Utilization of terrestrial organic matter by the bivalve <Emphasis Type="Italic">Corbicula japonica</Emphasis> estimated from stable isotope analysis

ABSTRACT:   Carbon and nitrogen isotopic ratios in tissue of the bivalve corbicula ( Corbicula japonica ) and particulate organic matter (POM) were measured along a salinity gradient in the Kushida Estuary, Japan. The bivalve exhibited a gradual isotopic enrichment from the uppermost estuarine site (δ¹³C = −24.8‰ and δ¹⁵N = 8.6‰) to the marine site (δ¹³C = −16.1‰ and δ¹⁵N = 11.8‰). Using the concentration-weighted mixing model, the bivalves' food source is estimated from the isotope values for the bivalves and POM from terrestrial plants, marine phytoplankton and benthic microalgae. The results indicated that the contributions of benthic micro algae and phytoplankton were small, while terrestrial particulate matter is significantly important for the corbicula diet, although the contribution varies among sampling sites.     

Use of stable isotopes to distinguish farmed from wild Atlantic salmon, Salmo salar

Abstract –  Stable isotopes of carbon and nitrogen ( δ ¹³C and δ ¹⁵N) were examined in wild and aquaculture origin Atlantic salmon, Salmo salar , to evaluate their utility to identify escaped farmed fish. Samples of muscle tissue obtained from wild Conne River, Newfoundland, salmon were significantly more enriched in nitrogen ( δ ¹⁵N: mean = 12.75; SD ± 0.38‰) but depleted in lipid corrected carbon ( δ ¹³C': mean = −20.51; SD ± 0.23‰) by comparison with aquaculture specimens obtained from Bay d'Espoir, Newfoundland ( δ ¹⁵N = 10.96 ± 0.19‰;  δ ¹³C' = −19.25 ± 0.17‰) resulting in a complete separation of the two groups. Aquaculture specimens differed in δ ¹³C' from analyses of commercial salmon diet by 0.24‰, within the enrichment range associated with trophic transfers, while the δ ¹⁵N values in salmon muscle were enriched by 5.01‰. Although differences occurred in direct comparisons of white muscle and adipose tissue ( N  = 49), the average δ ¹³C' and δ ¹⁵N signatures varied in absolute amounts by only 0.5‰, supporting the use of adipose tissue as a nonlethal means to determine isotopic signatures of Atlantic salmon.     

Patterns of stable carbon and nitrogen isotopes in the baleen of common minke whale Balaenoptera acutorostrata from the western North Pacific

ABSTRACT:   Stable carbon and nitrogen isotope ratios were determined in the baleen plates of 17 common minke whales Balaenoptera acutorostrata from the north-western Pacific Ocean off Japan, as well as prey species (krill Euphausia pacifica , Japanese anchovy Engraulis japonicus and Pacific saury Cololabis saira ) collected in the stomach contents, to investigate the trophic relationship between the minke whales and their prey. A few δ¹⁵N-depleted peaks occurred along the length of baleen plates for 10 males irrespective of stomach content (anchovies and sauries). Similar δ¹⁵N-depleted peaks were also found for one female and two immature individuals. It was likely that these δ¹⁵N-depleted peaks formed in early summer. The stable nitrogen isotope ratio (δ¹⁵N) values in Pacific saury (9.3 ± 1.4‰) did not differ significantly from that in Japanese anchovy (8.8 ± 0.9‰). In contrast, δ¹⁵N in krill (7.2 ± 0.5‰ in July and 8.0 ± 0.2‰ in September) were significantly lower than in the Pacific saury. Thus, these peaks may reflect the dietary change from krill to fishes in the feeding migration of the whales. Growth rate of the baleen plate was estimated to be 129 mm/y, and it appeared that a dietary record of about 1.4 years remained in the baleen plate. For two immature whales, the maximum value of δ¹⁵N occurred at the tip of baleen. This δ¹⁵N enrichment may possibly be useful for discriminating weanlings and older whales.     

