Growth Of Germlings Research Articles

Effects of short‐wavelength ultraviolet ray irradiation on the early development and induction of pigmentation mutants of conchospore germlings in Pyropia haitanensis (Rhodophyta)

Ultraviolet mutagenesis is a safe and efficient method to induce mutations for breeding new germplasm of laver. In this study, high-frequency short-wave ultraviolet (UV-C) irradiation (λ = 254 nm) with different doses (50, 100, 200, 300, 400 and 500 J m−2) was used to induce colour mutants during the germination of conchospores in Pyropia haitanensis. The early development of conchospore germination and the morphogenesis of tetrad germlings were observed, which revealed that low-dose irradiation (50 J m−2) promoted the germination and early development of conchospores, while irradiation doses above 100 J m−2 inhibited the germination of conchospores and growth of tetrad germlings. In the dose range of 50–500 J m−2, the survival rate and germination rate of conchospores gradually decreased, while the mutation rate of colour mutants increased first and then decreased with increasing doses. The highest mutation rate was observed with the dose of 300 J m−2 or with irradiation time 72 s. These results indicated that the optimal UV-C irradiation dose was 300 J m−2 for the mutagenesis of P. haitanensis conchospores. In addition, UV-C irradiation also had a significant effect on the early development of conchospores and phenotypes of pigmentation mutant arranged in tetrad germlings, which was mainly manifested in the large number of colour-sectored blades produced by irradiated conchospores and in the decrease in their aspect ratios. This study provides new insights in carrying out UV-C mutagenesis for the breeding of P. haitanensis.

Interactive effects of salinity and copper toxicity on the growth and photosynthetic efficiency of germlings and adult brown alga Fucus ceranoides (Fucales, Phaeophyceae)

Laboratory experiments were conducted to investigate the effect of copper enrichment (0.6, 2, 4, 8, 18 and 36 μg L−1) and salinity (8.5, 17 and 24%) on growth, photosynthetic efficiency “PE” (expressed as chlorophyll fluorescence) and copper accumulation in germlings and adult brown alga Fucus ceranoides. The PE for the algae exposed to 17% salinity was markedly stable throughout the experiment, while it was significantly (0.01 ˂ p ˂ 0.05) reduced in algae exposed to 8.5% salinity in the presence of 36 μg L−1 Cu by 20% when compared to those exposed to 0.6 μg L−1 Cu. Moreover, the maximum electron transport rate (ETRmax) was decreased significantly with increasing concentrations of Cu (p ˂ 0.001) and level of salinity (p ˂ 0.01); moreover, there was a significant interaction between Cu and salinity. The combination of copper and reduced salinity gave synergistic effects, as a consequence, this could limit the population growth of seaweeds in coastal areas. More research is needed to understand the basic requirements and stress tolerance in seaweeds for reef restoration and other management actions to be successful for sustainable development.The results of the present study suggest that any change in the environment will directly and significantly affect algal physiology, and thus it could be used for biomonitoring in situ. Moreover, the assessment of the physiological status of algae in combination with the analysis of thallus metal content will improve the trustworthiness of the biomonitoring process.

Artificial seed production and cultivation of <italic>Sargassum macrocarpum</italic> (Fucales, Phaeophyta)

Sargassum macrocarpum is a rich source of anti-inflammatory compounds. Recently, one of the compounds, tuberatolide B, has been reported as a functional anti-inflammatory additive for foods and nutraceuticals. The artificial seeding, growth and maturation of S. macrocarpum were investigated from May 2018 to September 2019. Indoor culture experiments for induction of egg release were conducted at temperatures of 17, 20, 23, and 26°C and irradiances of 0, 10, 20, 40, and 80 μmol photons m−2 s−1 under 14 : 10 h (L : D) photoperiod. Within a given treatment combination, higher temperatures and irradiance levels favoured the maturation of receptacles in S. macrocarpum. Using artificial temperature and irradiance control, thalli matured one month earlier than thalli in nature. Under natural condition, receptacle formation began in April, and the eggs were released in June and July. The release of eggs from the receptacles was promoted at 17–20°C and 40–80 μmol photons m−2 s−1, and the fastest growth of germlings occuring at 15–17°C and 40 μmol photons m−2 s−1. For mature thalli, 300 g wet-weight was sufficient to seed 100 m of seed string. Thalli grew to 10.5 ± 2.6 cm in length at a density of 6.7 ± 3.3 individuals m−1 after 1 year of cultivation, from germination. This study demonstrates that it is possible to cultivate S. macrocarpum for the production of anti-inflammatory products. Key words: cultivation; growth; maturation; Sargassum macrocarpum; seed production

