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The sensitivity of vegetated habitats to climate change and catastrophic disturbance, as well as their benefits to human beings, motivate efforts to estimate regional changes in distribution. This study examined the regional changes in the distribution of submerged macrophyte vegetation using aerial and satellite images from before and after the 2011 tsunami disturbance along the Pacific coast of northeastern Japan. We conducted an estimation of the change in the distribution of seagrass and macroalgal beds after the tsunami along the whole coastline (1,635 km). This was based on vegetation change in the 13 local areas (each <40 km) spanning 27% of the coastline and included 28% of the macroalgal area and 59% of the seagrass area documented in satellite imagery before the tsunami, using generalized linear modeling (GLM). We found that in the 13 local areas 716.8 and 1,990.3 ha of macroalgal beds and seagrass beds had disappeared, respectively, suggesting that seagrass beds were more impacted by the tsunami than macroalgal beds. Significant predictors in GLM indicated that more seagrass beds disappeared in geographically complex coastal areas, whereas macroalgal beds were only marginally affected in such areas. It was estimated that the total decline in seagrass beds was at least 76% along the whole coastline, whereas macroalgal beds decreased only by about 20%. The magnitude and predictors of losses in these two vegetated habitats were similar to earlier estimates, suggesting that our simplified method with GLM is sufficient to extrapolate monitoring data to a regional scale. [ABSTRACT FROM AUTHOR]

Harmonizing coastal fisheries with water-quality improvement has become an essential factor for the sustainable use of coastal ecosystem services. Here, we present the scope of our study based on an interdisciplinary approach including ecological actions, socio-economic actions and socio-psychological actions. We chose to focus on the interaction between oyster aquaculture and seagrass vegetation as a typical ecological action using the coastal ecosystem complex (CEC) concept. Coastal organisms have adapted their traits to the environment over a long period of time, so that restoration of the CEC represents reconstruction of the original process of coastal production. Subtidal seagrass vegetation with intertidal oyster reefs is the original CEC in Japan, which would be expected to enhance coastal production by improving the production efficiency without adding nutrients. A simple field experiment examining carbon and nitrogen contents and stable isotope ratios revealed that oyster spats cultivated on a tidal flat adjacent to seagrass beds had higher nitrogen contents and higher δ13C ratios than spats cultivated in an offshore area using only pelagic production. This result suggests that utilization of the CEC, which enables oysters to use both pelagic and benthic production, has potential to sustain a food provisioning service for humans, even in oligotrophic conditions. [ABSTRACT FROM AUTHOR]

Many fish species generally migrate among habitats because of ontogenetic changes in their resource requirements; therefore, clarifying linkages among habitats throughout their life cycle is important for the management and conservation of their populations. Although carbon (δC) and nitrogen (δN) stable isotope ratios are widely used for elucidating fish migrations, information is still scarce how each fish species, including marbled flounder ( Pleuronectes yokohamae), change the isotopic composition in their body tissues after they switch to a different diet during migrations. This study clarified isotopic turnover rates of marbled flounder during the juvenile stage using a diet-switch experiment in an aquarium. Furthermore, we statistically compared bulk samples (i.e., whole body without head and viscera) to partial muscle tissue samples to estimate the difference in the turnover rate as an index for diet switches. An exponential model was used to describe the temporal changes in δC and δN isotopic rates of juvenile marbled flounder. No significant difference was noted between the exponential models for changes in both δC and δN between muscle tissue and bulk samples, and the half-life values were similar for muscle and bulk samples for both δC and δN (14.0-18.5 days). These results suggest that bulk samples are a useful substitute for muscle tissues in isotopic analysis of juvenile fish and that stable isotope analysis and the estimated isotopic turnover rates in tissues of marbled flounder can be used to clarify their migration route in coastal areas. [ABSTRACT FROM AUTHOR]

A novel type of filial cannibalism has been reported in pipefishes, in which the eggs are absorbed through the male’s brood-pouch epithelium. The present study explored the applicability of stable isotope analysis for the detection of paternal brood cannibalism in the seaweed pipefish Syngnathus schlegeli . As expected, the δ 15 N values for liver, which conveys short-term dietary information about the recent reproductive season, were higher in males than in females. In contrast, the δ 15 N values for muscle, which reflects longer-term feeding habits that span both the reproductive and non-reproductive seasons, did not significantly differ between the sexes. This finding indicates that males occupy a higher trophic position than females only during the reproductive season, and it is probable that this difference is a result of paternal uptake of nutrients from embryos in the brood pouch. [ABSTRACT FROM AUTHOR]