Basin geochemistry and isotopic ratios of fishes and basal production sources in four neotropical rivers

Abstract –  We analysed stable carbon and nitrogen isotopic ratios of dissolved inorganic carbon (DIC), plants, detritus and fishes to estimate the relative importance of dominant production sources supporting food webs of four Venezuelan rivers with divergent geochemical and watershed characteristics. Based on samples taken during the dry season at each site, fishes from two nutrient-poor, blackwater rivers had significantly lower δ ¹³C values (mean = −31.4‰ and −32.9‰) than fishes from more productive clearwater and whitewater rivers (mean = −25.2‰ and −25.6‰ respectively). Low carbon isotopic ratios of fishes from blackwaters were likely influenced by low δ ¹³C of DIC assimilated by aquatic primary producers. Although floodplains of three savanna rivers supported high biomass of C₄ grasses, relatively little carbon from this source appeared to be assimilated by fishes. Most fishes in each system assimilated carbon derived mostly from a combination of microalgae and C₃ macrophytes, two sources with broadly overlapping carbon isotopic signatures. Even with this broad overlap, several benthivorous grazers from blackwater and whitewater rivers had isotopic values that aligned more closely with algae. We conclude that comparative stable isotopic studies of river biota need to account for watershed geochemistry that influences the isotopic composition of basal production sources. Moreover, isotopic differences between river basins can provide a basis for discriminating spatial and temporal variation in the trophic ecology of fishes that migrate between watersheds having distinct geochemical characteristics.     

Carbon source and trophic position of pelagic fish in coastal waters of south-eastern Izu Peninsula,Japan, identified by stable isotope analysis

ABSTRACT:   It is important to clarify trophic dynamics in marine ecosystems for management of the fishing ground. Organic carbon sources and trophic position of pelagic fishes in the coastal waters of the south-eastern Izu Peninsula, Japan, were examined on the basis of carbon and nitrogen stable isotope distributions. The δ¹³C of the fishes was mostly distributed from −19 to −16‰ for nektonic fishes (13 species of adults and immatures) and planktonic fishes (10 species of larvae and juveniles), close to the δ¹³C values of particulate organic matter and planktonic decapods. These δ¹³C signatures for the inhabitants of the water column were in contrast with the high δ¹³C values (mainly −16 to −13‰) for demersal fishes of Scorpaeniformes and benthic polychaetes collected in the surf zone. These results indicate that nektonic and planktonic fishes depend on phytoplankton for carbon supply. The δ¹⁵N signatures suggest that the trophic position ranged 3.1–4.5 for the nektonic fishes and 2.9–3.7 for the planktonic fishes, premised on trophic level 3 for larval Japanese anchovy Engraulis japonicus . Thus, planktivorous fishes should be mainly assigned to trophic levels 3 and 4 in this area.     

Evaluation of shrimp polyculture system in Thailand based on stable carbon and nitrogen isotope ratios

ABSTRACT: To quantify the contribution by cocultured animals to waste assimilation in an intensive shrimp farm in Thailand, the food web structures of the macrobenthos in a reservoir pond, a shrimp culture pond and water treatment ponds were examined using the stable C and N isotope ratio technique. Seawater for aquaculture was drawn from a creek, and stored in a reservoir pond, used for farming the banana prawn Fenneropenaeus merguiensis in culture ponds, and then recycled through treatment ponds where the green mussel Perna viridis was cultured to remove organic wastes discharged from the farming. The clam worm Nereididae sp. and the mud creeper Cerithideopsilla cingulata in the culture pond had δ ¹³C values of −21.0‰ and −18.4‰, respectively, suggesting that shrimp feed (mean δ ¹³C = −20.7‰) was the main food source for these species. The δ ¹³C analysis also suggested that sediments (−23.7‰) in the reservoir pond and particulate organic matter (POM) (−24.0‰) and/or sediments (−25.0‰) in the treatment pond supplied carbon for most macrobenthic animals. However, green mussels in the treatment pond had a mean δ ¹³C value of −20.5‰, suggesting that shrimp feed was the main food source for this species.     