Detrimental effects of sediment on attachment, survival and growth of the brown alga Sargassum thunbergii in early life stages

SUMMARYSediment loading by human activities has increased in recent years and sedimentation in coastal areas is problematic because it removes seaweed forests. In this study, we examined the effects of different sediment quantities (0, 2, 4, and 6 mg cm−2) and particles sizes (<100, 100–250, and 250–600 μm) on zygote attachment, and germling survival and growth of Sargassum thunbergii, an economically and ecologically important species. Zygote attachment was negatively correlated with increased sediment quantities. However, it was not significantly different among sediment particle sizes. In addition, survival and growth of germlings were significantly inhibited by increased sediment quantity. Smaller particle size (< 100 μm) had greater negative impact on the survival and growth than bigger ones. Results of the present study suggest that early development of S. thunbergii is significantly inhibited by sediment. This might be a vital factor that results in forest depletion in Korea.

감태, Ecklonia cava 유주자 침지시간에 따른 기질별 유엽의 부착밀도 및 초기성장

감태, Ecklonia cava 유주자 침지시간에 따른 기질별 유엽의 부착밀도 및 초기성장

Silencing of DND1 in potato and tomato impedes conidial germination, attachment and hyphal growth of Botrytis cinerea

BackgroundBotrytis cinerea, a necrotrophic pathogenic fungus, attacks many crops including potato and tomato. Major genes for complete resistance to B. cinerea are not known in plants, but a few quantitative trait loci have been described in tomato. Loss of function of particular susceptibility (S) genes appears to provide a new source of resistance to B. cinerea in Arabidopsis.ResultsIn this study, orthologs of Arabidopsis S genes (DND1, DMR6, DMR1 and PMR4) were silenced by RNAi in potato and tomato (only for DND1). DND1 well-silenced potato and tomato plants showed significantly reduced diameters of B. cinerea lesions as compared to control plants, at all-time points analysed. Reduced lesion diameter was also observed on leaves of DMR6 silenced potato plants but only at 3 days post inoculation (dpi). The DMR1 and PMR4 silenced potato transformants were as susceptible as the control cv Desiree. Microscopic analysis was performed to observe B. cinerea infection progress in DND1 well-silenced potato and tomato leaves. A significantly lower number of B. cinerea conidia remained attached to the leaf surface of DND1 well-silenced potato and tomato plants and the hyphal growth of germlings was hampered.ConclusionsThis is the first report of a cytological investigation of Botrytis development on DND1-silenced crop plants. Silencing of DND1 led to reduced susceptibility to Botrytis, which was associated with impediment of conidial germination and attachment as well as hyphal growth. Our results provide new insights regarding the use of S genes in resistance breeding.

Buffering and Amplifying Interactions among OAW (Ocean Acidification & Warming) and Nutrient Enrichment on Early Life-Stage Fucus vesiculosus L. (Phaeophyceae) and Their Carry Over Effects to Hypoxia Impact.

Ocean acidification and warming (OAW) are occurring globally. Additionally, at a more local scale the spreading of hypoxic conditions is promoted by eutrophication and warming. In the semi-enclosed brackish Baltic Sea, occasional upwelling in late summer and autumn may expose even shallow-water communities including the macroalga Fucus vesiculosus to particularly acidified, nutrient-rich and oxygen-poor water bodies. During summer 2014 (July–September) sibling groups of early life-stage F. vesiculosus were exposed to OAW in the presence and absence of enhanced nutrient levels and, subsequently to a single upwelling event in a near-natural scenario which included all environmental fluctuations in the Kiel Fjord, southwestern Baltic Sea, Germany (54°27 ´N, 10°11 ´W). We strove to elucidate the single and combined impacts of these potential stressors, and how stress sensitivity varies among genetically different sibling groups. Enhanced by a circumstantial natural heat wave, warming and acidification increased mortalities and reduced growth in F. vesiculosus germlings. This impact, however, was mitigated by enhanced nutrient conditions. Survival under OAW conditions strongly varied among sibling groups hinting at a substantial adaptive potential of the natural Fucus populations in the Western Baltic. A three-day experimental upwelling caused severe mortality of Fucus germlings, which was substantially more severe in those sibling groups which previously had been exposed to OAW. Our results show that global (OAW), regional (nutrient enrichment) and local pressures (upwelling), both alone and co-occurring may have synergistic and antagonistic effects on survival and/or growth of Fucus germlings. This result emphasizes the need to consider combined stress effects.

