Journal of Phycology最新文献

Cryptophytes (class Cryptophyceae) are bi-flagellated eukaryotic protists with mixed nutritional modes and cosmopolitan distribution in aquatic environments. Despite their ubiquitous presence, their molecular diversity is understudied in coastal waters. Weekly 18S rRNA gene amplicon sequencing at the Scripps Institution of Oceanography pier (La Jolla, California) in 2016 revealed 16 unique cryptophyte amplicon sequence variants (ASVs), with two dominant “clade 4” ASVs. The diversity of cryptophytes was lower than what is often seen in other phytoplankton taxa. One ASV represented a known Synechococcus grazer, while the other one appeared not to have cultured representatives and an unknown potential for mixotrophy. These two dominant ASVs were negatively correlated, suggesting possible niche differentiation. The cryptophyte population in nearby San Diego Bay was surveyed in 2019 and showed the increasing dominance of a different clade 4 ASV toward the back of the bay where conditions are warmer, saltier, and shallower relative to other areas in the bay. An ASV representing a potentially chromatically acclimating cryptophyte species also suggested that San Diego Bay exerts differing ecological selection pressures than nearby coastal waters. Cryptophyte and Synechococcus cell abundance at the SIO Pier from 2011 to 2017 showed that cryptophytes were consistently present and had a significant correlation with Synechococcus abundance, but no detectable seasonality. The demonstrated mixotrophy of some cryptophytes suggests that grazing on these and perhaps other bacteria is important for their ecological success. Using several assumptions, we calculated that cryptophytes could consume up to 44% (average 6%) of the Synechococcus population per day. This implies that cryptophytes could significantly influence Synechococcus abundance.

Nitrate, the form of nitrogen often associated with kelp growth, is typically low in summer during periods of high macroalgal growth. More ephemeral, regenerated forms of nitrogen, such as ammonium and urea, are much less studied as sources of nitrogen for kelps, despite the relatively high concentrations of regenerated nitrogen found in the Southern California Bight, where kelps are common. To assess how nitrogen uptake by kelps varies by species and nitrogen form in southern California, USA, we measured uptake rates of nitrate, ammonium, and urea by Macrocystis pyrifera and Eisenia arborea individuals from four regions characterized by differences in nitrogen availability—Orange County, San Pedro, eastern Santa Catalina Island, and western Santa Catalina Island—during the summers of 2021 and 2022. Seawater samples collected at each location showed that overall nitrogen availability was low, but ammonium and urea were often more abundant than nitrate. We also quantified the internal %nitrogen of each kelp blade collected, which was positively associated with ambient environmental nitrogen concentrations at the time of collection. We observed that both kelp species readily took up nitrate, ammonium, and urea, with M. pyrifera taking up nitrate and ammonium more efficiently than E. arborea. Urea uptake efficiency for both species increased as internal percent nitrogen decreased. Our results indicate that lesser-studied, more ephemeral forms of nitrogen can readily be taken up by these kelps, with possible upregulation of urea uptake as nitrogen availability declines.

Chlainomonas (Chlamydomonadales, Chlorophyta) is one of the four genera of snow algae known to produce annual pink or red blooms in alpine snow. No Chlainomonas species have been successfully cultured in the laboratory, but diverse cell types have been observed from many field-collected samples, from multiple species. The diversity of morphologies suggests these algae have complex life cycles with changes in ploidy. Over 7 years (2017–2023), we observed seasonal blooms dominated by a Chlainomonas species from late spring through the summer months on a snow-on-lake habitat in an alpine basin in the North Cascade Mountains of Washington, USA. The Bagley Lake Chlainomonas is distinct from previously reported species based on morphology and sequence data. We observed a similar collection of cell types observed in other Chlainomonas species, with the addition of swarming biflagellate cells that emerged from sporangia. We present a life cycle hypothesis for this species that links cell morphologies observed in the field to seasonally available habitat. The progression of cell types suggests cells are undergoing both meiosis and fertilization in the life cycle. Since the life cycle is the most fundamental biological feature of an organism, with direct consequences for evolutionary processes, it is critical to understand how snow algal life cycles will influence their responses to changes in their habitat driven by climate warming. For microbial taxa that live in extreme environments and are difficult to culture, temporal field studies, such as we report here, may be key to creating testable hypotheses for life cycles.

The evolutionary transitions of mating systems between outcrossing and self-fertilization are often suggested to associate with the cytological and genomic changes, but the empirical reports are limited in multicellular organisms. Here we used the unicellular zygnematophycean algae, the Closterium peracerosum–strigosum–littorale (C. psl.) complex, to address whether genomic properties such as genome sizes and chromosome numbers are associated with mating system transitions between homothallism (self-fertility) and heterothallism (self-sterility). Phylogenetic analysis revealed the polyphyly of homothallic strains, suggesting multiple transitions between homothallism and heterothallism in the C. psl. complex. Flow cytometry analysis identified a more than 2-fold genome size variation, ranging from 0.53 to 1.42 Gbp, which was positively correlated with chromosome number variation between strains. Although we did not find consistent trends in genome size change and mating system transitions, the mean chromosome sizes tend to be smaller in homothallic strains than in their relative heterothallic strains. This result suggests that homothallic strains possibly have more fragmented chromosomes, which is consistent with the argument that self-fertilizing populations may tolerate more chromosomal rearrangements.

