Crustacean epifauna of seagrass and macroalgae in Apalachee Bay,Florida, USA

Epifaunal crustaceans on turtlegrass (Thalassia testudinum) and five dominant macroalgae (Anadyomene stellata, Digenia simplex, Halimeda incrassata, Laurencia poitei and Penicillus lamourouxii) were quantitatively sampled bimonthly over a one-year period from September 1979 to September 1980 in a subtropical seagrass meadow in Apalachee Bay, Florida (northeastern Gulf of Mexico). These plant species exhibited a wide range of morphologies, with surface area-to-biomass ratios differing by over 2.5 times. A similar suite of crustaceans occurred on all macrophytes despite differences in shape or architecture among plant species. Relative abundances of many crustaceans, however, varied among plant hosts. Similarity analysis indicated that the epifaunal associates of T. testudinum were distinct from those of the macroalgae. Species richness was generally higher on turtlegrass than on any of the macroalgae. Abundances of total crustaceans per plant biomass or per plant surface area, on the other hand, were greater on all macroalgal species compared to the seagrass. Abundances (per plant biomass or plant surface area) of 14 of the 16 numerically dominant epifaunal species differed significantly among macrophytes. Twelve of the 16 species had greater abundance on one or more macroalgae, while only two species were more abundant on T. testudinum. Almost half of the dominant species had greatest abundances on the branching red alga L. poitei. Although abundances per plant biomass and plant surface area were greater on macroalgae relative to turtlegrass, densities (individuals per meter square of bottom) of animals associated with T. testudinum were significantly greater than those associated with macroalgae, primarily because of the greater abundance of turtlegrass in the grass bed. Both surface area-to-biomass ratios and degree of branching were poorly correlated with epifaunal abundance and number of species. Neither structural feature is an adequate predictor of faunal abundance and species richness among plant species, especially when macrophytes with very different morphologies are compared.     

Inorganic nitrogen metabolism inUlva rigida illuminated with blue light

Inorganic nitrogen metabolism in blue light was studied for the green algaUlva rigida C. Agardh collected in the south of Spain (Punta Carnero, Algeciras) in the winter of 1987. NH₄ ⁺ has been reported to inhibit NO₃ ^- uptake; however,U. rigida showed a net NO₃ ^- uptake even when the NH₄ ⁺ concentration of the external medium was three or four times greater than the concentration of NO₃ ^-. NO₃ ^- uptake rates were similar in both darkness and in blue light of various photon fluence rates (PFR) ranging from 17 to 160 mol m^-2 s^-1. Since NO₃ ^- uptake is an active mechanism involving the consumption of ATP, respiratory metabolism can provide enough ATP to maintain the energetic requirement of NO₃ ^- transport even in darkness. In contrast, NO₃ ^- reduction inU. rigida was highly dependent on the net photosynthetic rate. After 7 h in blue light, intracellular NO₃ ^- concentrations ([NO₃ ^-] _i ) were higher in specimens exposed to intensities below the light compensation point (LCP) than in those incubated at a PFR above the LCP. When PFR is below the light compensation point, NO₃ ^- reduction is low, probably because all the NADH produced by the cells is oxidized in the respiratory chain in order to produce ATP to maintain a steady NO₃ ^- transport rate. The total nitrogen (TN) and carbon (TC) contents decreased from darkness to 33 mol m^-2 s^-1 in blue light. In this range, catabolic processes prevailed over anabolic ones. In contrast, increases in TN and TC contents were observed above the light compensation point. The C : N ratio increased with light intensity, reaching a stable value of 17 at 78 mol m^-2 s^-1 in blue light. Intracellular NO₃ ^- concentration and NO₃ ^- reduction appear to be directly controlled by light intensity. This external control of [NO₃ ^-]_i and the small capacity ofU. rigida to retain incorporated NO₃ ^-, NO₂ ^- and NH₄ ⁺ ions may explain its nitrophilic character.     

Prenatal diagnosis of NADH:ubiquinone oxidoreductase deficiency

NADH:ubiquinone oxidoreductase (complex I of the mitochondrial respiratory chain) deficiency is a severe disorder with an often early fatal outcome. Prenatal diagnosis for complex I defects currently relies mainly on biochemical assays of complex I in fetal tissues such as chorionic villi (CV), and is only in a minority of cases possible by means of mutational analysis of nuclear-encoded genes of complex I. We report on our experience to date with prenatal diagnosis in pregnancies at risk for complex I deficiency. We measured complex I activity in native CV and/or cultured CV in 23 pregnancies in 15 families. In accordance with the results of the investigations in CV, 15 children were born clinically unaffected. Two prenatally diagnosed unaffected fetuses and two prenatally diagnosed affected fetuses were lost prematurely with spontaneous or provoked abortions, respectively. Two affected children were born (prenatally found to be affected). In two pregnancies a discrepancy between native and cultured cells was found. We conclude that prenatal diagnosis for complex I deficiency can be reliably performed. Pitfalls were encountered in using cultured CV as a result of maternal cell contamination (MCC). Future research on pathogenic nuclear mutations underlying complex I deficiency will extend the possibilities for prenatal diagnosis at the molecular level. Copyright © 2001 John Wiley & Sons, Ltd.