EPIPHYTES FROM A DEEP-WATER CHARACEAN MEADOW IN AN OLIGOTROPHIC NEW-ZEALAND LAKE - SPECIES COMPOSITION, BIOMASS AND PHOTOSYNTHESIS

1. The epiphytic flora of a characean meadow in Lake Coleridge, a deep , oligotrophic lake on the South Island of New Zealand, was dominated by diatoms, particularly Eunotia pectinalis and Achnanthes minutissima . The meadows occupied a depth range from 5 to 30 m. Adnate taxa predo minated at all depths below 5 m, while increased taxonomic diversity a t 5 m resulted from an increased abundance of erect taxa, including ch lorophytes and stalked diatoms. 2. Seasonal changes in epiphyte biomas s were followed using artificial substrata and by estimating epiphyte chlorophyll a concentration on host plants. The latter required develo pment of a novel technique utilizing the consistent relationship betwe en fucoxanthin and chlorophyll a concentrations in the epiphyton. Epip hyte chlorophyll a on host plants varied with depth and host species b etween 0.1 and 0.3 mg g(-1) dry weight. Maximum epiphyte biomass was a t 10-15 m depth. At depths of 15 m and less, epiphyte chlorophyll a re ached a maximum of approximate to 200-300 mg m(-2) in mid-summer, whil e at greater depths maximum biomass was less and coincided with a peri od of clear water in spring. 3. Photosynthetic carbon fixation was est imated from photosynthesis-radiation curves and estimates of radiation flux at sampling depths. At depths greater than 10 m, variability of the vertical extinction coefficient of lake water rather than seasonal fluctuations in incident radiation were responsible for determining t he temporal pattern of production. Chlorophyll a-specific photosynthes is was estimated to peak in summer at 5 m (8 mg mg(-1) day(-1)), and i n spring at all other depths. 4. Annual epiphyte production was estima ted as 27 g C m(-2) year(-1) at 5 m depth, falling to 15 g C m(-2) yea r(-1) at 15 m and 1 g C m(-2) year(-1) at 30 m. Areal biomass changes tended to be temporally but not quantitatively coupled to estimated in situ photosynthesis, and we hypothesize that epiphyte biomass may hav e been controlled by grazing gastropod snails.