Short-term effects of UVB radiation on chlorophyll fluorescence, biomass, pigments, and carbohydrate fractions in a benthic diatom mat

• The effects on UVB radiation on a subtidal, cohesive-sediment biofilm dominated by the diatom Gyrosigma balticum (Ehrenberg) Rabenhorst were investigated, Chlorophyll fluorescence parameters (F-v/F-m, phi(PSII)), pigment concentrations, cell densities, and carbohydrate fractions were measured in four treatments (no UVBR, ambient UVBR, +7%, and +15% enhancement with UVBR). Enhanced UVBR was provided by a computer-controlled system directly linked to natural diel UVBR levels, increases in phi(PSII) values in the UVBR-enhanced treatments and a decrease in the steady-state fluorescence yield (F-s) from the surface of the biofilms during the middle and latter part of daily exposure periods suggested that G, balticum responded to enhanced UVBR by migrating down into the sediment. Diatoms in the +15% UVBR treatment also had significantly higher concentrations of beta-carotene after 5 days of treatment, Although G. balticum responded to enhanced UVBR by migration and increased beta-carotene concentrations, significant reduction in maximum quantum yield of PSII (F-v/F-m) and in minimal fluorescence (F-o) and decreases in cell densities occurred after 5 days. Concentrations of different carbohydrate fractions (colloidal carbohydrate, glucan, exopolymers [EPS]) associated with diatom biomass and motility also decreased in the UVBR-enhanced treatments. Short-term responses (migration) to avoid UVBR appear insufficient to prevent longer-term decreases in photosynthetic potential and biofilm carbohydrate concentration and biomass.

Subject headings

NATURVETENSKAP  -- Biologi -- Ekologi (hsv//swe)

NATURAL SCIENCES  -- Biological Sciences -- Ecology (hsv//eng)

Keyword

benthic diatoms

carbohydrates

chlorophyll fluorescence

microphytobenthos

motility

sediments

subtidal

UV-B radiation

vertical migration

ULTRAVIOLET-B RADIATION

MICROBIAL MATS

MARINE-PHYTOPLANKTON

INTERTIDAL SEDIMENTS

QUANTUM EFFICIENCY

XANTHOPHYLL-CYCLE

CO2

ASSIMILATION

OXIDATIVE STRESS

EXPOSURE

LIGHT

Publication and Content Type

ref (subject category)

art (subject category)