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We collected the deep-water species Rhodymenia prostrata (Rhodymeniaceae, Rhodophyta), for the first time in nearly 50 years, from the type locality off Mageshima Island, Japan. Our combined rbcL, ...

We determined the chronic effects of dehydration on the photochemical efficiency of a cultivated brown alga, Undaria pinnatifida (Alariaceae, Laminariales), in young sporophytes as cultivated sporelings. The effective quantum yields of photosystem II (ΔF/Fm′) at 50% humidity decreased markedly after 20 min of emersion and dropped almost zero after 60 min of emersion; the values did not restore even after subsequent 1-day immersion. The decreasing values coincided with a decrease in absolute water content of less than 40%. However, under 99% humidity up to 5-day emersion, the ΔF/Fm′ well remained and the last state exhibited a similar level to the initial value after a 48-h emersion at 20 °C and after 72 h of emersion at 10 °C, suggesting that the thalli were not truly dehydrated under saturated humidity and that photosynthetic activity was maintained for several days even without immersion in seawater. In addition, the subsequent growth of young sporophytes exposed to transportation storage stress featuring (1) immersed in seawater with aeration (ST1), (2) those without aeration (ST2), and (3) wrapped in paper towels moistened with seawater (ST3) revealed that the sporophytes exposed at lower temperature exhibited a higher subsequent growth than those at a higher temperature. The subsequent growth of ST3 was lower than ST1; however, the values of ST3 were higher than those of ST2 more than 12 °C, associating with poor seawater quality without aeration. These results indicated that the maintenance of moisture in the alga at low temperatures might be essential for the transportation of the sporelings.

Single-gene markers, such as the mitochondrial cox1, microsatellites, and single-nucleotide polymorphisms are powerful methods to describe diversity within and among taxonomic groups and characterize phylogeographic patterns. Large repositories of publicly-available, molecular data can be combined to generate and evaluate evolutionary hypotheses for many species, including algae. In the case of biological invasions, the combination of different molecular markers has enabled the description of the geographic distribution of invasive lineages. Here, we review the phylogeography of the widespread invasive red macroalga Agarophyton vermiculophyllum (synonym Gracilaria vermiculophylla). The cox1 barcoding provided the first description of the invasion history and hinted at a strong genetic bottleneck during the invasion. Yet, more recent microsatellite and SNP genotyping has not found evidence for bottlenecks and instead suggested that genetically diverse inocula arose from a highly diverse source population, multiple invasions, or some mix of these processes. The bottleneck evident from cox1 barcoding likely reflects the dominance of one mitochondrial lineage, and one haplotype in particular, in the northern source populations in Japan. Recent cox1 sequencing of A. vermiculophyllum has illuminated the complexity of phylogeographic structure in its native range of the northwest Pacific Ocean. For example, the western coast of Honshu in the Sea of Japan displays spatial patterns of haplotypic diversity with multiple lineages found together at the same geographic site. By consolidating the genetic data of this species, we clarify the phylogenetic relationships of a well-studied macroalga introduced to virtually every temperate estuary of the Northern Hemisphere.

We investigated the effects of photosynthetically active radiation (PAR) and temperature on the photosynthesis of juvenile (JS) and mature sporophytes (MS) of a temperate edible brown alga Undaria pinnatifida cultivated in northeastern Japan, using optical dissolved oxygen sensors and pulse amplitude modulation (PAM)–chlorophyll fluorometry. Photosynthesis–PAR experiments at 8, 15, and 22 °C revealed that the maximum net photosynthesis differed with temperature. Values for compensation and saturation PAR indicated a high affinity for a low-light environment. The photosynthetic response of U. pinnatifida to temperature revealed an optimum temperature for oxygenic photosynthesis of 18 °C, which was lower than other laminarian kelps and inconsistent with the wide distribution range of this U. pinnatifida. High temperature and irradiance tolerance differed between MS and JS. Notably, Fv/Fm of MS remained above 0.5 at 28 °C after 168 h of incubation under dark conditions, whereas Fv/Fm was reduced to 0 for the juveniles. Six hours of constant exposure to 200 (low) and 1000 μmol (high) photons m−2 s−1 at 8, 15, and 22 °C induced chronic photoinhibition in all both MS and JS. In contrast to MS, the JS did not recover from photoinhibition in either of the PAR treatments, regardless of a period of darkness. The physiological performance of U. pinnatifida sporophytes indicate an affinity to low light, especially for JS. We expect that these finding will lead to further improvements in commercial production methods to prevent the withering of juvenile sporophytes.

The combined effects of temperature and irradiance and the influences of desiccation and salinity on the photochemical efficiency in a subtropical red alga, Phycocalidia tanegashimensis (= Pyropia tanegashimensis, Bangiaceae) from Tanegashima Island, Japan, were determined to reveal how this species has adapted to its habitat in the splash zone. Continuous 6-h exposure to irradiance of 200 (low) and 1000 (high) µmol photons m−2 s−1 at 12, 20, and 28 °C showed a decline in the effective quantum yields (ΔF/Fm′) of photosystem II (PSII) during the exposures; nevertheless, the maximum quantum yields (Fv/Fm) of PSII measured in subsequent 14-h dim-light acclimation almost returned to initial values at 20 and 28 °C, revealing its high capacity to recovery. In contrast, those under both low and high irradiances at 12 °C did not recover to initial values even after 14-h dim-light acclimation, signifying enhanced inhibition under irradiance at low temperature. The response to continuous desiccation (~ 480 min) under 50% humidity at 24 °C showed that the ΔF/Fm′ decreased with decreasing absolute water content (AWC). However, for the samples with an AWC above 10%, ΔF/Fm′ mostly recovered to initial levels after subsequent 1-day rehydration in seawater, suggesting relatively strong tolerance to desiccation. This alga also tolerated a broad range of salinity (i.e., 10–60 psu) under 3-day exposures. The adaptations of P. tanegashimensis to relatively high irradiance, warm temperature, and a strong osmotic (desiccation and salinity) tolerance may explain its high capacity to flourish in the splash zone in the subtropical environment of Japan.

