UV radiation effects on macro- and microalgae in laboratory experiments

3.3.1 MA C R O A L G A E

3.3.1.1 PHOTOSYNTHETIC PERFORMANCE

The Ik values of propagules investigated varied between species, reproductive cell type and habitat. Saturating irradiance (Ik) was highest in gametes of the eulittoral green macroalga Monostroma hariotii and lowest in monospores of supralittoral red macroalga Porphyra endiviifolium (Table 5). Comparison between different groups of algae showed a generally higher Ik in green followed by brown and lowest in red macroalgae.

The slope alpha (α), a parameter for the performance of both light-harvesting and photosynthetic conversion efficiency, varies between α = 0.06 in gametes of M. hariotii and α = 0.14 in zoospores of A. utricularis. The other species lie in between these values (Table 5). Photosynthetic capacity, expressed as rETRmax, was highest in the brown eulittoral species A. utricularis (9.04) and lowest in the red subtidal species I.

cordata (2.1; Table 5).

Optimum quantum yield of the PSII (Fv/Fm) of freshly released reproductive cells was highest in P. endiviifolium (0.488 ± 0.04) and lowest in M. hariottii (0.288 ± 0.04). In brown and red macroalgae, higher Fv/Fm was observed in supra- and eulittoral (A.

utricularis, P. endiviifolium and I. cordata) compared to sublittoral (A. mirabilis, I.

cordata) species (Table 5). Post cultivation under dim white light (4 µmol photons m^-2 s^-1) generally showed an increase in the photosynthetic efficiencies of germinating cells except for P. endiviifolium (decrease) and I. cordata from the eulittoral (equal, Table 5).

Exposure to different light treatments consisting of PAR (P), PAR + UV-A (PA) and PAR + UV-A + UV-B (PAB) showed species-specific responses in Fv/Fm, expressed as percent of control (Fig. 8a-c). All species except A. utricularis were already inhibited by exposure to PAR only (20 to 90% under 22 µmol photons m^-2 s^-1). The species most strongly inhibited in their photosynthetic efficiency were the sublittoral I. cordata and A. mirabilis (70 and 90% inhibition after 8 h exposure, respectively; Fig. 8a).

Table 5. Photosynthesis-irradiance curve parameters estimated using the hyperbolic tangent equation of Jassby and Platt 1976, and mean optimum quantum yield (Fv/Fm) of propagules immediately after release and after post cultivation under dim white light (4 ± 1 µmol photons m

-2 s^-1) for 48 h

P-I curve parameters Fv/Fm

Class/Species

Cell size

(µm) Ik Alpha rETRmax After release After 48h postculture ULVOPHYCEAE

M. hariotii 7^‡ 83 0.06 5.41 0.288±0.04 0.397±0.15 PHAEOPHYCEAE

A. utricularis 4^‡ 64 0.14 9.04 0.462±0.11 0.601±0.04 A. mirabilis 3 52 0.10 4.99 0.400±0.06 0.446±0.05 BANGIOPHYCEAE

P. endiviifolium 15 33 0.12 4.07 0.488±0.04 0.249±0.02

FLORIDEOPHYCEAE

I. cordata (eulittoral) 22 57 0.12 6.9 0.476±0.04 0.448±0.07 I. cordata (sublittoral) 20 31 0.07 2.1 0.445±0.04 0.523±0.02 I_k (µmol photon m^-2 s^-1) is the light intensity at which the initial slope of the curve intercepts the horizontal asymptote of the maximum relative electron transport rate (rETRmax). Cell sizes are in diameter, ‡ cell length

Additional UV-A further decreased Fv/Fm of propagules by 5 to 60% (Fig. 8b). The highest photoinhibition due to UV-A relatively to the P treatments occurred in A.

utricularis (30 to 60%) and was lowest in P. endiviifolium (5 to 18%). A further, but small decline of Fv/Fm in relation to the PA treatment could be seen in all species and most exposure times if UV-B was added to the spectrum (1 to 20%; Fig. 8c).

Post cultivation for 2 d under dim white light (4 µmol photon m^-2 s^-1) allowed reproductive cells of all macroalgal species to at least some extent recover their photosynthetic efficiencies. Complete recovery after all treatments and exposure times was only observed in P. endiviifolium monospores and A. utricularis zoospores (Fig.

8d-f). Recovery from PAB exposure was relatively more efficient in supra- and eulittoral species (P. endiviifolium, M. hariotii, A. utricularis and I. cordata) compared to sublittoral (A. mirabilis and I. cordata) species where an especially reduced recovery after 8 h exposure to PAB was observed (Fig. 8f).

