Changes In Seawater Temperature Research Articles

A study of the temperature distribution in the OTEC cold water pipe using a heat and mass transfer approach

Abstract The difference between sea water temperature at a depth of around 1000 m and sea water temperature at sea level is generally used as a parameter in the design of Ocean Thermal Energy Conversion (OTEC). In practice, electricity generation is determined by the difference between the temperature of the cold seawater coming out of the Cold Water Pipe (CWP) and the temperature of the seawater at the surface. The temperature of cold sea water increases due to heat transfer experienced by cold sea water flowing through the CWP, which comes into contact with surrounding sea water which has a higher temperature. This in turn provides a lower actual temperature difference, and therefore reduces the design power capacity. However, many previous studies did not consider these lower temperature differences. This may be acceptable for cases with practically small heat transfer such as CWP with low thermal conductivity combined with good insulation used in 1000 m CWP vertical floating systems. Unfortunately, this may not be the case for many of OTEC’s proposed alternative sites, which are located on land systems that require CWP lengths of five km or more. This raises the need for careful investigation to determine the temperature of the sea water coming out of the CWP, where it is necessary to calculate the temperature distribution of the cold sea water flowing through the CWP. This paper aims to estimate the temperature distribution of cold sea water flowing through the CWP and the increase in temperature of cold sea water leaving the CWP. Analysis based on the principles of mass and heat transfer was carried out in this research, where modelling was carried out numerically using a finite volume approach. For the case considered, the change in sea water temperature at CWP from depth to the surface occurs 1-3°C, which is the accumulation of each change in sea water depth. The results of this research illustrate that designing an OTEC system with a long CWP must consider the temperature distribution of cold sea water flowing through the CWP to produce a more realistic design.

Sea surface temperature budget in Indonesian seas: the role of vertical turbulent flux and its east–west variations

Abstract The vertical turbulent flux, which comprises heat flux and vertical mixing, is one of key processes governing seawater temperature changes in the vertical direction. In this study, the influence of vertical turbulent flux on sea surface temperature (represented by a layer between the free-surface and approximately 20 m depth) in Indonesian seas was diagnosed from an eddy-permitting ocean modeling experiment result. The heat flux, as the sum of the net heat flux at the surface and penetrative shortwave radiation at the base of the surface layer, induced a net cooling tendency in both eastern and western Indonesia (represented by the Java Sea and Banda Sea, respectively). The cooling tendency due to the heat flux was opposed by the warming tendency induced by vertical mixing at the base of the surface layer, preventing excessive heat loss in the surface layer. An exception occurred during the Boreal Autumn in the Banda Sea, when the heat flux and vertical mixing resulted in warming and cooling tendencies, respectively. It was further found that the effect of vertical mixing on the surface layer heat budget was sensitive to the selection of the base layer depth, highlighting the mixing-related dynamic variation within the water column. In summary, this study provides additional insights into the near-surface dynamics that govern sea surface temperature seasonality in Indonesian Seas.

Shrimp Farmer’s Perceptions and Adaptation Strategies to the Threat of Climate Change in Bangil District, East Java

As one of the main stakeholders in the fishing industry, shrimp farmers are directly affected by climate change that causes changes in seawater temperature, rainfall, and unpredictable weather patterns. Related to the issue, the threat to income may be felt by shrimp farmers. Therefore, in this study, we highlight two objectives as a basis for drawing up this article, namely (1) to understand shrimp farmers’ perceptions of climate change, and (2) to identify factors that influence farmers’ decisions in implementing adaptation strategies. There are two types of analysis that we use, namely descriptive analysis and logit regression analysis. Our findings show that the majority of shrimp farmers consider climate change manifested in the form of changes in rainfall patterns (96.21%), increases in pond water temperatures (98.71%), decreases in yield production (95.41%), and increases in shrimp pests and diseases (96.23%). The results of our logit regression analysis show that the decision-making factors of shrimp farmers are significantly influenced. These results indicate that the implementation of adaptation strategies in the fisheries sector can generate significant growth and reduce the risks posed by climate change. As a result, the government needs to encourage the development of more suitable climate change adaptation strategies for small-scale shrimp farmers in Indonesia.

