Effects of kelp canopy on underwater light climate and viability of brwon algal spores in Kongsfjorden (Spitsbergen)

Spores represent the most vulnerable life history stage of kelps. While UV-induced inhibition of spore germination has been readily documented, the impact of in situ underwater radiation below kelp canopies has been largely overlooked. We determined spectral composition and intensity of underwater radiation along a density gradient in an Alaria esculenta kelp forest at 3 m depth in Kongsfjorden, Svalbard. Accordingly, we set up a laboratory experiment simulating five different radiation conditions corresponding to irradiances under very dense to no canopy cover on a cloudless summer day. Spore responses (photosynthetic quantum yield, pigment and phlorotannin contents, swimming activity, and germination success) were determined after 4, 8, 16, and 24 h of exposure. In situ spectral radiation composition differed strongly from conditions applied in previous studies, which underestimated photosynthetically active radiation and overestimated UV-radiation effects. Furthermore, spore solutions differed significantly in quantum yield, pigment, and phlorotannin contents upon release. Nevertheless, spores reacted dynamically to different radiation conditions and exposure times. Highest radiation (PAR 61.8 W m−2, 1.9 W m−2 UVA, 0.01 W m−2 UVB) caused photodamage after exposure for ≥ 8 h, while intermediate radiation led to photoinhibition. Lowest radiation (PAR 0.23 W m−2, 0 W m−2 UVA, 0 W m−2 UVB) caused inconsistent reactions. There was a reduction of absolute pigment content in all treatments, but reduction rates of photosynthetic pigments were significantly different between radiation treatments. Soluble phlorotannin content decreased under all conditions but was not significantly affected by experimental conditions. High radiation reduced swimming activity of spores, but experimental conditions had almost no effect on germination success. Consequently, it seems unlikely that in situ radiation conditions negatively affect spores in present and future radiation scenarios

Cold thermal priming of Laminaria digitata (Laminariales, Phaeophyceae) gametophytes enhances gametogenesis and thermal performance of sporophytes

Thermal characteristics of kelp species have been studied in many ways, but potentially persistent effects of temperature across generations are yet poorly understood. In this context, the effect of thermal priming on fertility and growth of the N-Atlantic kelp species Laminaria digitata was investigated within and across life cycle generations in a two-step common garden experiment. Using vegetative clonal gametophytes from cold (5°C) and warm (15°C) pre-experimental cultivation (3 years), we first quantified gametogenesis and recruitment over two weeks at a common temperature of 10°C. Then, recruited sporophytes were transferred to a temperature gradient spanning the tolerance range of the species from 0°C to 20°C. We hypothesized that a warm gametophyte preexperimental cultivation promotes performance of sporophytes at warm temperatures and vice versa. Interestingly, gametogenesis speed and sporophyte recruitment were higher in gametophytes following cold compared to warm pre-experimental cultivation, which indicates carry-over effects of temperature within the gametophyte generation. Compared to warm pre-experimental cultivation of gametophytes, a cold preexperimental cultivation enhanced growth of juvenile Laminaria digitata sporophytes by more than 69% at the extreme low and high temperatures of 0 and 20°C. This is the first evidence for a cross-generational effect between gametophyte parents and offspring sporophytes. As cold gametophyte cultivation increased the trait performance of gametogenesis, recruitment and thermal tolerance of juvenile sporophytes, priming of early life cycle stages may be used to increase resilience and productivity of kelps in marine forest restoration efforts and kelp mariculture

Seasonal variations of Fucus vesiculosus fertility under ocean acidification and warming in the western Baltic

Ocean warming and acidification may substantially affect the reproduction of keystone species such as Fucus vesiculosus (Phaeophyceae). In four consecutive benthic mesocosm experiments, we compared the reproductive biology and quantified the temporal development of Baltic Sea Fucus fertility under the single and combined impact of elevated seawater temperature and pCO2 (1100 ppm). In an additional experiment, we investigated the impact of temperature (0–25°C) on the maturation of North Sea F. vesiculosus receptacles. A marked seasonal reproductive cycle of F. vesiculosus became apparent in the course of 1 year. The first appearance of receptacles on vegetative apices and the further development of immature receptacles of F. vesiculosus in autumn were unaffected by warming or elevated pCO2. During winter, elevated pCO2 in both ambient and warmed temperatures increased the proportion of mature receptacles significantly. In spring, warming and, to a lesser extent, elevated pCO2 accelerated the maturation of receptacles and advanced the release of gametes by up to 2 weeks. Likewise, in the laboratory, maturation and gamete release were accelerated at 15–25°C relative to colder temperatures. In summary, elevated pCO2 and/or warming do not influence receptacle appearance in autumn, but do accelerate the maturation process during spring, resulting in earlier gamete release. Temperature and, to a much lesser extent, pCO2 affect the temporal development of Fucus fertility. Thus, rising temperatures will mainly shift or disturb the phenology of F. vesiculosus in spring and summer, which may alter and/or hamper its ecological functions in shallow coastal ecosystems of the Baltic Sea

Thermal traits for reproduction and recruitment differ between Arctic and Atlantic kelp Laminaria digitata

