FOOD PREFERENCE OF FRESH-WATER INVERTEBRATES - COMPARING FRESH AND DECOMPOSED ANGIOSPERM AND A FILAMENTOUS ALGA

1. Fresh and decomposed Mougeotia sp. (a filamentous green alga) and E lodea nuttallii (a vascular plant) were offered as food to three speci es of aquatic macroinvertebrates (Lymnnea peregra, Asellus meridianus and Endochironomus albipennis) to test: (i) if filamentous algae are p referred to aquatic higher plants (hereafter, called 'macrophytes') an d (ii), as is known for higher plants, if decomposition also results i n greater palatability of filamentous algae. 2. Compared with the alga , the macrophyte in both states was of higher nutritional value. Condi tioning improved the nutritional value of both food types, but especia lly of the macrophyte. 3. Both fresh alga and fresh macrophyte were ea ten little by all animals except A. meridianus feeding upon the macrop hyte. Consumption was higher for both plants in their decomposed state . However, L. peregra consumed more decomposed macrophyte than the dec omposed alga. Both decomposed plants were eaten most by E. albipennis followed by A. meridianus and L. peregra. 4. Digestibility of both pla nts, but especially of the macrophyte, increased significantly after d ecomposition. The assimilation efficiencies of all animals on the fres h E. nuttallii were higher than on fresh Mougeotia sp. After decomposi tion, the efficiency increased significantly only on the alga. Consequ ently, both decomposed plants were assimilated with similar efficiency by all test animals. 5. Amongst aquatic macrophytes, the increase of their consumption and digestibility upon decomposition has hitherto be en known only for vascular plants but not for filamentous algae.