INVESTIGATION OF THE EFFECT OF SMAW PARAMETERS ON PROPERTIES OF AH36 JOINTS AND THE CHEMICAL COMPOSITION OF SEAWATER

Underwater wet welding (UWW) is a critical technique for repairing offshore structures, underwater pipelines, water transport infrastructure, docks, and harbor equipment. In this study, the mechanical and microstructural properties of AH36 low-carbon steel weldments were investigated using metal arc welding (SMAW), an underwater wet welding method, at various welding current strengths and seawater temperatures. The relationship between changes in seawater temperature and welding current parameters and their impact on seasonal variations in welding conditions and seawater composition was examined. In the first stage, the yield strength of AH36 was statistically modeled using a central composite design with input parameters of seawater temperature (ranging from 9.7 °C to 25.3 °C) and source current value (ranging from 49A to 90A). Optimal conditions were determined, resulting in a yield strength of 270MPa, achieved at a seawater temperature of 17.5 °C and a source current value of 69.5 A. In the second stage, data from optimization studies were utilized to develop elemental exchange equations for Cr (R2=87.3), Ni (R2=64.45), and Mn (R2=65.74) ions in seawater. The findings reveal that source current intensity primarily influences changes in Cr content in seawater, seawater temperature is correlated with Ni content, and both current intensity and seawater temperature affect the Mn content. The analytical techniques employed include Inductively Coupled Plasma Mass Spectrometry (ICP-MS) for seawater ion analysis, Energy Dispersive Spectroscopy (EDS) point analysis to determine the chemical composition of AH36, and Scanning Electron Microscopy (SEM) for microstructural analysis

Temporal and spatial dynamics of coral symbiont assemblages are affected by local and global impacts

The influence of abiotic variables and anthropogenic pressure on symbiodiniaceans associated with the scleractinian corals Mussismilia hispida and Siderastrea stellata were assessed quarterly at Armação dos Búzios, Brazil, for over 18 months. Thirty-eight Symbiodiniaceae ITS2 rDNA phylotypes were found by metabarcoding, with eight comprising new phylotypes. Both hosts maintained their generalist pattern, with 1–3 dominant lineages. An environmental pressure index and changes in seawater temperature explained the variations in the structure and diversity of Symbiodiniaceae assemblages over time and space. A mild bleaching event affected the photosymbiotic assemblage structure, even in non-bleached colonies. The highly dynamic and diverse photosymbiont assemblages were constantly driven by the influence of environmental variables and human-induced impacts. Furthermore, new strains of Symbiodiniaceae might be associated with lower temperatures caused by upwelling, which is characteristic of this subtropical coral community, highlighting the region's idiosyncrasy and the need for further studies of this coral system.

Thermal circuit model of DC submarine cable considering the influence of seawater property variations

The IEC 60287 standard, when calculating the steady-state current-carrying of DC submarine cables, does not take into account the influence of seawater property variations on changing the heat transfer efficiency of seawater, thereby affecting the current-carrying capacity of the cable. resulting in deviations in the calculated ampacity results. This paper considers the influence of seawater heat transfer characteristics on cable heat dissipation efficiency based on heat transfer theory, and Proposes an improved thermal circuit model for submarine DC cables that takes into account variations in seawater properties. Taking the example of a 160 kV submarine XLPE cable, the current-carrying capacity results of the improved model have an error of no more than 1.9 % compared to finite element simulation results. Under identical environmental conditions, the maximum deviation between the improved model and the IEC thermal circuit model is 123A, confirming the necessity of considering variations in seawater properties in the improved thermal circuit model. The seawater property variations studied in this paper include changes in seawater temperature, salinity, and pressure. If the impact of seawater property variations on submarine cable current-carrying capacity is not considered, the obtained current-carrying capacity results are higher, with a maximum error of 5.5 %. Among these variations, temperature has the most significant impact, with an error reaching 3.3 %, while salinity and pressure have relatively smaller impacts, with errors of 1.1 % each.

