Volume 68, Issue 5

Isotope tracing experiments can be used to trace organic material flow through the ecosystem by artificially adding labelled biomass into a system. The advantage of this process is the direct control of carbon and nitrogen addition to the system for measuring uptake rates by consumers, which can substantially reduce the uncertainties associated with food web models. This article details and discusses the steps involved in successfully culturing and isotopically enriching ( 13 C and 15 N) juvenile sporophytes of two common North Atlantic kelp species (Laminariales): Saccharina latissima and Laminaria digitata . A first successful isotopic enrichment study of S. latissima , as well as the first inclusion of 15 N enrichment for L. digitata , are detailed. This protocol provides a comprehensive description of the stable isotope enrichment process in two kelp species, potentially serving as a foundation for its application in other macroalgal taxa.

In 2013, a marine heatwave called the “Blob” caused northern California bull kelp ( Nereocystis luetkeana ) populations to decrease significantly. The loss of this foundation species motivated recent investigations on kelp thermal tolerance to understand how warming events might impact their physiological performance. We tested the effect of acclimation temperature on bull kelp by measuring the protein abundance of a molecular chaperone, heat shock protein 70 (Hsp70). Blades were collected from two sites (Big River and Russian Gulch) and acclimated for 7-days at two temperatures (13 and 17 °C) before tissues were subjected to a 1-h heat shock (13, 17, 20, 23, and 26 °C). Results showed a significant difference between acclimation temperature with 20 % greater total Hsp70 protein abundance in bull kelp acclimated to the warm treatment, while site was only marginally different. Heat shock temperature had no effect on total Hsp70 protein abundance. This study is the first to report about the heat shock response of bull kelp and found that thermal history of an organism is an important factor in determining whether an organism can mount a heat shock response. This information can help understand bull kelp’s tolerance to future marine heatwaves.

Interest in Ulva cultivation grows worldwide, but associated bottlenecks exist, including ineffective seeding methods, spontaneous reproduction or biomass loss, and high cultivation costs. Spontaneous biomass degradation causes significant losses, and the underlying biological process is still poorly understood. During a spontaneous degradation event in Ulva lacinulata and a reproduction event in Ulva compressa , production of natural protoplasts was observed. U. lacinulata produced high protoplast yields and parts of the original biomass regenerated. In U. compressa , protoplasts were found in fertile thalli, but the original biomass was lost. Protoplast germination rates were low (2.01 ± 0.48 % in U. lacinulata , 4.14 ± 3.31 % in U. compressa ), and resulted in three morphologies: unattached germlings, unattached discs, and cell masses. Discs and cell masses became fertile early and released gametes. Our results provide the first evidence of natural production of protoplasts in Ulva spp. We estimate that higher seeding yields can potentially be obtained by natural protoplast production (5.95 ± 4.50 × 10 10 individuals g −1 ) than by gametogenesis (2.03 ± 1.15 × 10 9 individuals g −1 ), thus closing an important knowledge gap in the life cycle of Ulva species. These results provide important insights into the reproductive cycle of Ulva spp. relevant for large-scale cultivation.

Species in the green algal order Cladophorales inhabit a wide range of aquatic ecosystems and display significant morphological variation. Identifying these species can be challenging due to their simple morphologies, which offer few diagnostic features. Furthermore, several characters exhibit extensive intraspecific variation and overlap between species. As a result, DNA-based approaches have become essential for accurate species identification. Cladophora , the most diverse genus in the order, is widely distributed and functions as an ecological engineer by shaping aquatic habitats. Accurate species identification is therefore important for sustainable management and effective conservation strategies. This study combines morphological analysis with DNA-based methods, using partial nuclear large subunit ribosomal DNA (LSU rDNA) sequences, to identify Cladophora species collected from various regions of the Aegean Sea (Turkey), and some locations in Greece. Our findings confirm the presence of six Cladophora species ( C. albida , C. hutchinsiae , C. laetevirens , C. prolifera , C. ruchingeri , and C. vagabunda ), along with Cladophoropsis membranacea . While these species have been previously reported from Turkey, our study highlights the continued importance of DNA-based methods for accurate identification within the genus Cladophora .

