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Trophic relationships within intertidal communities of the Brittany Coasts: A stable carbon isotope analysis
Abstract
More than 100 species belonging to plant and animal taxa that are commonly observed in the intertidal zone were collected on both rocky and soft bottom shores of Brittany, France, to be analysed for their 13C/12C ratio. Plant material displayed a wide range of δ13C values (from -12 to -34‰), with relatively distinct values among producer groups (Chlorophyceae, Fucales, Laminariales, Rhodophyceae, seagrasses, plankton), and among strata of intertidal zonation. Animal δ13C range was narrower (-15 to -22‰), and in general, values differed more between than within phyla or classes, according to the staple diet of organisms. A good correlation between the δ13C values of food and consumers was noted, together with a slight 13C-enrichment (~‰) with increasing trophic levels from suspension-feeders to predators.
... However, care was taken to sample representative taxa of the main trophic groups of the A. nodosum zone based on a priori literature knowledge (e.g. Dauby et al., 1998): ...
... Macroalgal isotope ratios are consistent with previously reported values (Dauby et al., 1998). The observed δ 13 C and δ 15 N variations can be due to differences within species over life and reproductive stages (Cloern et al., 2002) or to differences between species in carbon absorbing and fixing mechanisms. ...
... The isotopic compositions of grazers, filter-feeders and predators all fall within the range of previously reported values (Bode et al., 2006;Dauby et al., 1998;Kang et al., 2008). ...
Rocky shores dominated by canopy-forming macroalgae are characterized by complex communities making it difficult to assess whether the most abundant primary producers are at the base of the food web. This difficulty is exacerbated by the seasonal- and regional-scale variations of environmental and biotic factors that can affect the main trophic pathways. The food web structure of the Ascophyllum nodosum zone was studied during three seasons and at two sites separated by several 100s of kilometers by measuring the delta C-13 and delta N-15 of the major food sources and the dominant consumers of the zone. Despite the variability in isotopic compositions, both sites underwent similar significant seasonal variations. The main primary producers of the zone. A. nodosum, Fucus vesiculosus and Fucus serratus, were not at the base of the main trophic pathway but part of the diverse number of basal resources supporting the food web. The use of community-wide metric indices allowed further defining the food web structure of the A. nodosum zone as one characterized by trophic redundancy and numerous major trophic pathways. Indeed, grazers were dominated by generalists, filter-feeders utilized both planktonic and benthic organic matter, and predators displayed a high degree of omnivory. The range of values in delta N-15 showed a high spatiotemporal variability within and an important overlap between trophic groups. This prevented establishing distinctive trophic levels and further emphasized the complexity of the food web structure. The spatiotemporal stability of the relative isotopic composition of the dominant consumers within trophic groups and the low variability of the community-wide indices suggested a stability of the food web structure of the A. nodosum zone at a regional scale.
... However, care was taken to sample representative taxa of the main trophic groups of the A. nodosum zone based on a priori literature knowledge (e.g. Dauby et al., 1998): ...
... Macroalgal isotope ratios are consistent with previously reported values (Dauby et al., 1998). The observed δ 13 C and δ 15 N variations can be due to differences within species over life and reproductive stages (Cloern et al., 2002) or to differences between species in carbon absorbing and fixing mechanisms. ...
... The isotopic compositions of grazers, filter-feeders and predators all fall within the range of previously reported values (Bode et al., 2006;Dauby et al., 1998;Kang et al., 2008). ...
Rocky shores dominated by canopy-forming macroalgae are characterized by complex communities making it difficult to assess whether the most abundant primary producers are at the base of the food web. This difficulty is exacerbated by the seasonal- and regional-scale variations of environmental and biotic factors that can affect the main trophic pathways. The food web structure of the Ascophyllum nodosum zone was studied during three seasons and at two sites separated by several 100s of kilometers by measuring the δ13C and δ15N of the major food sources and the dominant consumers of the zone. Despite the variability in isotopic compositions, both sites underwent similar significant seasonal variations. The main primary producers of the zone, A.nodosum, Fucus vesiculosus and Fucus serratus, were not at the base of the main trophic pathway but part of the diverse number of basal resources supporting the food web. The use of community-wide metric indices allowed further defining the food web structure of the A. nodosum zone as one characterized by trophic redundancy and numerous major trophic pathways. Indeed, grazers were dominated by generalists, filter-feeders utilized both planktonic and benthic organic matter, and predators displayed a high degree of omnivory. The range of values in δ15N showed a high spatiotemporal variability within and an important overlap between trophic groups. This prevented establishing distinctive trophic levels and further emphasized the complexity of the food web structure. The spatiotemporal stability of the relative isotopic composition of the dominant consumers within trophic groups and the low variability of the community-wide indices suggested a stability of the food web structure of the A.nodosum zone at a regional scale.
... Here, we analyzed 22 TEs in fish from the Sulu Sea and the Celebes Sea and discussed the accumulation pattern, regional difference, and vertical distribution. Stable isotope ratios of d 15 N and d 13 C are known to be powerful tool to determine trophic level and source of diet, respectively, of organisms in the food chain (Hobson et al., 1995(Hobson et al., , 1997Hobson and Welch, 1992;Dauby et al., 1998). Therefore, d 15 N and d 13 C were measured to evaluate relationships between concentrations of TEs, and trophic levels and food source of organisms in these marine ecosystems. ...
... In this study, d 15 N values in fish significantly increased with fish size (p = 0.010), while there was no clear association of d 15 N with the feeding habit of fish. Similar to d 15 N, several studies have reported around 1‰ increase of d 13 C with trophic level of organisms (Hobson et al., 1995;Dauby et al., 1998). However, d 13 C was not significantly correlated with d 15 N as well as fish size and feeding habit in this study. ...
... Previous studies have suggested that d 13 C can indicate potential food sources whether they are coming from aquatic or terrestrial, inshore or offshore, and pelagic or benthic environment (Hobson et al., 1995;Dauby et al., 1998). In the Sulu Sea, d 13 C value in demersal fish (AM, À17.53‰) was significantly higher than that in pelagic fish (AM, À18.20‰) (p = 0.028). ...
