engleski

Invertebrates associated with Myriophyllum spicatum L. in Sakadaš lake within Kopački rit floodplain, Croatia

Sampling of invertebrates associated with submersed macrophyte species Myriophyllum spicatum L., was conducted once a week during July, August and September 2004, at three sites, noted as I, II and III, in Sakadaš lake within Kopački rit floodplain in the North-East Croatia. The weather and environmental parameters were as expected for summer season: high air temperatures, little rain, what influenced water temperature There was a statistical significance in difference between environmental parameters recorded in July and those recorded in August (R=0.647, p<0.001) and September (R=0.739, p<0.001), but there was no statistically important difference between sites for environmental parameters.as well as decrease in depth and transparency. Calculated TSI values (Carlson and Simpson, 1996), based on concentration of chlorophyll-a and amount of T-P, indicated states of eutrophy and hypertrophy, for some dates, what is analogue to results gathered during reseach conducted from 1997 to 2004 (Vidaković et al., 2002 ; Bogut et al., 2003). Myriophyllum spicatum first appeared in Sakadaš lake in the year 2004 and then the research on phytophilous invertebrate fauna began. In collected fauna we recorded 23 taxonomic groups and they are presented by their abundance as number of individuals per 100 g plant dry weight. Dominance in recorded invertebrate fauna had Insecta larvae (representatives of Zygoptera, Anisoptera, Chironomidae, Hemiptera, Ephemeroptera, Ceratopogonidae, Plecoptera, Trichoptera, Heteroptera, Dytiscidae and Muscidae), with the percentage rate ranging from 42% to 90% of total fauna at the research sites. The highest abundance (47258.9 individuals per 100 g of M. spicatum dry weight at the site I, 53886.4 ind. 100 g-1 d.w. at the site II and 17739.9 ind. 100 g-1 d.w. at the site III) was found for members of the family Chironomidae, what is 71% of all invertebrates at all three sites. At the site III high densities had Nematoda with 12086.3 ind. 100 g-1 d.w. and Oligochaeta with 9235 ind. 100 g-1 d.w, what representes 28% and 21% of all invertebrates at that site. Very successful invertebrates, present in high abundance in eutrophic waters are Chironomidae larvae (Lund, 2001) and Oligochaeta (Mackie, 2001). Predominance of Chironomidae larvae is usual in eutrophic waters associated with macrophytes (Soszka, 1975 ; Linhart, 1999). According to the non-metric multidimensional scaling, NMDS, and analysis of similarities, ANOSIM, statistically significant difference exists in invertebrate abundances between the site I and the site III (R = 0.772, p < 0.005), as well as between the site II and the site III (R = 0.514, p < 0.01). Also, there is statistically significant difference between months of sampling: July and August (R=0.647, p<0.001) and also July and September (R=0.739, p<0.001), regarding fauna abundance. Statistically significant correlation (p<0.02) was found between invertebrate number and M. spicatum dry weight at the site III. These results could be explained by the fact that the M. spicatum stand at the site III lasted continuously over the whole sampling period, while the stands at the sites I and II did no longer exist after the first half of August 2004.

invertebrates; Myriophyllum spicatum; trophic state; Sakadaš lake

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