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91.
Copepod grazing impact on planktonic communities has commonly been underestimated due to the lack of information on naupliar
feeding behaviour and ingestion rates. That is particularly true for small cyclopoid copepods, whose nauplii are mainly in
the microzooplankton size range (<200 μm). The trophic role of Oithona spp. nauplii was investigated off Concepción (central Chile, ~36°S) during the highly productive upwelling season, when maximum
abundances of these nauplii were expected. Diet composition, ingestion rates, and food-type preferences were assessed through
grazing experiments with different size fractions of natural planktonic assemblages (<3, <20, <100, and <125 μm) and cultures
of the nanoflagellate Isochrysis galbana. When the Oithona spp. nauplii were offered a wide range of size fractions as food (pico- to microplankton), they mostly ingested small (2–5 μm)
nanoflagellates (5–63 × 103 cells nauplius−1 day−1). No ingestion on microplankton was detected, and picoplankton was mainly ingested when it was the only food available. Daily
carbon (C) uptake by the nauplii ranged between 28 and 775 ng C nauplius−1, representing an overall mean of 378% of their body C. Our relatively high ingestion rate estimates can be explained by methodological
constraints in previous studies on naupliar feeding, including those dealing with “over-crowding” and “edge” effects. Overall,
the grazing impact of the Oithona spp. nauplii on the prey C standing stocks amounts up to 21% (average = 13%) for picoplankton and 54% (average = 28%) for
nanoplankton. These estimates imply that the nauplii of the most dominant cyclopoid copepods exert a significant control on
the abundances of nanoplankton assemblages and, thereby, represent an important trophic link between the classical and microbial
food webs in this coastal upwelling system. 相似文献
92.
Mechanical Property and Biodegradability of Cast Films Prepared from Blends of Oppositely Charged Biopolymers 总被引:1,自引:0,他引:1
M.?O.?Rutiaga L.?J.?Galan L.?H.?Morales S.?H.?Gordon S.?H.?ImamEmail author W.?J.?Orts G.?M.?Glenn K.?A.?Ni?o 《Journal of Polymers and the Environment》2005,13(2):185-191
Biodegradable cast films of about 50 m thickness were fabricated by blending oppositely charged biopolymers such as anionic starch–chitosan, and cationic starch–pectin. The tensile strength and elongation at break (%) of films were evaluated as well as their capacity to degrade in compost. Films recovered from soil every 48 h showed consistent degradation (weight loss), diminution of the polymers characteristic peak absorbance in the carbohydrate fingerprint region of the FTIR, and changes in the surface morphology via scanning electron microscopy (SEM). Anionic starch–chitosan films had much superior tensile strength and elongation compared to cationic starch–pectin, suggesting that the ionic bonds formed between anionic-starch and positively charged groups in chitosan polymer were much more stable and stronger. Initially, both films lost about 36% weight within 96 h, which also correlated well with the loss in the characteristic absorption peaks in the region of the infrared spectrum typical of biopolymers. The total mineralization of films by microorganisms in compost soil was also measured using respirometric techniques. Though the rate of mineralization differed for two formulations, total mineralization (extent) for both films were achieved within 45 days. 相似文献