The Strontium- and Yttrium-Binding Activity of Pectin from the Seagrass Phyllospadix iwatensis Makino, 1931 and Its Modified Derivative

Russian Journal of Marine Biology - Poorly esterified pectin was isolated from the seagrass Phyllospadix iwatensis Makino, 1931 and modified using acidic hydrolysis in 0.5 M HCl. The concentration...     

Linkages between seagrass,mangrove and saltmarsh as fish habitat in the Botany Bay estuary,New South Wales

Shallow-water vegetated estuarine habitats, notably seagrass, mangrove and saltmarsh, are known to be important habitats for many species of small or juvenile fish in temperate Australia. However, the movement of fish between these habitats is poorly understood, and yet critical to the management of the estuarine fisheries resource. We installed a series of buoyant pop nets in adjacent stands of seagrass, mangrove and saltmarsh in order to determine how relative abundance of fishes varied through lunar cycles. Nets were released in all habitats at the peak of the monthly spring tide for 12 months, and in the seagrass habitat at the peak of the neap tide also. The assemblage of fish in each habitat differed during the spring tides. The seagrass assemblage differed between spring and neap tide, with the neap tide assemblage showing greater abundances of fish, particularly those species which visited the adjacent habitats when inundated during spring tides. The result supports the hypothesis that fish move from the seagrass to the adjacent mangrove and saltmarsh during spring tides, taking advantage of high abundances of zooplankton, and use seagrass as a refuge during lower tides. The restoration and preservation of mangrove and saltmarsh utility as fish habitat may in some situations be linked to the proximity of available seagrass.     

Material exchange and food web of seagrass beds in the Sylt-Rømø Bight: how significant are community changes at the ecosystem level?

Material exchange, biodiversity and trophic transfer within the food web were investigated in two different types of intertidal seagrass beds: a sheltered, dense Zostera marina bed and a more exposed, sparse Z. noltii bed, in the Northern Wadden Sea. Both types of Zostera beds show a seasonal development of above-ground biomass, and therefore measurements were carried out during the vegetation period in summer. The exchange of particles and nutrients between seagrass beds and the overlying water was measured directly using an in situ flume. Particle sedimentation [carbon (C), nitrogen (N) and phosphorus (P) constituents] from the water column prevailed in dense seagrass beds. In the sheltered, dense seagrass bed, a net particle uptake was found even on windy days (7–8 Beaufort). Dissolved inorganic N and orthophosphate were mainly taken up by the dense seagrass bed. At times of strong winds, nutrients were released from the benthic community to tidal waters. In a budget calculation of total N and total P, the dense seagrass beds were characterised as a material sink. The seagrass beds with sparse Z. noltii were a source of particles even during calm weather. The uptake of dissolved inorganic N in the sparse seagrass bed was low but significant, while the uptake of inorganic phosphate and silicate by seagrasses and their epiphytes was exceeded by release processes from the sediment into the overlying water. Estimates at the ecosystem level showed that material fluxes of seagrass beds in the Sylt-Rømø Bight are dominated by the dense type of Zostera beds. Therefore, seagrass beds act as a sink for particles and for dissolved inorganic nutrients. During storms, seagrass beds are distinct sources for inorganic nutrients. The total intertidal area of the Sylt-Rømø Bight could be described as a sink for particles and a source for dissolved nutrients. This balance of the material budget was estimated by either including or excluding seagrass beds. Including the subtidal part, the function of the ecosystem as a source for particles increased, supposing that all seagrass beds were lost from the area. During the vegetation period, seagrass beds act as a storage compartment for material accumulated in the living biomass of the community. There was great biodiversity among the plant and animal groups found in intertidal seagrass beds of the Sylt-Rømø Bay, representing 50–86% of the total number of species investigated, depending on the particular group. Since most species are not exclusively seagrass residents, the loss of intertidal seagrass beds would be of minor importance for biodiversity at the ecosystem level. Food web structure in seagrass beds is different from other intertidal communities. Primary production and detritus input is high, but secondary production is similar to that of unvegetated areas, although the relative importance of the trophic guilds is different. The loss of seagrass beds leads to profound alterations in the food web of the total ecosystem. Historical as well as recent changes in material fluxes and energy flow due to man-made alterations to the ecosystem are discussed.     

