SUMMARY Hypnea species are distributed across tropical, subtropical, and temperate regions. They exhibit high intraspecific morphological variation, which complicates species delimitation based solely on morphological characteristics. Recently, molecular analyses have enabled the validation of numerous species, the identification of cryptic species, and the description of new taxa. In the present study, morphological and anatomical analyses (36 characters), along with the molecular markers rbcL and COI‐5P, were used to reevaluate the taxonomic identity of two Hypnea species frequently reported on the tropical Pacific coast of Mexico: Hypnea pannosa and H. spinella . Our study, based on morphological and molecular evidence, confirmed the presence of H. pannosa with its typical morphology of a great cushion‐shaped thallus of short axes and branches and identified an undescribed species characterized by erect, free branches. Our results suggest that H. spinella is not present along the Mexican tropical Pacific coast and that previous records should be considered misidentifications. We propose and describe this new species as Hypnea ixtapaensis sp. nov.
Excess light energy combined with environmental stress promotes the generation of reactive oxygen species and leads to cell death in most plants. In this study, we used high light conditions to screen for photosynthetic organisms with defense mechanisms protecting against photooxidative stress, which resulted in the isolation of eukaryotic microalgal strain WF1-2. Preliminary identification based on the small subunit ribosomal DNA (SSU rDNA) sequence suggested that strain WF1-2 belongs to the genus Elliptochloris. To clarify its taxonomic position within this genus, we performed morphological analyses, including light microscopy, scanning electron microscopy, and transmission electron microscopy, to examine the surface structure and cellular ultrastructure. We also conducted molecular phylogenetic analyses using the SSU-ITS1-5.8S-ITS2 region and the rbcL coding sequence as well as comparative analyses of RNA secondary structures. On the basis of this integrative analysis, strain WF1-2 was distinguished from its closest relative, Elliptochloris reniformis, and other known Elliptochloris strains. We therefore propose the name Elliptochloris lunaris sp. nov. for strain WF1-2.
Three new species of the coralline algal genus Arthrocardia (Corallinophycidae, Rhodophyta) are described from New Zealand: A. meridionalis, A. perplexa, and A. robusta. These species are difficult to distinguish based on morphoanatomical characters alone and require molecular sequence data for reliable identification. The northern A. meridionalis and southern A. robusta have non-overlapping geographic distributions, while each of these species overlaps with A. perplexa in central New Zealand. Based on sequence data, A. meridionalis is conspecific with a South African species of Arthrocardia designated as "sp. 1" in an earlier study. Additionally, the two species previously reported from New Zealand, A. corymbosa (based on South African type material) and A. wardii (from South Australia), are considered not to be present in New Zealand.
Eucheumatoids are the most extensively cultivated seaweeds in the Philippines, yet climate-driven abiotic stressors increasingly threaten their production. Desiccation during extreme low tides is a major but understudied stressor in shallow-water farms. This study examined how desiccation affects photosynthetic performance, moisture retention, and nutrient uptake in Eucheuma denticulatum. Thalli (n = 3 per treatment) were exposed to 2, 4, and 6 h of desiccation, while controls remained immersed. Maximum quantum yield (F v /F m) and moisture content were measured at initial, immediately after desiccation, after 1 h of reimmersion in enriched seawater, and after 24 h and 7 d in natural seawater. Nutrient uptake was quantified from changes in seawater concentrations of total ammonia nitrogen (TAN) and phosphate (PO4 3-) at 15, 30, 45, and 60 min post-rehydration. Only the 2-h treatment retained sufficient moisture to recover after 7 d (F v /F m = 0.684 +/- 0.048), comparable to the control (0.645-0.767), whereas longer exposures lost too much moisture to regain photosynthetic function. TAN uptake peaked at 15 min in the control, 4-h, and 6-h treatments, while the 2-h treatment showed a delayed peak at 45 min. In contrast, PO4 3- uptake was positive only in the control; all desiccated treatments exhibited negative values, with the magnitude of efflux varying among treatments. The 75% moisture retention under the 2-h treatment reflects a recoverable hydration range in this study, with greater water loss impairing photosynthetic recovery, rehydration, and PO4 3- uptake. Prolonged desiccation compromises nutrient acquisition and promotes solute loss, highlighting the vulnerability of E. denticulatum to extended air exposure under increasingly frequent low-tide extremes.
Understanding the physiological traits of dominant primary producers is crucial for characterizing oceanic energy input. Pavlomulina ranunculiformis S. Sym, R. Pienaar & M. Kawachi, the sole described species of the class Rappephyceae, is a large-sized, globally distributed haptophyte, yet its fundamental niche remains poorly defined. In this study, we investigated the growth characteristics of the type strain (NIES-3900) under various light, temperature, and salinity conditions and compared these with its global distribution using the Tara Oceans 18S rRNA gene dataset. In culture, P. ranunculiformis grew under photon flux densities of 25-100 mu mol photons m(-2) s(-1), temperatures of 15-25 degrees C, and salinities of 32-44 parts per thousand. The maximum specific growth rate was approximately 0.35 day(-1), which is lower than the specific growth rates reported from the smaller, bloom-forming haptophyte Gephyrocapsa huxleyi (Lohmann) P. Reinhardt (formerly known as Emiliania huxleyi). Notably, the strain failed to grow at temperatures <= 10 degrees C and >= 30 degrees C. These physiological limits generally align with environmental DNA data showing the species is widely distributed in low-to-mid latitudes but absent in the Arctic Ocean, contrasting with the cold-tolerant species such as G. huxleyi and Chrysochromulina leadbeateri Estep, Davis, Hargreaves & Sieburth. However, environmental DNA assigned to P. ranunculiformis was also detected in waters >30 degrees C (Indian Ocean) and in the aphotic mesopelagic layer (>200 m depth). The detection in the deep water is explained by the passive vertical transport of their sinking biomass. Meanwhile, the presence of its DNA in waters exceeding the thermal limits of the cultured strain points to several alternative hypotheses, including uncultivated regional ecotypes or potential phenotypic plasticity that was not fully captured due to limited laboratory acclimation.