Trace elements (TEs) and stable isotope ratios (δ15N and δ13C) were analyzed in fish from deep-water of the Sulu Sea, the Celebes Sea and the Philippine Sea. Concentrations of V and Pb in pelagic fish from the Sulu Sea were higher than those from the Celebes Sea, whereas the opposite trend was observed for δ13C. High concentrations of Zn, Cu and Ag were found in non-migrant fish in deep-water, while Rb level was high in fish which migrate up to the epipelagic zone, probably resulting from differences in background levels of these TEs in each water environment or function of adaptation to deep-water by migrant and non-migrant species. Arsenic level in the Sulu Sea fish was positively correlated with δ15N, indicating biomagnification of arsenic. To our knowledge, this is the first study on relationship between diel vertical migration and TE accumulation in deep-water fish.
... Many researchers have addressed questions about marine food webs by studying ratios of naturally occurring stable carbon ( 13 C/ 12 C) and nitrogen ( 15 N/ 14 N) isotopes (e.g. Dunton & Schell 1987, Hobson & Welch 1992, Dauby et al. 1998, Kaelher et al. 2000, Lesage et al. 2001, Jennings et al. 2002. Conventional dietary analysis only provides measurements of ingested food, whereas stable isotope analysis has the advantage of providing time-integrated averages of assimilated food (Fry 1988, Rau et al. 1992, Hobson et al. 1995. ...
... They suggested that variation in δ 13 C could be explained by storage of biochemical components of different isotopic composition. Both Dauby et al. (1998) and Raven et al. (2002) found δ 13 C signals from L. hyperborea to be in the same range as found in the present investigation, but did not state the part of lamina used. ...
... Some opisthobranchs are known for their ability to store chemical substances to make themselves venomous (Hayward et al. 1995). Dauby et al. (1998) report on another species of Aplysiidae, Aplysia depilans, to have δ 13 C signal of -29 ‰. According to Hayward et al. (1995), Aplysia punctata is a herbivorous species feeding on different species of algae, including Laminaria. ...
Samples of kelp Laminaria hyperborea, various species of red algae, phytoplankton, material from sediment traps, invertebrates, fish and seabirds were collected on the west coast of Norway and the abundance of stable isotopes was analyzed. Canopy plants of L. hyperborea were most 13C depleted in spring and there was a significant difference between the basal (δ 13C: -16.65‰) and distal (δ13C: -18.67‰) parts of the lamina. Young kelp plants were more 13C depleted (-23.59‰). The red algae fell into 2 groups: one in the same range as kelp plants (δ13C: -18.93 to -22.27‰) and the other highly depleted (δ13C: -32.85 to -34.38‰). Phytoplankton showed an average δ13C value of -24.44‰, δ15N values from L. hyperborea differed between the basal (δ15N: 5.54‰) and distal (δ15N: 3.54‰) part of lamina. δ15N values for all primary producers values were in the range of 3.52 to 5.78‰. Among the gastropods, Helcion pellucida proved to be a kelp plant grazer, Lacuna vincta probably fed on both kelp and various species of red algae, whereas Aplysia punctata grazed exclusively on the most 13C-depleted red algae. δ15N values for 2 other gastropods, Gibbula sp. and Calliostoma zizyphinum (8.64 and 10.30‰, respectively), suggest that they belong to higher trophic levels. Filter feeders occupied lower trophic levels and received variable carbon inputs from kelp. The only group of animals with δ13C signals in the same range as phytoplankton were amphipods. Based on δ15N values, the fish varied from intermediate to top consumers (trophic level: 2.6 to 3.3). Two species of seabirds were included in the study and their δ15N values suggested 2 different trophic levels, which correspond to their known feeding preferences. A mixing model suggests that kelp-derived carbon plays an important role in this nearshore system and that kelp may serve as a carbon source for marine animals with several different types of feeding strategies.
... This is because the isotopic composition of an animal's tissue mirrors that of its prey, with a slight trophic enrichment of δ13C and δ15N of the order of 1‰ and 3.4‰, respectively [78,79]. δ15N is used to estimate trophic position [80], while δ13C is used to indicate relative dietary contributions from different primary sources in a food web [81]. δ13C values are typically higher (less negative) in coastal areas or benthic food webs than in pelagic food webs [81]. ...
... δ15N is used to estimate trophic position [80], while δ13C is used to indicate relative dietary contributions from different primary sources in a food web [81]. δ13C values are typically higher (less negative) in coastal areas or benthic food webs than in pelagic food webs [81]. There are studies that have correlated stable nitrogen isotopes with concentrations of pollutants, such as Hg in fish tissues [82]. ...
Bioaccumulation is the process by which living organisms accumulate substances, such as pesticides, heavy metals, and other pollutants, from their environment. These substances can accumulate in the organism’s tissues over time, leading to potential health risks. Bioaccumulation can occur in both aquatic and terrestrial ecosystems, and can have a significant impact on the health of both humans and wildlife. The objective of this study is to find out if the concentrations of metals in the tuna species of the Canary Islands are suitable for human consumption and if they pose a health risk. Fifteen samples of Acanthocybium solandri, Katsuwonus pelamis, Thunnus albacares, Thunnus obesus and Thunnus thynnus present in canaries were analyzed. Ten grams of muscle were taken from each specimen and the metals Al, Cd, Cr, Cu, Fe, Li, Ni, Pb and Zn were determined by Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES). The tuna species that presented more metals with a higher concentration compared to the others was T. thynnus, reaching up to 100 times more than the other studied species in Fe content with 137.8 ± 100.9 mg/Kg, which may be due to the fact that it is the largest species that reaches ages of more than fifteen years. The species Thunnus thynnus should not be suitable for commercialization according to the current legislation on the concentrations of Cd in blue fish, since 75% of the specimens studied exceeded the concentration legislated for Cd. A total of 40% of the studied specimens of this this species exceeded the legislated values for the concentration of Pb in oily fish meat, so this species must be monitored to ensure that it does not pose a risk to human health.
... Trophic structure of these intertidal communities has been the focus of intensive research during the past decades, due to the emergence of the stable isotopic approach (e.g. Dauby et al., 1998;Sarà et al., 2007;Riera et al., 2009;Duarte et al., 2015). To our knowledge, only one study was however carried out in the context of vertical zonation (Steinarsdóttir et al., 2009). ...
