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381.
Quantitative data on digestive enzymes of bivalves are very limited and so this study was performed to obtain such information, and to find out whether some of these enzymes are well adapted to conditions in the digestive gland. The green musselPerna viridis was obtained from Clementi West Market in 1985. The results show that various carbohydrases are present in the digestive gland. The activities of-amylase, cellulase and-glucosidase are higher than that of other carbohydrases, whilst the activities of both lipase and protease, especially the former, are low. The pH optima of the following enzymes are also given:-amylase = 5.8; laminarinase = 5.5;-glucosidase = 5.8; trehalase = 4.8;-glucosidase = 5.5. The only enzyme which was not well adapted to conditions in the digestive gland (pH 6.2) was trehalase. The wide spectrum of enzymes present in this bivalve indicates that it has the ability to utilize a wide range of nutrients efficiently. 相似文献
382.
Phytoplankton carbon dynamics during a winter-spring diatom bloom in an enclosed marine ecosystem: primary production,biomass and loss rates 总被引:3,自引:0,他引:3
Phytoplankton production, standing crop, and loss processes (respiration, sedimentation, grazing by zooplankton, and excretion) were measured on a daily basis during the growth, dormancy and decline of a winter-spring diatom bloom in a large-scale (13 m3) marine mesocosm in 1987. Carbonspecific rates of production and biomass change were highly correlated whereas production and loss rates were unrelated over the experimental period when the significant changes in algal biomass characteristic of phytoplankton blooms were occurring. The observed decline in diatom growth rates was caused by nutrient limitation. Daily phytoplankton production rates calculated from the phytoplankton continuity equation were in excellent agreement with rates independently determined using standard 14C techniques. A carbon budget for the winter bloom indicated that 82.4% of the net daytime primary production was accounted for by measured loss processes, 1.3% was present as standing crop at the end of the experiment, and 16.3% was unexplained. Losses via sedimentation (44.8%) and nighttime phytoplankton respiration (24.1%) predominated, while losses due to zooplankton grazing (10.7%) and nighttime phytoplankton excretion (2.8%) were of lesser importance. A model simulating daily phytoplankton biomass was developed to demonstrate the relative importance of the individual loss processes. 相似文献
383.
A. Cornils S. B. Schnack-Schiel M. Böer M. Graeve U. Struck T. Al-Najjar C. Richter 《Marine Biology》2007,151(4):1261-1274
A total of 12 feeding experiments were conducted in the northern Gulf of Aqaba during spring (March/April) and autumn (September/October)
2002 at the Marine Science Station (MSS) in Aqaba. Females of three species of clausocalanids were selected: Clausocalanus
farrani, C. furcatus and Ctenocalanus vanus. Natural occurring particle (NOP) larger than 5 μm were investigated as food source. The ambient chlorophyll a concentration at sampling depth (∼70 m) ranged between 0.15 and 1.00 μg chl a l−1 and NOP concentrations ranged between 1.78 and 14.0 × 103 cells l−1 during the sampling periods. The division of particles into five size classes (5–10, 10–20, 20–50, 50–100 and >100 μm) revealed
that most of the particles were found in the size classes below 50 μm (81–98%), while most of the natural occurring carbon
(NOC) was concentrated in the size classes larger than 20 μm (70–95%). Ingestion rates were food density dependent rather
than size dependent ranging between 0.02 and 1.65 × 103 NOP ind−1 day−1 and 0.01 and 0.41 μg NOC ind−1 day−1, respectively, equivalent to a body carbon (BC) uptake between 0.4 and 51.8% BC day−1. The share of the size classes to the total ingestion resembled in most cases the size class composition of the natural particle
community. 相似文献
384.
Ammophila arenaria (marram grass) was introduced to South Africa from Europe as a means of stabilizing the Cape Flats in the 1870s, but was
only successfully established in the 1890s as it was found that seeds from the first introductions did not readily germinate.
By the end of the last century, it was successfully used as a dune stabilizing grass. It is now widely used in stabilization
projects along the Cape coastline, being established by planting cuttings or whole plants. Because of problems experienced
of marram becoming invasive, especially on the west coast of North America, and the fact that we have many invasive species
which threaten our indigenous dune fields, studies have been initiated on this plant in South Africa. Most work to date has
involved investigating the methods used to establish the plant in stabilization sites, and very little has been done on the
biology of the species in this country. Marram is generally thought not to seed in South Africa, and thus its spread has been
limited.
However, in the light of recent reports of successful germination of the seed, detailed studies on the phenology of seed production
and establishment in natural areas will be undertaken. Studies on the natural control by fungal species and nematodes will
be carried out in conjunction with work done in the Netherlands, so that a comparison of the biology of the species in South
Africa can be made with that in Europe, where it is used extensively to stabilize dunes. 相似文献
385.