Effects of lipid extraction on stable carbon and nitrogen isotope analyses of fish tissues: potential consequences for food web studies

Abstract –  We examined whether solvent-based lipid extractions, commonly used for stable isotope analysis (SIA) of biota, alters δ ¹⁵N or δ ¹³C values of fish muscle tissue or whole juvenile fish. Lipid extraction from muscle tissue led to only small (<1‰) isotope shifts in δ ¹³C and δ ¹⁵N values. By contrast, ecologically significant shifts (+3.4‰ for δ ¹³C and +2.8‰ for δ ¹⁵N) were observed for whole juvenile fish. Sample variance was not affected by lipid extraction. For tissue-specific SIA, two sample aliquots may be required: a lipid-extracted aliquot for stable carbon isotope analysis when differing lipid content among tissues is a concern, and a nonextracted aliquot for δ ¹⁵N determination. Whole organism SIA is not recommended because of the mix of tissues having different turnover times; for very small fish, we recommend that fish be eviscerated, decapitated, and skinned to minimise differences with samples of muscle tissue.     

Stable isotope analysis of trophic position and terrestrial vs. marine carbon sources for juvenile Pacific salmonids in nearshore marine habitats

Abstract  Stable isotope analysis was used to determine trophic position and the relative contributions of terrestrial-derived carbon (TDC) and marine-derived carbon for Chinook, Oncorhynchus tshawytscha (Walbaum), pink, Oncorhynchus gorbuscha (Walbaum), and chum, Oncorhynchus keta (Walbaum) salmon fry in near-shore marine habitats. Chum fry were enriched in δ ¹³C relative to pink fry, and enriched in δ ¹⁵N relative to both Chinook and pink fry. Between 5.5 and 39.7% of the carbon in the three species was TDC. The TDC was higher in chum fry (28.7 ± 4% SD) than in pink fry (24.9 ± 4.4% SD), but TDC did not differ between Chinook fry (27.8 ± 9.5% SD) and either chum or pink fry. The fry of these three species of Pacific salmon may form a trophic hierarchy with chum fry occupying the highest trophic position and the three species may also partition resources according to carbon source.     

Stable carbon and nitrogen isotopic evidence for ecotonal coupling between boreal forests and fishes

Abstract— As a result of water turbulence effects on boundary layer diffusion resistance and carbon isotopic discrimination, the δ¹³C values (ratios of ¹³C: ¹²C) of attached algae may often overlap those of terrestrial plants, thereby making it impossible to distinguish between the relative importance of these two potential food sources for aquatic animals. The present study used a dual isotope approach (δ¹³C and δ¹⁵N) to refine measurements of the incorporation of allochthonous organic matter into freshwater fishes. The dependence of five species of littoral fishes on terrestrial detritus for part of their energy sustenance was demonstrated. The littoral zones of boreal Canadian Shield lakes are, therefore, not isolated from their surrounding riparian forests in terms of carbon flow as present day timber management guidelines erroneously assume, but instead exhibit a measurable degree of ecotonal land-water coupling. As a result, clearcut logging of riparian forests to the lakeshore edge, permissible by law in most Canadian provinces containing boreal forests, may have to be reassessed as a forest harvesting strategy.     

Comparing trophic position of stream fishes using stable isotope and gut contents analyses

Abstract –  Stable isotope analysis (SIA) and gut contents analysis (GCA) are commonly used in food web studies, but few studies analyse these data in concert. We used SIA (δ¹⁵N) and GCA (% composition) to identify diets and trophic position (TP) of six stream fishes and to compare TP estimates between methods. Ordination analysis of gut contents identified two primary trophic groups, omnivores and predators. Significant differences in TP_GCA and TP_SIA were similar in direction among-species and among-trophic groups; neither method detected seasonal changes in omnivore diets. Within-species TP_GCA and TP_SIA were similar except for one omnivore. TP_GCA was less variable than TP_SIA for predators, but variation between methods was similar for omnivores. While both methods were equally robust at discriminating trophic groups of fishes, TP_SIA is less laborious to estimate and may facilitate cross-stream comparisons of food web structure and energy flow.     