0

Fv/Fm (% of control)

A. m irabilis A. utricularis P. endiviifolium I. cordata eu. I. cordata sub. M. hariotii

0

Fv/Fm (% of control)

0

Fv/Fm (% of control)

0

Fv/Fm (% of control)

0

Fv/Fm (% of control)

0

Fv/Fm (% of control)

After recovery After exposure

a) d)

b) e)

c) f)

Fig 8a-f. Mean optimum quantum yield ± SD (Fv/Fm) of propagules during exposure (1 to 8 h, left column) to (i) PAR (P), (ii) PAR + UV-A (PA) and (iii) PAR + UV-A + UV-B (PAB) and after 48 h of recovery under dim white light (right column) expressed as percentage of the respective control measurements. Applied doses (in kJ m^-2) were: PAR 17, 34, 68, 136; UV-A 16, 31, 63, 125 and UV-B 1.3, 2.5, 5.0, 10.1 for 1, 2, 4 and 8 h of exposure, respectively.

3.3.1.2 DNA DAMAGE AND RE PAIR

UVR induced DNA damage was lowest in species from the supra- and eulittoral and highest in sublittoral species. The supralittoral P. endiviifolium did not show any DNA damage at all, M. hariotii, I. cordata and A. utricularis from the upper to mid-intertidal showed little DNA damage, whereas CPD formation in A. mirabilis from the upper sublittoral was significantly higher (Fig. 9). DNA damage was also shown to be dose dependent with highest CPD formation under longer exposure times. DNA damage of M. hariotii and A. utricularis propagules was completely repaired after 48 h exposure to dim white light (Paper VI). In I. cordata and A. mirabilis DNA repair was still incomplete after 48 h of recovery (Paper VII & VIII).

0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0 45.0

1h 2h 4h 8h

PAB exposure (h) DNA damage (CPD Mb-1) Monostroma

Adenocystis Ascoseira Iridaea eulittoral

n.d. n.d.

n.d. = not detected

Fig 9. UV-B induced DNA damage (mean ± SD, n = 3, CPD concentration per million nucleotides) in M. hariotii, I. cordata, A. utricularis and A. mirabilis after exposure to 1, 2, 4 and 8 h to PAR + UV-A + UV-B (PAB). CPDs were not detected in P. endiviifolium after exposure.

3.3.1.3 MYCOSPORINE-LIKE AMINO ACIDS

Mycosporine-like amino acids (MAAs) were determined in Iridaea cordata tetraspores (Paper VIII). Tetraspores contained two different MAAs, shinorine (λmax= 334 nm) and palythine (λmax= 320 nm). The most abundant was palythine. The concentrations of both MAAs, shinorine and palythine increased from the P to the PA and to the PAB treatment during 8 h exposure (Fig. 10).

0 20 40 60 80 100 120

8 h P 8 h PA 8 h PAB

treatment

shinorine palythine

MAAs (% of P treatment)

Fig 10. MAAs relative between treatments (all MAAs in the P treatment = 100 %) after 8 h of exposure to P, PA and PAB. Analysis performed with HPLC.

3.3.2 MI C R O A L G A E

3.3.2.1 MID-TERM UV RADIATION EFFECTS ON BENTHIC DIATOMS

The studied benthic Antarctic diatoms were low light adapted as shown by the respective P-I curves (Paper IV). The maximum Ik value measured was 184 µmol photons m^-2 s^-1. Optimum quantum yields (Fv/Fm) were initially > 0.6 after that a decrease in Fv/Fm over time at non-saturating irradiances occurred probably due to nutrient limitation. Transient significant negative UV-B effects were found on optimum quantum yield and total cell number, disappearing after 13 or 16 days, respectively. No effects on species composition or specific growth rate were found.

A general succession irrespective of treatment occurred in these microalgal experiments. Some species grew better under culturing condition than others leading to a shift in species composition over time.

3.3.2.2 SHORT-TERM UV RADIATION EFFECT S ON BENT HIC DIATOMS

Two types of set-up were used to test for UVR effects on photosynthetic efficiency of microalgae in the short-term experiments (Paper V): intact diatom mats (measured with PAM 2000) and diatom suspensions (measured with Water PAM). The mats were not disturbed during the measurements, the fiberoptic was placed directly above the sediment (diatoms could escape UVR by downward migration into the sediment) whereas the diatom suspension was shaken and filled into a quartz cuvette for measurements (diatoms could not hide from UVR).

Maximal initial values of effective quantum yield (no dark adaptation) was 0.601 (mat experiments) and maximal initial optimum quantum yield (with dark adaptation) was 0.573 (suspension). Significant negative UV effects on Fv/Fm under UV exposure and recovery under light were observed in the mats but not in the suspensions. In darkness treatment, the effects disappeared and diatom photosynthesis recovered.