Effects of UVR and grazing on biomass and primary production of subtidal benthic algae in Antarctica.

CAMPANA, G., F. MOMO, M.L. QUARTINO AND G.A. FERREYRA

Reports on Polar and Marine Research

Año: 2008 vol. 571 p. 278 - 286

Marine benthic macro- and microalgae play a key role in Antarctic coastal ecosystems. They are important primary producers that contribute to the coastal food webs either directly (Iken et al., 1998) or indirectly, as a source of particulate and dissolved organic carbon (Fischer and Wiencke, 1992). Furthermore, macroalgae serve as habitat and shelter for various organisms (Momo et al., 1998) and provide a substrate for microalgal epiphytic communities (Klöser, 1998). Benthic microalgal assemblages are also found colonizing hard bottom substrata and are thought to affect the marine successional process, particularly at the early stages (Neushul et al., 1976). Ultraviolet radiation (UVR, 280-400 nm) has harmful effects on the aquatic biota. Ultraviolet B (UVBR, 280-315 nm) and ultraviolet A (UVAR, 315-400 nm) penetrate in the water column down to ecologically significant depths, directly or indirectly affecting several targets in the organisms (Häder, 2000). Over the past decades, Arctic and Antarctic organisms in particular have been exposed to seasonally increased levels of UVBR due to the spring and summer ozone depletion phenomenon (Perin and Lean, 2004). UVBR is known to be a stress factor that can negatively affect marine primary producers (Villafañe et al., 2003; Bischof et al., 2006). In this scenario and particularly at the beginning of a colonization process, species-specific or life stage-specific algal susceptibility to UVR are expected to alter the structure of the coastal systems (Lotze et al., 2002). Besides environmental factors, primary producers can be strongly controlled by their consumers (Lotze and Worm, 2002). Grazing has been shown to produce drastic changes in benthic algae physiognomy and cause reductions of the community biomass in freshwater (Steinman, 1996) and marine systems (Nicotri, 1977; Hillebrand et al., 2000). Studies focusing on the effects of UVR on benthic algae-herbivores interactions are particularly scarce for Antarctica (Wahl et al., 2004; Zacher et al., in press) and - to our knowledge - have not been performed on subtidal benthic hard bottom assemblages (see Zacher and Campana, this issue). In the present study we report the first results of long term field studies addressed to analyze the combined effects of ambient UVR and grazing on a subtidal benthic algal community in Antarctica, one of the regions that have been most seriously affected by the ozone depletion. We will focus this communication to report the effects of both factors (UVR and grazing) on the community biomass and net primary production and we discuss the possible consequences of the observed effects on trophic interactions. Studies focusing on the effects of UVR on benthic algae-herbivores interactions are particularly scarce for Antarctica (Wahl et al., 2004; Zacher et al., in press) and - to our knowledge - have not been performed on subtidal benthic hard bottom assemblages (see Zacher and Campana, this issue). In the present study we report the first results of long term field studies addressed to analyze the combined effects of ambient UVR and grazing on a subtidal benthic algal community in Antarctica, one of the regions that have been most seriously affected by the ozone depletion. We will focus this communication to report the effects of both factors (UVR and grazing) on the community biomass and net primary production and we discuss the possible consequences of the observed effects on trophic interactions.., 1976). Ultraviolet radiation (UVR, 280-400 nm) has harmful effects on the aquatic biota. Ultraviolet B (UVBR, 280-315 nm) and ultraviolet A (UVAR, 315-400 nm) penetrate in the water column down to ecologically significant depths, directly or indirectly affecting several targets in the organisms (Häder, 2000). Over the past decades, Arctic and Antarctic organisms in particular have been exposed to seasonally increased levels of UVBR due to the spring and summer ozone depletion phenomenon (Perin and Lean, 2004). UVBR is known to be a stress factor that can negatively affect marine primary producers (Villafañe et al., 2003; Bischof et al., 2006). In this scenario and particularly at the beginning of a colonization process, species-specific or life stage-specific algal susceptibility to UVR are expected to alter the structure of the coastal systems (Lotze et al., 2002). Besides environmental factors, primary producers can be strongly controlled by their consumers (Lotze and Worm, 2002). Grazing has been shown to produce drastic changes in benthic algae physiognomy and cause reductions of the community biomass in freshwater (Steinman, 1996) and marine systems (Nicotri, 1977; Hillebrand et al., 2000). Studies focusing on the effects of UVR on benthic algae-herbivores interactions are particularly scarce for Antarctica (Wahl et al., 2004; Zacher et al., in press) and - to our knowledge - have not been performed on subtidal benthic hard bottom assemblages (see Zacher and Campana, this issue). In the present study we report the first results of long term field studies addressed to analyze the combined effects of ambient UVR and grazing on a subtidal benthic algal community in Antarctica, one of the regions that have been most seriously affected by the ozone depletion. We will focus this communication to report the effects of both factors (UVR and grazing) on the community biomass and net primary production and we discuss the possible consequences of the observed effects on trophic interactions. Studies focusing on the effects of UVR on benthic algae-herbivores interactions are particularly scarce for Antarctica (Wahl et al., 2004; Zacher et al., in press) and - to our knowledge - have not been performed on subtidal benthic hard bottom assemblages (see Zacher and Campana, this issue). In the present study we report the first results of long term field studies addressed to analyze the combined effects of ambient UVR and grazing on a subtidal benthic algal community in Antarctica, one of the regions that have been most seriously affected by the ozone depletion. We will focus this communication to report the effects of both factors (UVR and grazing) on the community biomass and net primary production and we discuss the possible consequences of the observed effects on trophic interactions.