major monovalent cations, while NMDA ionophores also appear to be permeable to Ca2+. Interactions of agonists applied by iontophoresis may be correlates of phenomena such as LTP, which can be evoked by appropriate synaptic stimulation.     

The multifaceted role of aspartate-family amino acids in plant metabolism

Plants represent the major sources of human foods and livestock feeds, worldwide. However, the limited content of the essential amino acid lysine in cereal grains represents a major nutritional problem for human and for livestock feeding in developed countries. Optimizing the level of lysine in cereal grains requires extensive knowledge on the biological processes regulating the homeostasis of this essential amino acid as well as the biological consequences of this homeostasis. Manipulating biosynthetic and catabolic enzymes of lysine metabolism enabled an enhanced accumulation of this essential amino acid in seeds. However, this approach had a major effect on the levels of various metabolites of the tricarboxylic acid (TCA) cycle, revealing a strong interaction between lysine metabolism and cellular energy metabolism. Recent studies discussed here have shed new light on the metabolic processes responsible for the catabolism of lysine, as well as isoleucine, another amino acid of the aspartate-family pathway, into the TCA cycle. Here we discuss progress being made to understand biological processes associated with the catabolism of amino acids of the aspartate-family pathway and its importance for optimal improvement of the nutritional quality of plants.     

The biota of Antarctic pack ice in the Weddell sea and Antarctic Peninsula regions

Summary Pack ice surrounding Antarctica supports rich and varied populations of microbial organisms. As part of the Antarctic Marine Ecosystem Research in the Ice Edge Zone (AMERIEZ) studies, we have examined this community during the late spring, autumn, and winter. Although organisms are found throughout the ice, the richest concentrations often occur in the surface layer. The ice flora consists of diatoms and flagellates. Chrysophyte cysts (archaeomonads) of unknown affinity and dinoflagellate cysts are abundant and may serve as overwintering stages in ice. The ice fauna includes a variety of heterotrophic flagellates, ciliates, and micrometazoa. The abundance of heterotrophs indicates an active food web within the ice community. Ice may serve as a temporary habitat or refuge for many of the microbial forms and some of these appear to provide an inoculum for planktonic populations when ice melts. Larger consumers, such as copepods and the Antarctic krill, Euphausia superba are often found on the underside of ice floes and within weathered floes. The importance of the ice biota as a food resource for these pelagic consumers is unknown.     

Recognition of amino acids in solution: The role of the hydrophobic forces

Theoretical results for molecular structures and solvation clusters have been used for an interpretation of the experimental observations on the selectivity of an amino acid-sensitive cell in the adult Colorado beetle. As a consequence, it is postulated that strong polar interactions (involving the charged groups-NH ₃ ⁺ and -COO^–), given the appropriate steric conditions, make the determining contribution toward the anchoring of the substrate to the receptor, while the hydrophobic forces are responsible for the specificity.