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The loss on ignition (LOI) of fatty acids (FAs; including carbon numbers of C8–C24) in vegetal and animal organic reference samples at 200–500 °C was examined. The total FAs in the samples preferen...

Ocean warming is altering the biogeographical distribution of marine organisms. In the tropics, rising sea surface temperatures are restructuring coral reef communities with sensitive species being lost. At the biogeographical divide between temperate and tropical communities, warming is causing macroalgal forest loss and the spread of tropical corals, fishes and other species, termed “tropicalization”. A lack of field research into the combined effects of warming and ocean acidification means there is a gap in our ability to understand and plan for changes in coastal ecosystems. Here, we focus on the tropicalization trajectory of temperate marine ecosystems becoming coral-dominated systems. We conducted field surveys and in situ transplants at natural analogues for present and future conditions under (i) ocean warming and (ii) both ocean warming and acidification at a transition zone between kelp and coral-dominated ecosystems. We show that increased herbivory by warm-water fishes exacerbates kelp forest loss and that ocean acidification negates any benefits of warming for range extending tropical corals growth and physiology at temperate latitudes. Our data show that, as the combined effects of ocean acidification and warming ratchet up, marine coastal ecosystems lose kelp forests but do not gain scleractinian corals. Ocean acidification plus warming leads to overall habitat loss and a shift to simple turf-dominated ecosystems, rather than the complex coral-dominated tropicalized systems often seen with warming alone. Simplification of marine habitats by increased CO2 levels cascades through the ecosystem and could have severe consequences for the provision of goods and services.

Long-term exposure to CO2 -enriched waters can considerably alter marine biological community development, often resulting in simplified systems dominated by turf algae that possess reduced biodiversity and low ecological complexity. Current understanding of the underlying processes by which ocean acidification alters biological community development and stability remains limited, making the management of such shifts problematic. Here, we deployed recruitment tiles in reference (pHT 8.137 ± 0.056 SD) and CO2 -enriched conditions (pHT 7.788 ± 0.105 SD) at a volcanic CO2 seep in Japan to assess the underlying processes and patterns of algal community development. We assessed (i) algal community succession in two different seasons (Cooler months: January-July, and warmer months: July-January), (ii) the effects of initial community composition on subsequent community succession (by reciprocally transplanting preestablished communities for a further 6 months), and (iii) the community production of resulting communities, to assess how their functioning was altered (following 12 months recruitment). Settlement tiles became dominated by turf algae under CO2 -enrichment and had lower biomass, diversity and complexity, a pattern consistent across seasons. This locked the community in a species-poor early successional stage. In terms of community functioning, the elevated pCO2 community had greater net community production, but this did not result in increased algal community cover, biomass, biodiversity or structural complexity. Taken together, this shows that both new and established communities become simplified by rising CO2 levels. Our transplant of preestablished communities from enriched CO2 to reference conditions demonstrated their high resilience, since they became indistinguishable from communities maintained entirely in reference conditions. This shows that meaningful reductions in pCO2 can enable the recovery of algal communities. By understanding the ecological processes responsible for driving shifts in community composition, we can better assess how communities are likely to be altered by ocean acidification.

Previously, we reported seasonal variation in iodine contents in the seagrass Zostera marina. Herein, we sought the factors controlling this variation, and investigated relationships between iodine and carbohydrate contents, using extracts and residues of seagrass samples extracted with 0.1 N HCl. In plants, carbohydrates in HCl-extracted and residual fractions are considered to represent storage and structural carbohydrates, respectively. On average, 44% and 56% of total iodine in samples was contained in the HCl-extracted and residual fractions, respectively. Both HCl-extracted and residual iodine contents showed seasonal trends similar to that of total iodine, being high in winter–spring and low in summer. Total and HCl-extracted carbohydrate contents showed reverse seasonal trends from those of iodine, whereas residual carbohydrate contents had comparable values throughout the sampling period. In the total and HCl-extracted fractions, negative correlations between iodine and carbohydrate contents were confirmed, suggesting that carbohydrates do not play important roles in iodine accumulation. Although most monosaccharide contents were not correlated with iodine contents in these two fractions, residual galactose content was positively correlated with residual iodine. We accordingly suggest that one or more specific structural carbohydrate constituents may potentially function as an iodine store in Z. marina.

