Does ambient UV-B radiation influence marine diatom-dominated microbial mats? A case study

Abstract

Intact natural microbial mats collected from a shallow microtidal bay were incubated in the presence or absence of ambient ultraviolet-B radiation (UVBR) in an outdoor flow-through system for 2 and 6 wk, respectively. The microbial mats were cohesive and dominated by a large, motile diatom species, Gyrosigma balticum (Ehrenberg) Rabenhorst. The variables studied included biomass, composition of microalgae and meiofauna, bacterial biomass, pigment composition and presence of UV-absorbing compounds. Carbon assimilation and sediment oxygen microprofiles were measured as indicators of photosynthetic and respiratory activity. No significant effects were found on any of the measured variables when natural UVBR was excluded, suggesting that ambient UVBR did not exert any strong selective pressure on the particular type of microbial mat studied Biochemical screening by UV-absorbing compounds did not appear to be of major importance for avoiding UVBR damage. Visual observations, and to some extent oxygen profiles, indicated downward migration of the dominant diatom species as a response to high light levels. This may have been an important strategy also to avoid exposure to UVBR. Thus, vertical migration of benthic diatoms appears to be a factor that should be further investigated in relation to effects of both present and enhanced levels of UVBR.

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

“…Many studies have demonstrated that grazers are unaffected by UVR exposure (DeNicola & Hoagland 1996, Sundbäck et al 1996b, Hill et al 1997, Vinebrooke & Leavitt 1999. Our study agrees with these earlier experiments since we did not find any significant pattern of treatment effect on meiofauna, neither on nematode nor on ontogenic stages of harpacticoid copepod abundances.…”

“…Benthic microalgae can avoid UVR fluxes by migrating downward in the sediment since vertical migration offers substantial protection for cyanobacteria against UVR exposure (Nadeau et al 1999). Although this behavioral process probably applies for diatoms (Sundbäck et al 1996b), its longterm efficiency is doubtful ). Attenuation of UVR-induced impairments can also be achieved through the synthesis of various cellular com-ponents absorbing in the UVR band.…”

Microphytobenthic dynamics in a Wadden Sea intertidal flat – Part II: Seasonal and spatial variability of non-diatom community components in relation to abiotic parameters

“…Comparable densities of phytoflagellates in shallow intertidal sediments have been recorded previously (e.g. Sundba¨ck et al, 1996;Hoppenrath, 2000;Lee & Patterson, 2002).…”

“…Whitton & Potts, 2000). Vertical migration may perhaps be an additional strategy, providing an immediate response to PAR (Thajuddin & Subramanian, 2005) and UVR (Sundba¨ck et al, 1996;.…”

Occurrence of UVA- and UVB-absorbing compounds in 152 species (206 strains) of marine microalgae

“…These include damage to nuclear DNA (dimes formation, Karentz et al 1991a, Buma et al 1995 with consequent inhibition of cell growth rates, inhibition of photosynthesis with lesions in the Photosystem 11-D1 reaction centre protein (Jordan et al 1991), loss of, and changes to, the key photosynthetic enzyme, ribulose bis-phosphate carboxylase (Rubisco) (Strid et al 1990, Lesser et al 1994, Wilson et al 1995, Lesser 1996, decreased nitrogen uptake, metabolism and protein synthesis (Dohler et al 1987, Goes et al 1995, Dohler 1996, and loss of photo-orientation and motility in dinoflagellates, diatoms and other species (e.g. Hader & Hader 1988, Ekelund 1990, Donkor et al 1993, Nielsen & Ekelund 1993, Sundback et al 1996. The severity of these effects depends on the length and intensity of UVB exposure, the nutrient status of the cells, individual species responses, and supplementary radiation involved in repair processes (e.g.…”