The plasticity of different kelp populations to heat stress has seldom been investigated excluding environmental effects due to thermal histories, by raising a generation under common garden conditions. Comparisons of populations in the absence of environmental effects allow unbiased quantification of the meta-population adaptive potential and resolution of population-specific differentiation. Following this approach, we tested the hypothesis that genetically distinct arctic and temperate kelp exhibit different thermal phenotypes, by comparing the capacity of their microscopic life stages to recover from elevated temperatures. Gametophytes of Laminaria digitata (Arctic and North Sea) grown at 15°C for 3 years were subjected to common garden conditions with static or dynamic (i.e., gradual) thermal treatments ranging between 15 and 25°C and also to darkness. Gametophyte growth and survival during thermal stress conditions, and subsequent sporophyte recruitment at two recovery temperatures (5 and 15°C), were investigated. Population-specific responses were apparent; North Sea gametophytes exhibited higher growth rates and greater sporophyte recruitment than those from the Arctic when recovering from high temperatures, revealing differential thermal adaptation. All gametophytes performed poorly after recovery from a static 8-day exposure at 22.5°C compared to the response under a dynamic thermal treatment with a peak temperature of 25°C, demonstrating the importance of gradual warming and/or acclimation time in modifying thermal limits. Recovery temperature markedly affected the capacity of gametophytes to reproduce following high temperatures, regardless of the population. Recovery at 5°C resulted in higher sporophyte production following a 15°C and 20°C static exposure, whereas recovery at 15°C was better for gametophyte exposures to static 22.5°C or dynamic heat stress to 25°C. The subtle performance differences between populations originating from sites with contrasting local in situ temperatures support our hypothesis that their thermal plasticity has diverged over evolutionary time scales.FCT: PTDC/MAR-EST/6053/2014/ UID/Multi/04326/2019/ BIODIVERSA/0004/2015/ SFRH/BPD/122567/2016/ DL 57/2016/CP1361/CT0039/ SFRH/BSAB/150485/2019info:eu-repo/semantics/publishedVersio

The significance of new records of benthic red algae (Rhodophyta) for Hainan Island (and China) between 1990 and 2016

We present an annotated list of new finds of red algae from Hainan Island, Southern China, including those found in 1990 and 1992 during the German-Chinese expeditions to Hainan Island and in 2008–2016 by Titlyanova, Titlyanov, and Li. Between 1990 and 1992, a total of 64 taxa of red algae were newly recorded for Hainan Island. Of these 15 species were new records for China. During the period 2008–2016, a further 54 taxa were newly recorded for Hainan Island, of which 20 were new records for China. The full list of new taxa includes taxonomic forms, dates, and locales, together with known biogeographical distributions. During both periods, the apparent enrichment of red algal marine flora has occurred in a similar way—mainly at the expense of epiphytes with filamentous, thin-filamentous, and finely branched forms. We believe that the changes in the flora of Hainan Island have been influenced by both anthropogenic and natural factors including in particular exploitation of herbivores, nutrient pollution, and coral bleaching

Interactions of daylength, temperature and nutrients affect thresholds for life stage transitions in the kelp Laminaria digitata (Phaeophyceae)

Kelp beds worldwide are under pressure from ongoing climate and environmental change. Along European coastlines increases in seawater temperature and changes in nutrient conditions occur where upwelling events are disrupted and also along eutrophicated coasts. In addition, seaweed responses to change may interact with seasonal daylength cycles. We performed a factorial experiment to examine the combined effects of seawater temperatures, nutrient regimes and photoperiod (long and short days) in order to better understand how latitudinal or seasonal differences in daylengths affect the sensitivity of transient microscopic kelp stages of Laminaria digitata from the North Sea to warming and eutrophication. While the optimal temperature range for vegetative gametophyte growth was 10 degrees C-18 degrees C under long summer photoperiod conditions, gametogenesis was induced at lower temperatures between 5 degrees C and 15 degrees C, with maximum sporophyte development under long photoperiods and enriched nutrient regimes, which represent local late spring conditions. Although gametogenesis was fastest at 10 degrees C-15 degrees C, sporophyte recruitment was highest at 5 degrees C. As these particular early life cycle processes in L. digitata have different temperature optima, this may drive the seasonal cycle of recruitment in the field. Increasing summer temperatures due to global warming will increase gametophyte size due to enhanced vegetative growth and inhibition of gametogenesis. This will probably lead to delayed but enhanced recruitment of new sporophytes under cooler autumn to spring conditions over a wide geographical scale, preventing the formation of juvenile sporophytes under stressful summer conditions and possibly changing annual recruitment patterns.STSM Grant from the COST Action "Phycomorph" [FA1406]; Portuguese Science Foundation (FCT) programs [EXCL/AAG-GLO/0661/2012, UID/Multi/04326/2013]; BiodiVERsA [Biodiversa/0004/2015, PTDC/MAR-EST/6053/2014]info:eu-repo/semantics/publishedVersio

Sex-dependent and-independent transcriptional changes during haploid phase gametogenesis in the sugar kelp Saccharina latissima