The grapsoid crab XenograpsusTakeda & Kurata, 1977 inhabiting shallow-water hydrothermal vents shows a limited distribution in the western Pacific, thus providing a good opportunity to observe how a species expands its distribution and establishes and maintains a metapopulation. We analyzed four Japanese populations of Xenograpsus (Kueishan-dao, Showa Iwo-jima, Shikine-jima, and Omuro-dashi) distributed along the Kuroshio Current to assess whether population connectivity is affected by the current. The reconstructed phylogenetic tree indicated that the specimens analyzed belong to a single clade, including X. testudinatusNg, Huang & Ho, 2000 in Kueishan-dao. We could not include genetic data of X. novaeinsularisTakeda & Kurata, 1977 and tentatively refer to the specimens analyzed as X. testudinatus. All four populations shared the two major haplotypes. Statistically significant population differentiation was nevertheless recognized between Showa Iwo-jima and Omuro-dashi, about 1,000 km apart. The number of individuals analyzed in Shikine-jima (N = 11) and Kueishan-dao (N = 5) might not be enough to detect differences. The relative age of population expansion seemed to correlate with the direction of the Kuroshio Countercurrent. Together with knowledge on the distribution of the planktonic larvae, larvae of X. testudinatus stay and mostly contribute to its source population. The Kuroshio Current system occasionally transports the larvae and juveniles, or even adult individuals on floating pumice and other materials, to eventually settle into newly formed habitats after volcanic eruptions, thus expanding the distributional range of the species.

The characteristics of loss on ignition (LOI) at 200–500 °C of three types of authentic organic biomolecules (monosaccharides: MSs, fatty acids: FAs, and amino acids: AAs) are evaluated and compare...

Long-term environmental change, sudden pulses of extreme perturbation, or a combination of both can trigger regime shifts by changing the processes and feedbacks which determine community assembly, structure, and function, altering the state of ecosystems. Our understanding of the mechanisms that stabilise against regime shifts or lock communities into altered states is limited, yet also critical to anticipating future states, preventing regime shifts, and reversing unwanted state change. Ocean acidification contributes to the restructuring and simplification of algal systems, however the mechanisms through which this occurs and whether additional drivers are involved requires further study. Using monthly surveys over three years at a shallow-water volcanic seep we examined how the composition of algal communities change seasonally and following periods of significant physical disturbance by typhoons at three levels of ocean acidification (equivalent to means of contemporary ~350 and future ~500 and 900 μatm pCO

Ocean acidification (OA) is a major threat to the persistence of biogenic reefs throughout the world's ocean. Coralline algae are comprised of high magnesium calcite and have long been considered one of the most susceptible taxa to the negative impacts of OA. We summarize these impacts and explore the causes of variability in coralline algal responses using a review/qualitative assessment of all relevant literature, meta-analysis, quantitative assessment of critical responses, and a discussion of physiological mechanisms and directions for future research. We find that most coralline algae experienced reduced abundance, calcification rates, recruitment rates, and declines in pH within the site of calcification in laboratory experiments simulating OA or at naturally elevated CO2 sites. There were no other consistent physiological responses of coralline algae to simulated OA (e.g., photo-physiology, mineralogy, and survival). Calcification/growth was the most frequently measured parameters in coralline algal OA research, and our meta-analyses revealed greater declines in seawater pH were associated with significant decreases in calcification in adults and similar but nonsignificant trends for juveniles. Adults from the family Mesophyllumaceae also tended to be more robust to OA, though there was insufficient data to test similar trends for juveniles. OA was the dominant driver in the majority of laboratory experiments where other local or global drivers were assessed. The interaction between OA and any other single driver was often additive, though factors that changed pH at the surface of coralline algae (light, water motion, epiphytes) acted antagonistically or synergistically with OA more than any other drivers. With advances in experimental design and methodological techniques, we now understand that the physiology of coralline algal calcification largely dictates their responses to OA. However, significant challenges still remain, including improving the geographic and life-history spread of research effort and a need for holistic assessments of physiology.