... Particular attention was taken to collect consumers from the main trophic groups (filter-feeders, grazers and predators), based on literature knowledge (e.g. Dauby et al., 1998;Riera et al., 2009;Golléty et al., 2010). Stable isotope data for marine suspended particulate organic matter (POM) were obtained from the SOMLIT network, in a place located at approximately 600 m of our study site (Estacade sampling point, Roscoff, France, data available at http://somlit-db.epoc.u-bordeaux1.fr/ ...
... for Ulva and Coralina, respectively). d 13 C of Fucus serratus varied between À19.8 and À19.5&, similar to corresponding values reported along the French Atlantic coast Dauby et al., 1998). Polysiphonia lanosa, which lives as an epiphytic algae of Ascophyllum nodosum, showed d 13 C (average À19.5&) and d 15 N (average 5.5&) different from corresponding values for Ascophyllum nodosum (À16.2& and 5.9& for d 13 C and d 15 N, respectively). ...
... These species are also frequently observed on the rocky shores of the French Channel coast (Castric-Fey et al., 1997). Dauby et al. (1998). b Steneck and Watling (1982). ...
This study aimed to characterize the structure and functioning of the benthic food web associated with the Ascophyllum nodosum zone of the rocky shore of Roscoff by using δ13C and δ15N. Several characteristics of the trophic ecology of the invertebrates associated with this mid-littoral habitat and which belong to different functional groups (e.g., grazers, filter-feeders, predators and omnivores) were highlighted. In particular, the filter feeder species (including mostly sponges) used macroalgae-derived organic matter as a substantial food requirement. The results also pointed out an important stable isotopes variability for strict coexisting primary consumers which: (1) is directly related to the high δ15N range of the food sources; (2) makes it impossible to establish a unique trophic level scale based on δ15N values, as previously done in coastal environments; and (3) points out the existence of major co-occurring trophic pathways which characterise the Ascophyllum nodosum habitat.
... Their close proximity to the interface between land and water, along with their consistent interaction with water and sediments, renders them significant gauges of the marine and coastal ecosystem's well-being (Bagheri et al., 2014;Ferreira and Andrade, 2003;Jorissen et al., 2022). Through the processes of bioaccumulation and biomagnification, harmful substances within water and sediments progressively accrue within these organisms, reflecting the extent of pollution within their habitat (Bendell et al., 2020b;Dauby et al., 1998;Lozano-Bilbao et al., 2023b;Ruilian et al., 2008). Through the examination of tissues or bodily fluids from these organisms, scientists can evaluate the presence and concentration of diverse pollutants, ranging from heavy metals and organic compounds to other detrimental substances. ...
... Past studies of salt marsh succession by [8] as well as [23] suggest a decline in the use of marine resources with declining inundation frequency as a result of shore height. Trophic interactions, such as consumption of larval instars of rove beetles by the carabid beetle Dicheirotrichus gustavii [29] as well as consumption of algal wrack by the talitrid amphipod Talitrus saltator on the beaches of barrier islands [4,30], have been identified. While studying trophic interactions by direct observations is difficult due to the small size of the soil fauna and their prey, and the inaccessibility of their habitat, past studies of forest soils have suggested that food specialists are rare [26,31]. ...
Salt marshes exist along the gradient of the marine mudflat to the terrestrial dunes, with a gradient of shore height and associated plant zonation. The lower salt marsh (LSM) extends from the mean high tidal level to 35 cm above that level and is followed by the upper salt marsh (USM). Despite changes in the amount of allochthonous marine input and in abiotic conditions, little is known about changes in the trophic structure and used of basal resources by the soil macrofauna along marine-terrestrial boundaries. Natural variations in carbon stable isotope ratios (δ 13 C signatures) allow insight into basal resources of consumers such as marine algae, terrestrial C3 and C4 photosynthesising plants. Furthermore, variations in nitrogen stable isotope ratios (δ 15 N signatures) allow insight into the trophic position of consumers. We investigated spatial and temporal changes in stable isotope signatures in salt marsh soil macrofauna of the island of Spiekeroog, German Wadden Sea. The range of δ 15 N signatures indicated no changes in food chain length across salt marsh zones with consumers in both zones comprising primary decomposers, secondary decom-posers and first order predators. However, the trophic position of individual species changed between zones, but in particular with season. Contrasting δ 15 N signatures, the range in δ 13 C signatures in the LSM was twice that in the USM indicating a wider range of resources consumed. Bayesian mixing models indicated predominant autochtho-nous resource use in both the LSM and USM, with the use of marine allochthonous resources never exceeding 29.6%. However, the models also indicate an increase in the use of marine resources in certain species in the LSM with no use in the USM. Overall, the results indicate that the resource use of salt marsh macrofauna varies more in space than in time, with the food web being generally based on autochthonous rather than allochthonous resources. However, there also is trophic plasticity in certain species across both temporal and spatial scales including variations in the use of allochthonous resources. Generally, however, marine input contributes little to the nutrition of salt marsh soil macroinvertebrates.
... Past studies of salt marsh succession by Bakker et al. (2015) as well as Schrama et al. (2013) suggest a decline in the use of marine resources with declining inundation frequency as a result of shore height. Trophic interactions, such as consumption of larval instars of rove beetles by the carabid beetle Dicheirotrichus gustavii [29] as well as consumption of algal wrack by the talitrid amphipod Talitrus saltator on the beaches of barrier islands [4,30], have been identi ed. While studying trophic interactions by direct observations is di cult due to the small size of the soil fauna and their prey, and the inaccessibility of their habitat, past studies have suggested that specialists are rare [26,31]. ...
Salt marshes exist along the gradient of the marine mudflat to the terrestrial dunes, with a gradient of shore height and associated plant zonation. The lower salt marsh (LSM) extends from the mean high tidal level to 35 cm above that level and is followed by the upper salt marsh (USM). Despite changes in the amount of allochthonous marine input and in abiotic conditions, little is known about changes in the trophic structure and used of basal resources by the soil macrofauna along marine – terrestrial boundaries. Natural variations in carbon stable isotope ratios (δ¹³C signatures) allow insight into basal resources of consumers such as marine algae, terrestrial C3 and C4 photosynthesising plants. Furthermore, variations in nitrogen stable isotope ratios (δ¹ ⁵ N signatures) allow insight into the trophic position of consumers. We investigated spatial and temporal changes in stable isotope signatures in salt marsh soil macrofauna of the island of Spiekeroog. The range of δ¹⁵N signatures indicated no changes in food chain length across salt marsh zones with consumers in both zones comprising primary decomposer, secondary decomposer and first order predators. However, the trophic position of individual species changed between zones, but in particular with season. Contrasting δ¹⁵N signatures, the range in δ¹³C signatures in the LSM was twice that in the USM indicating a wider range of resources consumed. Bayesian mixing models indicated predominant autochthonous resource use in both the LSM and USM, with allochthonous resource use never exceeding 29.6%. However, the models also indicate an increase in the use of marine resources in certain species in the LSM with no use in the USM. Overall, the results indicate that the resource use of salt marsh macrofauna varies more in time than in space, with the food web being generally based on autochthonous rather than allochthonous resources. However, there also is trophic plasticity in certain species across both temporal and spatial scales including variations in the use of allochthonous resources. Generally, however, marine input contributes little to the nutrition of salt marsh soil macroinvertebrates.