Ecological and genetic differentiation among the Arctic charr of Lake Aigneau, Northern Québec

Abstract –  Two modal size groups of sexually mature Arctic charr ( Salvelinus alpinus ) differing in shape and found at different depths in Lake Aigneau in the Canadian sub-Arctic are described and tested for genetic and ecological differentiation. Forms consisted of a small littoral resident, mean size 21.7 cm, and a large profundal resident, mean size 53.9 cm. Mitochondrial DNA analysis indicated that seven of eight haplotypes were diagnostic for either the littoral or profundal fish, with 66.6% of the variation being found within form groupings. Pairwise tests of microsatellite data indicated significant differences in nine of 12 loci and a significant difference between the forms across all tested loci. Molecular variation was partitioned to 84.1% within and 15.9% between forms and suggestive of either restricted interbreeding over time or different allopatric origins. Stable isotope signatures were also significantly different, with the profundal fish having higher δ¹³C and δ¹⁵N values than the littoral fish. Overlap and separation, respectively, in the range of form δ¹³C and δ¹⁵N signatures indicated that carbon was obtained from similar sources, but that forms fed at different trophic levels. Littoral fish relied on aquatic insects, predominantly chironomids. Profundal fish were largely piscivorous, including cannibalism. Predominantly empty stomachs and low per cent nitrogen muscle-tissue composition among profundal fish further indicated that the feeding activity was limited to the winter when ice-cover increases the density of available prey at depth. Results provide evidence of significant differences between the modal groups, with origins in both genetics and ecology.     

Natural abundance of 15N and 13C in fish tissues and the use of stable isotopes as dietary protein tracers in rainbow trout and gilthead sea bream

For developing efficient diets, two sets of experiments examined whether the use and allocation of dietary protein can be traced by labelling with stable isotopes (¹⁵N and ¹³C) in two culture fish ( Oncorhynchus mykiss and Sparus aurata) . In the first experiment, natural abundance and tissue distribution of these isotopes were determined, by measuring the δ¹³C and δ¹⁵N values by isotopic ratio mass spectrometry, in fingerlings (14–17 g) adapted to diets differing in the percentage of fish meal replacement by plant protein sources. For both species, δ¹⁵N and δ¹³C were greater in tissues with higher protein and lower lipid content. Delta ¹⁵N of diets and tissues decreased as replacement increased, suggesting δ¹⁵N can be used as a marker for dietary protein origin. The ¹⁵N fractionation (δ¹⁵N fish − δ¹⁵N diet) differed between groups, and could thus be used to indicate protein catabolism. In the second experiment, fish (75–90 g) of each species ingested a diet enriched with ¹⁵N-protein (10 g kg⁻¹ diet) and ¹³C-protein (30 g kg⁻¹ diet). These proportions were suitable for determining that the delta values of tissue components were high enough above natural levels to allow protein allocation to be traced at 11 and 24 h after feeding, and revealed clear metabolic differences between species.     

Growth and food availability of silver and bighead carps: evidence from stable isotope and gut content analysis

A 2-year investigation of growth and food availability of silver carp and bighead was carried out using stable isotope and gut content analysis in a large pen in Meiliang Bay of Lake Taihu, China. Both silver carp and bighead exhibited significantly higher δ¹³C in 2005 than in 2004, which can probably be attributed to two factors: (i) the difference between isotopic compositions at the base of the pelagic food web and (ii) the difference between the compositions of prey items and stable isotopes. The significantly positive correlations between body length, body weight and stable isotope ratios indicated that isotopic changes in silver carp and bighead resulted from the accumulation of biomass concomitant with rapid growth. Because of the drastic decrease in zooplankton in the diet in 2005, silver carp and bighead grew faster in 2004 than in 2005. Bighead carp showed a lower trophic level than silver carp in 2005 as indicated by stable nitrogen isotope ratios, which was possibly explained by the interspecific difference between the prey species and the food quality of silver carp and bighead.     