To elucidate how variables of the seawater CO2 system in surface waters have been changing seasonally and the mechanisms responsible for these changes in the area off the south coast of central Honshu Island, Japan, we made time-series measurements of total dissolved inorganic carbon (DIC), total alkalinity (TA), inorganic macronutrient and chlorophyll a concentrations as well as temperature and salinity at a near-shore station off Shimoda city near the southern tip of the Izu Peninsula over 19 months from November 2011 to June 2013. The oceanographic setting in our study site is characterized by seasonal stratification, low salinity in summer, and well-mixed water column in winter. A large bloom of phytoplankton developed in spring, thereafter nutrients were depleted within the mixed layer in summer. DIC exhibited large seasonal variations and ranged from 1967 µmol kg−1 in summer to 2073 µmol kg−1 in winter when normalized to a salinity of 35, because of biological production in the spring and summer and vertical mixing in autumn and winter, as shown by multiple regression analysis in which variations of normalized DIC (nDIC) are estimated from variations in temperature (13.3–25.5 °C) and chlorophyll concentrations (0.27–3.9 μg l−1). We observed a decrease of TA due to dilution by precipitation and river runoff in summer and a trend of salinity-normalized TA increase over time. The saturation state of the calcium carbonate mineral aragonite Ωarg varied seasonally from 2.40 in winter to 3.58 in summer. The Ωarg in the present study was calculated using DIC, TA, temperature and salinity, and we applied sensitivity analysis for these parameters. Ωarg was predominantly controlled by the large variations of DIC. The combination of these results from the station off Shimoda and from an offshore station at 34° N, 137° E to the west allow us to predict Ωarg with high precision for temporal and spatial variations. It suggests that in winter, there is a meridional gradient of Ωarg in the region off the southern coast of central Honshu Island, with considerably lower Ωarg in the coastal zone.

Dissolved organic matter (DOM) can be partially converted into particulate organic matter via aggregation. Although surface coagulation by bubbles is known to be an aggregation process, a few studies have tested its efficacy for aggregating natural DOM. In the research described here, we tested surface coagulation by bubbles using natural seawater collected from different locations, and achieved organic matter aggregation (OCagg) at the concentrations up to 0.619 μM. In addition, the test using seawater enriched with nutrient showed that OCagg was 0.559 μM. We also evaluated aggregation in mesocosm through 40 days. The OCagg concentrations increased after nutrient depletion (0.858–1.34 μM), and the OCagg/DOC ratio reached its maximum on day 18 (1.24 ± 0.19%).

Brown algal species are among the most efficient iodine accumulators and thus heavily influence the biogeochemical cycling of iodine in coastal environments. Previously, we reported seasonal variability in iodine concentrations in the brown alga Ecklonia cava collected from the Japanese coast over a 2-year period. In this study, we sought to identify the factors controlling this observed variability by investigating the relationships between the concentrations of iodine and major organic compounds (carbohydrates and fatty acids). The concentrations of total carbohydrates and individual constituent monosaccharides showed no significant correlations with iodine concentration, implying that carbohydrate concentration and composition are not the dominant controls on iodine concentration in E. cava. However, fucose concentrations were significantly correlated when data points of highest iodine concentrations were removed, potentially suggesting some influence of structural carbohydrate on iodine variability. Significant positive correlations with iodine concentration were only observed in odd-chain fatty acids, which are known to be bacterial biomarkers; in particular, the C17:1 fatty acid showed the highest correlation (r = 0.83). The concentrations of the remaining fatty acids, as well as total concentration of fatty acids, did not correlate significantly with iodine concentrations. Our results suggest that, in general, the concentration and composition of fatty acids do not directly influence iodine variability and that iodine concentrations in E. cava are predominantly controlled by bacteria living on its surface.

Human activities are rapidly changing the structure and function of coastal marine ecosystems. Large-scale replacement of kelp forests and coral reefs with turf algal mats is resulting in homogenous habitats that have less ecological and human value. Ocean acidification has strong potential to substantially favour turf algae growth, which led us to examine the mechanisms that stabilise turf algal states. Here we show that ocean acidification promotes turf algae over corals and macroalgae, mediating new habitat conditions that create stabilising feedback loops (altered physicochemical environment and microbial community, and an inhibition of recruitment) capable of locking turf systems in place. Such feedbacks help explain why degraded coastal habitats persist after being initially pushed past the tipping point by global and local anthropogenic stressors. An understanding of the mechanisms that stabilise degraded coastal habitats can be incorporated into adaptive management to better protect the contribution of coastal systems to human wellbeing., Ben Harvey et al. use the gradient provided by a natural CO2 seep off Shikine Island, Japan and lab microcosm experiments to determine how ocean acidification promotes turf algal habitat conditions that create stabilizing feedback loops and hysteresis capable of locking turf systems in place. These results further our understanding of feedback loops initiated by ocean acidification, and can assist in the management of coastal habitats.

Seasonal variations in iodine concentrations were investigated for two years in a brown alga (Ecklonia cava Kjellman) and a seagrass (Zostera marina L.) occurring in the northwestern Pacific coast of central Japan. The iodine concentration in E. cava was 0.92–5.6 mg per gram dry weight (g‒ 1 DW) (mean ± SD:2.3 ± 1.1 mg g‒1 DW), and its variation was similar to that of other brown algae. In Z. marina, the iodine concentration was 17–110 μg g‒1 DW (61 ± 28 μg g‒ 1 DW) and displayed seasonal variation, as it was high in winter and spring and low in autumn.

