Impact of Solar Ultraviolet Radiation on Marine Phytoplankton of Patagonia, Argentina^¶

Abstract

Patagonia area is located in close proximity to the Antarctic ozone “hole” and thus receives enhanced ultraviolet B (UV‐B) radiation (280–315 nm) in addition to the normal levels of ultraviolet A (UV‐A; 315–400 nm) and photosynthetically available radiation (PAR; 400‐700 nm). In marine ecosystems of Patagonia, normal ultraviolet radiation (UVR) levels affect phytoplankton assemblages during the three phases of the annual succession: (1) prebloom season (late summer‐fall), (2) bloom season (winter‐early spring) and (3) postbloom season (late spring‐summer). Small‐size cells characterize the pre‐and postbloom communities, which have a relatively high photosynthetic inhibition because of high UVR levels during those seasons. During the bloom, characterized by micro‐plankton diatoms, photosynthetic inhibition is low because of the low UVR levels reaching the earth's surface during winter; this community, however, is more sensitive to UV‐B when inhibition is normalized by irradiance (i.e. biological weighting functions). In situ studies have shown that UVR significantly affects not only photosynthesis but also the DNA molecule, but these negative effects are rapidly reduced in the water column because of the differential attenuation of solar radiation. UVR also affects photosynthesis versus irradiance (P vs E) parameters of some natural phytoplankton assemblages (i.e. during the pre‐ but not during the postbloom season). However, there is a significant temporal variability of P vs E parameters, which are influenced by the nutrient status of cells and taxonomic composition; taxonomic composition is in turn associated with the stratification conditions (e.g. wind speed and duration). In Patagonia, wind speed is one of the most important variables that conditions the development of the winter bloom by regulating the depth of the upper mixed layer (UML) and hence the mean irradiance received by cells. Studies on the interactive effects of UVR and mixing show that responses of phytoplankton vary according to the taxonomic composition and cell structure of assemblages; therefore cells use UVR if >90% of the euphotic zone is being mixed. In fact, cell size plays a very important role when estimating the impact of UVR on phytoplankton, with large cells being more sensitive when determining photosynthesis inhibition, whereas small cells are more sensitive to DNA damage. Finally, in long‐term experiments, it was determined that UVR can shape the diatom community structure in some assemblages of coastal waters, but it is virtually unknown how these changes affect the trophody‐namics of marine systems. Future studies should consider the combined effects of UVR on both phytoplankton and grazers to establish potential changes in biodiversity of the area.

Photochemical responses of three marine phytoplankton species exposed to ultraviolet radiation and increased temperature: Role of photoprotective mechanisms

“…when the water column was mixed by wind. Because of the utmost importance of Patagonia within a photobiology context, i.e., the region normally receives high levels of UVR and it is periodically under the influence of ozone depletion events [23], this kind of studies are essential to assess the potential responses of local phytoplankton species under a scenario of climate change. [25].…”

An Unusual and Massive Bloom of Tetraselmis Sp. in the Valparaiso Bay, Chile

“…Photosynthesis is affected by the levels of photosynthetically active radiation (PAR: 400-700nm) and ultraviolet radiation (UVR: 290-400nm) penetration in the upper water column. Excessive PAR and UVR inhibit photosynthesis and damage cellular components [17][18][19][20][21][22]. UVB (290nm-320nm) radiation has raised concerns for its effects on marine ecosystems [23,24].…”

Biomass and Remote Sensing of Biomass

“…1) and has unique characteristics that would warrant UVR studies for several reasons. First, the area is occasionally under the influence of ozone-depleted air masses from the Antarctic polar vortex, thus experiencing periods of enhanced UV-B (Villafañe et al 2001;Helbling et al 2005). Second, its great variability in cloudiness, from high cover over the Andes and sub-Antarctic regions to the relatively clear skies on the mid-latitude Atlantic coast, creates a range of environments with variable UVR climatology.…”

“…the upwelling deep waters in the Pacific and the shallow and very productive Atlantic waters). Finally, high wind speed and frequency, especially during spring and summer (Villafañe et al 2004a;Helbling et al 2005) strongly condition the depth of the upper mixed layer (UML) and hence the underwater radiation field to which organisms are exposed. In addition the assessment of the UVR impact on phytoplankton from Argentinean Patagonia is essential since these organisms are responsible for an important share of primary productivity in the Argentinean Sea (Lutz et al 2010) and they constitute the base of a very rich food web that includes fishes (e.g.…”