Decomposition and nitrogen dynamics of turtle grass (<Emphasis Type="Italic">Thalassia testudinum</Emphasis>) in a subtropical estuarine system

Seagrass beds are pivotal in the functioning of coastal ecosystems in terms of productivity, organic matter turnover and nutrient cycling. Aiming to document decay and nitrogen (N) dynamics of turtle grass (Thalassia testudinum) in a subtropical estuarine system, decomposition patterns of leaves and rhizomes were characterized and compared. Nitrogen usage during decomposition of tissues, and of live tissues and epiphytes growing on live leaves, was also quantified and compared. Stable isotope ratios allowed tracing N within the seagrass bed, following N incorporation into seagrass tissues from the surrounding media (water, sediment). Leaves had a higher N content and decomposed at a faster rate (~6.4 times) compared to rhizomes. Leaching of soluble materials explain the rapid (0–3 days) initial mass loss of leaves (20%) and rhizomes (18%); with a loss of 85 and 56%, respectively, by the end of the study (77 days). Overall, leaves released N while rhizomes immobilized it. Nitrogen concentration was significantly different among live tissues. The main source of N for both seagrass tissues was the sediment, and water column for epiphytes. Differences in decomposition rates among seagrass tissues can be explained by the quality of the substrate and its susceptibility to microbial use. Seagrass leaves and rhizomes are equally important in taking up nutrients from either the water column or the sediments. This study provides a platform to study energy and matter transfers through detrital foodwebs linked to seagrass meadows.     

Investigation into the production of bacteriostatic substances by fungi VI. Examination of the larger Basidiomycetes

The present paper, the sixth of the series, gives the results of testing some 700 species of the larger Basidiomycetes for bacteriostatic properties. Initially, the 'juice' extracted from the sporophore was tested and this was followed in certain cases by a test of the metabolism solution produced by the fungus in culture. The results indicate that the larger Basidiomycetes are among the more promising fungus groups which produce antibiotics and that they compare favourably in this respect with the Aspergilli and the Penicillia. Of the 700 species tested approximately 70 are strongly and approximately 100 weakly positive against Staphylococcus aureus and/or Bacterium colt.     

Occurrence of okadaic acid in the feeding grounds of dugongs (Dugong dugon) and green turtles (Chelonia mydas) in Moreton Bay, Australia

Okadaic acid (OA) is a diarrhetic shellfish poison (DSP) produced by a number of marine organisms including the benthic dinoflagellate Prorocentrum lima, which are often found on seagrass. As seagrass forms the basis of the diet of dugong (Dugong dugon) and green turtle (Chelonia mydas), these herbivores may potentially be exposed to OA through ingestion of P. lima found on the seagrass. In this study, the abundance of epiphytic P. lima, on seagrass, and the concentration of OA produced by these epiphytic dinoflagellates was measured in Moreton Bay, Queensland, Australia. P. lima and OA were found on all four species of seagrass collected. OA was detected in epiphytic material collected from seagrass, with a maximum of 460 ng OA/kg_(wwtSG) found on Halophila spinulosa. From this information, the estimated maximum daily intake (DI) of OA by an adult dugong consuming 40 kg_(wwtSG)/day was 18,400 ng/day, and an adult turtle consuming 2 kg_(wwtSG)/day was 920 ng/day. Analysis by HPLC/MS/MS of 54 stranded dugongs and 19 stranded turtles did not yield OA above the detection limit of 10,000 ng/kg_{(animal tissue)}. OA was found on seagrass, however it was not detected in the tissue samples of dugongs and turtles.     

Metal binding activity of pectin isolated from seagrass Zostera marina and its derivatives

Low esterified pectin was isolated from the seagrass Zostera marina. Dynamics of the isolation process for the pectin from this seagrass was investigated. Two pectin derivatives: galacturonide (A) with molecular weight 30.55 kDa and galacturonide (B) with molecular weight 3.94 kDa were obtained using acidic hydrolysis of the native pectin from Zostera marina. Molecular weight parameters (Mw, Mn, Mw/Mn) of this pectin and its derivatives as well as of commercial apple pectin were determined using gel-filtration chromatography method. Comparative assessment of Cd²⁺, Pb²⁺, Y³⁺-binding activity of the native Zostera pectin, galacturonides A and B, and commercial apple pectin was performed. The results showed that galacturonide A with molecular weight 30.55 kDa possesses highest metal-binding capacity and may be considered as a candidate for development of medicines with metal-binding activity.     