Dynamics of fluorescent dissolved organic matter (FDOM) in ocean environments has received attention over the past few decades. Although it has appeared that in situ production of oceanic FDOM is mainly due to bacteria, the production and bio- and photodegradation processes of bacterial FDOM have not been elucidated. In this study, a culture experiment with bacteria was carried out to assess the production and biodegradation processes of bacterial FDOM. Photodegradation of bacterial FDOM and dissolved organic carbon (DOC) was also examined by exposure to a solar simulator. Bacterial FDOM consists of six components which were determined by parallel factor analysis (PARAFAC). Fluorescence intensities of protein-like FDOM increased with the bacterial biomass, but the increases of humic-like FDOM lagged behind the protein-like FDOM by 5–10 days. Exposure to simulated sunlight caused significant decreases in fluorescence intensities of all components; 52–94% of the initial intensities were lost during 24 h. While, the DOC concentration exhibited a small decrease through the experiment (1.9–11.1%). These results showed that photodegradability of bacteria derived DOC was much less than the fluorescence, indicating that the lifetime of bacteria-derived DOC is much longer than the length estimated by the fluorescence. The role of photobleached FDOM derived from bacteria may be significant in the biogeochemical cycle at the surface layer.

Environmental science and ecology are complex fields of study where research requires multiple scales (spatial and temporal) and levels (organismal, species, populations, ecosystems) to be considered. The aim of these fields of study is to understand or explain the distribution and abundances of organisms, including their interactions with the surrounding environment. The principal approach by a researcher will be to design an experiment where one or more parameters (of interest) are altered, while the other parameters remain at natural conditions. A well-designed experiment should allow the researcher to determine the parameters responsible for controlling the abundance and distribution of the species being studied. The design of experiments, including the correct use of controls and replicates, is therefore of the utmost importance, as badly designed experiments can lead to incorrect conclusions. Experimental design broadly incorporates the hypotheses being tested, parameters to be controlled, responses to be measured, methods of carrying out the experiment, statistical analysis that will be used, and interpretation of the results. The scope of the experiment will dictate the considerations required for the experimental design. For example, for physiological studies, a highly controlled isolated environment is often required, and these will often be conducted in small-scale aquariums or microcosms. For population- or community-level responses studies, mesocosms or manipulations in the field can be used. In this chapter, we will highlight the main experimental design considerations required for aquarium- and microcosm-based manipulative experiments, with some additional points highlighted about larger-scale mesocosm and field-based experiments. Given the large scope, statistical analysis will not be covered here.

In shallow coastal waters, the types of benthic communities are the result of both environmental and biological drivers. On a global scale, climate and temperature range play an important role in determining the type of benthic communities. Generally, high latitudes and temperate zones have ecosystems dominated by macroalgae, while lower latitudes and especially subtropical and tropical areas have less macroalgae and other types of ecosystems such as coral reefs. The substratum types (soft sediments, sand, or rock) and other environmental factors, such as nutrient load, light availability, or salinity, determine the fine distribution of the different ecosystems found. Each ecosystem will be shaped by a few species, often referred to as foundation species, which will create the habitats that sustain most of the associated biota. Biological interactions, such as top-down control of algae, are also an important determinant in shaping ecosystems. In this chapter, we will introduce three different types of benthic communities: kelp forests, seagrass meadows, and coral reefs.

The broadly accepted definition of algae is ‘oxygenic photosynthesisers other than embryophyte land plants’, and multicellular algae are generally termed macroalgae. The numbers of green, brown, and red algal species are estimated to be approximately 1100, 1500, and 4000–6000, respectively, worldwide. Embryophytes living in marine environments are mainly seagrasses, which are angiosperms adapted to nearshore areas with soft sediment. Seagrasses are less diverse than macroalgae; there are less than 60 species worldwide. The three groups of macroalgae have different subcellular structures and evolutionary histories. Green and red algae evolved from a common ancestral photosynthetic eukaryote, which acquired their plastids through primary endosymbiosis, in which a cyanobacterium was engulfed by an ancestral eukaryotic host cell. Brown algae evolved by secondary endosymbiosis, in which a red alga was engulfed by a eukaryotic host protist. Because of this, green and red algae have plastids with two envelope membranes, while brown algae have plastids with four envelope membranes. The green and red algae differ in their photosynthetic pigment composition, thylakoid structure and storage products. The three macroalgal groups became multicellular independently of each other from different unicellular ancestors. Both macroalgal and seagrass beds are very productive ecosystems as their photosynthesis per unit area can be the highest in the world. These macrophytes support biodiverse coastal ecosystems by providing energy and structural complexity.