Fluctuations in dissolved oxygen (DO) contents in natural waters can become intense during cyanobacteria blooms. In a reconnaissance study, we investigated DO concentrations and stable isotope dynamics during a laboratory experiment with the cyanobacterium Planktothrix rubescens in order to obtain insights into primary production under specific conditions. This observation was extended to sub-daily timescales with alternating light and dark phases. Dissolved oxygen concentrations and its isotopes (δ¹⁸O_DO) ranged from 0.02 to 0.06 mmol · L⁻¹ and from +9.6‰ to +23.4‰. The δ¹⁸O_DO proved to be more sensitive than concentration measurements in response to metabolic variation and registered earlier shifts to dominance by respiration. Oxygen (O₂) contents in the headspace and its isotopes (δ¹⁸O_O2) ranged from 2.62 to 3.20 mmol · L⁻¹ and from +9.8‰ to +21.9‰. Headspace samples showed less fluctuations in concentration and isotope trends because aquatic processes were hardly able to alter signals once the gas had reached the headspace. Headspace δ¹⁸O_O2 values were corrected for gas–water equilibration and were determined to be higher than the mean δ¹⁸O_H2O of −8.7‰. This finding suggests that counteracting respiration was important even during the highest photosynthetic activity. Additionally, headspace analyses led to the definition of a fractionation factor for respiration (α_R) of this cyanobacterium with a value of 0.980. This value confirms the one commonly used for cyanobacteria. Our findings may become important for the management of water bodies where decreases in DO are caused by cyanobacteria.

A reclassification of Cyanidium chilense under the new genus Cavernulicola was recently proposed together with a new family (Cavernulicolaceae) and a new order (Cavernulicolales). Unfortunately, due to an error in the required citation of the basionym, the name “Cavernulicola chilensis” was invalid and cannot be accepted as the generitype of Cavernulicola. This means that Cavernulicola, Cavernulicolaceae, and Cavernulicolales are likewise invalid names under the provisions of the International Code of Nomenclature for algae, fungi, and plants (ICN, Shenzhen Code). In this contribution, each of these names is validated.

Environmental changes associated with rapid climate change in the Arctic, such as the increased rates of sedimentation from climatic or anthropogenic sources, can enhance the impact of abiotic stressors on coastal ecosystems. High sedimentation rates can be detrimental to nearshore kelp abundance and distribution, possibly due to increased mortality at the spore settlement stage. Spore settlement and viability of the Arctic kelp Laminaria solidungula were examined through a series of lab-based sedimentation experiments. Spores were exposed to increasing sediment loads in three experimental designs simulating different sedimentation scenarios: sediment deposition above settled spores, settlement of spores on sediment-covered substrate, and simultaneous suspension of spores and sediments during settlement. Spore settlement was recorded upon completion of each experiment, and gametophyte abundance was assessed following a growth period with sediments removed to examine short-term spore viability via a gametophyte-to-settled-spore ratio. In all three types of sediment exposure, the addition of sediments caused a 30%–40% reduction in spore settlement relative to a no-sediment control. Spore settlement decreased significantly between the low and high sediment treatments when spores were settled onto sediment-covered substrates. In all experiments, increasing amounts of sediment had no significant effect on spore viability, indicating that spores that had settled under different short-term sediment conditions were viable. Our results indicate that depending on spore-sediment interaction type, higher rates of sedimentation resulting from increased sediment loading could affect L. solidungula spore settlement success with potential impacts on the long-term persistence of a diverse and productive benthic habitat.

Crustose coralline algae (CCA) are a highly diverse group of habitat-forming, calcifying red macroalgae (Rhodophyta) with unique adaptations to diverse irradiance regimes. A distinctive CCA phenotype adaptation, which allows them to maximize photosynthetic performance in low light, is their content of a specific group of light-harvesting pigments called phycobilins. In this study, we assessed the potential of noninvasive hyperspectral imaging (HSI) in the visible spectrum (400–800 nm) to describe the phenotypic variability in phycobilin content of an Antarctic coralline, Tethysphytum antarcticum (Hapalidiales), from two distinct locations. We validated our measurements with pigment extractions and spectrophotometry analysis, in addition to DNA barcoding using the psbA marker. Targeted spectral indices were developed and correlated with phycobilin content using linear mixed models (R² = 0.64–0.7). Once applied to the HSI, the models revealed the distinct phycoerythrin spatial distribution in the two site-specific CCA phenotypes, with thin and thick crusts, respectively. This study advances the capabilities of hyperspectral imaging as a tool to quantitatively study CCA pigmentation in relation to their phenotypic plasticity, which can be applied in laboratory studies and potentially in situ surveys using underwater hyperspectral imaging systems.