Stimulatory activity of four green freshwater sponges on aquatic mycotal communities
The influence of the four species of green sponges (Ephydatia muelleri, Heteromeyenia stepanowii, Spongilla fluviatilis, and Spongilla lacustris) on the occurrence of aquatic mycotal species in the water of three four water bodies of different trophy was investigated in this study. Seeds and snake exuviae were used as baits. For the measurement of the primary and extracellular production by symbiotic algae of green sponges and assimilation of those products by mycota, radioactive carbon (14C) was used. A total of 75 mycotal species were found to be growing on the baits. The fewest mycota were noted in the containers in water from oligotrophic Lake Hańcza; the most in the containers with eutrophic water from River Supraśl. More mycota were found to grow in the containers with green sponges (Sp) than in the controls (Co) in water from all water bodies. The mean ratio of Sp/Co in green sponges ranged from 2.30 (E. muelleri) to 4.80 (H. stepanowii); in brown colonies (without symbiotic algae) it was 0.90. Mean value of 14C fixation (primary production) in symbiotic algae of Spogilla fluviatilis was 5.67 mg C g-1 dry weight sponge per hour. The effect of green sponges on the abundance of aquatic mycotal species is caused by dissolved organic matter produced during photosynthesis by symbiotic zoochlorellae, a symbionts of green sponges and excreted into the water environment (S. fluviatilis excreted mean 12.8% of carbon fixation). Those excreted organic substances serve as nutrients for aquatic mycota. The mean value of extracellular products assimilated by mycota was 4.96 mg C g-1 dry weight mycelium per hour.
Key words: Sponges, symbiotic zoochlorellae, aquatic mycota, interactions, hydrochemistry.