Dietary tryptophan decreases the impacts of seawater temperature changes on behavior and gut health of the sea cucumber Apostichopus japonicus

Seawater temperature change is an important concern for seed production and pond culture of sea cucumbers. The present study found that tentacle activity frequency was significantly lower in sea cucumbers exposed to continuous and rapid temperature increases than that of those at ambient temperature. Feeding behavior directly determines food intake, and further affects physiology and growth efficiency of sea cucumbers. This means that the decline in feeding caused by continuous and rapid temperature increases needs to be addressed in sea cucumber aquaculture. However, a sudden temperature change of 5 °C had no significant effect on behaviors of sea cucumbers. This indicates that continuous temperature increases, rather than a sudden increase, result in behavioral impacts on sea cucumbers. Therefore, we recommend aqua-farmers reduce the feeding amount for sea cucumbers during continuous and rapid temperature increases.In the present study, feeding behavior was significantly higher in sea cucumbers fed with 3% dietary tryptophan than that of those fed with 0% and 5% dietary tryptophan. This indicates that 3% dietary tryptophan increases the food intake of sea cucumbers, and mitigates the feeding decline caused by continuous and rapid temperature increase. This indicates that tryptophan has the potential to promote the feeding of sea cucumbers in seed production and pond culture. Adhesion capacity of sea cucumbers fed with 5% dietary tryptophan was significantly higher than that of individuals fed with 0% and 3% dietary tryptophan. This suggests that dietary tryptophan increases the feeding of sea cucumbers exposed to continuous and rapid temperature increases in pond culture and seed production. In addition, this study found that sea cucumbers fed with 3% dietary tryptophan had higher intestinal colony richness under the continuously rapid temperature change. The present study provides an effective method to improve adhesion behavior and to alleviate the impacts on feeding behavior for seed production and pond culture of sea cucumbers exposed to continuous and rapid temperature increases.

Morphology of Hobagella saltata n. gen. and n. sp. (Syndiniophyceae, Miozoa) infecting the marine dinoflagellate Cucumeridinium coeruleum (Dinophyceae, Miozoa) and its potential onshore advection

Over the past decade, molecular phylogenies have placed endoparasites of the genus Euduboscquella in a distinct subclade within clade 4 of the Marine Alveolate (MALV) Group I. Recently, however, rRNA gene sequences have become available for four novel Euduboscquella-like species that infect dinoflagellates, with phylogenies including these sequences indicating that the genus Euduboscquella is paraphyletic. Here, we provide a morphological characterization of the intracellular and extracellular life-cycle stages of a novel species that infects Cucumeridinium coeruleum, a warm water pelagic species sometimes found in coastal environments. We formally describe the novel parasite, Hobagella saltata n. gen, n. sp., and identify a constellation of morphological and developmental characters that distinguish it, as well as Euduboscquella melo and E. nucleocola, both parasites of dinoflagellates, from Euduboscquella species that infect ciliates. We recommend the reassignment of E. melo and E. nucleocola as Hobagella melo n. comb. and H. nucleocola n. comb., respectively. We also propose the family Hobagellidae for these three congeners. We anticipate that the character set developed for distinguishing species of Euduboscquella and Hobagella will be valuable for sorting other Euduboscquella-Hobagella-like taxa scattered across the Group I phylogeny and will provide insight into morphological evolutionary patterns within Group I. Lastly, we consider the potential influence of summer-fall typhoons on the occurrence of H. saltata and its host C. coeruleum in near-shore waters along the southeastern coast of Korea and propose a hypothesis regarding the northward transport and onshore advection of host and parasite populations. If future research supports the hypothesized mechanisms, it could help us better understand parasite distribution and potential changes in biogeography associated with ongoing global changes in surface seawater temperature.

Responses of photosynthesis-related genes in Sargassum horneri to high temperature stress

Golden tide outbreak threatened the marine ecological environment. Sargassum horneri is a single dominant species of the Yellow Sea golden tide, which growth and development are affected by changes in sea water temperature. This study investigated the photosynthetic physiology of copper algae and found that the growth rate, chlorophyll a content, carotenoid content, Fv/Fm, and maximum electron transfer efficiency were significantly reduced, indicating that Sargassum horneri was under stress under high temperature. In this study, high-throughput sequencing was used to analyze the response mechanisms of photosynthesis-related genes in S. horneri under high temperature stress. The results showed that most of the photosynthesis-related genes in S. horneri were downregulated and photosynthesis was inhibited under high temperature stress. However, the expression levels of ferredoxin, ferredoxin-NADP reductase, light-harvesting protein complexes, and oxygen-evolving complex genes were significantly upregulated (P ≤ 0.05) after five days of high temperature treatment. This study found that photosynthesis related genes play a crucial role in regulating the photosynthetic response of S. horneri to high temperature stress.