... Perhaps the most intuitive pathway by which kelp production can support consumers is through direct grazing, where herbivorous taxa ingest fresh material, and then pass kelpderived energy and nutrients through the food web when consumed by other fauna. The best examples of this come from taxa with well-known associations with kelp, such as sea urchins (Stephenson et al. 1986, Rodriguez 2003, Won et al. 2007, Kang et al. 2008, Wing et al. 2008, Vanderklift and Wernberg 2010, Kelly et al. 2012, Galloway et al. 2013, Zapata-Hernández et al. 2016, Elliott Smith et al. 2018, Paar et al. 2019, and 'saddle-shaped' limpets (Bustamante and Branch 1996, Dauby et al. 1998, Fredriksen 2003, Steinarsdóttir et al. 2009, Schaal et al. 2010, Leclerc et al. 2013b, Reddin et al. 2015. Our data from 40 grazing/herbivorous taxa across the globe found tremendous variability in the degree of kelp-derived energy used by this functional group (Fig. 4, 5). ...
Kelp forests are highly productive coastal habitats that serve as biodiversity hotspots and provide valuable ecosystem services. Despite being one the largest marine biomes, kelp forests have been drastically understudied relative to other marine systems. Notably, while the role of kelp as habitat‐forming, or ‘foundation species', is well‐documented, a comprehensive understanding of kelp forest food web structure is lacking, particularly regarding the importance of kelp‐derived energy/nutrients to consumers. Here, we provide a biogeographic perspective on the energetic underpinning of kelp forests based on published literature. We targeted studies which used geochemical proxies – stable isotope analysis – to examine the transfer of carbon from kelp to local consumers. These studies (n = 94) were geographically skewed, with > 40% from Northern European Seas and Temperate Northeast Pacific. Quantitative estimates for the percentage of kelp energy (or kelp + macroalgae if sources were pooled) incorporated by local consumers came from 43 publications, which studied 141 species and 35 broader taxonomic groups. We examined these data for trends among functional groups and across upwelling regimes. No patterns are evident at present, perhaps due to the paucity or variability of available data. However, energetic subsides from kelps clearly support a wide range of diverse taxa around the globe. We also characterized biogeographic patterns in δ¹³C values of kelps and particulate organic matter (POM, a phytoplankton proxy), to evaluate potential limitations of stable isotope analysis in disentangling the relative contributions of pelagic versus benthic resources to coastal food webs. Globally, kelps and POM differed by > 4.5‰, but there was substantial variation among regions and kelp species. Accordingly, we discuss advances in stable isotope techniques which are facilitating more precise analysis of these complex energetic pathways. We end by proposing four main avenues of critical future research that will shed light on the resilience of these communities to global change.
... Filamentous epiphytic algae are overgrowing the stems of large Arctic kelp species after initial colonization . Average number of kelp species per square meter was used to estimate the epiphytic biomass (Table 1) (Dauby et al., 1998) seaweeds (Pedersen et al., 2014). The phytoplankton biomass (Table 1) present in the water column above the kelp belt was calculated from Chlorophyll a measurement recorded by the AWIPEV COSYNA underwater long-term fjord observatory in Kongsfjorden in 2012. ...
The reduced sea ice extent and duration in the Arctic releases the rocky shores from one of its key physical disturbances shaping the zonation and depth extension of seaweed assemblages. In order to determine the consequences of reduced disturbance by sea ice, we studied the changes in the functioning and structure of the kelp belt at Hansneset, Kongsfjorden, between 1996-1998 and 2012-2014 using ecological network analysis (ENA). For each time period, a kelp belt flow network was constructed for 2.5 m and 5 m water depths in summer (June-July). We conducted a data-guided uncertainty analyses to evaluate the strength of the difference observed in the ENA results. At 2.5 m, the total system throughput-indicating the size of the system-significantly increased between the two periods. The number of parallel pathways (relative redundancy), the number of interactions (flow diversity) and the number of indirect interactions (Indirect/Direct) in the system were as well significantly higher at 2.5 m and 5 m in 2012-2014 compared to 1996-1998. These changes were related to the persistent colonization of the shallow sublittoral by kelps, which led to a diversification of filter feeders and an increase in omnivorous species. At 5 m, however, the kelp biomass and production decreased most likely due to the reduction of the underwater light climate between 1996-1998 and 2012-2014. In contrast, the macro-zoobenthic biomass increased with a higher contribution of opportunistic and carnivorous species between these two periods. The increased values of these total system indicators suggest a more complex and mature kelp belt ecosystem in 2012-2014 compared to 1996-1998 probably due to the reduction of physical disturbances by ice. A future warming of the Arctic Ocean might enhance sea urchins grazing activity of kelp production as herbivory already increased between both periods. In a context of fast changes on ecosystem level triggered by concurrent multiple stressors, management objectives in the Arctic should be based on holistic approaches such as ENA. To do this, consistent monitoring of relevant food web components for model construction and data-guided uncertainty should be put in place.
... In addition to traditional biodiversity surveys, stable isotope analyses of assemblages (Fry 2008) can provide complementary data to help identify possible processes influencing community structure. Stable isotope analyses have been used extensively in temperate coastal systems to investigate trophic relationships (Dauby et al. 1998, Schaal et al. 2010, nutrient inputs (Machás & Santos 1999) and human impacts (McClelland et al. 1997). Natural isotopic ratios of carbon and nitrogen in organisms provide information relating to their trophic level relative to each other and possible dietary constituents (Phillips & Gregg 2003, Layman et al. 2012, which in turn can help reveal species interactions within a system. ...
