Journal of Phycology最新文献

The invasive seaweed Rugulopteryx okamurae, native to East Asia, is spreading rapidly along the western Mediterranean and southern Portugal, severely affecting coastal biodiversity, ecosystem structure, and economic sectors such as fisheries and tourism. This study examined the nutrient uptake kinetics of R. okamurae, including ammonium, nitrate, urea, amino acids, and phosphate, and their role in nitrogen and phosphorus budgets based on laboratory growth rates. R. okamurae demonstrated the highest uptake for ammonium (V_max = 57.95 μmol · g^-1 DW · h^-1), followed by urea (7.74 μmol · g^-1 DW · h^-1), nitrate (5.37 μmol · g^-1 DW · h^-1), and amino acids (3.71 μmol · g^-1 DW · h^-1). The species showed higher uptake affinity for urea (α = 1.8), which accounted for 70% of nitrogen uptake. Phosphate uptake was low, and total nitrogen uptake exceeded growth requirements. These findings suggest that R. okamurae relies on organic nitrogen (urea) and may guide toward effective management strategies to mitigate its spread in coastal ecosystems.

Biological invasions are a major threat for many aquatic ecosystems. In contrast to higher plants and animals, microbial invasions are less obvious and more difficult to detect. One of the most prominent microbial invaders is the cyanobacterium Raphidiopsis raciborskii. To better understand the environmental conditions favoring its invasion success, we studied invasion under three different temperature regimes (one constant and two variable) in experimental plankton communities by invader addition experiments. To account for intraspecific variation, we tested four different strains of R. raciborskii and the mixture of them. Invasion success of R. raciborskii was higher under constant temperature conditions than under fluctuations suggesting that the resident species responded faster to the environmental changes than the invaders. We observed a clear strain-specific effect, demonstrating that strain identity is an important determinant of invasion success. The interaction of temperature fluctuations and strain identity indicates that, among the tested strains, the response to the temperature regimes varied. The mixture of all four strains did not perform better than the best single strain showing no sign of a positive genetic diversity effect. In our experiment, environmental fluctuations did not widen a window of opportunity for the invasion of R. raciborskii.

The Asian brown macroalga Rugulopteryx okamurae has invaded the oligotrophic areas of Mediterranean coasts since 2015, with drastic impacts on environmental conditions and socioeconomic activities in coastal areas in Europe. Therefore, it is intriguing how this species is able to grow and expand at the observed rates. In this context, the physiological responses of R. okamurae to changing nutrient concentrations and temperature were analyzed. Two experiments were conducted, evaluating six combinations of nitrate and phosphate concentrations and their potential interaction with temperature. Nutrient uptake efficiency (NUE) and rates (NUR), photosynthetic responses, growth rates, and biomass composition were evaluated. Photosynthesis parameters, soluble proteins, and $N{O}_3^{-}$ -NUR increased with increasing N:P ratio; however, $P{O}_4^{3-}$ -NUR was very similar in all treatments. The species showed high capacity for nitrate assimilation, which was rapidly modulated by its external concentration and temperature (more than 90% of NO₃-NUE after 5 days in treatments with N:P rations of 5, 10, 16, 25, and 40 N to 1 P). Consequently, N-nutrients were removed from the water by R. okamurae and likely stored inside the cells. This process will allow the alga to maintain high growth rates if thalli are moved to oligotrophic areas, favoring its spreading to many marine environments. Additionally, fucoxanthin was the predominant carotenoid in this species, although its content was lower than in other brown macroalgae species (mean value of 0.51 ± 0.05 mg · g^-1 DW). However, since a huge amount of R. okamurae is observed recurrently on beaches, the use of this biomass might be proposed to compensate partially for its impacts.