Inhibition of neutrophil adhesion by pectic galacturonans

The inhibition of the adhesion of neutrophils to fibronectin by the fragments of the main galacturonan chain of the following pectins was demonstrated: comaruman from the marsh cinquefoil Comarum polustre, bergenan from the Siberian tea Bergenia crassifolia, lemnan from the duckweed Lemna minor, zosteran from the seagrass Zostera marina, and citrus pectin. The parent pectins, except for comaruman, did not affect the cell adhesion. Galacturonans prepared from the starting pectins by acidic hydrolysis were shown to reduce the neutrophil adhesion stimulated by phorbol 12-myristate 13-acetate (1.625 microM) and dithiothreitol (0.5 mM) at a concentration of 50-200 microg/ml. The presence of carbohydrate chains with molecular masses higher than 300, from 100 to 300, and from 50 to 100 kDa in the galacturonan fractions was proved by membrane ultrafiltration.     

Introduced species in seagrass ecosystems: Status and concerns

A literature review revealed that at least 56 non-native species, primarily invertebrates and seaweeds, have been introduced to seagrass beds, largely through shipping/boating activities and aquaculture. Four seagrass species also have been introduced. The introductions of the seaweeds Caulerpa taxifolia, C. racemosa v. cylindracea, Codium fragile ssp. tomentosoides, Sargassum muticum, the Asian mussel, Musculista senhousia, and the seagrass, Zostera japonica, are the best-known examples in seagrass beds. The ecological effects on seagrasses and associated communities have been examined for slightly less than half of the introduced species, which have predominantly negative effects. There is a paucity of experimental data for ecological effects, particularly for seagrass community structure and function. The exception to this finding is the introduction of the seagrass Z. japonica with oyster aquaculture to native eelgrass beds on the Pacific coasts of Canada and the USA. Recent experiments in several different seagrass ecosystems confirmed that disturbance contributes to the invasibility of seagrass beds. More definitive studies are required to elucidate the relative effects of nutrient pollution and introduced species in causing seagrass decline, particularly where reduced herbivory and boating activity also covary. Seagrass beds often are subject to multiple introduced species, but their cumulative effect has been virtually unstudied. The potential for compounded negative effects merits serious attention. Heightened attention to the issue of introduced species in seagrass beds is called for given the evidence that introduced species can contribute to seagrass decline, to biodiversity changes that could affect seagrass ecosystem functions, and that they can compromise seagrass restoration. Comprehensive surveys in seagrass beds, complemented by more stringent experimental and mensurative sampling designs, are needed. In the interim, conserving seagrass density and bed size can offer resistance to introduced species. Managing to prevent the introductions, including restricting transplantations of non-native biota during seagrass restorations, is likely to bear positive benefits for seagrass ecosystems.     

Measuring fertilization success of broadcast-spawning marine invertebrates within seagrass meadows

Increasing current velocity has been negatively correlated with the fertilization success of marine broadcast-spawning invertebrates. Seagrass has been shown to affect seawater hydrodynamics by slowing the movement of water. In this study we aimed to tease apart the relationship between fertilization success in sea urchins inside and outside of seagrass beds in St. Joseph Bay, Florida. Fluorescein dye diffusion, as a proxy for gamete diffusion, indicated higher rates of diffusion in sand habitats outside of seagrass beds. We quantified the proportion of eggs that remained on a female compared to being advected off a female over a 2-min interval in and out of grass beds. More eggs were collected inside of seagrass beds than over sand habitats, suggesting increased residence time of gametes within the beds. We induced sea urchins to spawn in experimental arrays in and out of grass beds and measured the fertilization success of eggs released from females and captured in the water column with a plankton pump. The fertilization success of eggs was significantly higher in grass beds. We concluded that seagrasses have the potential to mitigate gamete diffusion and increase the reproductive success of broadcast-spawning species that spawn in them.     

Varying foraging strategies of Labridae in seagrass habitats: Herbivory in temperate seagrass meadows?