Discrimination and abundance estimation of wild and released abalone Haliotis diversicolor using stable carbon and oxygen isotope analysis in north-eastern Taiwan

The discrimination between wild and released Taiwan abalone Haliotis diversicolor was performed by stable carbon isotope analysis. Abalone samples were collected from Mao Aw Gulf in north-eastern Taiwan. Live abalone and dead shells were collected by divers with an 80 × 80 cm frame. The densities and amounts of wild and released abalone, as well as the survival rates of released abalone, in 1997 and 1998 were estimated. The age of the specimens was also determined from the specific temperature of each month and the inverse relationship between oxygen isotope values and temperatures. Results show that examining stable isotopic profiles proves to be a practical and feasible method for stock discrimination as well as density and abundance estimation. These data would be helpful in assessing the success of abalone culture and release programs, which aim to enhance this valuable marine resource.     

Trophic structure in natural habitats of the abalone Haliotis discus hannai with distinct algal vegetation of kelp and crustose coralline algae: implication of ontogenetic niche shifts

The abundance, species composition, and stable isotope ratios of benthic organisms were investigated to determine the trophic structures in abalone (Haliotis discus hannai) habitats, which are characterized by contrasting vegetation of crustose coralline algae (CCA) and kelp beds. A size–frequency analysis revealed that juvenile abalones with shell lengths (SLs) smaller than ~30 mm primarily inhabited CCA beds, whereas adults were abundant in kelp beds. Stable isotope analyses indicated that CCA beds were composed of a single food chain, whereas kelp beds supported multiple food chains. The abalone were divided into three size groups to estimate potential species interactions during their ontogeny. A small gastropod, Homalopoma sangarense, was the most abundant species, but is suspected to be less competitive with abalone, especially in CCA beds. An abundant starfish Asterina pectinifera appeared to function as a potential predator of juvenile abalones in both CCA and kelp beds. We concluded that CCA beds are essential for immediate post-settlement processes of abalones, whereas kelp beds are more important for providing refuge and food sources for adult abalones. The present study highlights that ontogenetic niche shifting can be a successful life-history strategy to sustain the abalone population in a subtidal rocky shore ecosystem.     

Comparative performance of juvenile red abalone, Haliotis rufescens, reared in laboratory with fresh kelp and balanced diets

Juvenile Haliotis rufescens were reared in the laboratory in order to investigate the extent to which fresh kelp and formulated feeds with 250 g kg⁻¹ (25P) and 380 g kg⁻¹ protein content (38P) affected their growth rate, gut residence time (GRT), food consumption ( C ), food conversion ratio (FCR) and digestibility. Abalone from 38P attained the highest growth rate (70.5 ± 4.2 μm day⁻¹; 98.3 ± 6.95 μg day⁻¹), followed by 25P (47.9 ± 2.79 μm day⁻¹; 67.4 ± 2.82 μg day⁻¹) and kelp (23.6 ± 3.36 μm day⁻¹; 28.2 ± 4.11 μg day⁻¹). No significant differences were observed in consumption rate among treatments (0.61–0.68% body weight per day), yet kelp-fed abalone exhibited higher FCR (2.44), protein efficiency ratio (4.42), and apparent digestibility of dry matter (69.5%), protein (69.8%) and gross energy (79.2%) than 38P organisms (59.8, 62.4 and 62.2%, respectively). They also showed longer GRT (23.1 ± 0.93 h). This study demonstrated that formulated diets with 250 g kg⁻¹ and 380 g kg⁻¹ protein inclusion can sustain higher growth rates of juvenile H. rufescens than fresh algae. These differences seem to be due to the amount of dietary protein. Kelp meal appears to improve the consumption and digestibility of balanced diets, and its inclusion in formulated diets is recommended.     