We examined the effects of four stressors, irradiance, temperature, desiccation, and salinity on the photosynthesis of a red alga, Agarophyton vermiculophyllum (= Gracilaria vermiculophylla, Gracilariales, Rhodophyta) from its native distributional range in Hokkaido and Kagoshima, Japan. Photosynthesis–irradiance (P–E) curves at 8, 16, and 28°C showed that the maximum net-photosynthetic rates (NPmax) and saturation irradiance (Ek) were highest at 28°C for both strains. Gross-photosynthesis determined at 8–40°C at 200 μmol photons m-2 s-1 showed that the maximum gross-photosynthetic rate (GPmax) occurred at 25.3°C for Hokkaido and 28.0°C for Kagoshima ( $$ {T}_{opt}^{GP} $$ ), which is almost consistent with the summer-time seawater temperature at each habitat. The temperature responses (4–40°C) of effective quantum yields (ΔF/Fm') of photosystem II during 7-day exposures were similar to that of oxygenic photosynthesis and the optimum temperature ( $$ {T}_{opt}^{\varDelta F/ Fm\prime } $$ ) was 20.0°C for Hokkaido and 30.1°C for Kagoshima. In the desiccation experiment, the ΔF/Fm' decreased with decreasing absolute water content (AWC); nevertheless, for samples with an AWC above 20%, ΔF/Fm' retuned to initial levels after subsequent 1-day rehydration in seawater, suggesting relatively strong tolerance to desiccation. This alga also showed a broad range of tolerance to salinity ranging from 20 to 60 psu in 7-day exposures, and the ΔF/Fm' tolerated 0 psu at 3-day exposure. The adaptations of A. vermiculophyllum from its native range in Japan to relatively high irradiance, a broad range of temperature, and strong osmotic (desiccation and salinity) tolerance explain its potentially high invasive capacity.

We report two red algal species, Chondracanthus saundersii C.W. Schneider & C.E. Lane (Gigartinaceae, Gigartinales) and Schottera koreana M.S. Calderon, T.H. Seo & S.M. Boo (Phyllophoraceae, Gigartinales), from Japan for the first time based on molecular and morphological analyses. A C. saundersii specimen was collected at a depth of 35 m offshore of Mageshima Island, Kagoshima Prefecture, Japan. The rbcL and COI-5P (cox1) sequences of C. saundersii form a clade with the type specimen from Bermuda and additional specimens from Cuba and Brazil. Morphologically, C. saundersii is characterized by the presence of secondary attachments, compressed to flattened axes up to 1 mm in width, and a looser medulla. Two specimens of S. koreana were collected in lower intertidal to subtidal waters at Ohara, Chiba Prefecture, and Matsuyama, Ehime Prefecture, Japan. The rbcL sequences of S. koreana were closely related to reported sequences of specimens from South Korea including the type specimens. Morphologically, S. koreana is characterized by the presence of unicellular colorless hair developed from cortical cells.

The effects of temperature, irradiance, and desiccation on the photosynthesis of a cultivated Japanese green alga Caulerpa lentillifera (Caulerpaceae) were determined by a pulse amplitude modulation (PAM)-chlorophyll fluorometer and dissolved oxygen sensors. The photochemical efficiency in the photosystem II (Fv/Fm and ΔF/Fm') during the 72-h temperature exposures (8, 12, 16, 20, 24, 28, 32, 36, and 40°C) was generally stable at 16–32°C but quickly dropped at lower and higher temperatures. The photosynthesis–temperature curve at 200 μmol photons m−2 s−1 also revealed that the maximum gross photosynthesis (GPmax) occurred at 30.7°C (30.5–30.9, 95% highest density credible intervals). Photosynthesis–irradiance curves at 16, 24, and 32°C quickly saturated, then expressed photoinhibition, and revealed that the maximum net photosynthetic rates (NPmax) and saturation irradiance (Ek) were highest at 32°C and lowest at 16°C. Continuous 6-h exposure to irradiances of 200 (low) and 400 (high) μmol photons m−2 s−1 at 16, 24, and 32°C expressed greater declines in their ΔF/Fm' at 16°C, revealing chronic chilling-light stress. The response to continuous desiccation (~480 min) under 50% humidity at 24°C showed that ΔF/Fm' dropped to zero at 480-min aerial exposure, and the treatments of more than 60-min desiccation did not return to the initial level even after 24-h subsequent rehydration in seawater. Likewise, ΔF/Fm' fell when the absolute water content (AWC) of the frond dropped below AWC of 90% and mostly did not return to the initial level even after 24-h subsequent rehydration in seawater, signifying a low tolerance to desiccation.