As coastal cities around the world expand, and sea levels and the frequency of storms rise, natural shorelines are steadily being replaced by artificial defences such as seawalls. A growing number of studies have documented the assemblages that inhabit these novel environments, and some have contrasted them against those found in their natural analogues: rocky shores. Most of this work has, however, been conducted in temperate regions, and there is limited research on seawalls in the tropics. To address this, we conducted monthly surveys of adjacent seawall and rocky shores at multiple sites around Singapore for 1 yr. Our results concur with previous temperate studies — artificial seawalls support a lower diversity but share a substantial number of species with rocky shores. Multivariate analyses reveal that assemblage differences were largely driven by species that were found in both habitats (e.g. detritivore Ligia exotica, grazer Monodonta labio and carnivorous whelk Drupella margariticola) but occurred in different abundances. We also conducted (for the first time on seawalls) stable isotope analyses to elucidate the diets of the common species found in both habitats. Turf algae, which were found to be present in significantly lower abundances on seawalls, could possibly contribute substantially to the diets of many dominant herbivores. Future seawall enhancement efforts in the tropics could therefore look into whether enhancing turf algae will improve biodiversity.
... The potential food sources whether they are coming from aquatic or terrestrial, inshore or offshore, and benthic or pelagic environment can be indicated by δ 13 C (Dauby et al., 1998;Hobson, 1999;Hobson et al., 1995;Kwon et al., 2012). The δ 13 C of fish living in both fresh and marine water were significantly higher than the δ 13 C of fish only in fresh water, which is consistent with the study that δ 13 C values are typically higher in coastal than in offshore food webs (Hobson, 1999;Kwon et al., 2012), indicating higher δ 13 C in areas with higher salinity (Atekwana et al., 2003). ...
The Yellow River Estuary is a significant fishery, but at present there are few studies about the concentrations of arsenic (As), mercury (Hg) and vanadium (V) in fish from this area, which might cause potential health risk to fish consumers. The aim of this study was to research on the accumulation and potential sources of heavy metals in the fish of the Yellow River Estuary. Arsenic, Hg, V and stable isotope ratios (δ(15)N and δ(13)C) in 11 species of 129 fish were analyzed. Results showed that the concentrations of As and Hg were all lower than the guideline levels established by international organizations and legal limits by several countries. The mean concentrations of V in samples in this study were significantly higher than the results of previous studies on other regions. Arsenic, Hg and V significantly differed across species (P<0.05), which might be due to the different foraging habitats and dietary habits of the studied fish. Values of δ(15)N and δ(13)C in fish from the study area ranged from 5.1‰ to 14.6‰ and from -27.6‰ to -14.5‰, indicating a wide range of trophic positions and energy sources. There was evidence of bioaccumulation of Hg, which could be explained by the positive correlation between Hg concentrations and δ(15)N in fish. Through estimation of daily intake of inorganic As (iAs), Hg and V via fish consumption, the heavy metal contamination level of fish samples fell in an acceptable range, indicating no potentially hazardous for human health.
... Marín Leal et al. 2008;Piola et al. 2006), and because of their recognized role in nutrient cycles and ecosystem functioning (Montague et al 1981, Peterson 1999. Studies involving stable isotope analysis of tunicates or waterflea are most often part of a community wide food web assessment (Dauby et al. 1998, Sierszen et al. 2014, and stable isotope analysis of tunicates is particularly rare (but see Duineveld et al. 2007). ...
A developing concept in ecology is that broad niches predict geographical range size. Plasticity in resource use is often considered to be important for responding to novel environments, and study of species that are established across different ranges provides a model for determining the drivers of species spread and distribution. Contrasting distributions of invasive species are often associated with species-specific feeding ecology, but comparisons are rarely made for multiple taxa, spatial scales or between native and invaded ranges.
Stable isotopes of carbon (δ13C) and nitrogen (δ15N) are common tracers in food web ecology and provide a quantitative measure of intra and interspecific variation in dietary niche. In this dissertation, I compare the dietary niches (variation in δ13C and δ15N) of successful and less successful aquatic invasive species of fish and invertebrates established across broad and narrow ranges in invaded regions, fishes in native and invaded ranges, and the role of time since invasion for niche diversification in relation to habitat complexity and genetic diversity.
This dissertation demonstrates the importance of intra and inter-individual variation in resource use for successful widespread distribution of invasive fishes. Inconsistency in this trend for oysters, tunicates and waterflea suggested dietary niche breadth is less important for invasion success in aquatic invertebrates than it is for fishes. Moreover, dietary niche plasticity was associated with a broad body size range in fishes, but not invertebrates. Habitat complexity and environmental heterogeneity were associated with peaks in niche breadth that were exceptions to general trends of increasing niche breadth and genetic diversity with time established. Gain in niche breadth from native to invaded regions for populations of most successful invasive fishes, but loss of niche breadth for less successful species, further indicated the importance of intra-individual variation in resource use for widespread distribution. Loss of dietary niche breadth for less successful species implied that the invasion process could be associated with severe bottlenecks for less successful species, which could be a mechanism for limited spread. These findings highlight the potential for considerable impact from the invasion process for the ecology of the invader, and that establishment in novel environments can drive diversification in the absence of founder effects.
... La mati•re organique en suspension pr€lev€e au large, ainsi que les valeurs utilis€es dans le cadre de l'€tude dans le port de Brest, issues d'une publication ant€rieure (Lorrain et al. 2002) La diff€renciation isotopique des sources basales de nourriture, en particulier par le δ 13 C est un pr€ambule n€cessaire ‚ toute €tude isotopique visant ‚ d€terminer leur importance relative dans le r€gime de consommateurs (Peterson & Fry 1987). Les δ 13 C mesur€s pour les diff€rentes macroalgues durant cette th•se se r€partissent sur une large gamme (de -34,1 ‰ ‚ 12,2 ‰), correspondant ‚ la gamme de valeurs commun€ment observ€es ‚ l'€chelle mondiale (Raven et al. 2002) ainsi qu'‚ celle de la Bretagne (Dauby 1998 ...
