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Marine Food Webs (marine + food_web)
Selected AbstractsBioactive aldehydes from diatoms block the fertilization current in ascidian oocytesMOLECULAR REPRODUCTION & DEVELOPMENT, Issue 1 2003Elisabetta Tosti Abstract The effects of bioactive aldehydes from diatoms, unicellular algae at the base of the marine food web, were studied on fertilization and early development processes of the ascidian Ciona intestinalis. Using whole-cell voltage clamp techniques, we show that 2- trans -4- trans -decadienal (DD) and 2- trans -4- cis -7- cis -decatrienal (DT) inhibited the fertilization current which is generated in oocytes upon interaction with the spermatozoon. This inhibition was dose-dependent and was accompanied by inhibition of the voltage-gated calcium current activity of the plasma membrane. DD and DT did not inhibit the subsequent contraction of the cortex. Moreover, DD specifically acted as a fertilization channel inhibitor since it did not affect the steady state conductance of the plasma membrane or gap junctional (GJ) communication within blastomeres of the embryo. On the other hand, DD did affect actin reorganization even though the mechanism of action on actin filaments differed from that of other actin blockers. Possibly this effect on actin reorganization was responsible for the subsequent teratogenic action on larval development. The effect of DD was reversible if oocytes were washed soon after fertilization indicating that DD may specifically target certain fertilization mechanisms. Thus, diatom reactive aldehydes such as DD may have a dual effect on reproductive processes, influencing primary fertilization events such as gating of fertilization channels and secondary processes such as actin reorganization which is responsible for the segregation of cell lineages. These findings add to a growing body of evidence on the antiproliferative effects of diatom-derived aldehydes. Our results also report, for the first time, on the action of a fertilization channel blocker in marine invertebrates. Mol. Reprod. Dev. 66: 72,80, 2003. © 2003 Wiley-Liss, Inc. [source] Interactions between metabolism of trace metals and xenobiotic agonists of the aryl hydrocarbon receptor in the antarctic fish Trematomus bernacchii: Environmental perspectivesENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 6 2005Francesco Regoli Abstract Although Antarctica is a pristine environment, organisms are challenged with contaminants either released locally or transported from industrialized regions through atmospheric circulation and marine food webs. Organisms from Terra Nova Bay also are exposed to a natural enrichment of cadmium, but to our knowledge, whether such environmental conditions influence biological responses to anthropogenic pollutants has never been considered. In the present study, the Antarctic rock cod (Trematomus bernacchii) was exposed to model chemicals, including polycyclic aromatic hydrocarbons (benzo[a]pyrene), persistent organic pollutants (2,3,7,8-tetrachlorodibenzo- p -dioxin [TCDD]), cadmium, and a combination of cadmium and TCDD. Analyzed parameters included chemical bioaccumulation, activity, and levels of biotransformation enzymes (cytochrome P4501A); metallothioneins and the efficiency of the antioxidant system measured as individual defenses (catalase, glutathione, glutathione reductase, glutathione S -transferases, and glutathione peroxidases); and total scavenging capacity toward peroxyl and hydroxyl radicals. Reciprocal interactions between metabolism of inorganic and organic pollutants were demonstrated. Dioxin enhanced the accumulation of cadmium, probably stored within proliferating endoplasmic reticulum, and cadmium suppressed the inducibility of cytochrome P4501A, allowing us to hypothesize a posttranscriptional mechanism as the depletion of heme group availability. Clear evidence of oxidative perturbation was provided by the inhibition of antioxidants and enhanced sensitivity to oxyradical toxicity in fish exposed to organic chemicals. Exposure to cadmium revealed counteracting responses of glutathione metabolism; however, these responses did not prevent a certain loss of antioxidant capacity toward peroxyl radicals. The pattern of antioxidant responses exhibited by fish coexposed to cadmium and TCDD was more similar to that observed for cadmium than to that observed for TCDD. The overall results suggest that elevated natural levels of cadmium in Antarctic organisms from Terra Nova Bay can limit biotransformation capability of polycyclic (halogenated) hydrocarbons, thus influencing the bioaccumulation and biological effects of these chemicals in key sentinel species. [source] 132 Parasites and Phytoplankton, with a Special Emphasis on Dinoflagellate InfectionsJOURNAL OF PHYCOLOGY, Issue 2003M. G. Park Eukaryotic parasites are believed to play important roles in phytoplankton ecology and particularly in bloom dynamics of red-tide dinoflagellates. Apart from the prokaryotic parasites such as viruses and bacteria, certain flagellates and fungi have received some degree of attention as eukaryotic parasites of phytoplankton. Our understanding of fungal parasites is largely based on studies for freshwater diatoms and dinoflagellates, although fungal infections are known for some marine phytoplankton, including diatoms. By comparison, the dinoflagellate genus Amoebophrya and the newly described Perkinsozoa Pavilucifera infectans are widely distributed in coastal waters of the world and are well known as eukaryotic parasites of dinoflagellates. Recent work indicates that these parasites have significant impacts on the ecophysiology and behavior of dinoflagellate hosts. Thus, the ecological roles of Amoebophrya spp. and Pavilucifera infectans should be carefully considered in developing concepts about plankton dynamics and material flows in marine food webs. [source] The Protozooplankton,Ichthyoplankton Trophic Link: An Overlooked Aspect of Aquatic Food Webs,THE JOURNAL OF EUKARYOTIC MICROBIOLOGY, Issue 3 2010DAVID J. S. MONTAGNES ABSTRACT. Since the introduction of the microbial loop concept, awareness of the role played by protozooplankton in marine food webs has grown. By consuming bacteria, and then being consumed by metazooplankton, protozoa form a trophic link that channels dissolved organic material into the "classic" marine food chain. Beyond enhancing energy transfer to higher trophic levels, protozoa play a key role in improving the food quality of metazooplankton. Here, we consider a third role played by protozoa, but one that has received comparatively little attention: that as prey items for ichthyoplankton. For >100 years it has been known that fish larvae consume protozoa. Despite this, fisheries scientists and biological oceanographers still largely ignore protozoa when assessing the foodweb dynamics that regulate the growth and survival of larval fish. We review evidence supporting the importance of the protozooplankton,ichthyoplankton link, including examples from the amateur aquarium trade, the commercial aquaculture industry, and contemporary studies of larval fish. We then consider why this potentially important link continues to receive very little attention. We conclude by offering suggestions for quantifying the importance of the protozooplankton,ichthyoplankton trophic link, using both existing methods and new technologies. [source] | ||||||||||