We determined the effects of irradiance, temperature, and desiccation on the photosynthesis of a brown alga, Sargassum muticum (Fucales), from its native distributional range in Japan by using a pulse amplitude modulation (PAM)-chlorophyll fluorometer and optical dissolved oxygen sensors. Photosynthesis–irradiance curves at three temperatures (8, 20, and 28°C) showed that the maximum net photosynthetic rates (NPmax) and saturation irradiance were highest at 28°C. Gross photosynthesis determined at 8–36°C (every four increments) and 300 μmol photons m−2 s−1 showed that the maximum gross photosynthetic rate (GPmax) occurred at 19.5°C ( $$ {T}_{\mathrm{opt}}^{\mathrm{GP}} $$ ), which is consistent with the seawater temperature at its peaked abundance in Japan. The maximum quantum yields (Fv/Fm) of photosystem II (PSII) during the 72-h temperature exposures were above 0.60 at 8–28°C but dropped at higher temperatures. Continuous exposure (12 h) to irradiance of 200 (low) and 1000 (high) μmol photons m−2 s−1 at three temperatures showed remarkable decline in the effective quantum yields (ΔF/Fm') of PSII under high irradiance at 8°C only; the Fv/Fm measured after 12-h dark acclimation also did not recover to initial values, signifying its sensitivity to photoinhibition at 8°C. Furthermore, the alga exhibited tolerance to 2 h of desiccation with 80% of water loss from the thallus, and ΔF/Fm' recovered after 24 h of rehydration in seawater, suggesting potential of photosynthetic recovery of this alga at such low hydration threshold. In conclusion, the adaptation of S. muticum to relatively high irradiance, to broad range of temperature (8–28°C), and to desiccation explains its potentially high invasive capacity.

A new flattened species of Gracilariopsis from Mageshima Island, Japan is recognized based on morphological and molecular analyses of rbcL and cox1 DNA sequences. We name this new species Gp. mageshimensis sp. nov. The rbcL and cox1 analyses suggest that Gp. mageshimensis belongs to the Gracilariopsis clade, and that it is distinct from other Gracilariopsis species. Gracilariopsis mageshimensis is characterized by a flattened thallus, the lack of tubular nutritive cells, the lower gonimoblasts connect to the cystocarp floor cells via pit connections and small gonimoblasts filling the cystocarp cavity. The Gp. mageshimensis cystocarp is in accordance with the morphological concept of Gracilariopsis. Gracilariopsis mageshimensis is the second Gracilariopsis species with a flattened thallus to be described worldwide. Gracilariopsis mageshimensis is distinguished from Gp. silvana, the first flattened species by the rare production of lateral branches, a medulla consisting of fewer than five layers, and its deep-water habitat.

The effects of temperature on the photosynthesis and growth of a subtropical red alga, Phycocalidia tanegashimensis (= Pyropia tanegashimensis, Bangiaceae, Bangiales) from Tanegashima Island, Japan, were determined to better understand the ecology of the macroscopic gametophyte. Net photosynthesis–irradiance (P–E) curves, determined at 12, 20, and 28°C, revealed that the maximum net photosynthetic rates occurred at 28°C. A gross photosynthesis–temperature (P–T) curve, determined at temperatures between 8 and 36°C, supported this result and indicated that optimal temperature ( $$ {T}_{opt}^{GP} $$ ) for maximum gross photosynthetic rates was 27.3°C (25.9–28.8 95% highest density credible intervals, HDCI). However, after 4 days of incubation at constant temperature, the effective quantum yields (ΔF/Fm') of photosystem II, determined between 4 and 40°C under 50 μmol photons m−2 s−1 (12L:12D), were greatest at 22.1°C (20.9–23.4 HDCI) and declined quickly below 20°C and 32°C. The relative growth rate (RGR) was highest at 25.8°C (22.5–28.1 HDCI) at the conclusion of a 6-day culture (4 to 36°C) under 50 μmol photons m−2 s−1 (12L:12D). Compared to other temperate species of Bangiaceae, P. tanegashimensis appears to be well adapted to relatively high temperatures. The macroscopic gametophyte stage of Bangiaceae is regarded to be adapted to cold temperatures to overwinter; nevertheless, the significance of our study is that a year-round occurrence of P. tanegashimensis is enabled by its high optimal temperatures for photosynthesis and growth.

Domoic acid (1, DA), a member of the natural kainoid family, is a potent agonist of ionotropic glutamate receptors in the central nervous system. The chemical synthesis of DA and its derivatives requires considerable effort to establish a pyrrolidine ring containing three contiguous stereocenters. Recently, a biosynthetic cyclase for DA, DabC, was identified. This enzyme cyclizes the linear precursor of isodomoic acid A (IA) to IA, a bioactive DA analogue. In this study, we developed a bioconversion system to obtain DA analogues from linear substrates prepared by simple chemical synthesis using DabC expressed in Escherichia coli, in vivo. Three IA analogues with various substitutions at the C7′-geranyl terminus were prepared using this system: two minor natural analogues, 7′-methyl-IA (5) and 7′-hydroxy-IA (6), and one new unnatural analogue, 7′-amide-IA (7). In addition, the toxicity of these DA analogues in mice was examined by intracerebroventricular injection. Most of the mice injected with 5 (3 nmol) and 6 (3 nmol) did not show any adverse symptoms, whereas the mice injected with 7 (3 nmol) showed typical symptoms induced by DA (1, 0.7 nmol) and IA (2, 3 nmol). These results suggest that the 7′-carbonyl group in the side chain of IA (2) is crucial for its toxicity. The docking studies of DA, IA (2), 5, 6, and 7 to GluK1 supported these results.

The genus Meristotheca (Solieriaceae) includes fifteen currently accepted species. They are widely distributed throughout the tropics and subtropics of both hemispheres, inhabiting the intertidal and subtidal regions of rocky shores. Molecular phylogenetic studies allowed a precise understanding of the species diversity and biogeography of the genus. The commercial value of certain species of Meristotheca lies in its use primarily as food for direct human consumption and to some extent as raw materials for extraction of carrageenan and other bioactive compounds. Intensified harvesting of the seaweeds resulted in the depletion of their natural beds; hence, several attempts have been made for mariculture. The management effort for the farming of Meristotheca on a commercial scale is still at its early stage. Studies on the phenology, sporulation, callus induction and thallus regeneration, photosynthesis, and growth of these potentially useful species contributed to the advancement of cultivation technologies. Further research on the biochemistry and utilization of Meristotheca species is necessary for the commercial competitiveness of these promising seaweed resources.