Observed Anomaly of Temperature and Mixed Layer Depth Associated with the Madden Julian Oscillation (MJO) Active Phase in the Banda Sea, Indonesia

The eastward propagation of atmospheric waves along the equatorial band from the central equatorial Indian Ocean to the western Pacific Ocean passing through the Indonesian Maritime Continent (IMC), known as the intraseasonal Madden Julian Oscillation (MJO) event, plays an important role on modulating both atmospheric and upper ocean dynamics along its path. This study aims to investigate the MJO active phase dynamics and its impact on changes in near-surface seawater temperature and mixed layer depth (MLD) anomaly in the Banda Sea Indonesia, using multi-datasets of atmospheric reanalysis, satellites derived sea surface temperature (SST), and Argo float between 2017 - 2018. This study revealed that the MJO waves propagate eastward along the southern equator-line over the IMC and pass through the Banda Sea, associated with significant decreased on Outgoing Longwave Radiation (OLR) and increased in zonal wind speed at 850hPa. The study result shows anomalous increased on surface wind speed and SST cooling during of MJO active phase. The amplitude peaks of filtered ocean-atmosphere variables range between 30 – 60 days. Argo float datasets in the Banda Sea for the first time captured upper ocean responses to the arrival of the MJO active phase, as characterized by a negative temperature anomaly of ~0.3°C in the surface mixed layer, large temperature anomaly of ~0.8°C in the thermocline layer and the deepening of the MLD of ~25 m. Hence, the MJO active phase impacts significantly on surface and vertical temperature cooling and regulate upper ocean mixing intensity in the Banda Sea.

Performance analysis of a novel small-scale radial turbine with adjustable nozzle for ocean thermal energy conversion

Ocean thermal energy is acknowledged as one of the most promising ocean renewable energy sources in low latitude sea areas. In the ocean thermal energy conversion system, the turbine plays a significant role, and it is responsible for converting the working medium enthalpy into the shaft output power. The present study is focused on the performance analysis of a novel radial inflow turbine with an adjustable nozzle in the OTEC system in order to adapt to the changing operating conditions of the turbine, which vary with the change in seawater temperature. At the design point, the predicted overall isentropic efficiency is 86.5%, and the shaft output power is 15.3 kW, slightly higher than the expected 15 kW. Furthermore, a parametric study is performed, respectively, for the nozzle vane stagger angle and the nozzle-impeller radial clearance to explore the favorable geometric parameters for different conditions. The turbine’s overall efficiency increases slightly with deceasing nozzle-impeller radial clearance, and the variation of the nozzle vane stagger angle is much more influential on the turbine shaft power and overall efficiency. The optimum stagger angle point moves from 32° to 36° gradually with the increase in nozzle-impeller clearance. Finally, the feasibility of an adjustable nozzle for the turbine under off-design conditions was verified by combining the radial clearance and nozzle stagger angle.

Environmentally driven changes in Atlantic salmon oxidative status interact with physiological performance

Farmed Atlantic salmon in sea cages experience natural seasonal changes in seawater temperature and photoperiod. Atlantic salmon have more oxidized tissues in spring and early summer, and this corresponds to the period of increasing day length, temperature, and growth rate. However, the molecular mechanisms underlying the redox metabolism of Atlantic salmon exposed to the interaction of seasonal cues remain unclear. This study aims to investigate the effect of seasonal changes in temperature and photoperiod on the redox metabolism at the molecular level of Atlantic salmon. Salmon reared in tanks were subjected to simulated natural (for farmed salmon in sea cages) photoperiod and temperature to mimic spring and summer (March to August). We found that the changing photoperiod and temperature, which were simulated to spring and summer conditions, influenced the redox metabolism of Atlantic salmon over the experimental period. We showed that increased utilization of tissue antioxidants such as vitamin C, vitamin E, and reduced glutathione in the spring was restored in August. The more reduced glutathione-based redox potentials and the low levels of malondialdehyde (MDA) in August in liver and muscle suggest lowered tissue oxidative activity at that time. We further revealed that the expression profiles of genes involved in growth hormone signaling and cell cycle regulation were correlated with oxidative stress patterns. Together, these promising results reveal the molecular mechanisms underlying the ecological implications of oxidative status. The study provides new insight into the possible role redox signaling plays in the growth regulation of fish to the seasonal shift in environmental factors.

