Journal of Phycology最新文献

Since 2011, holopelagic Sargassum has been accumulating in a region of the tropical Atlantic now referred to as the Great Atlantic Sargassum Belt (GASB). Among the hypothesized contributors to these accumulations are the increased inputs of nitrogen (N) and phosphorus (P) in the tropical Atlantic Ocean. Little is known about the effects of N and P additions on Sargassum physiology and its microbiome. We studied the effects of N, P, and NP additions on the growth, photosynthetic efficiency, and microbiome composition of Sargassum fluitans III in a six-day experiment on the Caribbean Island of Curaçao. Sargassum fluitans III took up most nitrate and phosphate within 3 days with respective uptake rates of 0.343 and 0.0399 μmol · g⁻¹ DW · h⁻¹. Fv/Fm decreased in the control after 6 days but remained constant in nutrient treatments. Growth rates did not differ significantly among treatments, but a trend in higher growth rates in the NP treatment was discerned, suggesting a possible NP co-limitation. The relative abundance of epiphytic Cyanobacteria such as Schizothrix and bacteria such as Lentilitoribacter increased under N and P addition, while heterotrophic Rhodobacteraceae decreased in abundance. Microeukaryotic communities responded with varying changes in alpha diversity, possibly steered by increased photosynthesis and growth of S. fluitans III or bacterial interactions. The physiological response to N and P and rapid change of the microbiome demonstrates that the studied S. fluitans III can quickly benefit from increased nutrient concentrations, which might contribute to its growth success in the GASB.

The class Bolidophyceae, which consists of small phytoplankton distributed worldwide, is the sister group of diatoms. This class has contained only one order, the Parmales, until now. In this study, we established a new order Lepidoparmales Kamakura & S.Sato ord. nov. and a new family Lepidoparmaceae Kamakura & S.Sato fam. nov., within the Bolidophyceae, and described Lepidoparma frigida Kamakura & S.Sato gen. et sp. nov. from the Sea of Okhotsk. We conducted a comprehensive comparison of L. frigida with diatoms and other parmaleans through analysis of its molecular phylogeny, morphology, ultrastructure, ontogeny, distribution, and lipid composition. The cell surface of L. frigida is covered with numerous siliceous scales with radial patterns similar to centric diatom valves; this character distinguishes it from other known parmaleans. Intriguingly, its appearance resembles the hypothesized “pre-diatom,” which was proposed to be a precursor to primitive diatoms. The discovery and characterization of L. frigida will provide valuable insights into the evolutionary processes of both diatoms and bolidophytes and shed light on their common ancestor.

The genus Symbiochlorum, initially described from a single strain isolated from a coral in the South China Sea, was shown to be a sister lineage of Ignatius within the green algal order Ignatiales. Its significant phylogenetic divergence from Ignatius raises the possibility of its classification as a new family. To further investigate this hypothesis, we conducted a more elaborate analysis of sequence diversity within the Symbiochlorum clade. We aligned the 18S nuclear ribosomal DNA gene sequences of newly isolated Symbiochlorum culture strains from coral in the South China Sea and environmental sequences from the Great Barrier Reef. Strains isolated from Porites lutea coral colonies exhibited morphological similarities to typical S. hainanense (CCTCC M2018096). Analysis of the 18S nuclear ribosomal DNA gene revealed substantial diversity in both the V4 and V9 regions of the gene, with sequences clustering into two distinct lineages. Lineage 1 (L1), represented solely by environmental sequences from Great Barrier Reef sediment samples, displayed high levels of sequence divergence (2.2%–5.8%), suggesting it consists of multiple species. Lineage 2 (L2) included coral-derived strains and environmental sequences from the South China Sea and the Great Barrier Reef, as well as an ascidian-associated strain from Palau. The significant divergence between L1 and L2 (3.1%–9.1%) suggests they represent different genera. Based on these results, we propose the recognition of the new family Symbiochloraceae within the Ignatiales order.