Ocean acidification will likely change the structure and function of coastal marine ecosystems over coming decades. Volcanic carbon dioxide seeps generate dissolved CO2 and pH gradients that provide realistic insights into the direction and magnitude of these changes. Here, we used fish and benthic community surveys to assess the spatio-temporal dynamics of fish community properties off CO2 seeps in Japan. Adding to previous evidence from ocean acidification ecosystem studies conducted elsewhere, our findings documented shifts from calcified to non-calcified habitats with reduced benthic complexity. In addition, we found that such habitat transition led to decreased diversity of associated fish and to selection of those fish species better adapted to simplified ecosystems dominated by algae. Our data suggest that near-future projected ocean acidification levels will oppose the ongoing range expansion of coral reef-associated fish due to global warming.

The spatial and temporal variabilities of marine environments indicate the complexity of marine ecosystems. Since the Challenger expedition in the nineteenth century, techniques for surveying environmental factors have rapidly progressed. Recent developments of methods with sensors or other automated facilities have allowed us to reveal the spatiotemporal variations in environmental parameters within a short time. However, the analysis of seawater collected in situ remains effective for understanding environmental conditions in detail. Here, we introduce survey techniques for measuring basic oceanographic parameters, such as temperature, salinity, transparency, and solar irradiance. Becoming skilled on the analytical procedures for these parameters will help us to understand the mechanisms of marine ecosystems and assess environmental change.

Diatoms are so important in ocean food-webs that any human induced changes in their abundance could have major effects on the ecology of our seas. The large chain-forming diatom Biddulphia biddulphiana greatly increases in abundance as pCO2 increases along natural seawater CO2 gradients in the north Pacific Ocean. In areas with reference levels of pCO2, it was hard to find, but as seawater carbon dioxide levels rose, it replaced seaweeds and became the main habitat-forming species on the seabed. This diatom algal turf supported a marine invertebrate community that was much less diverse and completely differed from the benthic communities found at present-day levels of pCO2. Seawater CO2 enrichment stimulated the growth and photosynthetic efficiency of benthic diatoms, but reduced the abundance of calcified grazers such as gastropods and sea urchins. These observations suggest that ocean acidification will shift photic zone community composition so that coastal food-web structure and ecosystem function are homogenised, simplified, and more strongly affected by seasonal algal blooms.

The response of photosynthetic organisms to rising CO2 levels is a key topic in ocean acidification research. Most of the work in this field has focused on physiological responses in laboratory conditions which lack ecological realism. Studies using seeps as natural analogues for ocean acidification have demonstrated shifts in algal community composition, but the effect of CO2 on carbon fixation and export remains unclear. Here, we deployed artificial substrata in a warm-temperate region of Japan to collect algal communities using a CO2 seep off Shikine Island. Diatoms became dominant on settlement substrata in areas with elevated CO2 levels, whereas macroalgae dominated at present-day levels of CO2 (reference site). This was supported by pigment composition; fucoxanthin content, characteristic of diatoms, was higher at the high CO2 site, while more Chlorophyll b, which is characteristic of Chlorophyta, was found in the reference site. Algal communities that recruited in water with high levels of CO2 had elevated rates of photosynthesis. Algal biomass was similar on all settlement panels, regardless of CO2 concentration. Much of the carbon that was fixed by algae in the high CO2 conditions was exported, likely due to detachment from the substratum. Diatoms that dominated under high CO2 conditions are more easily transported away as they have no holdfast, whereas newly settled macroalgae became firmly attached at present-day levels of CO2. These results show that ocean acidification may fundamentally alter coastal carbon cycling, increasing photosynthesis and carbon export from coastal ecosystems in warm-temperate biogeographic regions due to a shift in community composition from perennial to ephemeral algae.

