Anja Eggert

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.

Differences in acclimation potential of photosynthesis in seven isolates of the tropical to warm temperate macrophyte Valonia utricularis (Chlorophyta)

A. Eggert, R.J.W. Visser, P.R. Van Hasselt and A.M. Breeman. 2006. Differences in acclimation potential of photosynthesis in seven isolates of the tropical to warm temperate macrophyte Valonia utricularis (Chlorophyta). Phycologia 45: 546–556. DOI: 10.2216/05-03.1 The potential to acclimate photosynthesis to sub- and supra-optimal temperatures was investigated in seven isolates of Valonia utricularis (Roth) C. Agardh, a green macrophyte with a tropical to warm-temperate distribution. Photosynthesis–light response curves were obtained by measuring chlorophyll a fluorescence characteristics of algae grown at optimal (25°C), sub- and supra-optimal temperatures. Suboptimal temperatures were chosen to support 30% of the maximum relative growth rate in each isolate. Thermal acclimation was investigated by comparing short-term and long-term temperature effects on the initial rate of increase of the relative electron transport rate (rETR) and the maximum rETR under light-saturating conditions. Isolates from the northeast Atlantic and the Mediterranean all showed a strong potential to acclimate maximum rETR to suboptimal growth temperatures, i.e. short-term temperature effects were diminished after acclimation. However, photoinhibition, measured as a decrease of the maximal quantum yield (Fv/Fm), was found when plants were grown at 30°C. The isolates reduced light harvesting at 30°C by decreasing total chlorophyll content and by increasing the chlorophyll a/b ratio. Up-regulation of photoprotective processes by the xanthophyll cycle pigments was not observed. In contrast, isolates from the Indo-west Pacific were unable to acclimate photosynthesis to suboptimal growth temperatures and these temperatures were strongly photoinhibiting, even though adjustments on the pigment level were observed. All Indo-west Pacific isolates reached comparable maximum rETR values at 30° and 25°C. Thus, the Atlantic/Mediterranean isolates had a stronger potential to acclimate photosynthetic rates at suboptimal growth temperatures compared to the Indo-west Pacific isolates, which was accompanied by losses at 30°C. The results are discussed in a biogeographical context.

Trehalose, digeneaside, and floridoside in the Florideophyceae (Rhodophyta) - a reevaluation of its chemotaxonomic value

U. Karsten, S. Görs, A. Eggert and J.A. West. 2007. Trehalose, digeneaside, and floridoside in the Florideophyceae (Rhodophyta) – a reevaluation of its chemotaxonomic value. Phycologia 46: 143–150. DOI: 10.2216/06-29.1 The qualitative and quantitative occurrence of low-molecular-weight carbohydrates (LMWCs) in the Florideophyceae was surveyed using 13C-nuclear magnetic resonance spectroscopy and high-performance liquid chromatography. Besides the joint occurrence of the heterosides floridoside and digeneaside in various Florideophycean orders (Ceramiales, Rhodymeniales, Gelidiales and Gigartinales), the disaccharide trehalose was detected only in several members of the Ceramiales. While some taxa of the latter order such as Aglaothamnion exhibited only trehalose, others, such as Delesseria sanguinea, showed trehalose together with digeneaside. The biosynthesis and physiological function of trehalose in red algae remains an open question. In addition, recent data from the literature indicate strong variation between phenotypic and genotypic formation of trehalose among red algal orders, and hence there exists some uncertainty to use this disaccharide as a chemotaxonomic marker. The occurrence of digeneaside in so many phylogenetically different Florideophycean taxa clearly negates any diagnostic value for this particular heteroside in the Ceramiales. In conclusion, while trehalose and digeneaside are unsuitable as chemotaxonomic markers for red algal phylogeny, other LMWCs, such as polyols and D-/L-isofloridoside, well support recent molecular taxonomic treatments.

