Dieter Hanelt

The genus Laminaria sensu lato : recent insights and developments

This review about the genus Laminaria sensu lato summarizes the extensive literature that has been published since the overview of the genus given by Kain in 1979. The recent proposal to divide the genus into the two genera Laminaria and Saccharina is acknowledged, but the published data are discussed under a ‘sensu lato’ concept, introduced here. This includes all species which have been considered to be ‘Laminaria’ before the division of the genus. In detail, after an introduction the review covers recent insights into phylogeny and taxonomy, and discusses morphotypes, ecotypes, population genetics and demography. It describes growth and photosynthetic performance of sporophytes with special paragraphs on the regulation of sporogenesis, regulation by endogenous rhythms, nutrient metabolism, storage products, and salinity tolerance. The biology of microstages is discussed separately. The ecology of these kelps is described with a focus on stress defence against abiotic and biotic factors and the role of Laminaria as habitat, its trophic interactions and its competition is discussed. Finally, recent developments in aquaculture are summarized. In conclusion to each section, as a perspective and guide to future research, we draw attention to the remaining gaps in the knowledge about the genus and kelps in general.

An inventory of UV-absorbing mycosporine-like amino acids in macroalgae from polar to warm-temperate regions

A qualitative and quantitative survey of 11 green, 27 brown and 30 red macroalgal species collected from polar (Spitsbergen), cold-temperate (Helgoland) and warm-temperate (southern Spain) regions revealed that all Rhodophyceae from the eulittoral zone contained several UV-absorbing mycosporine-like amino acid compounds (MAAs), which are assumed to function as natural UV-sunscreens. In contrast, deep-water red algae, as well as the Chlorophyceae and Phaeophyceae did not contain MAAs or exhibited only trace concentrations. Within all species investigated 9 distinct compounds were found, of which 7 were identified as mycosporine-glycine, shinorine, porphyra-334, palythine, asterina-330, palythinol and palythene. The remaining two substances are unknown; they had different retention times under the Chromatographie conditions used, but identical absorption spectra with a maximum at 357 nm. Both compounds are restricted to a few polar red algae. In Polysiphonia arctica J. Agardh (Rhodophyta) from Spitsbergen the concentrations of MAAs decreased from depths of 1 to 7 m. Shallow-water isolates contained > 5-fold higher total MAA amounts compared to deep-water samples. In addition, the contents of all MAAs correlated with the biogeographic region indicating that the lower the natural solar irradiance in the respective habitat the less MAAs are synthesised and accumulated. The red algal samples from Spain exhibited up to 2-fold higher MAA contents compared to species from cold-temperate and polar waters supporting the idea of a UV-dose-dependent induction and/or concentration. The data support the idea that MAAs represent a least for red macroalgae a natural defense system against exposure to biologically harmful UV-radiation.

Effects of ultraviolet radiation on photosynthesis and related enzyme reactions of marine macroalgae

Abstract. Changes in physiological parameters related to photosynthesis were studied in five macroalgal species from Spitsbergen (Monostroma arcticum, Laminaria solidungula, Alaria esculenta, Palmaria palmata, Phycodrys rubens) during a 72-h exposure to UV radiation. Maximal quantum yield of photochemistry (Fv/Fm) and maximal electron transport rate (ETRmax) were measured with a pulse-amplitude-modulated fluorometer; the activity of the Calvin cycle enzymes ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) and glyceraldehyde-3-phosphate dehydrogenase (G3PDH) were estimated using a photometric test. Proteins of crude extracts were separated by SDS gel electrophoresis and changes in cellular concentrations of Rubisco were determined. Moreover, the concentration of chlorophyll a (Chl a), and protein content, were measured photometrically. In all species, Chl a content, maximal quantum yield as well as ETRmax decreased during the UV treatment. Changes in ETRmax were related to the changes in the overall activity of Rubisco. Analysis of SDS gels showed that in P. rubens, L. solidungula, M. arcticum and A. esculenta decreasing Rubisco activity partly resulted from a degradation of the enzyme. However, in A. esculenta, the formation of a high-molecular-weight polypeptide was observed. In all species, the activity of Rubisco was more strongly impaired than that of G3PDH. Exposure to UV resulted in loss of total protein only in the deepwater species L. solidungula and P. rubens. The different sensitivities to UV exposure of the species tested reflect their zonation pattern in the field.