The diets of five species of Labridae in south-western Australia were examined to determine whether: (1) grazing of seagrass and epiphytic algae is a prominent feature of the food web within the deeper seagrass meadows of this temperate region; (2) levels of grazing differ among different seagrass systems; and diets differ among these closely-related species. Fish were collected seasonally from three seagrass habitats mainly comprising either Posidonia sinuosa, Posidonia coriacea or Amphibolis griffithii between the summer of 1996/97 and spring of 1997. Consumption of considerable amounts of algae and seagrass by Odax acroptilus and seagrass by Haletta semifasciata indicates that macrophyte grazing by fish is a component of the trophic dynamics of south-western Australian seagrass meadows. O. acroptilus and H. semifasciata were both omnivorous, feeding on a range of epifauna, infauna and flora, whereas Siphonognathus radiatus, Neoodax balteatus and Notolabrus parilus were carnivorous, feeding predominantly on motile epifauna, such as molluscs and crustaceans. The level of macrophyte grazing is likely to be underestimated in temperate offshore meadows of P. sinuosa and A. griffithii where omnivorous labrids, monacanthids and terapontids are abundant. Stable isotope data for O. acroptilus from the study region suggest that animal prey is more important to tissue maintenance than macrophyte material. Macrophytes may be grazed to acquire attached animal prey or for fulfilling energy requirements. Based on the distribution of prey, it appears that species in A. griffithii meadows forage within and below the seagrass canopy, whilst species in P. sinuosa meadows are likely to forage towards the basal area of this seagrass.     

Bacterial interactions in the rhizosphere of seagrass communities in shallow coastal lagoons

Rooted phanerogam communities in the shallow intertidal and subtidal coastal zone represent productive and healthy ecosystems. Inorganic nutrients are assimilated into seagrass biomass. Much of the organic matter resulting from moribund seagrass is rapidly mineralized, principally by bacteria. The microbial community of the rhizosphere is also highly active due to the supply of organic matter released during photosynthesis. This active sediment community plays an important role through carbon, nitrogen and phosphorous cycling in maintaining the stability and productivity of seagrass meadows. Over the last two decades, however, seagrass meadows in European coastal areas have declined due to increasing pollution. As eutrophication advances a trasition occurs from rooted phanerogram dominated communities to planktonic algal blooms and/or cyanobacterial blooms. Such changes represent the decline of a stable, high biodiversity habitat to an unstable one dominated by a few species. These changes of community structure can occur rapidly once the internal nutrient and organic matter control cycles are exceeded. A field investigation was undertaken to establish the spatial distribution of bacterial populations of Zostera noltii colonized and uncolonized sediment in the Bassin d'Arcachon, France. Bacteria were enumerated using both plate count and MPN techniques for different functional groups as well as determining the total bacterial populations present. Nitrogen fixation, ammonification, sulphate reduction rates, as well as alkaline phosphatase activity were also determined. Colonization of the Z. noltii roots and rhizomes was studied by light and scanning electron microscopy. Results confirmed that higher bacterial populations were present in the rhizosphere of Z. noltii compared to uncolonized sediments. Furthermore, electron microscopy identified the rhizome as the main site of colonization for a diverse range of morphological groups of bacteria. Sulphate reducing bacteria were identified as the key group of bacteria involved in N-fixation in the rhizosphere of Z. noltii. The data will be discussed in relation to the role played by the rhizosphere microflora in supplying and mobilising nutrients in Z. noltii.     

Structure of major seagrass beds from three coral reef atolls of Lakshadweep, Arabian Sea, India

Detritus-based marine ecosystems such as mangrove and seagrass are of immense ecological importance. Major seagrass meadows from three coral atolls of the Lakshadweep group (Arabian Sea) were studied for their floral components. Seagrass beds were heterogeneous, comprising mainly of Thalassia hemprichii and Cymodocea rotundata, in Agatti and Kavaratti and it was observed to be monospecific (T. hemprichii) in the Kalpeni lagoon. Maximum (0.34 km²) and minimum (0.005 km²) extent of seagrass beds were observed in Kavaratti and Agatti lagoons, respectively. Seagrass weight (dry) of 43.97, 30.88 and 0.74 t were estimated from Kavaratti, Kalpeni, and Agatti, respectively. Maximum biomass occurred from 0–2 m depth, mainly contributed by the aboveground shoots, and was found to be negatively correlated with depth (r=0.71, p<0.05). Sediments were devoid of seed reserves indicating seagrass growth mainly by vegetative propagation. Epiphytes, on an average, contributed 7.5% of the seagrass biomass and were dominated by algae such as Melobesia spp., Microcoleus lyngbyaceus and Ceramium spp. Epiphytic biomass, too, decreased with increasing depth. Associated marine algae were represented by 66 species, dominated by rhodophytes.     