Quantification of algal biofilms colonising building materials: chlorophyll a measured by PAM-fluorometry as a biomass parameter

Abstract The aim of this study was to quantify algal colonisation on anthropogenic surfaces (viz. building facades and roof tiles) using chlorophyll a (chl a) as a specific biomarker. Chl a was estimated as the initial fluorescence F0 of ‘dark adapted’ algae using a pulse-modulated fluorometer (PAM-2000). Four isolates of aeroterrestrial green algae and one aquatic isolate were included in this study. The chl a concentration and F0 showed an exponential relationship in the tested range between 0 and 400 mg chl a m−2. The relationship was linear at chl a concentrations <20 mg m−2. Exponential and linear models are presented for the single isolates with large coefficients of determination (exponential: r2 > 0.94, linear: r2 > 0.92). The specific power of this fluorometric method is the detection of initial algal colonisation on surfaces in thin or young biofilms down to 3.5 mg chl a m−2, which corresponds to an abundances of the investigated isolates between 0.2 and 1.5 million cells cm−2.

Ecophysiological performance of the primitive red alga Dixoniella grisea (Rhodellophyceae) to irradiance, temperature and salinity stress: growth responses and the osmotic role of mannitol

A. Eggert, S. Raimund, D. Michalik, J. West and U. Karsten. 2007. Ecophysiological performance of the primitive red alga Dixoniella grisea (Rhodellophyceae) to irradiance, temperature and salinity stress: growth responses and the osmotic role of mannitol. Phycologia 46: 22–28. DOI: 10.2216/06-12.1 A culture strain of the benthic unicellular red alga Dixoniella grisea was investigated under different stress conditions. The effects of salinity, temperature and irradiance on growth rates were examined in two-factorial experiments and the accumulation of mannitol in response to increasing salinity investigated. The strain grows in a broad salinity range, from brackish water to twice seawater (60 psu). At optimal salinity (10 psu) and optimal temperature conditions (25–30°C), D. grisea grew best at moderate photon flux densities (PFDs; 50–100 μmol photons m−2 s−1). However, interactive effects between all factors were present. At suboptimal salinities and temperatures, maximal growth rates were shifted to lower PFD and growth was considerably reduced at 50 and 100 μmol photons m−2 s−1. The polyol mannitol was the main low molecular weight carbohydrate in D. grisea. This was verified by 13C-nuclear NMR spectroscopy and HPLC analysis. Mannitol levels increased from 2 to 52 μmol g−1 dry weight (dw) with increasing salinities between 10 and 60 psu, indicating its role as an osmolyte for the first time in a unicellular red alga.

Low Molecular Weight Carbohydrates in Red Algae – an Ecophysiological and Biochemical Perspective

The red algae (Rhodophyta) represent a distinct eukaryotic lineage characterized by the accessory photosynthetic pigments phycoerythrin, phycocyanin, and allophycocyanins arranged in phycobilisomes, and the absence of flagella and centrioles (Woelkerling,1990). While some rhodophytes are unicellular, most species grow as filaments or membranous sheets of cells. The evolutionary relationships of simpler red algae, both unicellular and multicellular, have been the subject of extensive investigations for many years (Seckbach,1994). The paleontological specimen Bangiomorpha pubescens from the 1,200-million-year-old Hunting Formation in the Canadian Arctic is morphologically very similar to the contemporary genus Bangia(Butterfield et al., 1990), and hence represents the earliest putative record for taxonomically resolvable complex multicellularity among eukaryotes, as well as for the early evolutionary origin of the multicellular red algae.

Ecotypic differentiation in thermal traits in the tropical to warm-temperate green macrophyte Valonia utricularis