Altered seawater salinity levels affected growth and photosynthesis of Ulva fasciata (Ulvales, Chlorophyta) germlings

Seawater salinity is greatly influenced by tide, evaporation and rain falls. In this study, we investigated the growth and photosynthetic responses of zygote-derived Ulva fasciata Delile germlings to short-term (minutes) and prolonged (days) exposure to different salinity gradients, to evaluate the effect of salinity variation on the early stage of life history in this seaweed. The results showed that, the maximum net photosynthetic rates (NPRm) of U. fasciata germlings was observably decreased in desalted (25 and 15) and high (45) salinity seawater in short-term exposure tests (in minutes). However, after 30 min, the photosynthesis activity in medium salinity (25) was maintained at a relative high level (above 70%). After 8 d prolonged culture, the photosynthesis and mean relative growth rate (RGR) of germlings were all markedly lowered, whereas the malondialdehyde (MDA) contents increased as the salinity desalted from 34 to 15. The salinity decrease from 34 to 25 had no significant effect on the RGR, but obviously influenced the morphology of the germlings. High salinity level (45) significantly depressed the RGR and photosynthesis of U. fasciata germlings, while it notably increased the MDA contents. The results showed that the salinity elevation had more detrimental effects on Ulva fasciata germlings than salinity decrease did. The germlings grown at the salinity seawater levels from 25 to 34, performed preferable photosynthetic acclimation both in temporary and prolonged culture. Broad salinity tolerance from 25 to 34 in U. fasciata germlings may have partly evolved as a response to regular diurnal tides.

Effects of periodic air-exposure and nutrients on the competition of Ascophyllum nodosum and Fucus vesiculosus germlings

To examine the relationship between competition and environmental factors, the germlings of Ascophyllum nodosum (L) Le Jolis and Fucus vesiculosus L. were cultured in monocultures and mixtures of the two species under two different exposure and nutrient levels. Both intra- and inter-specific competition were examined in comparison of the mortality and growth of germlings in monocultures and mixtures of the two species. The mortality of germlings increased with increasing density and emergence periods both in the monoculture and mixtures of the two species, and the mortality of Ascophyllum was significantly higher than that of Fucus both in submerged and emerged treatments. The growth of germlings of both species reduced with increasing density but F. vesiculosus always grew faster than Ascophyllum. The values of log output ratio were more than 0.1, indicating that Fucus ‘won’ in the competitive battles with Ascophyllum under two nutrient- and air-exposure levels. Log output ratio was greater in high than in low nutrients, indicating that the growth of Fucus is more enhanced than that of Ascophyllum in high nutrients. In the present study, the outcome of inter specific competition between germlings of Fucus vesiculosus and Ascophyllum nodosum was slightly altered by duration of emergence and nutrient concentration, but not to such an extent as to change the outcome.

ẢNH HƯỞNG ÁNH SÁNG VÀ DINH DƯỠNG TRONG QUÁ TRÌNH NHÂN GIỐNG RONG MƠ - SARGASSUM POLYCYSTUM C. AGARDH TỪ HỢP TỬ

Increasing the growth of germlings and decreasing fouling algae are two main constraints for the seedling production of Sargassum in laboratory condition. These results indicate that the growth of germlings was best in nutrient concentration of NaNO­­3 : KH2PO4= 4 : 0,4 mg/L and photon irradiance of 510 µmol photon/m2/s. During the experiment, fouling was controlled by degration of photon irradiance. Seedlings of > 0.2cm length could be achieved after 2 month of tank culture. However, seedlings of 2 cm length could be achieved after 4,5 month of tank culture from seedlings of 0.2 cm length. These results indicate that the growth of seedling was low during their nursery cultivation stage at laboratory. Therefore, successful cultivation in nursery stage is essential for field conduction.