This study examined the effects of temperature and irradiance on photosynthetic characteristics of the macroscopic sporophyte (SPO) and microscopic gametophyte (GAM) stages of a subarctic brown alga, Saccharina japonica var. japonica (Laminariales) from Hokkaido, Japan. In vitro measurements under short- and long-term exposures were carried out by using optical dissolved oxygen sensors and the pulse amplitude modulation (PAM)-chlorophyll fluorometer, respectively. The heteromorphic life history stages of S. japonica showed photosynthetic optima at 23–23.3 °C, derived from the gross photosynthesis–temperature model. Maximum quantum yields (Fv/Fm) of SPO and GAM after 72 h of temperature exposures in the dark were reduced to near zero above 24 °C, indicating PSII inactivation. Such similarity in their temperature characteristics suggests the co-occurrence of both generations in the habitat despite the seasonal growth and reproduction of the species. Net photosynthesis–irradiance experiments in the two life history stages at 8, 16, and 24 °C revealed similarity in their light-saturated photosynthetic rates (NPmax = 3.02–4.41 μg O2 gww−1 min−1, SPO; 2.87–3.73 μg O2 gww−1 min−1, GAM), but saturation irradiances of SPO (Ek = 81–102 μmol photons m−2 s−1) were higher than those of GAM (48–69 μmol photons m−2 s−1). A slight decrease in net photosynthetic rates of GAM above 500 μmol photons m−2 s−1 was likewise observed. This difference may be related to the light regime of their natural habitat, suggesting the low irradiance adaptation of the microscopic stage that settles on rock crevices beneath algal canopies.

Understanding the physiological responses of kelp to environmental parameters is essential for the conservation of natural kelp beds and increased cultivation yield. We investigated the effects of ...

The reproductive structures, early development and carotenoid composition of Umbraulva kuaweuweu, which is a deep-water ulvacean species recently reported from Hawaii, are reported for the first ti...

The chronic effects of three different stressors, irradiance, temperature, and desiccation, on Photosystem II (PSII) photochemical efficiency were investigated in two heteromorphic life-history stages of a cultivated red alga, Pyropia yezoensis f. narawaensis (Bangiales) from Japan. The maximum quantum yields of PSII (Fv/Fm) over the range of temperature between 4 and 36 °C for 96-h exposure showed different responses in the two life-history stages. In the macroscopic gametophyte, the highest value (0.47) occurred at 12.0 °C; however, Fv/Fm quickly decreased at higher temperatures. In contrast, Fv/Fm in the microscopic sporophyte were less sensitive to temperature, suggesting adaptation to the broad range of temperature with a high value (0.40) that occurred at 21.1 °C. Continuous 6-h exposures to the 50, 100, and 1000 μmol photons m−2 s−1 revealed greater decline in their effective quantum yields of PSII (ΔF/Fm′) in the sporophyte. As known in the photoprotective response and its PSII repair system in the photosynthesis, the recovery of quantum yield in two life-history stages after subsequent acclimation (darkness and dim-light treatments) was more accelerated in dim-light than those of darkness. The response to continuous desiccation (240-min aerial exposure) in two life-history stages was also different, and the ΔF/Fm′ in the gametophyte returned to initial values after re-immersion in seawater. In contrast, those in the sporophyte dropped to zero after a 5-min aerial exposure and did not return to initial values, suggesting that farming protocols for the conchospore seeding in Nori-net cultivation need to pay careful attention to desiccation to ensure successful production.

This study investigated the effects of different light spectral qualities and temperature on the photosynthesis and pigment content of a subtidal edible red alga, Meristotheca papulosa. Photosynthesis–irradiance (P–E) experiments were carried out under red (660 nm), blue (450 nm), green (525 nm, light-emitting diodes), and white light (visible light, metal halide lamp), and at 12, 20, and 28 °C, respectively. Maximum net photosynthetic rates (NPmax) were highest under green light. Other P–E parameter estimates were similar among algae under red, blue, and green light, including their lower initial slope (α) and higher saturation irradiances (Ek) as compared to those under white light. Additionally, NPmax and Ek under white light were highest at 28 °C, and lowest at 12 °C with characteristic photoinhibition at irradiances greater than 150 μmol photons m−2 s−1. Photosynthesis–temperature (P–T) experiment revealed that the maximum gross photosynthetic rate (GPmax) occurred at 22.1 °C, which was within the optimal temperature range of Fv/Fm (21.5–23.6 °C). Exposures to the different light qualities at 100 μmol photons m−2 s−1 for 7 days showed increased phycoerythrin (PE) concentration of algae under blue and green light, while chlorophyll-a and phycocyanin (PC) showed little variation in all light qualities. Therefore, considering future management prospects for M. papulosa mariculture, we suggest that green light could be utilized to enhance photosynthesis. Furthermore, if the aim is to achieve high PE content for an improved reddish-color fresh product, exposure to blue or green light could be a good alternative.

