Effects of UVB radiation on a marine microphytobenthic community growing on a sand‐substratum under different nutrient conditions

Abstract

The effect of ultraviolet-B radiation (UVBR) on a microphytobenthic community, dominated by diatoms, was studied under different nutrient conditions in a 9 day outdoor experiment on the Swedish west coast. The microalgal assemblage was isolated from the sediment and resettled onto acid-cleaned sand placed in petridishes. The experimental treatments were: ''ambient'' or ''enhanced'' UVBR with no nutrient addition, ''ambient'' or ''enhanced'' UVBR with nutrient addition (N, P, Si). Enhanced UVBR (ϩ15%) was provided by a computer-controlled system. Primary productivity, carbon allocation, chlorophyll a (Chl a) concentrations, composition of algae and pigments and intra-and extracellular carbohydrate fractions were measured. Most UVBR effects were seen in treatments without nutrient addition. Exposure to enhanced UVBR resulted in statistically significant decreases in primary productivity, Chl a and in the biomass of Haslea ostrearia and Nitzschia spp. The relative amount of carbon allocated to proteins increased when exposed to enhanced UVBR. The effect of enhanced UVBR on microalgae subjected to nutrient addition was less pronounced, and observed for Chl a, algal intracellular storage of carbohydrates (glucans) and concentration of extracellular ''colloidal'' carbohydrates. Enhanced UVBR ϩ nutrients resulted in a significantly greater ratio between glucan and total carbohydrates and a decreased concentration of colloidal carbohydrates compared to the ambient UVBR ϩ nutrients treatment. These results indicate that availability of inorganic nutrients acts to mitigate the negative effects of UVBR on microphytobenthic communities and that UVBR acts as a selective force during early growth and succession.

Grazing and UV radiation effects on an Antarctic intertidal microalgal assemblage: a long-term field study

“…, hypothesized that the lack of UV effects on structural variables in earlier field-experiments was due to the study of already established diatom communities and inadequate (too short) experimental periods. Microbenthic assemblages during early succession, as in our study, should therefore be more UV susceptible (Wulff et al 2000). Nevertheless, no UV effects were found on any of the tested structural variables during the 3.5 month sampling period.…”

“…Nevertheless, no UV effects were found on any of the tested structural variables during the 3.5 month sampling period. It should be pointed out, however, in a few studies transient UV effects on e.g., biomass and species composition have been found in an early stage of microalgal succession (Santas et al 1998;Wulff et al 2000). The authors related these effects to a species-specific response to UV-B radiation.…”

“…Earlier field-studies on UV effects on benthic microalgae have mainly focussed on soft bottom communities where benthic diatoms seem to be very tolerant to UV-B radiation (Peletier 1996; and references therein). The main variable to some extent affected in these communities was primary productivity while structural variables such as the overall biomass and microalgal pigments appeared unaffected (Odmark et al 1998;Sundbäck et al 1997;Wulff et al 1999;Wulff et al 2000). , hypothesized that the lack of UV effects on structural variables in earlier field-experiments was due to the study of already established diatom communities and inadequate (too short) experimental periods.…”

Effects of UVB radiation and salt stress on growth, pigments and antioxidative defence of the marine diatom Cylindrotheca closterium

“…Resale or republication not permitted without written consent of the publisher flats during low tides, may be more UV-sensitive; such examples include the benthic diatoms Nitzschia and Synedra (Francoeur & Lowe 1998, Wulff et al 2000. The experiment in this paper will focus on a representative of these relatively UV-sensitive diatoms, Cylindrotheca closterium, in particular as regards its defence against UV-and salt-induced production of active oxygen species.…”

Haslea karadagensis(Bacillariophyta): a second blue diatom, recorded from the Black Sea and producing a novel blue pigment

“…In north-western Europe, records come from the coasts of Great Britain (Sprat, 1669;Hustedt & Aleem, 1951), Belgium (M'harzi et al, 1998), Norway (Hendey, 1964), Sweden (Wulff et al, 2000), Denmark (Limfjord; Petersen, 1916), and the Baltic Sea (Snoeijs & Kasperovicˇien_ e, 1996). In the northern Atlantic Ocean, 'blue diatoms' have been found in the Canary Islands (SCCAP, Gert Hansen), and different places along the North American coast, including North Carolina (Beaufort) and Rhode Island (Narragansett Bay) (Kennett & Hargraves, 1991;Gary Wickfors, personal communication); Virginia (Chesapeake Bay; Mitchell & Barney, 1918); New Jersey (Sullivan, 1977); Florida (Biscayne Bay; Julian Sprung, personal communication); and possibly in Honduras (Grunow, 1877).…”