ẢNH HƯỞNG ÁNH SÁNG VÀ DINH DƯỠNG TRONG QUÁ TRÌNH NHÂN GIỐNG RONG MƠ - SARGASSUM POLYCYSTUM C. AGARDH TỪ HỢP TỬ

Increasing the growth of germlings and decreasing fouling algae are two main constraints for the seedling production of Sargassum in laboratory condition. These results indicate that the growth of germlings was best in nutrient concentration of NaNO­­3 : KH2PO4= 4 : 0,4 mg/L and photon irradiance of 510 µmol photon/m2/s. During the experiment, fouling was controlled by degration of photon irradiance. Seedlings of > 0.2cm length could be achieved after 2 month of tank culture. However, seedlings of 2 cm length could be achieved after 4,5 month of tank culture from seedlings of 0.2 cm length. These results indicate that the growth of seedling was low during their nursery cultivation stage at laboratory. Therefore, successful cultivation in nursery stage is essential for field conduction.

Intraspecific genetic analysis, gamete release performance, and growth of Sargassum muticum (Fucales, Phaeophyta) from China

Sargassum muticum is one of the most abundant and conspicuous native macroalgae species on the northern coasts of China. It often forms large-scale seaweed beds in subtidal zones. This investigation was designed to understand the intraspecific genetic relationships of this alga based on samples collected from four northern coastal sites of China, and to evaluate gamete release and growth capacity in laboratory conditions. The nuclear internal transcribed spacer 2 (ITS2) sequences of 16 samples from four locations were identical. Based on cox3 gene and partial rbcLS operon sequences, intraspecific genetic variability was detected with three and two ribotypes, respectively. Temperature, not irradiance, was shown to significantly affect gamete release and fertilization. Elevated temperature and irradiance enhanced the growth of germlings and vegetative branchlets. Maximum growth rate of germlings was detected at 18–24°C and an irradiance of 60–100 μmol photons/(m2·s). Under ambient conditions (12–25°C and 60–125 μmol photons/(m2·s)), relative growth rate of young branchlets could reach 7.5%/d.

High tolerance to fluctuating salinity allows Sargassum thunbergii germlings to survive and grow in artificial habitat of full immersion in intertidal zone

In this study, a four-way factorial experimental design (three temperatures, four salinities, two frequencies and three durations of osmotic stress) was used to test the tolerance of Sargassum thunbergii germlings shortly released from fertile thalli to osmotic stress. Results showed that the growth and survival of germlings were significantly affected by salinity and duration of osmotic stress, rather than by osmotic frequency. In addition to the main effects, all two-way, three-way and four-way interactions between the four stresses on the growth were significant. Germlings showed quick growth with relative growth rate (RGR, % day −1) over 16% when cultured at 32 psu combined with 30 °C. Although growths of germlings subjected to hypo-osmotic and hyper-osmotic conditions were significantly inhibited, RGRs over 12% were obtained except for those at 35 °C with the RGRs below 10%. In comparison to growth, survival was more tolerant to osmotic stress. Germlings showed high survivals over 60% when exposed to most osmotic stresses, by the end of experiment. Only under extreme conditions (12 psu for 4 h or 8 h at 35 °C) were the survivals reduced to below 10%. Although the effects of osmotic stress on the growth and survival were significant, germlings exhibited quick growth and high survival under most conditions. And those extreme conditions which had great destructive effect on germlings barely exist in field. Therefore, the construction of artificial tanks is feasible for the restoration of S. thunbergii beds in the intertidal zone.

Tolerance of Sargassum thunbergii germlings to thermal, osmotic and desiccation stress

The construction of artificial seaweed beds in the intertidal zone is a challenge due to extreme levels of physical stress. In order to provide a basis for the construction using the dispersal of microscopic juveniles, a three-way factorial experimental design was used to evaluate the tolerance of Sargassum thunbergii germlings shortly released from fertile thalli to temperature, salinity and desiccation in this study. Results revealed that temperature, salinity and desiccation significantly affected the growth and survival of germlings. Germlings showed rapid growth with relative growth rate (RGR, % day −1) over 16% when cultured at 25 °C and full immersion in normal seawater. Although growths of germlings subjected to moderate conditions were significantly inhibited, RGRs over 13% were obtained. The RGRs of germlings below 10% were observed only at 35 °C and 9 h desiccation treatments. In comparison to growth, survival was less affected by physical stress. Germlings showed low mortalities below 10% under appropriate conditions (25 °C and 30 °C combined with full immersion), and below 60% under moderate conditions, by the end of experiment. However, the mortality rates increased to over 90% under extreme conditions (9 h desiccation and 35 °C combined with full immersion in salinity of 12). These results showed that S. thunbergii germlings had high tolerance to physical stresses. In addition to the main effects, both two-way and three-way interactions between temperature, salinity and desiccation were significant. Based on the magnitude of effect, desiccation was the predominant factor affecting both growth and survival. According to the results, construction of artificial tanks in natural habitat to minimize desiccation may be an effective strategy for S. thunbergii restoration using germlings.