The temperature and light responses of photosynthesis in two freshwater red algae, Virescentia helminthosa and Sheathia arcuata (Batrachospermaceae), were determined by a pulse amplitude modulation (PAM) chlorophyll fluorometer and dissolved oxygen sensors. Net oxygenic photosynthesis–photosynthetically active radiation (PAR) models of V. helminthosa and S. arcuata revealed similar low PAR-adapted responses, with a compensation PAR (Ec) of 6.95 and 11.5 μmol photons m−2 s−1 (5.58–8.42 and 9.10–11.42, 95% Bayesian prediction interval, BPI) and saturating PAR (Ek) of 18.8 and 17.7 μmol photons m−2 s−1 (14.5–24.7 and 13.0–23.90, BPI), respectively. A temperature-dependent model of net photosynthesis and dark respiration for two species also showed similar temperature responses, and the gross photosynthetic rate (GPmax), 1.79 and 1.19 μg O2 gww−1 min−1 (1.62–1.96 and 1.08–1.29, BPI), was highest at 26.4 and 30.3 °C (23.9–28.7 and 28.3–32.1, BPI). The maximum quantum yields (Fv/Fm) for two species also had similar responses with respect to temperature; however, it was generally stable at low temperatures (8–20 °C) with the highest value of 0.52 and 0.56 (0.49–0.54 and 0.54–0.58, BPI) occurring at 18.5 and 20.9 °C (17.1–19.7 and 19.8–21.9, BPI). Continuous exposure (12 h) to PAR of 100 (low) and 1000 (high) μmol photons m−2 s−1 at 12, 16, and 24 °C revealed greater declines in their effective quantum yield (ΦPSII) in the two species under high PAR. Nevertheless, their Fv/Fm mostly recovered after a subsequent 12-h dim-light acclimation, suggesting the potential of recovery from daytime chronic photoinhibition.

To determine the species distribution of an amnesic shellfish poisoning (ASP) toxins-producing diatom Nitzschia navis-varingica outside its current restricted geographical distribution range in Asian coastal waters, samples were collected from two sites of Bootless Bay, located on southwest coast of Papua New Guinea near Port Moresby. A total of twenty-one strains of N. navis-varingica were isolated and the clonal cultures established. The species identity was confirmed by molecular characterization based on the ribosomal DNA markers. The LSU rDNA phylogenetic inference revealed a monophyletic clade of all strains, clustered with N. navis-varingica with high bootstrap supports. ASP toxin production in the strains was investigated by HPLC with fluorescence detection and subsequently confirmed for the representative isolates by LC-MS/MS with multiple reaction monitoring (MRM) mode. All eleven strains from site A showed presence of domoic acid (DA) and isodomoic acid (IB); the toxin quota ranged from 0.70 to 4.63 pg cell

Domoic acid (DA), the causative agent of amnesic shellfish poisoning, is produced by select organisms within two distantly related algal clades: planktonic diatoms and red macroalgae. The biosynthetic pathway to isodomoic acid A was recently solved in the harmful algal bloom-forming diatom Pseudonitzschia multiseries, establishing the genetic basis for the global production of this potent neurotoxin. Herein, we sequenced the 507-Mb genome of Chondria armata, the red macroalgal seaweed from which DA was first isolated in the 1950s, identifying several copies of the red algal DA (rad) biosynthetic gene cluster. The rad genes are organized similarly to the diatom DA biosynthesis cluster in terms of gene synteny, including a cytochrome P450 (CYP450) enzyme critical to DA production that is notably absent in red algae that produce the simpler kainoid neurochemical, kainic acid. The biochemical characterization of the N-prenyltransferase (RadA) and kainoid synthase (RadC) enzymes support a slightly altered DA biosynthetic model in C. armata via the congener isodomoic acid B, with RadC behaving more like the homologous diatom enzyme despite higher amino acid similarity to red algal kainic acid synthesis enzymes. A phylogenetic analysis of the rad genes suggests unique origins for the red macroalgal and diatom genes in their respective hosts, with native eukaryotic CYP450 neofunctionalization combining with the horizontal gene transfer of N-prenyltransferases and kainoid synthases to establish DA production within the algal lineages.

Domoic acid (DA), the causative agent of amnesic shellfish poisoning, is produced by select organisms within two distantly related algal clades: planktonic diatoms and red macroalgae. The biosynthetic pathway to isodomoic acid A was recently solved in the harmful algal bloom-forming diatom

The evolutionary and population demographic history of marine red algae in East Asia is poorly understood. Here, we reconstructed the phylogeographies of two upper intertidal species endemic to East Asia, Gelidiophycus divaricatus and G. freshwateri. Phylogenetic and phylogeographic inferences of 393 mitochondrial cox1, 128 plastid rbcL, and 342 nuclear ITS2 sequences were complemented with ecological niche models. Gelidiophycus divaricatus, a southern species adapted to warm water, is characterized by a high genetic diversity and a strong geographical population structure, characteristic of stable population sizes and sudden reduction to recent expansion. In contrast, G. freshwateri, a northern species adapted to cold temperate conditions, is genetically relatively homogeneous with a shallow population structure resulting from steady population growth and recent equilibrium. The overlap zone of the two species roughly matches summer and winter isotherms, indicating that surface seawater temperature is a key feature influencing species range. Unidirectional genetic introgression was detected at two sites on Jeju Island where G. divaricatus was rare while G. freshwateri was common, suggesting the occurrence of asymmetric natural hybrids, a rarely reported event for rhodophytes. Our results illustrate that Quaternary climate oscillations have left strong imprints on the current day genetic structure and highlight the importance of seawater temperature and sea level change in driving speciation in upper intertidal seaweed species.

“Monitoring Sites 1000” – Japan's long‐term monitoring survey was established in 2003, based on the Japanese Government policy for the conservation of biodiversity. Ecological surveys have been conducted on various types of ecosystems at approximately 1000 sites in Japan for 15 years now and are planned to be carried out for 100 years. Since 2008, seaweed communities had been monitored at six sites, featuring the kelp (e.g. Saccharina and Ecklonia; Laminariales) and Sargassum (Fucales) communities in the subarctic and temperate regions of Japan. Annual surveys were carried out during the season when these canopy‐forming seaweeds are most abundant. A non‐destructive quadrat sampling method, with permanent quadrats placed along transects perpendicular to the shoreline, was used to determine species composition, coverage, and vertical distribution of seaweeds at these sites; while destructive sampling was done every 5 years to determine biomass. The occurrence of canopy‐forming species Saccharina japonica (var. japonica) and Ecklonia cava have appeared to be stable at the Muroran (southwestern part of Hokkaido Island) and Shimoda (Pacific coast of middle Honshu Island) sites, respectively; whereas the coverage of Ecklonia radicosa (= Eckloniopsis radicosa) at the Satsuma‐Nagashima site in southern part of Kyushu Island was highly variable until its sudden disappearance from the habitat in 2016. Thalli of E. radicosa lost most of their blades through browsing by herbivorous fish, and thus, this may be one of the causes of the decline. A shift in the community structure related to environmental changes had also been observed at some other sites. Pre‐ and post‐disaster data revealed the impact of the 2011 earthquake and tsunami disasters, including a shift in the vertical distribution of Ecklonia bicyclis (= Eisenia bicyclis) to shallower depths at the Shizugawa site in the Pacific coast of northern Honshu Island, due to seafloor subsidence.