Humic-like fluorescent dissolved organic matter (FDOM) has been widely used as tracers for bio-refractory dissolved organic matter (RDOM) to understand its dynamics in the oceans. Vertical distributions of humic-like FDOM are controlled by microbial production in the ocean interiors and photobleaching in surface layers. Although humic-like FDOM is expected to be actively produced in surface layers with high bacterial activity, its production in surface seawater is not well understood. To examine the diurnal variations in humic-like FDOM due to microbial production and photobleaching in surface seawater, we conducted seven experiments from night to day using surface seawater in the subtropical Pacific and coastal regions. Parallel factor analysis (PARAFAC) determined that FDOM in the incubated seawater was composed of three components: two types of humic-like FDOM and a protein-like FDOM. The fluorescence intensity of humic-like FDOM increased to 104.0 ± 2.5% of the initial intensity during the night and decreased to 101.2 ± 2.5% under sunlight exposure during the day. Conversely, its intensity significantly increased to 114.0 ± 2.7% under dark conditions during the day. The turnover rates of humic-like FDOM by the increase and decrease in its intensity were estimated to be 0.14 and 0.11 day–1, respectively. These comparable turnover rates indicated that the production and photobleaching of humic-like FDOM were almost in equilibrium in the surface layer, with a low level of humic-like FDOM. Linear correlations between the intensity of humic-like FDOM and concentrations of dissolved oxygen (DO) in all experiments under dark conditions indicated that humic-like FDOM were produced as the by-products of microbial respiration processes in the surface seawater. Using global bacterial respiration rates, the net production rate of humic-like FDOM in the global photic layer was estimated as 4.2–5.5 × 1017 R.U. year–1, contributing to 75% of its production in the entire ocean.

Shallow CO 2 seeps, where CO 2 gas is venting underwater, offer great potential for studies into the effects of ocean acidification at the ecosystem level. To our knowledge, only two tropical system and two temperate systems of such seeps have been described worldwide. Here we describe two new temperate systems: the Mikama Bay and Ashitsuke sites, located on Shikine Island, Japan. The Mikama Bay site is located in a shallow bay. Investigation of the gas and water chemistry showed that the gas contained 98% CO 2 and up to 90 ppm H 2 S. Total alkalinity was constant in time and space with an average of 2265±10 μ mol kg −1 . Mapping of Eh and pH showed that the low pH zones were the largest when currents were moderate. Under moderate currents, Eh values were globally higher and total sulfides concentration lower, supporting that a longer residence time of the bay water allow the oxidation of the sulfides to sulfates. Zones suitable for acidification studies: with a pH lower than 8.0, low saturation state of calcite and aragonite, and non-detectable sulfide concentration, can be defined a few meters from the main venting zone. The second site, Ashitsuke, is located in the inter-tidal zone on a shore composed of boulders. Several areas showed reduced pH sometimes restricted to a few meters and up to 20 m long along the shoreline. Temperature was higher in some of the reduced pH zones suggesting the presence of hot springs in addition to vents. This paper also highlights the need for discovering additional CO 2 seeps, which by their nature often lack comparable replicates and can be confounded by factors other than CO 2 . In this regard, Japan offers great potential as it is home to numerous active volcanoes, representing potential venting sites in climates ranging from tropical to sub-polar.

A large fraction of primary production of macroalgae is released as dissolved organic matter (DOM), and it constitutes a part of the coastal DOM pool. Since photochemical decomposition could be involved in the dynamics of marine DOM, we observed the time course of macroalgal DOM exposed to artificial sunlight. During 24 h of irradiation at 400–765 W m − 2 , concentrations of dissolved organic carbon constantly decreased and 72%–77% of the initial concentration remained, suggesting that macroalgal DOM is mineralized by solar radiation in comparison with the DOM of other marine organisms such as phytoplankton and bacteria. A shift in organic composition was evaluated using analyses of absorption and fluorescence spectra. We found a decrease in the absorption coefficient at 270 nm, suggesting molecular destruction of phenolic compounds. In addition, increases in slope value and ratio could imply a shift towards lower-sized compounds with low aromaticity. The fluorescence analysis showed an increase in humic-like peak in the region with shorter wavelengths. Since it would reflect an accumulation of degradation products with lower molecular weight and less aromaticity, the results of the fluorescence analysis were consistent those of the absorption spectra analysis. The mineralization and molecular shift suggest that sunlight exposure accelerates the decomposition of macroalgal DOM in coastal environments.

Effects of nutrient enrichment on 400-L coastal phytoplankton community cultures were examined under 3 pCO2 levels [ambient (400), 800 and 1200 μatm]. Three days after addition of the nutrients, rapid increases in phytoplankton pigments and cell numbers were noticed. Relative growth rates of diatoms and dinoflagellates were higher than prasinophytes and haptophytes during early stages of the culture experiment, and only limited effects of increased CO2 were observed on nutrient consumption, biomass and cell numbers. Ocean acidification showed significant effects on phytoplankton composition during the post-blooming period with negligible dissolved nutrients; up to 70 % of total cells were picoplankton in the 1200-μatm condition as compared to 20 % in the ambient condition. An increase in chlorophyll b and a flow cytometry analysis of the cultured strains strongly suggested Micromonas-like (Prasinophyceae) picoplankton dominated in the acidified conditions. It is likely that the effects of ocean acidification are significant in low-nutrient conditions such as during the post-blooming period.

