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Verlag: LIGHTNING SOURCE INC, 2021
ISBN 10: 1013833929ISBN 13: 9781013833922
Anbieter: moluna, Greven, Deutschland
Buch
Kartoniert / Broschiert. Zustand: New.
Verlag: LIGHTNING SOURCE INC, 2021
ISBN 10: 1013501314ISBN 13: 9781013501319
Anbieter: moluna, Greven, Deutschland
Buch
Zustand: New.
Erscheinungsdatum: 1992
Anbieter: ConchBooks, Harxheim, Deutschland
Long and short-term laboratory experiments were conducted to examine biological responses of sea scallops (Placopecten magellanicus) to relatively dilute bentonite clay suspensions. The effect of bentonite addition (0, 2 and 10 mg dm?3 treatments) to a natural diet of phytoplankton and organic detritus (seston) on somatic and reproductive tissue growth was examined over 68 days during the period of gametogenesis. Filtration, ingestion and pseudofaeces production rates and particle retention efficiency were measured for scallops which were fed mixtures of algae (dried Tetraselmis suecica) or natural seston and bentonite (0 to 15 mg dm?3). Pre-ingestive particle-selection capabilities were examined through chlorophyll a, organic content and carbon and nitrogen analyses of suspended particles and pseudofaeces. The results indicate a low tolerance to suspended bentonite. Extensive chronic mortalities and significant impacts on somatic and reproductive tissue growth were exhibited at 10 mg dm?3. Despite an inability to effectively retain clay-size particles, sea scallop feeding activity was altered by dilute bentonite suspensions. Animals fed natural seston without added bentonite displayed filtration rates twice as high as when 2 mg bentonite per dm3 was added, but tissue growth in both groups was similar. When provided with a diet of Tetraselmis, a similar reduction in filtration rate required bentonite concentrations exceeding 6 mg dm?3; levels lower than 1.0 mg dm?3 enhanced filtration rates. Sea scallops displayed two feeding mechanisms for actively enhancing the quality of ingested matter when exposed to elevated levels of suspended clay. Scallops were less efficient at retaining bentonite particles at concentrations exceeding 2 mg dm?3 than at lower levels. This shift in retention efficiency did not require a period of acclimation. Above a threshold bentonite concentration of 2 mg dm?3, scallops produced pseudofaeces and selectively ingested seston or Tetraselmis over clay particles. Selection efficiencies, determined from relative chlorophyll a, AFDW, POC and the PN-concentration of retained particles and pseudofaeces, were low compared with values published for other suspension-feeding bivalves. 14 pp., 12 figs, gr. 8.
Erscheinungsdatum: 1985
Anbieter: ConchBooks, Harxheim, Deutschland
The distribution of Macoma balthica in Cumberland Basin and Shepody Bay is very patchy and the zone of greatest abundance consistently occurs near the upper mudflat boundary where exposure time is greatest. The primary factors influencing distribution appear to be food availability, sediment stability and mortality. Sediment properties appear to play a minor role in this environment. Ice scour, sediment instability, predation and possibly high temperatures contribute to the high specific mortality rate (?0.5 y?1) resulting in a maximum age of 5 years. Growth and reproductive cycles of Macoma are the same as observed elsewhere except that lower winter temperatures delay growth to a few months between May and August. Annual Macoma production, averaged over several entire mudflats, is 0.5 and 3.9 g flesh dry weight m-2 for Cumberland Basin and Shepody Bay respectively, or 10 and 50% of the estimated total macrofauna production. 12 pp., 5 figs, gr. 8.