The effects of irradiance, temperature, thermal‐ and chilling‐light sensitivities on the photosynthesis of a temperate alga, Sargassum macrocarpum (Fucales) were determined by a pulse amplitude modulation (PAM)‐chlorophyll fluorometer and dissolved oxygen sensors. Oxygenic photosynthesis–irradiance curves at 8, 20, and 28°C revealed that the maximum net photosynthetic rates (NP ₘₐₓ) and saturation irradiance were highest at 28°C, and lowest at 8°C. Gross photosynthesis and dark respiration determined over a range of temperatures (8–36°C) at 300 μmol photons m⁻² s⁻¹ revealed that the maximum gross photosynthetic rate (GPₘₐₓ) occurred at 27.8°C, which is consistent with the highest seawater temperature in the southern distributional limit of this species in Japan. Additionally, the maximum quantum yields of photosystem II (F ᵥ/F ₘ) during the 72‐h temperature exposures were stable at 8–28°C, but suddenly dropped to zero at higher temperatures, indicative of PSII deactivation. Continuous exposure (12 h) to irradiance of 200 (low) and 1000 (high) μmol photons m⁻² s⁻¹ at 8, 20, and 28°C revealed greater declines in their effective quantum yields (Φ PSII) under high irradiance. While Φ PSII under low irradiance were very similar with the initial F ᵥ/F ₘ under 20 and 28°C, values rapidly decreased with exposure duration at 8°C. At this temperature, F ᵥ/F ₘ did not recover to initial values even after 12 h of dark acclimation. Final F ᵥ/F ₘ of alga at 28°C under high irradiance treatment also did not recover, suggesting its sensitivity to photoinhibition at both low and high temperatures. These photosynthetic characteristics reflect both the adaptation of the species to the general environmental conditions, and its ability to acclimate to seasonal changes in seawater temperature within their geographical range of distribution.

Effects of photosynthetically active radiation (PAR) and temperature on the photosynthesis of a subarctic edible brown alga, Saccharina angustata (Laminariaceae, Laminariales), from Hokkaido, Japan...

A new species of marine sand-dwelling dinoflagellate, Plagiodinium ballux N. Yamada, Dawut, R. Terada & T. Horiguchi is described from a deep (36 m) seafloor off Takeshima Island, Kagoshima Prefecture, Japan in the subtropical region of the northwest Pacific. The species is thecate and superficially resembles species of Prorocentrum, but possesses an extremely small epitheca. The cell varies from ovoid to a rounded square, and is small (15.0-22.5 mu m in length) and laterally compressed. The thecal plates are smooth and the thecal plate arrangement (Po, 1 ', 0a, 5 '', 5C, 2S, 5"', 0p, 1 '''') is similar to that of Plagiodinium belizeanum, the type species of the genus. Molecular phylogenetic analyses based on SSU rDNA and partial LSU rDNA reveal that the dinoflagellate is closely related to P. belizeanum, but it can be clearly distinguished by its size and cell shape. This suite of morphological and molecular differences leads to the conclusion that this deep benthic dinoflagellate represents a new species of the genus Plagiodinium.

The effect of photosynthetically active radiation (PAR) and temperature on the photosynthesis of an endangered Japanese freshwater red alga, Thorea okadae (Thoreaceae, Thoreales), was determined by using pulse-amplitude modulation (PAM) fluorometry and dissolved oxygen sensors. The macroscopic life history stage (gametophyte) was observed on pebbles and cobbles in a shallow riverbed from early winter to late spring (December–May), in direct sunlight (∼800 μmol photons m−2 s−1) during winter noon time with a clear sky. A net oxygenic photosynthesis–PAR model revealed that the net photosynthetic rate increased linearly and saturated, with a compensation (Ec) and saturating PAR (Ek) of 13.3 μmol photon m−2 s−1 (10.3–16.3, 95% Bayesian prediction interval, BPI) and 55.2 μmol photon m−2 s−1 (42.2–72.9, 95% BPI), respectively. A temperature-dependent (i.e., 8–36°C range) model of net photosynthesis and dark respiration was fitted and showed that the gross photosynthetic rate, 17.3 μg O2 gww−1 min−1 (16...

The effect of photosynthetically active radiation (PAR) and temperature on the photosynthesis of a temperate Japanese edible brown alga, Cladosiphon umezakii (Chordariaceae, Ectocarpales), from Honshu Island, Japan, was determined in the heteromorphic life history stages (macroscopic and microscopic) by using pulse-amplitude modulation (PAM) fluorometry and optical dissolved oxygen sensors. The microscopic stage is well-adapted to relatively low PAR environment, as revealed by its lower maximum net photosynthesis (NPmax), saturation (Ek), and compensation PAR (Ec), and higher value of the initial slope (α) compared to the macroscopic stage. Both stages share similar temperature optima ( $$ {T}_{opt}^{GP} $$ 15.9–25.8 °C for macroscopic stage, 12.6–27.4 °C for microscopic stage), suggesting the possible occurrence of both generations in their habitats throughout the year. While these optimum temperatures are within the range of seawater temperature in the distribution of this species, they are close to the physiological limit of thermal inhibition. Continuous exposures (6 h) to 200 (low) and 1000 (high) μmol photons m−2 s−1 at 8, 16, and 28 °C revealed greater declines in effective quantum yields of photosystem II (ΦPSII) in the microscopic stage, confirming its low PAR adaptation. Low temperature-induced photoinhibition was likewise observed in both stages. Existing farming methods for Japanese Cladosiphon (especially for subtropical Cladosiphon okamuranus from Ryukyu Islands, Japan) may need to be modified to meet the optimum requirements of C. umezakii in the temperate region of Japan.