Gaetice depressus is one of the most dominant macrozoobenthos species in boulder shores of intertidal coastal ecosystems in Japan. As recorded in previous studies, this species is also considered as having high density and biomass. Consequently, it is thought to be one of the more important species in the organic matter flow of boulder shores, especially through the food web. In this study, some taxonomic problems related to G. depressus were tackled and the autoecology and ecological processes in the intertidal ecosystem of G. depressus, such as organic matter flow, were investigated. Furthermore, in order to clarify the taxonomy description, resolve inconsistencies in the scientific name, and learn about the life history, a literature review was conducted. Seasonal changes in density, morphology pattern and population structure were determined based on the data obtained in Ebisu Island, Japan. Then, the role of G. depressus was determined by estimating the intake and emittance fluxes of organic carbon and nitrogen through ingestion and egestion process in the boulder shores of Ebisu Island. A feeding rate experiment was also conducted in order to estimate the intake flux by using the catch-release-recapture method. Meanwhile, to estimate the emittance flux, a defecation rate experiment was conducted by catching some individuals of G. depressus, and then incubating them in the laboratory. The feeding rate measured by the speed of diet consumption of G. depressus was about 12.6 mg ind-1 h-1. Considering the average density, the intake flux through the feeding process could be estimated as 25.2 mgC m-2 h-1 and 2.6 mgN m-2 h-1. On the other hand, G. depressus egested fecal pellet at the rate of 5.4 mg ind-1 h-1. The average emittance flux through the fecal pellet egesting process is estimated at 5.6 mgC m-2 h-1 and 0.7 mgN m-2 h-1. Therefore, it can be estimated that about 25% of organic matter from diet is egested as fecal pellet, which means that about 75% of the intake flux of organic carbon and nitrogen is used for the total assimilation of G. depressus. Intake flux was also considered as affecting the high dynamism of primary producer consumption. The total population of G. depressus is estimated to consume about 18.4% of primary producer in average throughout the year. Therefore, the turnover time of primary producer by consumption of G. depressus was about five days.

Dimethylsulfide (DMS) is produced by phytoplankton in the ocean and plays an important role in biogeochemical cycles and climate system of the Earth. Previous field studies reported a possible relationship between DMS enhancement and anoxic condition, although the governing processes are still to be identified. Here we show the first direct evidence for the enhancement of DMS production by natural planktonic assemblages caused by anoxic stress. Under the anoxic condition, DMS production was considerably enhanced and DMS bacterial consumption was inhibited, resulting in an eightfold higher rate of gross DMS production than that under the oxic condition. Our results demonstrated that anoxic stress is one of important “environmental factors” in the marine DMS dynamics, suggesting the possible global importance due to ubiquity of anoxic conditions in the coastal oceans. This process would become more important in the future due to expansion of coastal hypoxic and anoxic zones by global warming.

Vertical and seasonal variations in the concentrations of total dissolved iodine (TDI), iodide (I−), iodate (IO3−), and dissolved organic iodine (DOI) were examined for seawaters from the northwestern Pacific coast of central Japan (48 m water depth, ca. 1 km offshore) from 2012 to 2016. The annual averages of TDI and iodate concentrations in the upper layer (water depth

Dissolved organic matter (DOM) in coastal environments has various origins; one of the most intensely studied sources is terrestrial DOM input via rivers. On the other hand, contributions from other significant DOM sources, such as macroalgae, to the coastal DOM pool have not been extensively studied. The present study quantified the contribution of macroalgae to the DOM pool in the coastal environment using, firstly, a bag-covering experiment on a brown alga, Ecklonia cava, and identifying fluorescent DOM components by parallel factor analysis of three-dimensional excitation–emission matrix spectra. Using the fluorescent DOM as an indicator, we evaluated the horizontal distribution of macroalgal DOM in the coastal area, showing that the fluorescent DOM component had a synchronous gradient with dissolved organic carbon (DOC) concentrations along the transect line from the coast to offshore. On the basis of the correlation between DOC and fluorescent DOM, we evaluated concentrations of DOC originating from macroalgae, accounting for up to 20% of total DOC concentrations. This implies that in contrast to previous studies, macroalgae do make a measurable contribution to the coastal DOM pool.

