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A comparison of daphnid gut particles with the sestonic particles present in two Thames Valley reservoirs throughout 1970 and 1971
Author(s) -
NADINHURLEY C. M.,
DUNCAN A.
Publication year - 1976
Publication title -
freshwater biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.297
H-Index - 156
eISSN - 1365-2427
pISSN - 0046-5070
DOI - 10.1111/j.1365-2427.1976.tb01595.x
Subject(s) - seston , biology , algae , phytoplankton , plankton , particle (ecology) , zooplankton , hypolimnion , ecology , botany , eutrophication , nutrient
Summary The numerically most abundant component of the seston in two of the Thames Valley storage reservoirs of the Metropolitan Water Board consisted of flocculent organic material which, together with the hyaline, transparent and blackened particles, formed the non‐living sestonic fraction. The abundance of bacterio‐plankton was estimated from plate counts which are known to provide an under‐estimate of the bacteria present. The phytoplankton consisted of the larger flagellates present throughout the year together with a seasonal succession of algae in much greater numbers, namely the smaller flagellates, diatoms, colonial greens, Tribonema and Anabaena. A seasonal analysis of the gut contents of Daphnia magna, D. pulex and D. hyalina (occurring as important grazers in the reservoirs), revealed the presence of organic particles throughout the year plus cells or filaments of the prevailing alga at different seasons. During the summer, there were periods when the guts contained recognizable animal and plant debris. Flagellate and bacterial remains were never seen intact in the guts although these were abundant in the seston during early spring. The filamentous Tribonema was ingested when large crops of it were present. The most frequent size of ingested particle was between 1–2 μm and up to 60% of the animals examined contained particles which were neither longer nor wider than 20μm. Most of these animals ranged between 0·5–1·9 mm in length. A limiting factor for ingestion was thought to be width rather than length of particle and most very large particles found in the gut were long narrow and pliant filaments like Tribonema, or gelatinous colonial green algae, or flexible, foldable crustacean filtering limbs. There appeared to be no difference in the nature or size of particle ingested by the three different species of daphnids and any difference in maximal particle width observed was more likely to be related to body size than to species of consumer.