DIET OF THE RED SWAMP CRAYFISH PROCAMBARUS-CLARKII IN NATURAL ECOSYSTEMS OF THE DONANA-NATIONAL-PARK TEMPORARY FRESH-WATER MARSH (SPAIN)

As a result of the introduction of the crayfish Procambarus clarkii, t he functioning and structure of the fresh-water marsh in the Donana Na tional park have been dramatically altered. Because those changes have been attributed mostly to trophic interactions between the crayfish a nd existing food webs. the aim of this study was to explore the diet o f this species in natural ecosystems in this park. A total of 502 stom achs was analyzed from 3 sites on 2 dates (March and May). The stomach contents were classified into 13 food categories. The most frequent f ood item in the population was non-green plants (80% occurrence in the pooled data), followed by rhizomes of Scirpus sp. (50%), green plants (36.8%), and organic sediment (30.1%). Animal food items were represe nted mainly by insects (24.9%), which included a wide variety of aquat ic larvae. cladocerans (16%), and Gambusia holbrooki (14%). Both immat ure and adult size-classes of this crayfish ingested mainly plants and organic detritus, but a higher proportion of food of animal origin ha s been found in young (<30-mm carapace length) compared to adult crayf ish. The mean number of food categories per stomach varied between 2 a nd 3, and no significant differences were found between seasons, sexes , and size classes (ANOVA, P > 0.05), except for March when we found l ower means in the Manecorro and La Rocina stations than during May, Th e trophic index calculated was D = 25.3. Thus, the diet of P. clarkii indicates that this crayfish is a polytrophic species.