Linking migratory patterns and diet to reproductive traits in female brown trout (Salmo trutta L.) by means of stable isotope analysis on ova

Abstract –  Many populations of vertebrates display alternative reproductive strategies involving delays in maturation processes and migrations to more productive habitats. Notably for females, migratory patterns and diet could influence reproductive traits such as ova size and number. To test this hypothesis, we targeted anadromous and freshwater-resident female brown trout of various sizes during their return to spawn in tributaries, and carried out stable isotope analyses (δ¹⁵N and δ¹³C) on ova to identify their feeding areas and diet. The study was performed in the Oir River (France), a small coastal system where trout migrations to sea and within the river basin have been monitored for the last 20 years. General trends were observed in reproductive traits, such as the positive correlation between female fork length, fecundity and ova size. Fecundity was size-dependent whatever the migratory origin of females, but major divergences were seen for ova size and isotopic ratios. Freshwater residents displayed a constant increase in ova size and a ¹⁵N-enrichment in ova, suggesting an investment in larger ova and a shift to piscivory as the fish become larger and older. Conversely, anadromous females had smaller ova compared with freshwater-resident females of similar body size and achieved higher fecundity as they grew bigger. Our results suggest the existence of a continuum of reproductive traits for freshwater-resident females whereas anadromous females clearly show a break with this continuum. This major dissimilarity could be explained by the difference in growing environments in terms of food availability and quality.     

Settlement of larval top shell <Emphasis Type="Italic">Turbo (Batillus) cornutus</Emphasis> in response to several marine algae

ABSTRACT:     The settlement of larval top shell Turbo  ( Batillus )  cornutus in response to seven macroalgal and three benthic diatom species was examined in the laboratory. The percentages of larval settlement differed significantly among algal species, and were significantly higher on two red algal species ( Marginisporum crassissima , an articulated coralline alga, and Gelidium elegans , an agarophyte) than on the green algae, brown algae and benthic diatoms tested. Marginisporum crassissima induced larval settlement most strongly throughout the experiments. The percentage of larval settlement on a crustose coralline alga (unidentified species), which is known as a suitable substratum for abalone larvae, was much lower than on M. crassissima and G. elegans , which have morphologically complex growth forms . The percentage of settled individuals on ethanol-killed M. crassissima was much lower than on intact M. crassissima . The results indicate that physical structure is unlikely to be the main inducer of settlement; therefore, settlement of top shell larvae seems to be strongly induced by chemicals from the two red algal species. The specific distribution of juvenile top shell in the field may be at least partly determined by the strong induction of larval settlement by articulated coralline and gelidiacean algae.     

不同单胞藻饵料培养九孔鲍早期稚贝的研究

以单种培养的6种底栖硅藻和具有底栖习性的亚心形扁藻(Platymoras sp.)为饵料,培养九孔鲍(Haliotis diversi-color supertexta)受精后12 d的早期稚贝并观察其生长和存活,培养期为28 d,目的是筛选能维持早期稚贝高存活率和生长率的藻种。实验结果表明,培养稚贝成活率最高的3个藻种由大到小依次是爪哇曲壳藻亚缢变种(Achnanthes javanica var.)、流水双眉藻(Amphora fluninensis)和亚历山大菱形藻(Nitzschia alexandrina),使稚贝生长最快的3个藻种由大到小依次是流水双眉藻、爪哇曲壳藻亚缢变种和亚历山大菱形藻。研究结果揭示了适宜的底栖硅藻种类对鲍早期稚贝阶段生长和存活的重要性。个体小或者胞外产物量大的藻类很可能对九孔鲍早期稚贝的培养是有利的。     

Carbon sources of Amazonian fisheries

Variation in the seasonal and spatial isotopic composition of plant C₄ (aquatic macrophytes) and C₃ (forest, C₃ aquatic macrophytes and algae), and that of fish [ Prochilodus nigricans Agassiz, Mylossoma duriventre (Cuvier), Colossoma macropomum (Cuvier), Semaprochilodus insignis (Schomburgk) and S. taeniurus Steindachner in the Amazon floodplain were analysed to test whether the fisheries deliver plant carbon to the population of Manaus in the same proportion as it is available in the floodplain. The contribution of C₄ plants was significantly lower in ¹³C during the season of high water levels and increased toward the west of the basin. Mylossoma duriventre and C. macropomum changed δ¹³C levels, while the δ¹³C of P. nigricans and C. macropomum shifted spatially. The contribution of C₄ to the fisheries yield was small. C³ plants (excluding phytoplankton) also contributed less than expected. This was explained by the importance of detritivores to the yield of the fisheries and the dependence of these species on algal carbon.