For primitively eusocial insects in which a single foundress establishes a nest at the start of the colony cycle, the solitary provisioning phase before first worker emergence represents a risky period when other, nestless foundresses may attempt to usurp the nest. In the primitively eusocial sweat bee Lasioglossum malachurum (Hymenoptera, Halictidae), spring foundresses compete for nests which are dug into hard soil. Nest-searching foundresses (‘floaters’) frequently inspected nests during this solitary phase and thereby exerted a usurpation pressure on resident queens. Usurpation has been hypothesised to increase across the solitary provisioning phase and favour closure of nests at an aggregation, marking the termination of the solitary provisioning phase by foundresses, before worker emergence. However, our experimental and observational data suggest that usurpation pressure may remain constant or even decrease across the solitary provisioning phase and therefore cannot explain nest closure before first worker emergence. Levels of aggression during encounters between residents and floaters were surprisingly low (9% of encounters across 2 years), and the outcome of confrontations was in favour of residents (resident maintains residency in 94% of encounters across 2 years). Residents were significantly larger than floaters. However, the relationship between queen size and offspring production, though positive, was not statistically significant. Size therefore seems to confer a considerable advantage to a queen during the solitary provisioning phase in terms of nest residency, but its importance in terms of worker production appears marginal. Factors other than intraspecific usurpation need to be invoked to explain the break in provisioning activity of a foundress before first worker emergence. 相似文献
386.
In three delphinid species (Pacific spotted dolphin, Stenella attenuata; common dolphin, Delphinus delphis; harbor porpoise, Phocoena phocoena) the enzyme lysozyme and the peptide group -defensins are demonstrated for the first time in cetaceans as products of the thick integument. Lysozyme was found between the lamellae of the stratum corneum, in the cells of the stratum spinosum, free cells of the dermis, and in endothelial cells of dermal blood vessels. -defensins (especially type 3) were clearly located in cells of the upper stratum spinosum, and concentrated between the upper five or six layers of the stratum corneum. The occurrence and localization of such substances that may serve as a non-specific defense against bacteria, fungi, algae, and ectoparasites, was known until now only for haired marine mammals with typical skin glands, like in pinnipeds.Communicated by O. Kinne, Oldendorf/Luhe 相似文献
387.
Bioavailability of sediment-sorbed compounds may vary with increasing contact time. This may result in the dietary uptake route becoming more significant as conditions in the gut flora aid the extraction of contaminants, which have migrated into sites within the sediment particle. Such mechanisms may have important implications on risk assessments performed on substances released into the environment. A series of experiments were carried out using sediment spiked with 14C-labelled pyrene, a polycyclic aromatic hydrocarbon. The sediment was left at room temperature over a period of 220 days. Periodically (at 0, 1, 14, 28, 70, 220 days) the sediment was used to perform a bioaccumulation study using the freshwater oligochaete Lumbriculus variegatus. A novel methodology using feeding and (decapitated) non-feeding worms, allowed differentiation between uptake via ingestion and simple sorption. Results showed that there was a decline in bioavailability with time and that this was a 3 stage process. A rapid initial decline was observed over the first day when a 40% decrease was measured, an intermediate period were levels remained stable (day 14 to day 70) and an ultimate decrease in pyrene activity in worm tissue of 70% after 220 days. Over this period the chemical extractability of pyrene also decreased by 50%, as the chemical migrated deeper into unavailable sites within the sediment matrix. Normalising bioavailability to the chemically extractable fraction of pyrene within the sediment provided an overall decrease in bioavailability of 58%. The importance of the dietary route of uptake for pyrene varied during the sediment aging process, reflecting the changes in the physico-chemical interactions between the pyrene, sediment and pore water. 相似文献
388.
Borgmann U Nowierski M Grapentine LC Dixon DG 《Environmental pollution (Barking, Essex : 1987)》2004,129(1):39-48
Sediments from lakes near Rouyn-Noranda, Quebec, contain elevated concentrations of several metals, including Cd, Cu, Pb and Zn. Amphipods, fingernail clams, mayflies and tanytarsid midges were absent, and sediment toxicity was observed in chronic tests with Hyalella in sediments from Lac Dufault, the lake closest to Rouyn-Noranda. Bioaccumulation by Hyalella demonstrated elevated bioavailability of Cd, Co, Cr, Pb and Tl, but only Cd was accumulated to levels close to the toxic threshold. Copper, which is regulated by Hyalella, was not elevated in these amphipods, but it was elevated in overlying water in the toxicity tests. Toxic effects in Lac Dufault sediments are probably caused primarily by Cd, at least in amphipods, with a possible minor contribution from Cu. An integrated assessment, including sediment chemistry, benthic community composition, sediment toxicity, metal bioaccumulation in benthos, and comparison of bioaccumulation and/or overlying water concentrations with threshold effect concentrations, provides the best indication of effects and their cause. 相似文献
389.
390.
Heavy metal pollution from a point source has been demonstrated by the levels of mercury in flesh of mussels, . 相似文献