Monoclonal female gametophytes of Saccharina japonica, when cultured independently, can develop into female sporophytes. Previous research has shown that the chromosomes in female sporophytes of S. japonica may naturally duplicate, forming diploids, and these diploid female sporophytes are capable of forming sori and releasing zoospores. In contrast, male sporophytes derived from culturing monoclonal male gametophytes failed to form sori and produce meiospores; thus, it was hypothesized that these male sporophytes are haploid and unable to perform meiotic division. In order to explore whether the chromosomes in male sporophytes can naturally duplicate and whether such diploid male sporophytes can effectively form sori and produce meiospores, we obtained 62 male sporophytes and cultivated them into adults. Only male-specific DNA markers were detected in all of these male sporophytes, indicating their male nature. Ten microsatellite markers were used to estimate the relatedness of the parental gametophytes and the corresponding sporophytes. Results revealed that the genotypes of the male sporophytes matched exactly with the corresponding male gametophytes. Both diploid and haploid sporophytes were detected in these 62 male sporophytes when analyzed by flow cytometry. After 16 months of cultivation, none of the male sporophytes formed sori regardless of their ploidy. As controls, both female and hybrid sporophytes developed sori and released viable zoospores. These findings suggest that the sterility of male sporophytes in S. japonica is not related to their ploidy; rather, it is attributed to the absence of essential elements for sori formation that may be present only in the female.

Cyanobacteria are known for forming associations with various animals, including sea turtles, yet our understanding of cyanobacteria associated with sea turtles remains limited. This study aims to address this knowledge gap by investigating the diversity of cyanobacteria in biofilm samples from loggerhead sea turtle carapaces, utilizing a 16S rRNA gene amplicon sequencing approach. The predominant cyanobacterial order identified was Nodosilineales, with the genus Rhodoploca having the highest relative abundance. Our results suggest that cyanobacterial communities become more diverse as sea turtles age, as we observed a positive correlation between community diversity and the length of a sea turtle's carapace. Since larger and older turtles predominantly utilize neritic habitats, the shift to a more diverse cyanobacterial community aligned with a change in loggerhead habitat. Our research provides detailed insights into the cyanobacterial communities associated with loggerhead sea turtles, establishing a foundation for future studies delving into this fascinating ecological relationship and its potential implications for sea turtle conservation.

Dissolved organic carbon (DOC) released by macroalgae is an intrinsic component of the coastal ocean carbon cycle, yet knowledge of how future ocean warming may influence this is limited. Temperature is one of the primary abiotic regulators of macroalgal physiology, but there is minimal understanding of how it influences the magnitude and mechanisms of DOC release. To investigate this, we examined the effect of a range of temperatures on DOC release rates and physiological traits of Ecklonia radiata, the most abundant and widespread kelp in Australia that represents a potentially significant contribution to coastal ocean carbon cycling. Juvenile sporophytes were incubated at eight temperatures (4-28°C) for 14 days, after which time, DOC concentrations and physiological traits (growth, photosynthesis, respiration, F_v/F_m, photosynthetic pigment content, and carbon, and nitrogen content) were analyzed using thermal performance curves (TPCs) or regression analyses. Thermal optima were 15.63°C for growth and 25.84°C for photosynthesis, highlighting vulnerability to future ocean warming. Dissolved organic carbon concentrations increased when the temperature was above ~22°C, being greatest at the highest temperature tested (28°C), which was likely driven by photosynthetic overflow and thermal stress. Mean F_v/F_m, total chlorophyll, and total fucoxanthin content were lowest at 28°C. The C:N ratio of blades increased linearly with temperature from 23.9 ± 1.30 at 4°C to 33.0 ± 1.22 at 28°C. We demonstrate increased DOC release by E. radiata under elevated seawater temperatures and discuss potential implications for coastal carbon cycling under future ocean warming given the complex and uncertain fate of macroalgal DOC in the marine environment.

The freshwater red alga Batrachospermum gelatinosum has a well-documented distribution spanning historically glaciated and unglaciated eastern North America. This alga has no known desiccation-resistant propagule; thus, long-distance dispersal events are likely rare. We predicted strong genetic structure among drainage basins and admixture among sites within basins. We predicted greater genetic diversity at lower latitude sites because they likely serve as refugia and the origin of northward, post-Pleistocene range expansion. We used 10 microsatellite loci to investigate genetic diversity from 311 gametophytes from 18 sites in five major drainage basins: South Atlantic Gulf, Mid-Atlantic, Ohio River, Great Lakes, and Northeast. Our data showed strong genetic partitioning among drainage basins and among sites within basins, yet no isolation by distance was detected. Genetic diversity varied widely among sites and was not strictly related to latitude as predicted. The results from B. gelatinosum provide strong support that each stream site contributes to the unique genetic variation within the species, potentially due to limited dispersal and the prevailing reproductive mode of intragametophytic selfing. Simulations of migration suggested post-Pleistocene dispersal from the Mid-Atlantic. Batrachospermum gelatinosum potentially persisted in refugia that were just south of the ice margins rather than in the southernmost part of its range. Research of other taxa with similar ranges could determine whether these results are generally applicable for freshwater red algae. Nevertheless, these results from B. gelatinosum add to the growing literature focused on the patterns and genetic consequences of post-Pleistocene range expansion by eastern North American biota.