山东东营和烟台潮间带海草床食物网结构特征

为了探明海草床内主要生物类群间的营养关系以及食物网结构, 作者于2018年8月分别在东营黄河口潮间带和烟台西海岸潮间带海草床采集大型底栖生物样品, 采用δ ¹³C和δ ¹⁵N稳定同位素方法, 对生物样品的碳、氮同位素组成进行了测定和分析。结果表明: 东营海草床内生物的δ ¹³C、δ ¹⁵N值范围分别为-21.99‰至-12.13‰和5.23‰-11.05‰, 烟台海草床内生物的δ ¹³C、δ ¹⁵N值范围分别为-18.11‰至-14.06‰和6.60‰-10.22‰。东营海草床主要生物的营养级范围为2.00-3.85, 烟台海草床主要生物的营养级范围为2.00-3.15。根据δ ¹⁵N值计算所得的营养级图分析可知两区域海草床内初级消费者主要为滤食性双壳类和多毛类, 次级消费者为植食性或杂食性甲壳类,肉食性鱼类和腹足类。与近海海域大型底栖生物食物网相比, 海草床内底栖生物的营养级均值普遍较低。     

Seagrass depth limits

Examination of the depth limit of seagrass communities distributed worldwide showed that sea-grasses may extend from mean sea level down to a depth of 90 m, and that differences in seagrass depth limit (Z_c) are largely attributable to differences in light attenuation underwater (K). This relationship is best described by the equation

log Z_c (m) = 0.26 − 1.07 log K (m⁻)

that holds for a large number of marine angiosperm species, although differences in seagrass growth strategy and architecture also appear to contribute to explain differences in their depth limits. The equation relating seagrass depth limit and light attenuation coefficient is qualitatively similar to previous equations developed for freshwater angiosperms, but predicts that seagrasses will colonize greater depths than freshwater angiosperms in clear (transparency greater than 10 m) waters. Further, the reduction in seagrass biomass from the depth of maximum biomass towards the depth limit is also closely related to the light attenuation coefficient. The finding that seagrasses can extend to depths receiving, on average, about 11% of the irradiance at the surface, together with the use of the equation described, may prove useful in the identification of seagrass meadows that have not reached their potential extension.     

Evidence for secondary planktonic transport of post‐larvae of seagrass‐associated King George whiting

Stomach contents and stable isotope analyses were used to determine if secondary planktonic dispersal of King George whiting Sillaginodes punctata post‐larvae from shallow inshore habitats in a large embayment in south‐eastern Australia was initiated by wave disturbance. Benthic harpacticoid copepods, which live in and amongst seagrass shoots, were found in the stomachs of S. punctata caught offshore in the plankton only during rough weather. Stable isotope analyses showed that the base of nutritional support, estimated from values of δ¹³C, of S. punctata collected in the plankton changed significantly during rough (waves > 0·25 m) compared to calm (waves < 0·25 m) weather conditions. Values of δ¹³C collected from S. punctata in the plankton during rough weather were more consistent with S. punctata values found in the seagrass. Sillaginodes punctata collected in the plankton and seagrass during rough and calm weather failed to show differences in δ¹⁵N values. Dietary and isotope analyses support a model whereby newly arrived S. punctata larvae can be resuspended from seagrass beds and dispersed offshore by wave action during onshore winds. Secondary planktonic dispersal in S. punctata would provide a mechanism by which seagrass beds further inside Port Phillip Bay are colonized.     

Natural recolonisation of seagrasses at a disused sewage sludge outfall

Digested sludge from a sewage outfall that operated for 15 years adjacent to Adelaide in South Australia caused total seagrass loss in a 365 ha area around the outfall. Eight years after its closure, an underwater survey was conducted to determine the extent of seagrass recovery in a 2 ha area immediately adjacent to the disused outfall. Total seagrass cover was estimated to be 28% comprising 23% Halophila australis, 3% Posidonia angustifolia, 1% Posidonia sinuosa, and less than 1% each for Zostera tasmanica and Amphibolis antarctica. The recovery of seagrasses at the outfall site is probably due to recolonisation by propagules from a distant source. While results from this study suggest that seagrasses can return to a severely polluted site if the pollution source is removed and that Posidonia can be a primary coloniser of disturbed sites, they also suggest that it will take many decades for the seagrass community to recover to its former state.     