The combined effects of irradiance and temperature on photosystem II (PSII) photochemical efficiency were investigated in the microscopic sporophyte and macroscopic gametophyte stages of the cultivated red algae Pyropia yezoensis f. narawaensis and Pyropia tenera (Bangiales) from Kyushu Island, Japan. Continuous 12-h exposures to 10, 100, and 1000 μmol photons m−2 s−1 at 8, 20, and 28 °C revealed that sporophyte and gametophyte stages of both species have different tolerance characteristics to irradiance and temperature. Effective quantum yields (ΦPSII) of sporophytes declined at 100 and 1000 μmol photons m−2 s−1, and their maximum quantum yields (Fv/Fm) did not fully recover even after 12 h of dark acclimation, indicating photodamage. Furthermore, this depression was greatest at 8 °C, suggesting low temperature-enhanced photoinhibition. Larger declines of ΦPSII and subsequent failure of Fv/Fm recovery in the gametophyte were observed only at 1000 μmol photons m−2 s−1, suggesting that the macroscopic stage is more tolerant to relatively higher irradiance than the sporophyte. Farming protocols, including the timing of conchospore seeding, as well as depth range and duration for Nori-net cultivation need to be optimized to ensure sustainable production of these high-valued seaweed cultivars.

In Japan, fresh cultivated green alga, Caulerpa lentillifera (Caulerpaceae, Bryopsidales), are packed into polystyrene containers without seawater. They can stay fresh for 1 week inside the container under room temperature, suggesting a high tolerance to desiccation. This tolerance was evaluated in the present study by employing methods based on pulse amplitude modulation (PAM) fluorometry. The chronological change of the photochemical efficiency of photosystem II (PSII) of C. lentillifera in response to desiccation under conditions experienced during the commercial shipping was examined. Desiccation experiments were carried out for 2, 4, 8, and 12 days at 20 °C. Maximum quantum yields (Fv/Fm) were measured at the initial state, after each desiccation period, and after 10-min and 3, 6, and 24-h re-immersion in seawater. Fv/Fm of samples after a 2-day desiccation remained relatively high (0.78 ± 0.04 standard deviation (SD)), while those after 4- and 8-day desiccation periods decreased and yet were considered active with values greater than 0.40 following rehydration. Samples under the 12-day desiccation had the greatest decline in Fv/Fm, (0.10 ± 0.10), along with 72% critical water loss. Failure of the seaweed to recover from desiccation stress further indicates deactivation of the photosystem, which is perhaps associated with multiple cellular alterations that result at the end in a dysfunctional alga. The packaging system that makes use of polystyrene containers for thermal insulation and an absorbent sheet for moisture control may have provided an optimal environment for the seaweed to extend its “freshness” up to 1 week by maintaining photochemical efficiency.

Photosynthetic responses to photosynthetically active radiation (PAR) and temperature were investigated in the macroscopic sporophyte (SPO) and microscopic gametophyte (GAM) stages of the brown alga Costaria costata from Hokkaido, Japan. Measurements of net photosynthesis, respiration rates and photochemical efficiency were carried out using dissolved oxygen sensors and a pulse amplitude–modulated fluorometer. Net photosynthesis–irradiance curves of the two life history stages revealed a similarity in their light-saturated photosynthesis rates but a difference in initial slopes, with lower efficiency in oxygenic evolution for SPO than for GAM. Consequently, compensation PAR (Ec = 9 μmol photons m−2 s−1) and saturation PAR (Ek = 243 μmol photons m−2 s−1) of the sporophyte were higher than for the gametophyte (Ec = 1 μmol photons m−2 s−1; Ek = 44 μmol photons m−2 s−1). This reflects the low-PAR adaptation of the microscope stage that is commonly found on the underside of rocks or in crevices where...

The combined effects of photosynthetically active radiation (PAR) and temperature on the photosynthesis of a temperate Japanese brown alga, Sargassum patens (Fucales), were determined by field and laboratory measurements. Underwater measurements of the natural population of this alga in Kagoshima, Japan, revealed that the effective quantum yield (Φ PSII ) declined with increasing incident PAR, with minimum Φ PSII occurring during noon to early afternoon. Φ PSII recovered in the evening, indicating dynamic photoinhibition. In laboratory experiments, Φ PSII was also negatively correlated with PAR, which decreased after 12 h of continuous exposure to 200 (low) and 1000 (high) μmol photons m−2 s−1 at 8, 20, and 28 °C. Maximum quantum yield (F v /F m ) at 8 °C with low PAR failed to recover after 12 h of dark acclimation, suggesting the influence of low temperature in chronic photoinhibition. Photosynthesis–irradiance (P–E) curves likewise revealed lower net photosynthetic rates and photoinhibition at 8 °C. Gross photosynthesis and dark respiration experiments determined over a range of temperatures (8–40 °C) revealed that the maximum gross photosynthetic rate (GP max) occurred at 26.9 °C. F v /F m after 72 h of temperature exposures was stable at 8–32 °C; but it was deactivated at 36 and 40 °C. This species is well-adapted to the current range of temperature in the temperate region of Japan (7–28 °C). However, the combined effects of low temperature and PAR may influence algal photosynthetic efficiency and so may be limiting at the marginal region of northern distribution of this temperate species.