Influence of UV radiation on the photosynthesis of Arctic macroalgae in the field

Abstract The photoinhibition in brown and red macroalgae from Spitsbergen (79°N, 12°E) was investigated to study the effects of UV under balanced UV /photosynthetically active radiation (PAR) conditions. Algae were collected from different depths and exposed to natural solar radiation. Various parts of the UV radiation spectrum were successively cut off by filters absorbing wavelengths of less than 295 nm, less than 320 nm and less than 400 nm. The samples were covered with these filters and exposed to daylight 10 cm below the water surface in outdoor tanks near the shore supplied with running seawater. PAR and UV radiation were continuously measured during the experiments. The degree of photoinhibition was observed during the course of the day by measuring the in vivo fluorescence of photosystem II ( F v F m ). In addition, the transmittance of the water body of the Kongsfjord (Spitsbergen, Norway) related to the UV and PAR wavelength ranges was determined. Even on a sunny day in August, only relatively low fluence rates of UVA (approximately 13 W m−2), UVB (approximately 0.14 W m−2) and PAR (approximately 1100 μmol m−2 s−1 ) were measured in the air at noon due to the low position of the sun at this high latitude. The UV transmittance of the water body in the fjord was also low. As a result, UV stress occurred only in seaweeds growing in the intertidal zone or in shallow water. The photoinhibition of photosynthesis was mainly induced by white light in shallow water. The inhibitory effects of UV radiation caused a delay in the recovery processes in the afternoon and evening, rather than an inhibitory effect on photosynthesis in the morning. Fucus distichus, growing in the upper intertidal zone, was most insensitive to UV radiation. Algae from the sublittoral zone had problems coping with the natural UV radiation in shallow water, whereas those from the intertidal zone were acclimatized to the unfavourable UV /PAR conditions. By cutting off sequentially the shorter wavelengths of the UV range, the investigated brown algae showed no significantly different effects. In contrast, the red alga Palmaria palmata showed a clear response to the different UV ranges, i.e. the UVB wavelength range was very effective in causing photoinhibition. In addition, the recovery phase was delayed in spite of the low fluence rates impinging on the alga during the course of the day.

Acclimation of brown algal photosynthesis to ultraviolet radiation in Arctic coastal waters (Spitsbergen, Norway)

Abstract In field studies conducted at the Kongsfjord (Spitsbergen) changes of the irradiance in the atmosphere and the sublittoral zone were monitored from the beginning of June until the end of August 1997, to register the minimum and maximum fluxes of ultraviolet and photosynthetically active radiation and to characterise the underwater light climate. Measurements of photosynthesis in three abundant brown algal species (Alaria esculenta, Laminaria saccharina, Saccorhiza dermatodea) were conducted to test whether their photosynthetic performance reflects changing light climate in accordance with depth. Plants sampled at various depths were exposed to controlled fluence rates of photosynthetically active radiation (400–700 nm), UV-A (320–400 nm) and UV-B (280–320 nm). Changes in photosynthetic performance during the treatments were monitored by measuring variable chlorophyll fluorescence of photosystem II. In each species, the degree of inhibition of photosynthesis was related to the original collection depth, i.e. shallow-water isolates were more resistant than plants from deeper waters. The results show that macroalgae acclimate effectively to increasing irradiance levels for both photosynthetically active and ultraviolet radiation. However, the kinetics of acclimation are different within the different species. It is shown that one important strategy to cope with higher irradiance levels in shallow waters is the capability for a faster recovery from high light stress compared to isolates from deeper waters.

Solar ultraviolet radiation affects the activity of ribulose-1,5-bisphosphate carboxylase-oxygenase and the composition of photosynthetic and xanthophyll cycle pigments in the intertidal green alga Ulva lactuca L.

Abstract. The effect of solar UV radiation on the physiology of the intertidal green macroalga Ulva lactuca L. was investigated. A natural Ulva community at the shore of Helgoland was covered with screening foils, excluding UV-B or UV-B + UV-A from the solar spectrum. In the sampled material, changes in the activity and concentration of ribulose-1,5-bisphosphate carboxylase-oxygenase (Rubisco), and the concentration of photosynthetic and xanthophyll cycle pigments were determined. Exclusion of UV radiation from the natural solar spectrum resulted in an elevated overall activity of Rubisco, related to an increase in its cellular concentration. Among the photosynthetic pigments, lutein concentration was substantially elevated under UV exclusion. In addition, marked UV effects on the xanthophyll cycle were found: exclusion of solar UV radiation (and particularly UV-B) resulted in an increased ratio of zeaxanthin concentration to the total xanthophyll content, indicating adverse effects of UV-B on the efficiency of photoprotection under high irradiances of photosynthetically active radiation. The results confirm a marked impact of present UV-B levels on macroalgal physiology under field conditions.

PHOTOINHIBITION AND RECOVERY AFTER HIGH LIGHT STRESS IN DIFFERENT DEVELOPMENTAL AND LIFE‐HISTORY STAGES OF LAMINARIA SACCHARINA (PHAEOPHYTA)

The capacity to cope with high light stress was investigated in different life‐history and developmental stages of Laminaria saccharina Lamour. sporophytes and gametophytes. Changes in photosynthetic efficiency and in the level of photoinhibition were measured by in vivo fluorescence changes of photosystem II. Pigment content was studied using high performance liquid chromatography. Additionally, the morphology of the various developmental stages during the life cycle was studied by light microscopy in relation to the photosynthetic parameters.