The molecular mechanism for receptor-stimulated iron release from the plasma iron transport protein transferrin

Human transferrin receptor 1 (TfR) binds iron-loaded transferrin (Fe-Tf) and transports it to acidic endosomes where iron is released in a TfR-facilitated process. Consistent with our hypothesis that TfR binding stimulates iron release from Fe-Tf at acidic pH by stabilizing the apo-Tf conformation, a TfR mutant (W641A/F760A-TfR) that binds Fe-Tf, but not apo-Tf, cannot stimulate iron release from Fe-Tf, and less iron is released from Fe-Tf inside cells expressing W641A/F760A-TfR than cells expressing wild-type TfR (wtTfR). Electron paramagnetic resonance spectroscopy shows that binding at acidic pH to wtTfR, but not W641A/F760A-TfR, changes the Tf iron binding site > or =30 A from the TfR W641/F760 patch. Mutation of Tf histidine residues predicted to interact with the W641/F760 patch eliminates TfR-dependent acceleration of iron release. Identification of TfR and Tf residues critical for TfR-facilitated iron release, yet distant from a Tf iron binding site, demonstrates that TfR transmits long-range conformational changes and stabilizes the conformation of apo-Tf to accelerate iron release from Fe-Tf.     

An in vitro study of LH release, synthesis and heterogeneity in pituitaries from proestrous and short-term ovariectomized rats

It is known that acute ovariectomy (OVX) greatly attenuates the pituitary luteinizing hormone (LH) response to gonadotropin-releasing hormone (GnRH) in vitro. The present study evaluated possible quantitative and/or qualitative differences in the biosynthesis and secretion of LH in pituitaries from proestrous and acutely (72 h) OVX rats. Paired anterior pituitary glands were incubated for 4 h in a medium containing +/- 10 nM GnRH. Pituitary and secreted LH were measured by radioimmunoassay with differences in total LH (tissue plus medium) +/- GnRH being indicative of GnRH-stimulated LH synthesis. Qualitative changes in LH were evaluated by isoelectrofocusing (IEF). The results show that the major form of LH stored in and released from the pituitaries consisted of LH molecules with an isoelectric point (pI) in the alkaline pH range (alkaline LH), and a lesser amount (approximately 30%) of LH molecules in the acidic pH range (acidic LH). The ratio of alkaline/acidic LH observed in the pituitary and medium was similar in the proestrous and OVX groups, although the amount of alkaline and acidic LH release in response to GnRH was 2-3 times greater in the proestrous group. In both groups, the alkaline/acidic LH ratio of secreted LH was higher in the presence of GnRH than in its absence. Alkaline LH synthesis was increased by GnRH in both groups, with the response being greater in the proestrous than in the OVX group; GnRH-stimulated acidic LH synthesis was observed only in the proestrous group. In both groups, the amount of LH synthesized was about 60% of the amount released, which suggests that LH synthesis does not fully account for differences in GnRH-stimulated LH release. Treatment of pituitary extracts with neuraminidase decreased acidic LH, and proportionately increased alkaline LH. These results suggest that the quality of LH stored in and secreted from pituitaries of proestrous and OVX rats is similar, and that there is a preferential release of the major alkaline LH isoform in response to GnRH. The ovarian steroid environment, presumably estradiol, proportionately increases the amount of alkaline and acidic LH released, and differentially affects the amounts of the various isoforms synthesized in response to GnRH. The charge heterogeneity of alkaline and acidic LH may be related to the sialic acid content of the LH molecule.     

Variation in δC values for the seagrass Thalassia testudinum and its relations to mangrove carbon

Carbon isotope ratios (¹³C/¹²C) were measured for the leaves of the seagrass Thalassia testudinum Banks ex König and carbonates of shells collected at the seagrass beds from seven sites along the coast of southern Florida, U.S.A. The δ¹³C values of seagrass leaves ranged from −7.3 to −16.3‰ among different study sites, with a significantly lower mean value for seagrass leaves from those sites near mangrove forests (−12.8 ± 1.1‰) than those far from mangrove forests (−8.3 ± 0.9‰; P < 0.05). Furthermore, seagrass leaves from a shallow water area had significantly lower δ¹³C values than those found in a deep water area (P < 0.01). There was no significant variation in δ¹³C values between young and mature leaves (P = 0.59) or between the tip and base of a leaf blade (P = 0.46). Carbonates of shells also showed a significantly lower mean δ¹³C value in the mangrove areas (−2.3 ± 0.6‰) than in the non-mangrove areas (0.6 ± 0.3‰; P <0.025). In addition, the δ¹³C values of seagrass leaves were significantly correlated with those of shell carbonates (δ¹³C seagrass leaf = −9.1 + 1.3δ¹³C shell carbonate (R² = 0.83, P < 0.01)). These results indicated that the input of carbon dioxide from the mineralization of mangrove detritus caused the variation in carbon isotope ratios of seagrass leaves among different sites in this study.