The food source utilization and trophic relationship of the fish assemblage in the Red River mangrove ecosystem, Vietnam were examined using dual isotope analysis. The carbon and nitrogen stable isotope signatures of 23 fish species ranged from −24.0 to −15.7‰ and from 8.8 to 15.5‰, respectively. Cluster analysis based on the δC and δN signatures clearly separated the mangrove fish into five feeding groups, representing detritivores, omnivores, piscivores, zoobenthivores, and zooplanktivores, which concurred with the dietary information. The results suggested that mangrove carbon contributed a small proportion in the diets of the mangrove fish, with dominant food sources coming from benthic invertebrates, including ocypodid and grapsid crabs, penaeid shrimps, bivalves, gastropods, and polychaetes. The δN values showed that the food web structure may be divided into different trophic levels (TLs). The lowest TLs associated with Liza macrolepis, Mugil cephalus, and Periophthalmus modestus; 18 fish species had TLs between 3.0 and 3.8; and Pennahia argentata had the highest TL (c. 4.0). [ABSTRACT FROM AUTHOR]

Abstract: Dual stable isotope signatures (δ13C and δ15N) were applied to determine the contribution of mangrove materials and other organic carbon sources to the invertebrate community in an ecologically important mangrove ecosystem of Vietnam. We have analyzed 181 specimens of 30 invertebrate species and found δ13C and δ15N ranging from −14.5 to −26.8‰ and from 1.3 to 12.1‰, respectively. From taxa measured for stable isotopes, polychaete, gastropods, bivalves, and grapsid crabs living in mangrove forest showed relative low δ13C values, while fiddler crabs inhabiting in the land–water ecotone showed the highest δ13C values. The δ13C showed that just a few mangrove inhabitants directly relied on the mangrove materials. The wide ranges of δ13C and δ15N signatures indicated that the invertebrates utilized heterogeneous diets, comprising benthic microalgae, marine phytoplankton, particulate organic matter, sediment organic matter, mangrove detritus, and meiofauna and rotten animal tissues as the supplemental nutrient food sources. Moreover, the significant correlation between δ13C values and body sizes of invertebrates showed that snails Littoraria melanostoma and Terebralia sulcata, bivalve Glauconome virens, and portunid crab Scylla serrata exhibited ontogenetic shifts in diets. The present study showed that adjacent habitats such as tidal flat and mangrove creeks seem to contribute an important microalgal food resource for invertebrates and highlighted the need for conservations of mangrove forests and the adjacent habitats. [Copyright &y& Elsevier]

The life history and ecology of the glowbelly Acropoma japonicum a commercially important fishery resource, were investigated in the Uwa Sea, Japan. Newly settled juveniles (0+) appeared at the end of the breeding season and reached maturity in the next season, i.e. when they became yearlings (1+). The yearlings made a gametic effort comparable to that of older fish. During the breeding season, the somatic conditions were more deteriorated for males than for females. That the deterioration of male somatic conditions was not attributable to a sexual difference in energy gain from feeding suggests that the males incurred higher energetic costs of reproduction despite their relatively low gonadosomatic indices. Such an energy depletion may increase the mortality risk, resulting in female-biased sex ratios in the older age classes. Most of the 1+ fish disappeared in winter following their first breeding. For A. japonicum, the observed precocity and short life span is notable because it is a higher consumer that is generally expected to show later maturation and longer life. As possible explanations for their disappearances, predation and postbreeding emaciation were less likely. While fishing is one of the most influential factors, the possibility of age-specific migration toward deeper waters remains to be examined. [ABSTRACT FROM AUTHOR]

Abstract: Tuna-farming is expanding worldwide, necessitating the monitoring/managing of its effects on the natural environment. In Japan, tuna-farming is conducted on coral reefs that have been damaged by mass-bleaching events and crown-of-thorns starfish (COTS) outbreaks. This study focused on the coral community on an artificial substrate of tuna-farm to reveal the possible effects of tuna-farming on the natural environment. Corals flourished on ropes suspended in the farm in the Amami Islands, southern Japan. These were moored 3 m below the sea-surface in 50-m-deep water. The coral community on the rope was analyzed and compared with those on natural substrata on two adjacent COTS-damaged reefs and with that in a protected reef. Corals were monitored throughout a year. Sixty coral species grew on the ropes, that corresponds to 27.3% of the 220 species known from Amami. The coral community was unique, dominated by massive faviid corals. On the ropes, the water temperature rarely exceeded 30.0 °C and no corals on the rope were severely bleached or covered by sedimentation during the observations. The tuna-farm infrastructure provided corals with a suitable habitat, and species-rich coral communities were established. These coral communities are an important node connecting tuna-farms and the natural environment. [Copyright &y& Elsevier]

