Effects of reduced UV radiation on a microbenthic community during a microcosm experiment

Abstract

A microcosm experiment was conducted over a 77 d period (from 6 July to 21 September 1999) to investigate the response of a microbenthic community to the long-term reduction of ambient ultraviolet-B (UVBR, 280 to 320 nm) and ultraviolet-A (UVAR, 320 to 400 nm) radiation. Intact sediment cores were harvested from a muddy intertidal flat in the lower St. Lawrence Estuary (Quebec, Canada) and placed in an outdoor flow-through system under 3 treatments: ambient solar radiation, reduced UVBR and reduced UVR (280 to 400 nm). Both autotrophic (primary production, microalgal biomass, accessory pigments, diatom composition and abundance and UVR absorbing compounds) and heterotrophic (meiofaunal abundance) components were investigated. It was found that neither nematode nor ontogenic stages of harpacticoid copepod abundances were affected by the treatments. The temporal variations of the nauplius, copepodite and copepod populations correspond to the normal ontogenic evolution of harpacticoids. The microphytobenthic community, dominated by small (≤15 µm) pennate diatoms, presented significantly higher carbon fixation under UVR protected treatments on Days 14 and 21, suggesting a simultaneously detrimental but weak effect of UVBR and UVAR on photosynthesis. Occurring in very low concentrations in the sediment, UVR absorbing compounds did not seem to be a major UVR-attenuation mechanism within the microbenthic community. The screening of UVBR and UVR also resulted in a stepwise decrease of microalgal biomass on Days 7, 21, 28, 35 and 42, and of diatom abundance on Day 35. The simultaneous accumulation of pheopigments likely reflected an enhanced grazing pressure under both UVshielded treatments, presumably by microfaunal grazers. The fact that these noticeable changes were observed between the 3 treatments implies that both UVBR and UVAR influence the microphytobenthic community. There was a lack of treatment effect during the second half of the experiment when UVR fluxes showed their normal seasonal decrease. Thus, our results indicate that effects of ambient UVR on microbenthos occur only under high solar irradiance. During this period, both ambient UVBR and UVAR exerted a controlling effect on the microalgal standing stock in muddy intertidal flats in the lower St. Lawrence Estuary.

Effects of UV Radiation on Wetland Periphyton: Algae, Bacteria, and Extracellular Polysaccharides

“…These findings contrast with prior studies of epipelon, where EPS was occasionally less abundant in +UV treatments (Underwood et al 1999, Roux et al 2002. It is possible that periphytic EPS in our study system was relatively more resistant to UV degradation, or that any UV-induced degradation of EPS was offset by increased periphytic biomass or EPS production.…”

“…Underwood et al (1999) observed a reduction in EPS and concomitant reductions in epipelon biomass and chlorophyll a under an ambient +15% UV-B treatment. In another epipelon study, EPS was reduced in +W plots as compared to -UV plots, but only on a few sample days (Roux et al 2002). In contrast, glycan-rich EPS production increased significantly in the cyanobacterium Nostoc commune under laboratory exposures to UV-B but not UV-A (Ehling-Schulz et al 1997).…”

Particulate organic carbon export in the upper twilight zone during the decline of the spring bloom

“…POC concentrations were determined in duplicate with a Perkin-Elmer Model 2400 CHN Analyzer from samples concentrated on pre-combusted (450°C for 5 h) Whatman GF/F filters and kept frozen (-20°C) in Petri dishes before analysis in the laboratory. In order to assess the solubilization of particulate organic material during the deployment period (Kähler & Bauerfeind 2001), dissolved organic carbon (DOC) was measured in the traps before and after deployment using a TOC-5000A Shimadzu analyzer following the procedure explained in Roux et al (2002). The export ratio (e-ratio, i.e.…”

UV radiation effects on pigments, photosynthetic efficiency and DNA of an Antarctic marine benthic diatom community

“…However, the benthic diatom community almost exclusively consists of pennate diatoms, producing very low, if any, amounts of UV-absorbing compounds , Roux et al 2002. Other strategies to reduce negative effects of excessive radiation including UVR are vertical migration , Waring et al 2007) and, on a community level, 'self-shading', i.e.…”