engleski

Interactions between fish, zooplankton and macrophytes in the lake restoration

Uspostava i održavanje submerznih makrofita i kontrola predacije riba su nezaobilazni čimbenici restauracije jezera. Eutrofikacija, obogaćivanje hranjivim tvarima, je dobro poznati pokretač promjena iz prozirnog u mutno stanje vode. U ovom istraživanju nastojali smo utvrditi sposobnost submerznih makrofita u restauraciji jezera uzimajući u obzir promjene sastava zooplanktona i predacijskog pritiska riba. Stoga je ovo istraživanje provedeno u rukavcu rijeke Sutle (SZ Hrvatska), koji se sastoji od dva međusobno povezana bazena: gornji, proziran, sa submerznim makrofitima (Ceratophyllum demersum) i donji bazen, zamućen i bez makrofita. Osim uzorkovanja prirodne zajednice planktona, u mutnom bazenu je bio postavljen mesokozmos pokus, s malo modificiranim prirodnim sastavom planktona i riba, koristeći male (BM, 10 mm,  ribe) i velike (BV, 40 mm , + riba) promjere oka mrežastih bazena. U mesokosmsu izloženom predaciji riba dominirali su detritivorni kolnjaci i mali rašljoticalci, što pokazuje veliku sličnost sa sastavom mutnog bazena. U mesokozmosu bez riba, makrofiti su ostali u velikoj gustoći, a povećala se abundancija velikih rašljoticalca i veslonožaca, koji su pokazivali značajnu sličnost s litoralom prozirnog bazena. Rezultati ovog istraživanja potvrdili su da ponovno uspostavljanje makrofita ima sposobnost brze promjene biocenoza i okolišnih uvjeta. Restablishment and maintenance of submerged macrophytes and control of fish predation are inevitable factors in the lake restoration. Eutrophication, nutrients enrichment, is well known in shifting of transparent vs. turbid states. This study was focused on the capacity of submerged macrophytes in the lake restoration by alteration of biotic interactions. The research was carried out in Sutla River backwater (NW Croatia), consists of two interconnected basins: the upper, transparent and vegetated with submerged macrophytes (Ceratophyllum demersum) and the lower, turbid and non-vegetated. Except sampling of natural community, a mesocosms experiment was set up within turbid basin, with slightly modified natural community, using small (BS, 10 mm,  fish) and large (BL, 40 mm, + fish) mesh sizes in the basins construction. In the mesocosms under fish top-down control, macrophytes coverage decreased, and in plankton dominated detritovorous rotifers and small cladocerans. This assemblage was similar to the pelagial of turbid and unvegetated basin. In the mesocosms without fish, macrophytes remained very dense, and large-bodied algivorous cladocerans and copepods increased abundance and exhibited significant similarity to the littoral stands in the transparent basin. Results of this study confirmed that reestablishment of macrophytes has a great capacity in the lake restoration by causing rapid changes in the biotic interactions and environmental conditions.

eutrophcation; top-down control; zooplankton; cladocerans

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