Biofilm development and extracellular enzyme activities on wood in billabongs of south‐eastern Australia

SUMMARY1  The accrual of organic matter, chlorophyll a and bacteria, and the activities of various extracellular enzymes were studied during biofilm formation on River Red Gum ( Eucalyptus camaldulensis ) wood submerged in two temperate Australian billabongs for 24 weeks over summer and winter of 1989–90. 2  Peak organic matter content of the biofilm ranged from 0.7 to 3.3mg AFDW cm −2 , chlorophyll a content from 1.3 to 4. 2μg cm −2 and bacterial abundance from 18 × 10 6 to 94 × 10 6 cells cm −2 . Most variation in organic matter content, chlorophyll a content and bacterial abundance in the biofilms couid be attributed to the duration of immersion (28–48% of variation) and to the interaction between site and submergence period (11–12%). Differences between sites and between seasons were less important in explaining total variation. 3  Alkaline phosphatase, aminopeptidase and [3‐D‐glucosidase activities, determined per unit substratum surface area, were up to 138 ± 26 nmol cm −2 h −1 , 113 ± 1 nmol cm −2 h −1 and 9.3 ± 2.2 nmol cm −2 h −1 , respectively. Activities of these three enzymes determined per unit organic biomass were up to 203 ± 25, 157 ± 13, and 16 ± 2.1 nmol mg 1 AFDW h −1 respectively. Enzyme activities expressed on an area‐ or biomass‐specific basis responded differently to the effects of season, site and duration of substratum exposure. 4  Few consistent relationships could be established between the activity of a given enzyme system and the activity of other enzymes, nor with the various biomass parameters, such as total organic matter content, chlorophyll a content or bacterial abundance. 5  We suggest that submerged wood of the River Red Gum is an important site for biofilm development in lentic systems in south‐eastern Australia, and thus as a food resource for grazing invertebrates and for transformations of various nutrients and organic matter.