Effects of temporary and periodic emersion on the growth of Fucus spiralis and Pelvetia canaliculata germlings

The stress tolerance ability of Pelvetia canaliculata (L.) Dcne. Et Thur. and Fucus spiralis L. to temporary and periodic emersion stress was examined in order to test the following hypotheses: The upper shore alga, P. canaliculata is more tolerant to desiccation than F. spiralis in the germling stage and the former outgrows the latter under desiccation stress; Germling stress tolerance of the two species is age-specific; Crowding of germlings protects them from desiccation, ir respective of the species involved. Germling growth of the two species was retarded with increasing exposure period and was age-specific, as they were air-exposed at an earlier stage. After 16 days, the length of Pelvetia germlings was similar between 2-day-old germlings (125-140 µm) and 7-day-old germlings (134-140 µm), which were air-exposed during the same period (0, 6, 12, 24, 48, and 72 h) at the two different ages. However, Fucus germlings were significantly larger at 7-day-old germlings (211-277 µm) than at 2-day-old germlings (184-278 µm), especially in the treatments of 48 and 72 h. These results indicate that Fuscus grow faster than Pelvetia and that the growth response of germlings to temporary emersion stress is more sensitive in Fucus than that in Pelvetia. Growth of germlings of both species was reduced with increasing density under favorable growth conditions (submerged control and 6 h / 12 h exposure treatments) in the periodic air-exposed experiments using tidal tanks, but was enhanced under severe emersion stress conditions. P. canaliculata showed better growth at 6 h exposure treatment than that of the control, under continuous submergence, indicating that Pelvetia germlings require a periodic exposure period. Fucus germlings always grew faster than those of Pelvetia and did best in mixed cultures, whereas Pelvetia did least well when mixed with Fucus germlings. The adverse effects of F. spiralis on P. canaliculata were greater than those of Pelvetia cohorts. The outcome of interspecific competi tion between F. spiralis and P. canaliculata gemlings was slightly altered by exposure period but not to such an extent as to change the outcome.

An investigation of the relationship between sediment particles size and the development of green algal mats (Ulva prolifera) on the intertidal flats of Muan, Korea

The relationship between median grain size of sediments and the abundance in the wild of green algal mats (Ulva prolifera) on the intertidal flats of Muan, Korea, were investigated. The impact of substratum particle size on the growth and survival of germlings was examined in the laboratory. In the wild, the average annual density of algal mats was 7,950 ind m−2. The algal mats mainly occurred in sands and exhibited patchy distribution. Statistical analysis indicates significant spatial analysis differences and a significant relationship between density and the ratio of sands to silts, suggesting that the distribution and density of this species were related to particle size. In laboratory experiments, the survival rate of U. prolifera germlings was the lowest value (22%) on sediments with a median grain size of 63–125 μm. Laboratory experiments have generally shown a positive relationship between attachment or survival of the alga and substratum particles size. Our laboratory results indicate a clear link between germling settlement/survival and substratum particle size. These results explain the spatial differences in abundance observed in the field in relation to the distribution and ratio of sands to silt on the Muan flats.

Seasonality and thallus ontogeny of edible seaweed Monostroma latissimum (Kützing) Wittrock (Chlorophyta, Monostromataceae) from Tosa Bay, Kochi, Japan

Monostroma latissimum (Kutzing) Wittrock is an intertidal rock-dwelling green algal species of commercial importance in Japan. This article reports on the seasonality of its growth and occurrence from three distinct habitats of marine and estuarine regions in Tosa Bay, Japan, for two consecutive growth seasons. Thallus lengths of individuals and environmental parameters were monitored monthly between November 2005 and July 2007. Culture studies were carried out to establish the species-level identity of the specimens. Nuclear encoded ITS 1 (Internal Transcribed Spacer 1) sequences reveal that the naturally occurring strain of M. latissimum has identical nucleotide sequences to those of the commercially cultivated strain from the Shimanto river estuary. We have also found that the two strains are cross-fertilizing. Seasonal fluctuations in thallus length were found to be distinctive to the habitat where the strain grows and re-occur annually. Algal cover was highest during winter months and lowest during the summer. However, we found only a very weak positive correlation between chosen environmental parameters and thallus length. Appearance and decay of thalli occurred earlier in high saline habitats. Therefore, it is likely that salinity influences the maturation of microscopic sporophytes or the growth and survival of germlings in M. latissimum.