Endoplura , a genus of crustose brown algae, has consisted of five species: E. aurea , E. gyeokpoensis , E. jejuensis , E. koreana , and E. limpeticola . The genus is characterized by intercalary plurangial reproductive structures, which are made up of 2–4 separate parallel filaments that end in 2–5 sterile cells, as well as by cells containing numerous chloroplasts. In this study, phylogenetic analyses of the concatenated rbc L and COI-5P dataset revealed six well-supported lineages within Endoplura . The specimens from Korea formed a distinct and strongly supported clade (BPP, 1.0/BS, 100) representing the new species. This clade was designated as Endoplura geojensis sp. nov., resolved as the sister clade of E. gyeokpoensis , with low support. Genetic distances between E. geojensis sp. nov. and its congeners ranged from 2.6 % to 8.4 % for rbc L and 10.9 %–13.7 % for COI-5P. E. geojensis sp. nov. is characterized by small, yellowish to dark brown crustose thalli up to 1.5 cm in size, a tuft of hairs emerging from the mid to apical cells of erect filaments, plurangia composed of 2–5 separate parallel reproductive filaments ending in 2–3 sterile cells, and unangia associated with paraphyses and soral filaments.

Crustose coralline algae (CCA) beds are lower-diversity ecosystems compared to typical algal beds. However, we found many turf-forming algae growing on CCA beds in the East Sea of Korea during an ecological survey. We investigated species diversity using molecular markers, focusing on the most commonly found algal genus, Gelidium . Phylogenetic analyses of rbc L sequences revealed six Gelidium species, including three undescribed species from collections of CCA. In addition, mitochondrial cox 1 and plastid psa A sequences were analyzed to confirm their phylogenetic positions. Of these, we describe one as a new species; Gelidium cristatum sp. nov. is distinguished by its small size and erect branches arising radially from the dorsal surface of the prostrate axes in the same position the brush-like haptera grow from the ventral surface, and tetrasporangial sori and cystocarps borne on determinate erect axes. We speculate that Gelidium may possess higher species diversity than previously assumed. However, data on turf-forming species on CCA beds are lacking. Therefore, continuous investigation and observations are necessary.

Knowledge about pathogens of diatoms and macroalgae in the Mediterranean is scarce. This paper reports the first record of the oomycete Diatomophthora perforans subsp. pleurosigmae infecting the Mediterranean microphytobenthic diatom Pleurosigma cf. intermedium , which was detected in the context of marine environmental surveys of the brine outfalls of two seawater desalination plants.

Halophila stipulacea is a dioecious seagrass native to the Red Sea and the western Indian Ocean. It has rapidly expanded to the Mediterranean and Caribbean Seas. While sexual reproduction has been reported within its native range, observations of reproductive structures across its invasive ranges are limited, particularly within the Caribbean. We report instances of staminate flowers of H. stipulacea in a recently established population in the United States. Neither fruits nor pistillate flowers were detected. As this species can be fecund across its native range, additional information on its reproductive ecology is key to understanding its spread into novel regions.

Recent research has evidenced that deep-sea extreme ecosystems represent untapped reservoirs of distinctive microbial species with potential biotechnological applications. Herein, we described the fungal community associated with sediments collected in deep-sea hydrothermal vent systems and an oxygen minimum zone in the Gulf of California and explored their biotechnological potential through an integrated approach based on the culture of the strains in different conditions and a metabolomic analysis. A total of 32 Ascomycota isolates were obtained and taxonomically identified into 14 operational taxonomic units (OTUs) based on their morphology and analysis of the internal transcribed spacers (ITS) of rDNA and the beta-tubulin gene ( benA ). Selected isolates were tested for their growth under different temperatures and for their antibacterial activity against a set of human microbial pathogens. Based on their observed antimicrobial activities, extracts of Aspergillus cejpii (isolate I), Leiothecium ellipsoideum (isolate O), and Aspergillus sp. 2 (isolate W) were selected for a bioactivity-directed chemical study, which produced several secondary metabolites with reported antibacterial, antiparasitic and cytotoxic activities. These results evidence that the explored deep-sea extreme systems harbor promising fungal genetic resources and pave the way towards comprehending deep-sea fungal diversity and its potential utilization.