Genomic resources have yielded unprecedented insights into ecological and evolutionary processes, not to mention their importance in economic and conservation management of specific organisms. However, the field of macroalgal genomics is hampered by difficulties in the isolation of suitable DNA. Even when DNA that appears high quality by standard metrics has been isolated, such samples may not perform well during the sequencing process. We here have compared Oxford Nanopore long-read sequencing results for three species of macroalgae to those of nonmacroalgal species and determined that when using macroalgal samples, sequencing activity declined rapidly, resulting in reduced sequencing yield. Chemical analysis of macroalgal DNA that would be considered suitable for sequencing revealed that DNA derived from dried macroalgae was enriched for polyphenol-DNA adducts (DNA with large polyphenols chemically attached to it), which may have led to sequencing inhibition. Of note, we observed the strongest evidence of sequencing inhibition and reduced sequence output when using samples dried using silica gel-suggesting that such storage approaches may not be appropriate for samples destined for Oxford Nanopore sequencing. Our findings have wide-ranging implications for the generation of genomic resources from macroalgae and suggest a need to develop new storage methods that are more amenable to Oxford Nanopore sequencing or to use fresh flash-frozen tissue wherever possible for genome sequencing.

Life cycles with a prolonged haploid phase are thought to be correlated with greater rates of selfing and asexual reproduction. In red algae, recent population genetic studies have aimed to test this prediction but have mostly focused on marine species with separate sexes. We characterized the reproductive system of the obligately monoicous (i.e., hermaphroditic) freshwater red alga Batrachospermum gelatinosum and predicted that we would find genetic signatures of uniparental reproduction because of its haploid-diploid life cycle. We sampled 18 sites and genotyped 311 gametophytes with 10 polymorphic microsatellite loci to describe the reproductive system. Genotypic richness was low (<0.5) and pareto β values (describing clonal membership) were <0.7 for most sites. In taxa with separate sexes, these patterns are typically indicative of asexual reproduction. However, the genetic consequences of selfing in monoicous gametophytes are indistinguishable from those caused by asexual processes. Since we sampled gametophytes and have not yet genotyped the chantransia (i.e., the diploid phase), we interpreted low diversity as a signature of intragametophytic selfing. Additionally, to understand the factors that drive selfing, we tested latitude and several other environmental variables, but none was significantly correlated with the genetic variation we observed. Nevertheless, future studies should genotype the chantransia to measure observed heterozygosity among other summary statistics to disentangle the effects of selfing versus asexual reproduction. Together, these data, coupled with further characterization of abiotic factors that influence population genetic patterns, will allow us to test potential drivers of reproductive system evolution.

One of the reactive forms of oxygen is hydrogen peroxide (H₂O₂), which has been investigated as a key component of growth processes and stress responses. Different methods for the determination of H₂O₂ production by animal and bacterial cells exist; however, its detection in algal cell cultures is more complicated due to the presence of photosynthetic pigments in the cells and the complex structure of cell walls. Considering these issues, a reliable, quick, and simple method for H₂O₂ detection is needed in phycological research. The aim of this methodological study was to optimize an Amplex UltraRed method for the fluorometric detection of H₂O₂ produced by microalgae cells, using a wild-type strain of Chlamydomonas reinhardtii as a model. The results showed that (i) potassium phosphate is the most suitable reaction buffer for this method, (ii) a 560 nm wavelength variant is the most appropriate as the excitation wavelength for fluorescence spectra measurement, (iii) a 50:50 ratio for the reaction mixture to sample was the most suitable, (iv) the fluorescence signal was significantly influenced by the density of the microalgae biomass, and (v) sample fortification with H₂O₂ allowed for an increase of the method's reliability and repeatability. The proposed protocol of the Amplex UltraRed method for the fluorometric detection of H₂O₂ produced by microalgae cells can yield a sensitive and accurate determination of the content of the test compound, minimizing measurement errors, eliminating chlorophyll autofluorescence problem, and compensating for the matrix effect. This method can be applied to the study of other microalgae species.