Light, sediment, temperature, and the early life-history of the habitat-forming alga Cystoseira barbata

Recruitment is essential for the maintenance of populations, but far more is typically known about the more easily-observed adult stages than their smaller, often microscopic early life-history counterparts. This discrepancy can be particularly problematic for populations of foundation species that create biogenic habitat for a multitude of other taxa, but are themselves prime candidates for exploitation, fragmentation, and loss, and therefore become the focus of restoration efforts partly or fully dependent on recruitment. The purpose of this study was to improve ecological understanding for early life-history stages of the habitat-forming marine alga Cystoseira barbata (Stackhouse) C. Agardh (Fucales: Sargassaceae), member of a genus that has experienced considerable fragmentation and population decline on European coasts. Using experimental manipulations of water temperature, light intensity, and sediment accumulation, we observed that sediment virtually precluded recruitment of C. barbata, and greatly impacted the survival of recently settled germlings (up to ~83% mortality). Stronger intensities of light facilitated the growth of germlings, including the capacity for ~50% of them to outgrow detrimental sediment and survive. Temperature (10 vs. 16°C) had no effect on early recruitment, survival, or growth. This information helps to identify likely causes and locations of recruitment failure, and by extension, the conditions needed (either naturally or through human intervention) to facilitate recruitment and possible habitat restoration. Ultimately, this knowledge can increase our capacity to predict population persistence and the likely success of restoration efforts.

Early development of germlings of Sargassum thunbergii (Fucales, Phaeophyta) under laboratory conditions

Morphology and culture studies on germlings of Sargassum thunbergii (Mertens et Roth) Kuntze were carried out under controlled laboratory conditions. Growth characteristics of these germlings grown under different temperatures (from 10 to 25°C), irradiances (from 9 to 88 μmol photons m−2 s−1), and under blue and white light conditions are described. The development of embryonic germlings follows the classic “8 nuclei 1 egg” type described for Sargassaceae. Fertilized eggs spent 5–6 h developing into multicellular germlings with abundant rhizoids after fertilization. Under conditions of 20°C, 44 μmol photons m−2 s−1 and photoperiod of 12 h, young germlings with one or two leaflets reached 2–3 mm in length after 8 weeks. Temperature variations (10, 15, 20, 25°C) under 88 μmol photons m−2 s−1 significantly influenced the growth rate within the first week, although this effect became less obvious after 8 weeks, especially at 15 and 20°C. Variation in germling growth was highly significant under different irradiances (9, 18, 44, 88 μmol photons m−2 s−1) at 25°C. Low temperature (10°C) reduced germling growth. Growth of germlings cultured under blue light was lower than in white light. Optimal growth of these germlings occurred at 25°C and 44 μmol photons m−2 s−1.

Grazer-controlled recruitment of the introduced Sargassum muticum (Phaeophyceae, Fucales) in northern Europe

Sargassum muticum (Yendo) Fensholt was introduced to European coasts during the 1970s. We studied survival and growth of seeded S. muticum germlings in field experiments on the southwestern coast of Norway, close to its present northernmost limit of distribution in Europe. A cage experiment was conducted twice (using different starting densities of germlings) at 2 localities during the summer and autumn of 2002, each experiment lasting 1 mo. Germling survival was significantly higher within grazer-excluding cages than on unprotected substrate. Germlings within cage controls (cages accessible to mesograzers) experienced intermediate mortality, which was nevertheless closer to that of unprotected than to cage-protected germlings. At a third locality, survival of unprotected germlings was recorded from September 2000 to February 2001, and only 0.6% of the germlings had survived by February. When relating proportion of mortality to initial density of germlings, we found no tendency of positive density-dependent mortality; on the contrary, on the substrate where grazers had access to the germlings, there was a tendency for high mortality when initial density was low and lower mortality when initial density was high. This suggests a ‘swamping’ effect of high germling densities on grazers. The growth of germlings during autumn and winter was very low compared with earlier reported measurements from Spain, and we suggest that relatively slow growth rates may make the germlings vulnerable to grazing impact. The results indicate that herbivorous grazing on early post-settlement stage germlings may be a limiting factor for the spread of S. muticum in southwestern Norway.