Phenology and thallus size in a non-native population of Gracilaria vermiculophylla.

Phenology, or seasonal variation in life cycle events, is poorly described for many macroalgal species. We describe the phenology of a non-native population of Gracilaria vermiculophylla whose thalli are free-living or anchored by decorating polychaetes to tube caps. At a site in South Carolina, USA, we sampled 100 thalli approximately every month from January 2014 to January 2015. We assessed the reproductive state and measured thallus size based on wet weight, thallus length, and thallus surface area from herbarium mounts. Because life cycle stage cannot be assigned using morphology, we implemented a PCR assay to determine the life cycle stage-tetrasporophyte, female gametophyte, or male gametophyte-of each thallus. Tetrasporophytes dominated throughout the year, making up 81%-100% of thalli sampled per month. Reproductive tetrasporophytes varied between 0% and 65% of monthly samples and were most common in warm summer months (July through September) when thalli also tended to be larger. The vast majority of the reproductive thalli were worm-anchored and not fixed to hard substratum via a holdfast. Thus, free-living thalli can be reproductive and potentially seed new non-native populations. Given G. vermiculophylla reproduction seems tied closely to temperature, our work suggests phenology may change with climate-related changes in seawater temperatures. We also highlight the importance of understanding the natural history of macroalgae to better understand the consequence of range expansions on population dynamics.

Seawater temperature changes in the southern Baltic Sea (1959–2019) forced by climate change

The study included the analysis of changes in sea surface and water column temperature and air temperature in the years 1959–2019 in the southern Baltic Sea based on in situ measurement (CTD probe), satellite data, and model data (ERA5). SST increased on average by 0.6°C per decade. Analyses at different depths showed that the highest temperature increase per decade at 0.60–0.65°C characterised the layers from 0 to 20 m. The smallest increase (0.11°C) was recorded at a depth of 70 m, below which the temperature change per decade increases again to 0.24°C. The results from satellite observations covering 1982–2019 were consistent with measurement data. The most intense water warming occured in the spring – summer (0.8–1°C per decade); in the winter, the change did not exceed 0.2°C. In the offshore area, in 1951–2020, air temperature increased by approx. 2°C, with an average increase of 0.37°C per decade. The average increase in seawater temperature in the coastal zone was 0.2°C per decade. The most intense warming characterised March to May (0.25–0.27°C). The average annual air temperature increase on the coast from 1951 to 2020 was 0.34°C per decade. The results represent an important contribution to research and prediction of changes in the marine environment caused by global climate change.

Seasonal distribution of solitary and colonial benthic ascidians (Chordata) with ecological gradients in and around Andaman and Nicobar Islands, India

AbstractAscidians are rapidly emerging biofouling organisms that generally occur on the natural and artificial substratum of the marine environment. However, very few studies have been reported on their species diversity and distribution patterns. This present investigation focuses on the seasonal impact on ascidians diversity. The distributions of ascidians were recorded by the collection of samples in six sampling stations from Andaman and Nicobar Islands. A total of 43 species of ascidians (32 colonial, 11 solitary) were recorded and most of the species are under the Didemnidae family. Various diversity indexes were utilized to examine the diversity, richness and evenness of species and to look at the assorted variety among tests and their likeness regarding species composition. The greatest (3.227) individuals were observed during summer season in Pigeon Island and the lowest (2.063) number of species were recorded during the monsoon season in Haddowharf harbour. The Margalef richness (d) fluctuated between in the range of 2.033 and 5.53 during the monsoon in Haddowharf harbour and Carbyns Cove beach in summer seasons. The Pielou's evenness record (J′) changed from 0.7409 to 0.9713. Diversity indexes were recorded as followed the order of 0.9642, 0.9552, 0.9482 and 0.9292 at Carbyns Cove shoreline, Burmanella, Pigeon Island and Campbell Bay individually during summer season. Present findings in the cluster examination uncovered that the species at various stations have framed four gatherings. Most elevated species rates were spread in summer. Field observation shows that species distribution is able to tolerate temperature ranges of 26.9–30.3°C and salinity of 32.1–34.64 ppt. Occasional examples of space occupation by colonial ascidians corresponded with seasonal changes in seawater temperature and salinity.