Ecological stability is central to understanding how disturbances challenge the persistence of populations and communities through time, especially when key species are impacted. The bull kelp Durvillaea incurvata is a foundation, habitat-forming species that provides food and shelter for various species and supports the livelihoods of human communities along the Chilean coast. Harvesting of Durvillaea has raised concerns about the long-term viability of its populations, but the stability responses of Durvillaea to anthropogenic disturbances remain unclear. Here, we conducted a manipulative experiment in which we removed, once, all Durvillaea individuals from two sites in southern Chile to simulate the spatial scale of harvesting and to describe the population resilience and recovery following disturbance. In 1-m² plots interspersed in matrices of dense Durvillaea stands, we removed fronds and holdfasts, a practice not typically developed by gatherers, testing an alternative harvesting strategy. For 25 months, we quantified Durvillaea recruitment, holdfast densities, percent cover, frond length and density, biomass, and population size structure. All metrics completely recovered within 5–7 months across sites. The removal of Durvillaea did not have a significant impact on recruitment, which was constant during the experiment. The small spatial scale of the disturbances, the constant recruits supplied by the surrounding bull kelp matrix, and the removal of holdfasts that released settlement substratum allowed for the strong stability responses in these populations. Therefore, harvesting strategies that promote spatial heterogeneity, such as the removal of whole individuals at a small spatial scale, should be prioritized in management schemes of natural seaweed stands.

Microalgae are natural producers of essential nutrients and pigments for both human and animal nutrition as well as medical applications. This study aimed to characterize some microalgae by their taxonomy and biochemical composition. Molecular techniques were used to categorize the microalgal strains into the genera of Chlorococcum, Coccomyxa, and Ochromonas. Subsequently, microalgal growth under laboratory conditions was assessed and the microalgal cells were harvested to determine the pigments, proximate composition, fatty acid, and amino acid profiles. The findings indicated that the cell densities of Coccomyxa sp. and Ochromonas sp. were nearly identical. Additionally, all microalgae exhibited chlorophyll a as the main pigment component, whereas Coccomyxa sp. and Chlorococcum sp. showed significantly highest (p < 0.05) chlorophyll a (7.79 ± 0.07 μg · mL⁻¹) and chlorophyll b (2.74 ± 0.002 μg · mL⁻¹), respectively. Significantly higher (p < 0.05) carotenoid and total phycobiliproteins content were found in Ochromonas sp. Furthermore, Coccomyxa sp. was determined to have significantly higher (p < 0.05) protein (31.9% ± 0.46% dry weight) and lipid content (18.2% ± 1.34% dry weight), while the maximum carbohydrate was detected for Ochromonas sp. (29.2% ± 0.1% dry weight). Lastly, essential amino acid (EAA) levels were considerably higher (p < 0.05) in Chlorococcum sp.; however, Coccomyxa sp. produced more polyunsaturated fatty acids (PUFA) in comparison to the other experimental species. The results indicate that the investigated microalgae possess immense potential as multi-nutrient sources and can be optimized for sustainable application in aquaculture, pharmaceuticals, and nutraceutical industries.

Seaweeds can be negatively affected by low salinity, but the negative impacts may be ameliorated by the presence of high nutrient levels from the freshwater inputs. We tested this hypothesis on the eucheumatoids Kappaphycus alvarezii, K. striatus, and Eucheuma denticulatum by determining their nutrient uptake, growth, and biochemical responses to experimental treatments of lowering salinity with a consequent increase in nutrient concentrations. Ambient seawater with varying salinity and nutrient concentrations was sourced offshore (O) and nearshore (N) and diluted with nutrient-replete natural spring water to obtain six (6) treatments: O-LN-34, O-MN-30, O-HN-27, N-MN-30, N-HN-27, and N-HN-24 (corresponding to water source-relative nutrient concentration- salinity, where LN = low nutrient; MN = medium nutrient; HN = high nutrient). Nutrient uptake varied among inorganic nutrient species and different eucheumatoid species. All eucheumatoids showed uptake preference for NH₄⁺ regardless of the treatment while NO₃⁻ uptake was generally higher in treatments with higher NO₃⁻ concentration. Growth rates were species-specific but generally higher at lower salinities with higher nutrient concentrations. Total soluble carbohydrate, total protein, and total polyphenol content did not significantly vary among treatments, except for E. denticulatum. These results provide insights into the potential of farming eucheumatoids nearshore with fluctuating salinity provided that the freshwater outflow is nutrient-rich to ameliorate the negative effects of low salt concentration.