Gaetice depressus , a varunid crab common on intertidal boulder shores, is a potential key organism for monitoring organic matter flow through the food web. In order to elucidate its biogeochemical role, the diet source and trophic position of this crab on the boulder shore of an island off the Izu Peninsula, Japan, were estimated using three approaches: foregut content examination, stable isotope signature (δ 13 C and δ 15 N) and pigment biomarkers. The results suggest that G. depressus utilizes green macroalgae ( Ulva sp., Ulvaria sp.) as its main diet source together with red macroalgae ( Gloiopeltis complanata, Gl. furcata ). This crab also utilizes periphytic and planktonic microau-totrophs (occasionally tissues of heterotrophs) when macroalgae prove insufficient due to seasonal change. Therefore, G. depressus can be considered to be an omnivore since it consumes both autotrophs and heterotrophs, although it obtains organic matter mostly from autotrophs. Key words: diet source, foregut content

We developed a simple aquatic microbial ecosystem model in order to examine potential effects of zinc on microorganisms and the related degradation of dissolved organic matter (DOM). The model is a combination of both a traditional food chain and a microbial loop. The traditional food chain is mainly composed of phytoplankton and zooplankton, whilst the microbial loop is composed of DOM, bacteria and bacterivorous protozoa. We incorporated the suppressive effect of zinc on the bacterial uptake of DOM and assessed the steady state responses of the model for various zinc concentrations. The analytical and numerical results of the model implied that either zooplankton or bacterivorous protozoa might be the most vulnerable group to excessive zinc load than bacteria, depending on the grazing preference of zooplankton between phytoplankton and bacterivorous protozoa. The sensitivity analyses supported that the microbial loop solely is more sensitive to zinc than the coupled system combining both the traditional food chain and the microbial loop.

Measurement of uronic acids (URAs) which are a group of acidic sugar, would be useful for the understanding of dynamics of bacterial extracellular polymeric substances (EPS) in marine environments. However, the URA analysis using traditional hydrolysis method which is used for neutral sugar analysis poses serious problems in URA that is unstable under hydrolysis. We developed the methanolysis method, which deploymerizes polysaccharides while retaining quantitative information. Our method was applied to coastal seawater, and the URAs distribution was compared with that of transparent exopolymer particles (TEP) which are acidic sugar containing particles. Since the relationship of URA with TEP was relatively weak, URA-containing polysaccharides present in bacterial EPS would not participate as a structural component of TEP.

The effect of ocean acidification, caused by the increase in pCO2 in seawater, on phytoplankton population and on related organic nitrogen production was experimentally examined by use of a natural coastal microbial population. pCO2 and pH were controlled by aeration with air in which pCO2 was at the current level (control), for which ambient air was used, and with air in which pCO2 was “800” and “1200” ppm, in 500-L culture vessels. The experiment was continued for 15 days after addition of the inorganic nutrients such as nitrate, phosphate, and silicate. During most of the experimental period, a minor increase in phytoplankton biomass was noted, probably because of low irradiance, an increase in phytoplankton biomass was observed at the end of the experiment. Flow cytometric and microscopic observations revealed that this increase was because of Chrysochromulina sp. (Haptophyceae). The growth of Chrysochromulina sp. was most obvious in the control vessel, and tended to be obscured by increasing pCO2 (decrease in pH), indicating the possibility that ocean acidification inhibits the growth of specific phytoplankton groups, for example Chrysochromulina sp. Production of particulate organic nitrogen (PON), determined by the 15N tracer method, also diminished under acidified conditions compared with that at the current level.

To understand the role of zinc (Zn) in the biogeochemical cycle in coastal environments, we examined the bacterial remineralisation of dissolved organic matter (DOM) with 2 composite experiments using microcosms supplemented with Zn. In Expt 1, using samples collected from 2 stations in the Seto Inland Sea, Japan, we found that a decrease in DOM due to bacterial remineralisation during a 14 d experimental period had negative responses to Zn at both sites, but we found an inhibitory effect on bacterial abundance only at a station in the western part of the Seto Inland Sea. In Expt 2, comparison of the response of the remineralisation process to Zn among 3 kinds of organic substrate showed that Zn has little effect on 2 authentic standards (laminarin and bovine serum albumin) and that remineralisation of DOM originating from natural seawater was significantly suppressed by the addition of Zn. Based on the regression curves, we estimated the potential impact of Zn on the remineralisation of DOM. At a water quality standard of Zn concentration (86 ug Zn 1- 1 ), DOM concentrations at the end of the experimental period (Day 14) increased 2.4 to 6.9 %, and turnover time prolonged with a timescale of weeks to months. These potential shifts induced by Zn suggest that the allochthonous input of Zn into the coastal environment leads to suppression of energy flow in the microbial loop and enhances transport of DOM from coastal to offshore areas.