Marine Biological Laboratory

The marine labile dissolved organic carbon (DOC) pool is a dynamic reservoir of thousands of molecules that cycles approximately one-quarter of Earth's primary production within days to weeks. After excretion by phytoplankton and other microbes, metabolites are rapidly consumed, resulting in low standing concentrations (picomolar to low nanomolar). Despite the decades-long search for labile DOC sources and molecular identities, marine phytoplankton exometabolomes are not well characterized, largely due to difficulties in measuring small polar molecules in saline water. Here, we profiled the exometabolomes of six axenic phytoplankton species representing key functional groups including a diatom (Thalassiosira pseudonana CCMP1335), a picoeukaryote (Micromonas commoda RCC299), a coccolithophore (Gephyrocapsa huxleyi CCMP371), a diazotrophic cyanobacterium (Crocosphaera watsonii WH8501), and two picocyanobacteria (Prochlorococcus marinus MIT9301 and Synechococcus WH8102). From these cultures, we quantified 56 amine- and alcohol-containing exometabolites representing 11 compound classes which in sum comprised up to 23.4% of phytoplankton-excreted DOC. We estimated that these phytoplankton-derived exometabolites could supply up to 5% of the daily carbon quota of the dominant heterotrophic bacterium SAR11 in the surface ocean. Substantial variations in exometabolite identity and concentration across phytoplankton taxa underscore taxonomic diversity as a key driver in the supply and composition of labile DOC. This taxonomic variation predicts geographic and seasonal differences in the distribution of marine dissolved metabolites that underpin the cycling of labile DOC back to carbon dioxide (CO2). Overall, our work suggests that phytoplankton exometabolites are key chemical currencies that mediate significant carbon fluxes within the ocean's carbon cycle.

Stentor, the genus of large trumpet-shaped ciliates, is well-known for its complex morphology and striking behaviors. Members of this genus are distributed throughout the world in a wide and diverse pool of freshwater ecosystems. Recently, the molecular phylogeny of Stentor has been explored through comparison of 18 S small subunit (SSU) ribosomal DNA (rDNA) sequences, clarifying several previously mischaracterized species and species complexes. However, despite their wide distribution, to-date, only about a dozen species of Stentor have been described and verified by phylogenetic means. Here, we introduce the discovery of a new species within genus Stentor: Stentor stipatus spec. nov., so named for their distinctive cytosolic dark pigmented granules which surround the macronucleus and are also present cortically alongside cortically-distributed green microalgae. We present morphological, phylogenetic, ecological, and behavioral characterizations of these cells. Phylogenetic analysis of S. stipatus spec. nov. by comparison of SSU rDNA sequence suggests it is a distinct species from its closest relative, S. amethystinus. We demonstrate that S. stipatus spec. nov. is capable of habituation in response to repeated mechanical stimulation. Further, S. stipatus spec. nov. exhibits strongly directed positive phototaxis, like its relative S. pyriformis, but with a distinct action spectrum from both S. coeruleus and S. pyriformis. Finally, S. stipatus phototaxis response strength varies in a consistent pattern throughout the day, providing evidence of potential circadian regulation. This work expands the current understanding of the ecological distribution of and behavioral features present within genus Stentor.

Subtropical coastal bays significantly mediate land-ocean carbon fluxes, yet their responses to concurrent warming and intensified river discharge remain unclear. Using monthly observations over a decade in Xiamen Bay and integrating flow cytometry, high-throughput sequencing, Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), and NanoSIMS carbon tracing, we explored how microbially driven carbon cycling responds to these dual forces. Our findings reveal that under present-day conditions, a +4 °C warming would increase the abundances of Synechococcus (∼19%) and microeukaryotic algae (∼5%), suggesting an enhanced potential for labile dissolved organic matter (LDOM) production. NanoSIMS experiments showed a 5-fold increase in heterotrophic bacterial assimilation of phytoplankton-derived carbon at elevated temperatures (30 °C versus 22 °C). Concurrently, intensified riverine discharge delivered terrestrial recalcitrant DOM (RDOM), altering DOM molecular composition and decreasing overall bioavailability. These combined stressors restructured microbial communities, accelerating heterotrophic carbon processing and reducing the ratio of ecologically persistent DOM to recalcitrant dissolved black carbon. We propose a Dual-DOM Forcing framework that formalizes how thermal (autochthonous LDOM) and hydrological (allochthonous RDOM) drivers jointly regulate microbial carbon processing, DOM persistence, and coastal carbon sequestration potential. This framework provides a transferable basis for assessing the vulnerability of coastal blue carbon sinks to concurrent warming and altered river discharge.

Hofstenia Bock, 1923, the type genus of Hofsteniidae, was originally established for H. atroviridis Bock, 1923, from Misaki, Kanagawa Prefecture, Japan. This study describes Hofstenia sugashimaensis sp. nov., discovered in water tanks at the Sugashima Marine Biological Laboratory (Nagoya University) and Toba Aquarium, both situated at the mouth of Ise Bay in Mie Prefecture, along the Pacific coast of central Japan. Morphologically, it resembles H. miamia Corrêa, 1960 (commonly known as the “three-banded panther worm”) but is distinguished by two transverse bands and dorsal midline markings based on intra- and interspecific comparisons. Phylogenetic analysis of partial sequences of the cytochrome c oxidase subunit I, 18S rRNA, and 28S rRNA supports its genetic distinction from H. miamia.