The aim of this thesis was to characterize food web’s structure and functioning on Northern Brittany infralittoral fringe ecosystems, with Laminaria digitata canopy or in highly man-disturbed environments. Contrarily to previous studies; the food webs did not exhibit any functional or structural simplifications, likely owing to the topographical complexity of the habitat, which allows the coexistence of various trophic pathways including predators foraging in different trophic niches. Our results show in the three sites studies that the food web is based on a wide diversity of sources and, in particular, that L. digitata does not represent the main food source for most consumers. The use of this alga by the different trophic groups seems to vary according to local conditions, both as fresh food or as detritic food. Finally, our results show the link between habitat microscale spatial structure of rocky shores and the variability of trophic pathways at very fine spatial scale. Our results suggest that these ecosystems are characterized by an important functional diversity, which supports the high biodiversity of these environments.
... Among the different feeding types, the grazing invertebrates, the mollusc-feeders and (strikingly) the ctenophores are strongly 13 C-enriched. Deposit-feeders have been shown to be more enriched in δ 13 C than suspension-feeders, suggesting 2 different isotopic carbon signatures for suspended particulate matter and a mixture of suspended and sedimentary organic matter respectively (Dauby et al. 1998). Coastal or continental inputs are important in this area, leading to 13 C-enrichment of the particulate matter of the Channel and the North Sea compared to the Bay of Biscay (Dauby et al. 1994). ...
... Schaal, Riera & Leroux digitata is one of the most 13 C-enriched of co-occurring macroalgae on English Channel rocky shores (Dauby et al. 1998), which is confirmed by our data. The d 13 C of fresh kelps was used as a proxy for detritus in this study. ...
Kelp holdfasts are highly reticulated structures which host a large diversity of small fauna. These microhabitats have been reported to play a crucial role in the biodiversity associated to kelp forest ecosystems. This study aimed at identifying trophic links and the main food sources sustaining food webs within communities associated with kelp holdfasts, through a stable isotope (δ13C and δ15N) approach. Sampling of the main invertebrates inhabiting Laminaria digitata holdfasts, and of their potential food sources, took place in February and May 2007. Stable isotope results reveal that most of the primary consumers, including filter‐feeders and deposit‐feeders, rely on the particulate organic matter sedimented within kelp holdfasts. Only three grazers departed from this general pattern. The correspondence between the stable isotope ratios of predators and sediment consumers indicated that this source is at the base of the main pathway through which energy and matter transit in the food web. δ15N ranges found for consumers revealed that the food web associated with kelp holdfasts is composed of 3.5 levels. In spite of the low diversity of food sources at the base of the food web, these microhabitats can therefore be considered micro‐scale ecosystems, from a functional perspective.
... The latter behaviour is expected, for instance, for Gibbula cineraria (Steneck & Watling 1982) whose feasible diet was poorly resolved (Table 5). Unlike this species, the bluerayed limpet Patella pellucida is a known direct kelp grazer living on kelp blades (Dauby et al. 1998, Fredriksen 2003, Schaal et al. 2010, Leblanc et al. 2011, Leclerc et al. 2013). The observation of over 560 individuals on 1 kelp lamina in November, and observed enriched δ 13 C values confirmed these reports; therefore, kelp was considered as its exclusive potential source (Table 4). ...
Owing to their productivity, kelps may be the main primary carbon source for consumers in coastal areas. Their contribution has often been compared to that of phytoplankton, but the potential involvement of the red algae associated with kelp forests has been overlooked. All these 3 primary sources have distinct life cycles and may contribute to the particulate organic matter pool differently according to season. In the present study, we characterised the trophic structure of a pristine Laminaria hyperborea forest off the coast of Brittany (France) in terms of the organic carbon biomass of the main primary producers and consumer trophic groups on 4 sampling dates over a 1 yr period. Senescence of many red algae species occurred during their resting period (i.e. before November), whereas the kelp regrowth period (i.e. before March) was accompanied by the fragmentation of old lamina. During these periods, when phytoplankton biomass is
comparable, stable isotope analyses (δ13C and δ15N) were conducted in an attempt to link structure to trophic functioning. By combining analyses of temporal variability in primary source and consumer isotopic ratios and using mixing models, we inferred changes in the trophic significance of macroalgae in the associated food web. Decaying kelp laminae were a major contributor to the particulate organic matter pool, and the fragmentation of old lamina promoted their contribution to the diet of deposit- and suspension-feeders in March. Growth of red algae enhanced direct grazer consumption in March, while their senescence contributed significantly to primary consumer diets in November via indirect consumption.
... Mean significant differences are summarized as *** (P < 0.001), ** (P < 0.01), * (P < 0.05), nS (P > 0.05), derived from Student's t-test or Mann-Whitney test, according to homoscedasticity of the data and Wernberg 2010). For instance, the blue-rayed limpet Patella pellucida, consistently reported as a direct kelp grazer (Dauby et al. 1998;Fredriksen 2003;Leblanc et al. 2011), was 13 C-enriched by 1 ‰ compared to kelp at both sites. Moreover, both Patella pellucida and young fronds of Laminaria hyperborea on which the gastropod lives displayed enriched δ 13 C values by 4 ‰ in roscoff compared with Molène. ...
The relative contribution of kelps and other food sources to the diet of consumers in shallow coastal communities has been hotly debated in recent years. It has been suggested that considering proxies instead of phytoplankton isotopic signatures can lead to an overestimation of kelp contribution through isotopic mixing models. We analysed spatial patterns in carbon isotopic ratios of the dominant primary sources and consumers at two subtidal sites in Brittany (France) prior to the anticipated 2011 phytoplankton bloom to determine which of kelp and phytoplankton is the dominant food source in Laminaria hyperborea forests. We found simultaneous spatial variations for consumers, kelps and deposited particulate organic matter, suggesting that kelp-derived organic matter is a key component of associated food webs for at least part of the year.
... The δ 15 N ratio is often used as a predictor of the relative trophic level (Vander Zanden et al., 1997;Pinnegar et al., 2002;Post, 2002), whereas δ 13 C values can be useful in evaluating sources of primary production in marine systems. Indeed, δ 13 C values are typically higher in inshore-benthic food webs than in plankton-based systems (Hobson et al., 1995;Dauby et al., 1998), with the exception of coastal areas colonized by C3 plants (Créach et al., 1997). Conversely to stomach content analysis or direct observations which reflect the diet composition of an animal at the moment, stable isotope measurements of carbon and nitrogen in an organism's tissue provide a time-integrating method depending on the tissue's turnover rates (Hesslein et al., 1993). ...