We present a mathematical model of the maintenance of polymorphism of fluvial and amphidromous types in a fish population. Downstream drifting of offspring after hatching and their subsequent upstream migration have an important effect on the maintenance of an upstream population. This model, which assumes a linear relationship of offspring mortality rate, nutritional conditions, and flow rate or inclination with the distance from the river mouth, enables us to calculate the number of recruits to the mother population. From the present analysis, we can predict that the fluvial type producing large embryos is selected in the upper reaches under conditions where there are large differences in offspring mortality and flow rate between the upper and lower reaches, and a small difference in nutritional conditions between these sites. Therefore, the fluvial type can be more easily evolved in tropical regions than temperate regions where the difference in nutritional conditions is relatively larger. This selection is promoted when offspring mortality decreases greatly with their size. Conversely, at the lower reaches of the same river, the amphidromous type producing many small embryos is favored. These two populations can be the polymorphism of a single population species in a river, and can be established as different species in terms of pre- or post-reproductive isolation mechanisms, such as assortative mating or habitat preference, even if their members mate with each other in a river. We can assert that sympatric speciation is common in fluvial environments, when this process really works, because other taxonomic groups, such as Annelida, Crustacea, and Mollusca, also have the same sympatric pair of fluvial and amphidromous species derived from marine origin, that is, so called the evolutionary invasion from marine to terrestrial environments. [Copyright &y& Elsevier]

The traditional growth models, such as the von Bertalanffy and logistic models, and their generalized forms have been frequently used for several decades in animal physiology, theoretical ecology, and applied ecology as experimental equations for describing finite animal growth. The coefficients of these models have, however, no meaning in relation to the structure of the model. In the present study, a simple energy balance model incorporating the reallocation of stored energy was developed, and its derivative growth equation is presented as follows:where B is the body mass, excluding storage and gonads, α is a coefficient representing the residual amount of surplus energy, which means assimilated energy minus allocated energy to body mass, and β is a coefficient representing the allocation rate to storage. This equation can express both infinite and finite growth curves. When β/α ≤1, the system shows indeterminate growth without an upper limit of body weight, and when β/α >1, it shows determinate growth. The growth equation developed has characteristics that are intermediate between those of the traditional models with respect to the specific growth rate in relation to body mass. Moreover, it can be used to demonstrate that control of the residual amount of surplus energy through storage is essential for the regulation of body mass, i.e. the growth process. [Copyright &y& Elsevier]

Abstract: An investigation of food web structures in the northwestern soft-bottom area, including the intertidal and subtidal zones, of inner Ariake Bay, suggests that resuspended BM are substantial for offshore secondary production, and the main source of BM would be outwelling from the intertidal mudflat. Carbon and nitrogen stable isotope ratios were measured for macrobenthos samples from the intertidal mudflats, subtidal fringe and offshore subtidal zones, together with their potential food sources. Carbon and nitrogen signatures indicated that most macrobenthos assimilated offshore particulate organic matters (POM) (δ13C: −23.9 ± 0.1‰; δ15N: 8.2 ± 0.1‰) and benthic microalgae (BM) (δ13C: −16.8 ± 1.5‰; δ15N: 8.0 ± 0.4‰) among other potential sources. The relative BM contribution to filter feeders significantly decreased seaward from about 50% in the mudflats to 25% in the offshore zone, and the 99% confidence intervals of the contribution did not include zero even in the offshore zone. [Copyright &y& Elsevier]

Abstract: A cross-system analysis of bulk sediment composition, total organic carbon (TOC), atomic C/N ratio, and carbon isotope composition (δ13C) in 82 surface sediment samples from natural and planted mangrove forests, bank and bottom of tidal creeks, tidal flat, and the subtidal habitat was conducted to examine the roles of mangroves in sedimentation and organic carbon (OC) accumulation processes, and to characterize sources of sedimentary OC of the mangrove ecosystem of Xuan Thuy National Park, Vietnam. Sediment grain sizes varied widely from 5.4 to 170.2μm (mean 71.5μm), with the fine sediment grain size fraction (<63μm) ranging from 11 to 99.3% (mean 72.5%). Bulk sediment composition suggested that mangroves play an important role in trapping fine sediments from river outflows and tidal water by the mechanisms of tidal current attenuation by vegetation and the ability of fine roots to bind sediments. The TOC content ranged from 0.08 to 2.18% (mean 0.78%), and was higher within mangrove forests compared to those of banks and bottoms of tidal creeks, tidal flat, and subtidal sediments. The sedimentary δ13C ranged from −27.7 to −20.4‰ (mean −24.1‰), and mirrored the trend observed in TOC variation. The TOC and δ13C relationship showed that the factors of microbial remineralization and OC sources controlled the TOC pool of mangrove sediments. The comparison of δ13C and C/N ratio of sedimentary OC with those of mangrove and marine phytoplankton sources indicated that the sedimentary OC within mangrove forests and the subtidal habitat was mainly composed of mangrove and marine phytoplankton sources, respectively. The application of a simple mixing model showed that the mangrove contribution to sedimentary OC decreased as follows: natural mangrove forest>planted mangrove forest>tidal flat>creek bank>creek bottom>subtidal habitat. [Copyright &y& Elsevier]