Abstract Differentiation of thermal traits (i.e. growth, survival and reproduction) was studied in the green macrophyte Valonia utricularis (Roth) C. Agardh, which has a world-wide tropical to warm-temperate distribution. Ecotypic differentiation between northeast Atlantic/Mediterranean and Indo-west Pacific isolates occurred with respect to all investigated temperature characteristics. The Atlantic/Mediterranean group is more eurythermal and cold-tolerant compared to the Indo-west Pacific group, which is stenothermal and cold-sensitive. Isolates of Atlantic/Mediterranean origin show clearly higher growth rates at low temperatures (lower temperature limit: 5–8 vs. 18–20 °C) and a much better tolerance to low temperatures than the Indo-west Pacific isolates (0–5 vs. 16 °C). Large shifts towards low temperatures are accompanied by parallel but smaller shifts at high temperatures. Differences in upper survival temperatures amounted on average to 4 °C (32–33 °C vs. 34–37 °C) and growth ceased in the Atlantic isolates at 30 °C, whereas the Indo-west Pacific isolates still reached significant growth at 33 °C. Additionally, temperature requirements for reproduction were shifted towards lower temperatures in the Atlantic/Mediterranean isolates [18–20 and 25 °C vs. 28–30(33) °C]. The cold-adapted Atlantic/Mediterranean ecotype retained a strong tropical imprint with high temperature tolerance and high growth rates at temperatures > 25 °C. The northern distribution limit in the northeastern Atlantic Ocean at 39 °N (at the 13 °C February and 17 °C August isotherms) is probably set by a growth and/or reproduction boundary. The northern distribution limit in the Pacific Ocean at 26 °N (at the 21 °C February and 29 °C August isotherms) is probably set by low lethal winter temperatures. The different latitudes of these boundaries must be attributed to the occurrence of more cold-adapted populations in the northeastern Atlantic Ocean compared to the northwestern Pacific Ocean. The development of cold-adaptation in the northeastern Atlantic Ocean and its absence in the northwestern Pacific Ocean has been related to different impacts of Pleistocene glaciations.

Biochemical characterization of mannitol metabolism in the unicellular red alga Dixoniella grisea (Rhodellophyceae)

The mannitol cycle has been verified in a unicellular red alga (Rhodellophyceae) for the first time. All four enzymes involved in the cycle (mannitol-1-phosphate dehydrogenase, Mt1PDH: EC 1.1.1.17; mannitol-1-phosphatase, Mt1Pase: EC 3.1.3.22; mannitol dehydrogenase, MtDH: 1.1.1.67; hexokinase, HK: 2.7.1.1.) were detected and characterized in crude algal extracts from Dixoniella grisea. These enzymes, with the exception of Mt1Pase, were specific to their corresponding substrates and nucleotides. The activities of enzymes in the anabolic pathway (fructose-6-P reduction by Mt1PDH and mannitol-6-P reduction by Mt1Pase) were at least 2- to 4-fold greater than those of the catabolic pathway (mannitol oxidation by MtDH and fructose oxidation by HK). There appears to be, therefore, a net carbon flow in D. grisea towards a high intracellular mannitol pool. The mannitol cycle guarantees a rapid accumulation or degradation of mannitol within algal cells in response to changing salinity in natural habitats. Moreover, the demonstration of the mannitol cycle within the Rhodellophyceae provides evidence that this metabolic pathway is of ancient origin in the red algal lineage.

Distribution of three submersed macrophytes in coastal lagoons of the German Baltic Sea: comparison of laboratory and field data

Abstract The distributions of three submersed macrophytes Najas marina, Myriophyllum spicatum and Zostera noltii were surveyed in the inner coastal lagoons of the German Baltic Sea. Growth and photosynthetic performances of these species were investigated in crossed laboratory experiments (salinity × irradiance). Z. noltii showed the potential to grow in mesohaline lagoons, while N. marina seemed to be restricted to oligohaline areas. The potential distribution area of M. spicatum overlapped with those of the other two species. The laboratory results for N. marina and M. spicatum correspond with the recent distribution of the two species in the investigation area. However, neither historical nor recent distribution records of Z. noltii match the potential of this species to grow at 3 and 8 psu. Potential depth limits were calculated for the three species at their collection sites. Accordingly, N. marina had the potential to grow at 0.9–1.1 m depth in the Saaler Bodden, M. spicatum at 1.1–2.1 m depth in the Großer Jasmunder Bodden and Z. noltii down to 2.5–5.1 m depth in the Salzhaff. N. marina grows maximally at 1.0 m in the Saaler Bodden, M. spicatum at 2.0 m in the Großer Jasmunder Bodden and Z. noltii at 3.0 m in the Salzhaff. Thus, recent and modelled historical values of all three species do not differ, and recent distribution limits do not indicate an eutrophication-induced decrease in depth distributions of these species at their respective collection sites.