Photosynthesis and UV-B tolerance of the marine alga Fucus vesiculosus at different sea water salinities

Abstract

The marine algal species in the Baltic Sea are few due to the low sea water salinity. One of the few species that can be found is Fucus vesiculosus. Even this species is affected by the low salinity and becomes smaller in size in the Baltic. In present work the photosynthesis of F. vesiculosus in the northern Baltic (Bothnian Sea) was compared to the photosynthesis of F. vesiculosus in the Atlantic. Oxygen evolution was measured before and after exposure to 2.3 W of UV-B (280-320 nm) radiation for 5 h, as well as after 48 h recovery in low light. The plants were kept in their own sea water salinity as well as in a changed salinity, this to examine possible correlations between salinity and photosynthesis. The results show a significant higher initial maximal photosynthesis (P max ) for Atlantic plants (10.3 nmol O 2 g −1 FW s −1 ) compared to Baltic plants (4.0 nmol O 2 g −1 FW s −1 ). The Baltic plants were found more sensitive to UV-B with a 40-50% decrease of P max as well as a lower degree of recovery (60-70% compared to 75-95% for the Atlantic plants). The higher salinity (35 psu) had a positive effect on the Baltic F. vesiculosus with increased P max as well as increased tolerance to UV-B. The lower salinity (5 psu) had a negative effect on the Atlantic plants with a decreased P max as well as a lower tolerance to UV-B. Pigment content was found higher in Atlantic F. vesiculosus. The pigment content decreased then the Atlantic plants were transferred to 5 psu. The concentration of Chl a as well as the total content of violaxanthin, diadinoxanthin and zeaxanthin in Baltic plants increased when transferred to 35 psu. The Atlantic F. vesiculosus can not survive the low salinity in the northern Baltic (died within 8 weeks). It is likely that a long time acclimation or adaptation to low salinity has taken place for F. vesiculosus in northern Baltic. If this is an ecotypic or genotypic development it is too early to say.

FLUORESCENCE EMISSION SPECTRA OF MARINE AND BRACKISH‐WATER ECOTYPES OF FUCUS VESICULOSUS AND FUCUS RADICANS (PHAEOPHYCEAE) REVEAL DIFFERENCES IN LIGHT‐HARVESTING APPARATUS1

“…Faster electron transfer rate in the Baltic algae, in turn, would disagree with the data showing faster oxygen evolution in the Atlantic ecotype (Bäck et al. 1992, Nygård and Ekelund 2006). Thus, we conclude that the strong PSII fluorescence in the Bothnian Sea ecotype of F. vesiculosus reflects better ability of PSII to harvest the blue excitation light used in the fluorescence measurements, rather than a high PSII/PSI ratio.…”

“…Nygård and Ekelund (2006), however, measured higher chl a and c concentrations in the Norwegian Sea ecotype from samples collected in January. The chl a / c ratios of Nygård and Ekelund (2006) were higher than those measured in the present study (Table 2), 18 for the Baltic Sea ecotype of F. vesiculosus and 24 for the Norwegian Sea ecotype. These data indicate that light‐harvesting complexes of Fucus decrease during winter but increase in May.…”

“…Photosynthesis is slower in the Baltic Sea ecotype than in the Atlantic ecotype of F. vesiculosus in its natural water (Bäck et al. 1992, Nygård and Ekelund 2006, Nygård and Dring 2008), but if the Baltic Sea ecotype is kept for 1 week in Atlantic water, its photosynthetic rate increases considerably (Nygård and Ekelund 2006).…”

“…Effect of salinity on the emission spectrum of the Bothnian Sea ecotype of F. vesiculosus. Treatment of the low‐salinity ecotype of F. vesiculosus in high‐salinity water increases the rate of oxygen evolution and photosynthetic electron transport (Nygård and Ekelund 2006, Nygård and Dring 2008). The effect on oxygen evolution was observed already after 1 week of growth in 35 psu.…”

The photokinetics of thermo‐tolerance in Symbiodinium

“…Lower levels of Chl a were partly responsible for the lower light absorption capacity observed for type D corals in this study (which was identified by a less acute initial slope, α, in the RLCs) but did not fully explain the 38% lower α when normalized to cellular Chl a . Some alternative explanations may be that, compared with type C2, type D symbionts may have smaller or fewer photosynthetic units for capturing incident light (Nygård & Ekelund 2006), fewer PSII reaction centres or PQ molecules (Honti 2007), or that there are differences in the optical properties of the host tissue. Alternatively, type D symbionts may divert more of the incident light energy to ATP production via cyclic phosphorylation through the Mehler cycle (Raven 1976), which does not result in the evolution of oxygen or the fixation of carbon (McCabe‐Reynolds et al.…”