Abstract. Nickel (Ni) is an essential micronutrient for marine microorganisms, being involved in enzymes controlling the nitrogen cycle and metabolic responses to oxidative stress. In this study, we examine the covariation between the abundance of Ni-related enzymes and Ni isotope fractionation. To do so, dissolved Ni concentrations and isotope compositions are presented together with metagenomics on samples from the Antarctic Circumnavigation Expedition. Overall, results reveal lower Ni concentrations and higher δ60Ni values in surface waters north of the Sub-Antarctic Front compared to southerly stations. One exception is seen near the high-latitude Mertz Glacier, where the systematics between Ni and δ60Ni better resemble those of low-latitude stations. Relative abundances of urease and Ni-SOD in metagenomes are found to correlate with δ60Ni, potentially suggesting preferential biological uptake of Ni by the organisms using these enzymes. We find a particularly high abundance of urease in diatoms and alphaproteobacteria near the Mertz Glacier, matching the surprisingly high δ60Ni. We thus hypothesise that urea could serve as a nitrogen source for microbial organisms in the late stage of polynya diatom blooms, perhaps causing the observed Ni drawdown and isotope fractionation. This study represents an initial exploration of the influence of biological processes on Ni and δ60Ni distributions. It constitutes a first step towards the further analyses (e.g., culture experiments and metatranscriptomics) needed to determine which exact processes lead to the δ60Ni biogeochemical divide observed between low-latitude and high-latitude waters.

ABSTRACT Understanding how nervous systems mediate responses to sensation requires whole-body maps of periphery-to-brain connections. Octopuses exemplify this challenge with distributed control of eight arms and hundreds of suckers, yet their long-range microanatomical wiring remains elusive due to limitations in microscopy. We extend histotomography (Ding et al. 2019), a form of soft tissue microCT customized for volumetric characterization of cells and tissues, to centimeter range with a custom micro-CT imaging system (Ding et al., 2019). With its 10-mm field of view and 0.7-µm isotropic voxels we created a high-resolution digital intact small octopus. This multi-tissue 3D blueprint enabled us to (i) elucidate previously uncharacterized chemotactile pathways from the suckers to the brain, (ii) discern subdivisions of the nerve ring connecting neighboring arms, and (iii) segment over 300 structures across organ systems at histology-like resolution. We release the labeled interactive digital specimen to facilitate collaborative whole-organism phenotyping as a practical foundation for digital organismal biology . ONE-SENTENCE SUMMARY Whole-body 3D histology reveals neural and organ architecture throughout a small octopus .

FoxQ2 is a highly conserved Forkhead-box transcription factor expressed anteriorly in cnidarians and bilaterians, yet its evolution is marked by rapid divergence and lineage-specific duplications or losses. Moreover, its presence and localization in vertebrate groups remains unclear. To reconcile these conflicting reports of conservation and divergence, we combine phylogenetic and synteny analyses of FoxQ2 sequences from 21 animal phyla. We uncover three ancient FoxQ2 paralogs in bilaterians—FoxQ2I, FoxQ2II, and FoxQ2III. All three were present in the chordate ancestor, and two are retained in vertebrates, indicating a richer FoxQ2 repertoire in vertebrates than previously recognized. To assess FoxQ2 expression, we analyzed mollusk, acoel, amphioxus, and zebrafish single-cell transcriptomic datasets, and conducted fluorescent in situ hybridization in amphioxus, lamprey, skate, zebrafish, and chicken. FoxQ2I and FoxQ2II show conserved anterior expression, while FoxQ2III is expressed in the gut endoderm in chordates, including amphioxus, lamprey, and skate. We also predict conserved transcription factor binding sites across amphioxus genera, revealing stage- and cell-type-specific regulatory interactions for FoxQ2I in deuterostomes. Overall, this work clarifies FoxQ2’s evolutionary history, identifies the endodermally expressed paralog FoxQ2III, and proposes that early duplication of FoxQ2I/II enabled subfunctionalization, driving the fast evolutionary rate of FoxQ2 sequences observed in bilaterians.

Two new deep-sea myzostomid species, Pulvinomyzostomum unicorne sp. nov. and Eenymeenymyzostoma abyssale sp. nov., are described from the Northwest Pacific off Japan. Pulvinomyzostomum unicorne sp. nov. was collected from the crinoid host Pentametrocrinus varians at a depth of 1506 m near Shima Spur, Japan, NW Pacific Ocean, characterized by its distinctive scalloped body margin with 20 equal-sized conical cirri, lack of dorsal ridges or color patterns, a smooth proboscis, and a single cirrus extending from the base of the parapodia. Eenymeenymyzostoma abyssale sp. nov., the deepest record for the genus, was found at 511 m depth on the black coral Leiopathes cf. annosa at the Nishi-Shichito Ridge, Japan, NW Pacific Ocean. This species exhibits an oval, thick body without marginal cirri, transparent and orange coloration internally when alive, and uniquely lacks parapodial cirri. Molecular phylogenetic analyses based on COI, 16S, and 18S sequences strongly supported the placement of these new species within their respective genera.

ABSTRACT Oriented cell division is essential for establishing the anterior-posterior body (A-P) axis in diverse species. However, in Xenopus laevis , blocking cell division during gastrulation does not impair the development of the neural tube and body elongation. Here, we demonstrate that neither neurulation nor dorsal mesoderm formation is dependent on cell division. On the other hand, neural plate elongation and A-P patterning are impacted in the absence of cell division, resulting in trunk defects and anterior defects that appear during tailbud stages. We also show that cell division is abundant around the ectoderm of the gastrulating embryo. Still, it is more intense in the dorsal ectoderm (presumptive neural plate), where there is a clear preference for A-P oriented cell divisions. Taken together, our results highlight a conserved mechanism of A-P oriented cell division that is present during neural plate elongation and patterning.