Relations entre les compositions en acides amines des particules en voie de sedimentation, du contenu intestinal des holothuries abyssales et du sediment environnant

The amino acid composition of the gut content of two species of deposit-feeding holothurians (Deima validum validum and Pseudostichopus villosus) is compared with that of the sediment trap particles and the surrounding sediment collected from the Demerara abyssal plain in the equatorial Atlantic Ocean at a depth of 4800 m.Amino acid concentrations are 10, 50 and 100 μmol g⁻¹ in superficial sediment, sediment trap particles and ingested sediments, respectively. Compositions of the latter two are nearly identical and differ slightly from that of the former.No selective absorption of amino acids is noticed through the digestive tract. The acid-soluble (cold 2 N HCl) hydrolysed category, nearly absent in sediment trap particles from that depth as well as in superficial sediment, increases in gut contents for both species as a result of digestive system action on particulate matter. Glutamic acid which is largely predominant in this fraction may be partly secreted by the organisms or may result from bacterial activity. Similarly diaminopimelic acid (DAP) is important in gut contents only, but entirely in the free form. The bacterial cell numbers calculated from DAP concentrations are 100-fold that of direct epifluorescent microscopy counts but cannot be considered as the numbers of visible cells because the cell-wall mureid complex containing DAP is normally insoluble in water. Nevertheless, DAP concentrations lead pointedly to the fact that remains of larger bacterial populations or more intense bacterial activity exist in gut content compared to that of sinking particles and superficial sediment.In the superficial sediment, β-alanine and γ-aminobutyric acid account for about 8 mol%, almost entirely in the residual hydrolysed category. In sinking particles and gut contents they account for 1.5 mol% only, but their total amounts are similar to that of the superficial sediment. In gut contents about 40% of β-alanine and γ-aminobutyric acid are found in acid- and alkali-soluble hydrolysed categories, maybe as a result of the general decomposition of ingested organic matter. Absolute concentrations do not appear to change through the digestive tract. The inefficiency of organism assimilation systems and the intimate contact between mineral particles and digested organic compounds which occur in the digestive tract of deposit-feeders may be partly responsible for their increased relative abundance in pelagic sediments.

Résumé

La comparaison entre la composition en acides aminés des particules en voie de sédimentation et celles du sédiment superficiel et des contenus intestinaux d'holothuries abyssales permet de caractériser les échanges entre ces organismes et leur milieu.L'absorption lors du transit intestinal d'une partie du stock ingéré d'acides aminés, de composition identique à celle des particules récoltées par le piège à sédiment, s'effectue d'une manière non sélective.Les contenus intestinaux sont riches en composés protidiques solubles dans l'eau dont une partie non absorbée est rejetée avec les excréments et enrichit le sédiment environnant. Cette fraction soluble est caractérisée par sa richesse en acide glutamique qui peut être due à des sécrétions digestives des organismes, mais également être liée à des phénomènes bactériens mis en évidence par la richesse particulière des contenus intestinaux en acide diaminopimélique.La β-alanine et l'acide γ-aminobutyrique ne semblent pas être absorbés lors du transit, l'éventualité de leur association avec les phases minérales du sédiment sous une forme organique résiduelle pendant le transit intestinal est discutée.     

Teneurs en benzo 3,4 pyrène chez Mytilus edulis L. de l'estuaire et du golfe du Saint-Laurent

Blue mussels (Mytilus edulis L.) taken from 27 stations along the estuary and gulf of St. Lawrence were analyzed for their content in 3,4-benzopyrene. Most of the concentrations are below the detection limit for the analytical method, i.e. 0·15 μg kg^?1 (dry weight) and probably reflect the natural baseline level. However, mussels from two stations located at the mouth of Saguenay Fjord exhibit very high contents: 24 and 28·5μg kg^?1 (dry weight). A mussel transplantation experiment has shown that the entire Fjord is contaminated by anthropogenic 3,4-benzopyrene.     

Incidence de la cinetique de decroissance de la temperature apres le choc thermique sur les modifications d'activite des esterases et les possibilites de survie de Scolelepis (malacoceros) fuliginosa (annelide polychete)

Scolelepis fuliginosa reared in the laboratory at 13°C were put through 10-min thermal shocks at 16°C and 18°C and were then submitted to either a slow or a rapid temperature reduction. After the thermal shock, a posterior fragment of each specimen was cut off at intervals, until six days. Samples were submitted to electrophoresis on polyacrylamide gel, esterase activity being determined with α-naphthyl acetate.Enzymograms show that thermal shocks act on esterases in decreasing the activity of the main fractions. Immediate effects result in a very precocious enzymic response; more long-term effects depend on the maximum temperature, the animal's sex and the kinetics of the post-shock thermal reduction.Females are more sensitive than males. For a given Δt, esterase changes are greater and more long-lasting. After a 16°C Δt, a rapid decrease in temperature prevents the loss of activity of the middle and fast fractions in males and delays, by about 10 h, the alteration of female esterases. After 18°C ΔT, loss of activity of the middle and fast fractions occurs in less than 1 h, independently of the thermal kinetics, but survival is only possible—solely for males—with a rapid decrease in temperature which also delays females' deaths by between 24 and 48 h.In conclusion, a rapid decrease in temperature gives organisms a better resistance to thermal shock, as determined by esterase activity and controls the lethality of a high Δt.