Holobiont responses of mesophotic precious red coral Corallium rubrum to thermal anomalies

Marine heat waves (MHWs) have increased in frequency and intensity worldwide, causing mass mortality of benthic organisms and loss of biodiversity in shallow waters. The Mediterranean Sea is no exception, with shallow populations of habitat-forming octocorals facing the threat of local extinction. The mesophotic zone, which is less affected by MHWs, may be of ecological importance in conservation strategies for these species. However, our understanding of the response of mesophotic octocoral holobionts to changes in seawater temperature remains limited. To address this knowledge gap, we conducted a study on an iconic Mediterranean octocoral, the red coral Corallium rubrum sampled at 60 m depth and 15 °C. We exposed the colonies to temperatures they occasionally experience (18 °C) and temperatures that could occur at the end of the century if global warming continues (21 °C). We also tested their response to extremely cold and warm temperatures (12 °C and 24 °C). Our results show a high tolerance of C. rubrum to a two-month long exposure to temperatures ranging from 12 to 21 °C as no colony showed signs of tissue loss, reduced feeding ability, stress-induced gene expression, or disruption of host-bacterial symbioses. At 24 °C, however, we measured a sharp decrease in the relative abundance of Spirochaetaceae, which are the predominant bacterial symbionts under healthy conditions, along with a relative increase in Vibrionaceae. Tissue loss and overexpression of the tumor necrosis factor receptor 1 gene were also observed after two weeks of exposure. In light of ongoing global warming, our study helps predict the consequences of MHWs on mesophotic coralligenous reefs and the biodiversity that depends on them.

Mogućnost aklimatizacije kvrgavog volka Hexaplex trunculus (Linnaeus, 1758) nakon dugotrajne izloženosti niskom pH

Previous work on ocean acidification highlighted contrasting response between marine species and population. This so-called species-specific response was hypothesized to be partly a consequence of local adaptation to the present range of natural variability in the carbonate chemistry. Under that hypothesis, species tolerance threshold should be correlated to its environmental pH niche. This paper aims to evaluate shell growth rate of Hexaplex trunculus, an important predatory gastropod in benthic communities of Mali Ston Bay. A long-term experiment (310 days) was designed to test a range of pH treatments covering present and future pH levels relevant in the context of future ocean acidification (7.95-7.22 pHT) at the sampling site. Sex had an effect on the shell growth rate irrespective of pH, and was only significant after 236 days. As growth rate in all pH treatments followed seasonal patterns correlating to changes in seawater temperature, the data were divided into 3 time periods. A positive relationship between shell growth rate (SGR, mm day-1) and pH was observed for the period 1-59 days (temperature ranging between 26.5 & 18.8 °C), whereas SGR decreased significantly with pH for the following period (60-236 days, temperature ranging between 20.6 & 8.5 °C). After 236 days (temperature ranging between 27.5 & 14.1 °C), there was no significant difference in SGR among pH. Similar temperature was experienced between the first and third period and the difference in response could be explained as a consequence of an acute negative response versus a longer exposure indicating possible potential for acclimation. Our results highlight the modulating effect of temperature and the importance of long-term experiments to better assess impacts of ocean acidification on marine organisms.