The ontogenic variations of nitrogen and carbon stable isotopic signatures (δ15N and δ13C) were investigated in two spider crab (Maja brachydactyla) populations inhabiting in different biotopes of Western Europe. The Iroise Sea population is localized in Western Brittany and characterized by a seasonal migration occurring on a large bathymetric and habitat gradient while the Seine Bay population, in the Eastern English Channel, remains in a more homogeneous environment during its migration. In the Iroise Sea population, δ13C values increased significantly both with body size and age, revealing a shift towards “benthic-component” prey with spider crab growth. On the contrary, neither body size nor ageing gave rise to a significant trophic level change (derived from the δ15N). In this M. brachydactyla population, the seasonal migrations from coastal waters in summer to offshore habitats in winter involved significant but slight differences in both δ13C and δ15N. In the Seine Bay population, low variations for both carbon and nitrogen were recorded related to either sex or size or seasonal migration. Thus, the δ13C and δ15N variability in the spider crab depends on the availability and diversity of prey in its different living habitats, as well as on the morphological aptitudes of individuals to feed on prey (individual's size).
... For nitrogen, enrichment in 15 N typically shows a stepwise increase with trophic level within a food chain with a trophic enrichment value of about 3‰ (Hobson & Welch, 1992). Thus, carbon-13 value, rather than being a reliable indicator of the trophic level, is preferentially used to indicate relative contributions to the diet of different potential primary sources in a trophic network, indicating the aquatic vs. terrestrial, inshore vs. offshore, or pelagic vs. benthic contribution to food intake (Hobson et al., 1995;Dauby et al., 1998). ...
Thirty-five deep sea fishes belonging to 22 species and one unidentified specimen obtained from the Sulu Sea, located in the southwestern area of the Philippines were analyzed in the late 2002, for 23 trace elements using ICP-MS, HG- AAS and CV-AAS. Predominant accumulation of strontium (Sr) was observed in all the samples. This stems from the fact that the whole body of fish was homogenized since Sr is known to accumulate in bones and hard tissues. Mercury concentrations in all the 36 samples were below the detection limit. Cadmium concentrations were generally below 1 µg/g dry weight (dw) except in Pterygotrigla spp. (4.29 µg/g dw) and Sternoptyx pseudodiaphana (2.89 µg/g dw). Concentrations of Pb were predominantly low with about 90% of the specimens having less than 1 µg/g dw. In general, concentrations of Sr, Zn, Cu, Se and Cd appeared to increase with increasing depth of occurrence of the species. Manganese, Tl, Pb, Bi, In, Cs and As showed significant positive correlation (p < 0.05) with δ 15 N, suggesting that these elements were biomagnified. To our knowledge, this is the first study reporting Tl biomagnification in fish. Rubidium and Cs showed significant positive correlation with δ 13 C, implying that Rb and Cs would originate from offshore waters as oceanic plankton has high δ 13 C. Comparing results from this study to the dietary standards and guidelines for Hg, Pb, Cu and Zn in fish and shellfish of the Ministry of Agriculture, Fisheries and Food of the United Kingdom, these levels were not high to warrant concern if they were to be consumed by humans. However, 16.7% of the fish samples had high Cr levels when compared with the Hong Kong's safe limit of 4 µg/g dw for Cr in sea food. This constitutes a health risk to humans, as Cr is potentially toxic.
... A few studies have attempted to trace the epilithic microalgal organic matter using stable isotopes. Dauby et al. (1998) showed the close similarity in the d 13 C values between periwinkles and limpets inhabiting the rocky substratum along the Brittany coast in France (approximately Ϫ18.0‰) and the algal film (Ϫ17.9‰) covering the rock, which mainly consisted of cyanobacteria and minute green and red algae. ...
Glass plates were immersed in the surface layer (1 m) in Gokasho Bay during a 7 day period every month over an annual cycle to allow periodic collection of epilithic microalgae and to analyze their year-round stable carbon and nitrogen isotope ratios. The bulk of the attached material was diatoms throughout the year. The δ13C and δ15N of epilithic microalgae varied seasonally, ranging from −22.0 to −14.6‰ and from 3.6 to 10.2‰, respectively. The δ13C increased during a period from August to November when large microalgal biomasses were found, while the δ15N decreased after November through January in the next year. Such seasonal variations are discussed from the viewpoints of the algal growth and ambient nutrient concentrations. Comparison of the δ13C (yearly mean=−19.8‰) and δ15N (7.7‰) for epilithic microalgae with the previously reported values for primary producers and organic matter in Gokasho Bay shows that the overlap of the δ13C with marine phytoplankton (−20.4‰), which will result in poor resolution of sources.
... Carbon isotopic ratios were in the range of those available for organic matter sources in the Mediterranean Sea literature (Carlier et al., 2007;Dauby, 1989;Dauby et al., 1998;Lepoint et al., 2000;Pinnegar and Polunin, 2000). Mytilus galloprovincialis was highly 13 C-enriched in comparison with SPOM. ...
Organisms inhabiting shallow coastal ecosystems are potentially exposed to damaging levels of solar UV radiation. UV-sunscreen compounds such as mycosporine like amino-acids (MAAs) are a widespread bio-chemical strategy among many marine organisms to counteract UV stress. These molecules are produced through a metabolic pathway restricted to cyanobacteria, various algal groups and fungi. This study was designed to search for UV sunscreen compounds in benthic invertebrates of the Catalan medio-littoral rocky shore of the north-western Mediterranean Sea. The relationship between food sources and consumers was investigated using the stable isotope approach in order to elucidate the potential pathways of MAA transfer. The food web associated with the littoral Catalan rocky shore is characterized by a high level of func-tional complexity. The variability of δ 13 C and δ 15 N among and between trophic guilds provides evidence of the diversity of coexisting trophic levels and trophic pathways in a single habitat type. MAAs were present in all sampled metazoan species. We observed a higher MAA diversity in animals than in food sources. This may be explained by the incorporation of MAAs from several trophic resources, by the conversion of the MAAs acquired from the food or by translocation from a symbiont. The amount of MAAs in sea urchins was fairly low compared to other trophic groups. This cannot be explained by depletion of MAAs in their diets, and hence other UV-protective strategies may be more important. Complementary experimental studies should be performed to determine the ability of primary and secondary consumers to assimilate MAAs and convert these compounds.