Photosynthetic responses to photosynthetically active radiation (PAR) and temperature were examined in the red alga Solieria pacifica from deep (35 m) and shallow (5 m) portions of the sublittoral zone in Kagoshima, Japan. Dissolved oxygen sensors and pulse-amplitude modulated (PAM) fluorometry were used for the measurements of net photosynthesis, dark respiration rates, and photochemical efficiency. The photosynthetic performances of the deep- and shallow-water ecotypes provided substantial evidence of their adaptation to the ambient PAR and temperature conditions of their respective habitats. Both algal samples showed different temperature optima for photosynthesis: 19.5–19.9 °C for S. pacifica from Mageshima (MAG) and 18.6–27.0 °C for species from Yatsushiro Bay (YAT), that reflect the temperature ranges in the 35- and 5-m depths of the sublittoral zone, respectively. Maximum net photosynthetic rate (P max = 3.73 μg O2 gfw −1 min−1), compensation PAR (E c = 21 μmol photons m−2 s−1), and saturation PAR (E k = 131 μmol photons m−2 s−1) were higher in YAT S. pacifica than in MAG samples (P max = 1.55 μg O2 gfw −1 min−1, E c = 3 μmol photons m−2 s−1, E k = 15 μmol photons m−2 s−1), which can be attributed to the higher PAR levels experienced by the seaweeds occurring at depths of 5 m. The large depressions in effective quantum yields (Φ PSII) after chronic PAR exposures and failed recovery in maximum quantum yields (F v /F m) after dark acclimation of MAG S. pacifica suggest a greater tendency for photodamage in the deep-water ecotype. As for the shallow-water S. pacifica (YAT), complete recovery occurred only at 20 °C. Low temperature limitation may account for the decreased gross photosynthetic rates and delayed recovery of post-dark acclimation F v /F m of YAT S. pacifica at temperatures below their optimum, which can occur during winter.

The successful cultivation of the Japanese Kappaphycus sp. (K. striatus auctorum japonicorum) in Okinawa, Japan, requires the detailed understanding of its physiological response to environmental factors. The photosynthetic performance of this native red alga was investigated under a variety of temperature and photosynthetic active radiation (PAR) conditions by employing methods based on pulse amplitude modulation–chlorophyll fluorometry and dissolved oxygen sensors. The net photosynthesis–irradiance (P–E) curve at 24°C revealed that the compensation (Ec) and saturation (Ek) irradiances were 26 [95% Bayesian prediction interval (BPI), 11–29 μmol photons m−2 s−1] and 140 (95% BPI, 98–192) μmol photons m−2 s−1, respectively. No inhibition in oxygenic evolution and quantum yield was observed at the highest PAR of 1000 μmol photons m−2 s−1. However, the ability of the seaweed to recover from photoinhibition was complicated following long-term PAR exposures at 18°C but not at 28°C. The Japanese Kappa...

SUMMARY A new species of benthic marine dinoflagellate, Pyramidodinium spinulosum Horiguchi, Moriya, Pinto & Terada is described from the deep (36 m) seafloor off Mageshima Island, Kagoshima Prefecture, Japan in the subtropical region of the northwest Pacific. The life cycle of the dinoflagellate consists of a dominant, attached, dome-shaped, vegetative form and short-lasting, motile cell. Asexual reproduction takes place by the formation of two motile cells within each non-motile cell. The released motile cells swim only for a short period and transform directly into the dome-shaped vegetative form. The duration of the cell cycle varies and can be extremely long, ranging 5–38 days under culture conditions. The non-motile cell is enclosed by a cell wall and its surface is covered with many (80–130) spines of various length. The dinoflagellate is photosynthetic and contains many (more than 50) discoidal chloroplasts. Phylogenetic analysis reveals that the dinoflagellate is closely related to the type species of the genus Pyramidodinium, P. atrofuscum which also possesses a dominant, attached, non-motile form. However, P. spinulosum can be clearly distinguished from P. atrofuscum by the cell shape (dome-shaped vs. pyramid-shaped) and surface ornamentation (spines vs. wart-like processes) of the non-motile form. Based on these morphological differences together with molecular evidence, it was concluded that this organism from a deep water sand sample should be described as a second species of the genus Pyramidodinium, P. spinulosum.

SUMMARY The chronological change of photosynthetic efficiency in a frozen storage treatment of the Japanese Nori cultivation industry was examined in the cultivated red alga, Pyropia yezoensis f. narawaensis (Saga-#5 Strain, Bangiales) by using pulse-amplitude fluorometry. During the desiccation process that was conducted after the nursery cultivation season in November, the maximum quantum yield (F v/F m) of the gametophytic sporelings growing on the Nori-net decreased monotonically with decreasing absolute water content (AWC), and was around 0.1 at 20% AWC. During frozen storage of the Nori-net, the F v/F m of the frozen gametophyte was low but stable, and ranged between 0.10 ± 0.02 SD and 0.14 ± 0.05 SD. The magnitude of F v/F m for the gametophyte of the freezing treatment, after 10 min and 3 h of immersion in seawater, recovered quickly. After 10 min and 3 h of immersion, these values were 0.29 ± 0.12 SD and 0.47 ± 0.05 SD during the 14 days of freezing treatment, and 0.15 ± 0.02 SD and 0.29 ± 0.04 SD after 71 days of freezing treatment, and suggest that the ability to recover gradually decreased as the storage duration increased. The response of F v/F m from general cultivation (i.e., directly cultivated from the nursery cultivation season) and those after 47 days of freezing were almost identical, suggesting that the current Nori -net frozen storage period (6 or 7 weeks) was not detrimental to the gametophyte.