Zeaxanthin content and the degree of photoinhibition are linearly correlated in the brown alga Dictyota dichotoma

Photoinhibition of photosynthesis of the brown alga Dictyota dichotoma was studied by measuring changes of photosystem II fluorescence, oxygen production and xanthophyll pool (zeaxanthin, antheraxanthin and violaxanthin). The experiments were carried out with a pulse-amplitude modulation fluorometer (PAM), a homemade oxygen measuring device and high performance liquid chromatography (HPLC) for pigment analysis. Increasing fluences of a photoinhibitory white light caused a decrease of Fv/Fm (ratio of variable to maximal fluorescence), a decrease of oxygen production and concomitantly an increase in the contribution of zeaxanthin to the xanthophyll pool. Fv/Fm and oxygen production rate both showed a negative linear correlation to the zeaxanthin-xanthophyll pool ratio of D. dichotoma. Dithiothreitol (DTT), an inhibitor of the de-epoxidase of the xanthophyll-cycle, suppressed the interconversion from violaxanthin to zeaxanthin and the decrease of the initial fluorescence (Fo) during strong-light irradiation. However, DTT was not able to prevent a decrease of Fv/Fm. With DTT, higher fluences of inhibitory white light were necessary to cause the same decrease of Fv/Fm as in the controls without DTT. The results indicate that the xanthophyll-cycle may play an important role in dynamic photoinhibition and recovery of photosynthesis in D. dichotoma.

Sensitivity of the Early Life Stages of Macroalgae from the Northern Hemisphere to Ultraviolet Radiation

The reproductive cells of macroalgae are regarded as the life history stages most susceptible to various environmental stresses, including UV radiation (UVR). UVR is proposed to determine the upper depth distribution limit of macroalgae on the shore. These hypotheses were tested by UV‐exposure experiments, using spores and young thalli of the eulittoral Rhodophyceae Mastocarpus stellatus and Chondrus crispus and various sublittoral brown macroalgae (Phaeophyceae) with different depth distribution from Helgoland (German Bight) and Spitsbergen (Arctic). In spores, the degree of UV‐induced inhibition of photosynthesis is lower in eulittoral species and higher in sublittoral species. After UV stress, recovery of photosynthetic capacity is faster in eulittoral compared to sublittoral species. DNA damage is lowest while repair of DNA damage is highest in eulittoral compared to sublittoral species. When the negative impact of UVR prevails, spore germination is inhibited. This is observed in deep water kelp species whereas the same UVR doses do not inhibit germination of shallow water kelp species. A potential acclimation mechanism to increase UV tolerance of brown algal spores is the species‐specific ability to increase the content of UV‐absorbing phlorotannins in response to UV‐exposure. Growth rates of young Mastocarpus and Chondrus gametophytes exposed to experimental doses of UVR are not affected while growth rates of all young kelp sporophytes exposed to UVR are significantly lowered. Furthermore, morphological UV damage in Laminaria ochroleuca includes tissue deformation, lesion, blistering and thickening of the meristematic part of the lamina. The sensitivity of young sporophytes to DNA damage is correlated with thallus thickness and their optical characteristics. Growth rate is an integrative parameter of all physiological processes in juvenile plants. UV inhibition of growth may affect the upper distribution depth limit of adult life history stages. Juveniles possess several mechanisms to minimize UVR damage and, hence, are less sensitive but at the expense of growth. The species‐specific susceptibility of the early life stages of macroalgae to UVR plays an important role for the determination of zonation patterns and probably also for shaping up community structure.

Involvement of solar UV-B radiation in recovery of inhibited photosynthesis in the brown alga Dictyota dichotoma (Hudson) Lamouroux

Daily variations of photosynthetic performance of the brown alga Dictyota dichotoma (Hudson) Lamouroux (Dictyotales) (estimated by Fv/Fm ratio and net O2-based photosynthesis) have been determined under full-spectrum solar radiation (PAR+UV-A+UV-B), solar radiation depleted of ultraviolet-B (PAR+UV-A) and solar radiation depleted of total ultraviolet (photosynthetically active radiation, PAR). In the daily course, the photosynthetic response of the alga is inhibited by the three solar radiation conditions at midday, but recovers during the afternoon to those values measured in the early morning only under PAR + UV-A + UV-B, or PAR alone. Under solar radiation depleted of UV-B, the recovery of photosynthesis is significantly lower than in the other two solar radiation conditions. The relative electron transport rate (ETR) as a function of PAR is calculated for the three radiation treatments, at noon after 2 h exposure. The ETR is strongly inhibited under these conditions. In the PAR and PAR + UV-A + UV-B treatments, photosynthesis recovers after 1.5 h in low irradiance (< 10 μmol photons m−2 s−1) and attains values measured in the early morning. In the absence of UV-B, the inhibitory effect is persistent, visible as a low initial slope and lower ETR at higher levels of irradiance. These data suggest that UV-B may be involved both in the impairment and the recovery of photosynthesis of D. dichotoma.