In haplodiplontic lineages, sexual reproduction occurs in haploid parents without meiosis. Although widespread in multicellular lineages such as brown algae (Phaeophyceae), haplodiplontic gametogenesis has been little studied at the molecular level. We addressed this by generating an annotated reference transcriptome for the gametophytic phase of the sugar kelp, Saccharina latissima. Transcriptional profiles of microscopic male and female gametophytes were analysed at four time points during the transition from vegetative growth to gametogenesis. Gametogenic signals resulting from a switch in culture irradiance from red to white light activated a core set of genes in a sex-independent manner, involving rapid activation of ribosome biogenesis, transcription and translation related pathways, with several acting at the post-transcriptional or post-translational level. Additional genes regulating nutrient acquisition and key carbohydrate-energy pathways were also identified. Candidate sex-biased genes under gametogenic conditions had potentially key roles in controlling female- and male-specific gametogenesis. Among these were several sex-biased or -specific E3 ubiquitin-protein ligases that may have important regulatory roles. Females specifically expressed several genes that coordinate gene expression and/or protein degradation, and the synthesis of inositol-containing compounds. Other female-biased genes supported parallels with oogenesis in divergent multicellular lineages, in particular reactive oxygen signalling via an NADPH-oxidase. Males specifically expressed the hypothesised brown algal sex-determining factor. Male-biased expression mainly involved upregulation of genes that control mitotic cell proliferation and spermatogenesis in other systems, as well as multiple flagella-related genes. Our data and results enhance genome-level understanding of gametogenesis in this ecologically and economically important multicellular lineage.FCTprograms UID/Multi/04326/2019, GENEKELP-PTDC/MAR-EST/6053/2014,MARFOR-Biodiversa/0004/2015, FRH/BPD/122567/2016. Swedish Research Council Formas, Naturvardsverket French National Research Agency (ANR) Spanish Government, FRCT, German Research Foundation (DFG), Pew Marine Fellowship, STSM Grant from the COST Action "Phycomorph" FA1406info:eu-repo/semantics/publishedVersio

Transgenerational temperature effects in the kelp Laminaria digitata

Transgenerational effects (effects of parental environment on offspring traits) have recently gained attention as a means of fast response to changing environmental conditions, e.g. under climate change. In temperate and polar rocky coastal ecosystems, kelps form the base of complexly structured and highly diverse species associations. This study investigates the potential for temperature-mediated transgenerational plasticity along the development from haploid parents (gametophytes) to their juvenile diploid offspring (sporophytes) in a geographically isolated population of the brown alga Laminaria digitata from the island of Helgoland (North Sea). We sampled spores from wild donor sporophytes, which we raised at 5 and 15 °C during gametogenesis, and reared the resulting young sporophytes for three months in a full-factorial split design while keeping genetic lineages separate. A concluding 12-day experiment on growth, biochemistry (carbon, mannitol content) and photosynthetic characteristics (maximum quantum yield Fv/Fm, maximum electron transport rate rETRmax) of five genetic lineages allowed for the separation of late temperature (12 day) responses, within-generation plasticity (early temperature) and transgenerational plasticity (gametogenesis temperature) in response to 5 and 15 °C. We observed significant two- and three-way interactions between gametogenesis temperature and early and late sporophyte temperatures for all parameters. While interactive effects between early and late experimental temperatures probably represent acclimation processes, interactions involving gametogenesis temperature indicate transgenerational effects. The direction of these effects differed between parameters. A main effect is that only with a history of 5 °C as gametogenesis and early temperature, sporophytes are growing faster at 5 than 15 °C over 12 days late temperature. According to our results, the temperature experienced by parents during gametogenesis influences temperature reaction norms in three- to four-month-old Laminaria digitata sporophytes. This, to our knowledge, is the first evidence for transgenerational plasticity in kelps

Video survey of deep benthic macroalgae and macroalgal detritus along a glacial Arctic fjord: Kongsfjorden (Spitsbergen)

In Kongsfjorden (Spitsbergen), we quantified the zonation of visually dominant macroalgal taxa and of detached macroalgae from underwater videos taken in summer 2009 at six transects between 2 and 138 m water depth. For the first time, we provide information on the occurrence of deep water red algae below the kelp forest and of detached macroalgae at water depth > 30 m. The presence and depth distribution of visually dominant red algae were especially pronounced at the outer fjord, decreased with proximity to the glacial front and they were absent at the innermost locations. Deepest crustose coralline red algae and foliose red algae were observed at 72 and 68 m, respectively. Brown algae were distributed along the entire fjord axis at 2–32 m. Green algae were only present at the middle to inner fjord and at areas influenced by physical disturbance at water depths of 2–26 m. With proximity to the inner fjord the depth distribution of all macroalgae became shallower and only extended to 18 m depth at the innermost location. Major recipients of detached macroalgae were sites at the shallower inner fjord and at the middle fjord below the photic zone at depths to 138 m. They may either fuel deep water secondary production, decompose or support carbon sequestration. Univariate and community analyses of macroalgal classes including detached macroalgae across transects and over depths reveal a considerable difference in community structure between the outermost sites, the central part and the inner fjord areas, reflecting the strong environmental gradients along glacial fjords