Reproductive characteristics and gamete development of the soft coral Sclerophytum cf. heterospiculatum in Okinawa Island, Japan

AbstractSexual reproduction data are important to understand how organisms can replenish their populations and proliferate on coral reefs. Despite the importance of such data, the reproductive characteristics of most soft coral species are still unknown. Here, we examined the reproductive strategies of a species from the often‐dominant genus Sclerophytum in a coral reef on subtropical Okinawa Island, Japan. DNA barcoding and histological examinations of the tissues were conducted to confirm colony conspecificity and identify reproductive characteristics, respectively, between March 2020 and March 2021. Results indicated that the studied species, identified as Sclerophytum cf. heterospiculatum, exhibits gonochorism with longer oogenesis and shorter spermatogenesis. Female colonies produced immature oocytes throughout the year, with mature oocytes observed from late July to early September, and thus, extended spawning is likely characteristic of this species. In male colonies, spermatogenesis took place over ~5 months, with spermaries present from April through August. Mature spermaries were noted beginning in July and the inferred peak of sperm release was between late August and early September, which suggests that spermatogenesis duration was ~5 months. The largest mean oocyte and spermary sizes (628.45 ± 61.36 and 240.04 ± 49.49 μm, respectively) were both recorded in August. Gamete spawning presumably occurred during the summer season, which suggests seasonality in reproduction as influenced by changes in seawater temperature. However, the proximate cue for exact dates of spawning could be the lunar period because the inferred release of spawning materials seemed to occur between full moon and last‐quarter moon phases in both the months of August and September. The results of this study represent the first detailed report of reproductive characteristics of the genus Sclerophytum in Japan.

Physiological changes during torpor favor association with Endozoicomonas endosymbionts in the urochordate Botrylloides leachii.

Environmental perturbations evoke down-regulation of metabolism in some multicellular organisms, leading to dormancy, or torpor. Colonies of the urochordate Botrylloides leachii enter torpor in response to changes in seawater temperature and may survive for months as small vasculature remnants that lack feeding and reproductive organs but possess torpor-specific microbiota. Upon returning to milder conditions, the colonies rapidly restore their original morphology, cytology and functionality while harboring re-occurring microbiota, a phenomenon that has not been described in detail to date. Here we investigated the stability of B. leachii microbiome and its functionality in active and dormant colonies, using microscopy, qPCR, in situ hybridization, genomics and transcriptomics. A novel lineage of Endozoicomonas, proposed here as Candidatus Endozoicomonas endoleachii, was dominant in torpor animals (53-79% read abundance), and potentially occupied specific hemocytes found only in torpid animals. Functional analysis of the metagenome-assembled genome and genome-targeted transcriptomics revealed that Endozoicomonas can use various cellular substrates, like amino acids and sugars, potentially producing biotin and thiamine, but also expressing various features involved in autocatalytic symbiosis. Our study suggests that the microbiome can be linked to the metabolic and physiological states of the host, B. leachii, introducing a model organism for the study of symbioses during drastic physiological changes, such as torpor.

Protist dynamics in the eastern Tsugaru Strait, Japan from 2010 to 2018: Implications for the relationship between decadal climatology and aquaculture production

Environmental changes such as seasonality, decadal oscillation, and anthropogenic forcing may shape the dynamics of lower trophic-level organisms. In this study, 9-years (2010–2018) of monitoring data on microscopic protists such as diatoms and dinoflagellates, and environmental variables were analyzed to clarify the relationships between plankton and local/synoptic environmental changes. We found that time-series temperature increased in May, whereas it decreased in August and November. Nutrients (e.g., phosphate) decreased in May, remained unchanged in August, and increased in November from 2010 to 2018. The partial pressure of CO2 increased in May, August, and November over time. It is notable that the change in seawater temperature (−0.54 to 0.32 °C per year) and CO2 levels (3.6–5.7 μatm CO2 per year) in the latest decade in the eastern Tsugaru Strait were highly dynamic than the projected anthropogenic climate change. Protist abundance generally increased or stayed unchanged during the examined period. In August and November, when cooling and decreases in pH occurred, diatoms such as Chaetoceros subgenus Hyalochaete spp. and Rhizosoleniaceae temporally increased from 2010 to 2018. During the study period, we found that locally aquacultured scallops elevated soft tissue mass relative to the total weight as diatom abundance increased, and the relative scallop soft tissue mass was positively related to the Pacific Decadal Oscillation index. These results indicate that decadal climatic forcing in the ocean modifies the local physical and chemical environment, which strongly affects phytoplankton dynamics rather than the effect of anthropogenic climate change in the eastern Tsugaru Strait.