... Hobson et al. (1997) reported how changes in these ratios have been used to explain trophic relationships within marine food webs. The δ 13 C is used to indicate relative contributions to the diet of different potential primary sources in a trophic network, indicating the aquatic vs. terrestrial, inshore vs. offshore, or pelagic vs. benthic contribution to food intake (Dauby et al., 1998; Asante et al., 2008). An animal is on average enriched in δ 13 C by about 1‰ relative to its diet (DeNiro and Epstein, 1978; Michener and Schell, 1994). ...
The giant mudskipper (Periophthalmodon schlosseri) is one of the
commonly found mudskipper species living and it makes a significant biomass value in the
mangrove ecosystem. Samples of this mudskipper species were collected and analysed for
stomach content and stable isotope ratios (δ13C and
δ15N) to determine their food preference. The stomach
content analysis showed four groups of food items: fiddler crabs (Uca
sp.), medaka fish (Oryzias sp.), juveniles of indeterminate fish
species and indeterminate remains of prey items. P. schlosseri females
prefer to prey on Oryzias sp. (57.8%), Uca sp. (26.7%)
and juveniles of indeterminate fish species (6.7%), while the males prefer to prey on
Uca sp. (84.6%) and Oryzias sp. (7.7%). The
indeterminate remaining prey items were 8.9% and 7.7% for respective sexes. The stable
isotope analysis showed Uca sp. and Oryzias sp. being
the main food items for P. schlosseri. The values of
δ13C and δ15N ratios also showed
differences in food preference among sexes, where females of all life stages prefer to
prey more on Oryzias sp. and little Uca sp. In contrast,
the male P. schlosseri prefer to prey only on Uca sp.
throughout their life, with the exception of juvenile male P. schlosseri,
which suggested they also consume a small amount of Oryzias sp.
Behavioural differences among the sexes and life stages were suggested to cause
differences in food selection. The size of the food items also influences food preference.
... Stable nitrogen isotopes undergo fractionation between predator and prey, leading to an enrichment in 15 N with increasing trophic level Epstein 1981, Minagawa andWada 1984), thereby denoting an animal's trophic position. The ␦ 13 C value is close to that of the diet and is used to indicate relative contributions to the diet of two different potential primary sources in a trophic network, indicating for example the aquatic vs. terrestrial, inshore vs. offshore, or pelagic vs. benthic contribution to food intake (Hobson et al. 1995, Dauby et al. 1998). Geographic differences in ␦ 13 C values can be used to indicate foraging locations of animals in marine environments (Kelly 2000, Kurle andWorthy 2002). ...
Effects of physiological processes such as gestation, lactation and nutritional stress on stable isotope ratios remain poorly understood. To determine their impact, we investigated these processes in simultaneously fasting and lactating northern elephant seals (Mirounga angustirostris). Stable carbon and nitrogen isotope values were measured in blood and milk of 10 mother-pup pairs on days 5 and 22 of lactation. As long- and short-term integrators of diet, blood cells and serum may reflect foraging data or energy reserves from late gestation and lactation, respectively. Limited changes in isotopic signatures of maternal blood over the lactating period were highlighted. Nitrogen isotope fractionation associated with mother-to-offspring transfer of nutrients was generated between mother and offspring during gestation and lactation. This fractionation was tissue and time-specific, it varied between early and late lactation from +0.6‰ to +1.3‰ in blood cells and from +1.1‰ to nonsignificant value in serum. Therefore, if pups appear to be good proxies to investigate the female trophic ecology especially for C sources, much more caution is required in using δ15N values. Further studies are also needed to better define the relative impact of fasting and lactation on the enrichment or depletion of isotopes in different tissues.
... Therefore, d 15 N can be used as an indicator of trophic levels of organisms in the food webs. On the other hand, d 13 C, rather than being a reliable indicator of the trophic level, is preferentially used to indicate relative contributions to the diet of different potential primary sources in a trophic network, indicating the aquatic vs. terrestrial, inshore vs. offshore, or pelagic vs. benthic contribution to food intake (Hobson et al., 1995;Dauby et al., 1998). By using stable isotope analyses, biomagnification of a chemical through the food web can also be estimated. ...
Trace elements (22) and stable isotope ratios ( delta super(1) super(5)N and delta super(1) super(3)C) were analyzed in marine organisms from shallow (SW) and deep-water (DW) of the East China Sea to understand biomagnification and prey source of trace elements. In the benthic marine organisms from DW, delta super(1) super(5)N values were negatively correlated with Ba, Cu, Ag, Mo, Sr, As, and Co concentrations. This may be due to the specific accumulation in lower trophic animals and/or the biodilution through the food web in DW. Relationships between delta super(1) super(5)N and concentrations of Co, Cr, Bi, and Tl in fish and Ag, Bi, V, Hg, and Tl in crustaceans showed positive correlations, suggesting that trophic position was affecting the concentrations of those elements in phyla, with higher trophic animals retaining higher concentrations than the lower trophic animals. Positive correlations between delta super(1) super(3)C and Rb were observed in marine organisms. Therefore, Rb may be a possible substitute of delta super(1) super(3)C as tracer of prey source in the East China Sea although further investigation is required.
... Among the different feeding types, the grazing invertebrates, the mollusc-feeders and (strikingly) the ctenophores are strongly 13 C-enriched. Deposit-feeders have been shown to be more enriched in δ 13 C than suspension-feeders, suggesting 2 different isotopic carbon signatures for suspended particulate matter and a mixture of suspended and sedimentary organic matter respectively (Dauby et al. 1998). Coastal or continental inputs are important in this area, leading to 13 C-enrichment of the particulate matter of the Channel and the North Sea compared to the Bay of Biscay (Dauby et al. 1994). ...
The harbour porpoise Phocoena phocoena, grey seal Halichoerus grypus, harbour seal Phoca vitulina and white-beaked dolphin Lagenorhynchus albirostris are regularly found stranded along southern North Sea coasts. Occasionally, offshore species such as the fin whale Balaenoptera physalus, the white-sided dolphin L. acutus and the sperm whale Physeter macrocephalus are also found stranded. In order to trace their diet, we measured delta(13)C and delta(15)N in their muscles as well as in 49 invertebrate and fish species collected from the southern North Sea. The delta(15)N data indicate that the harbour seal, grey seal and white-beaked dolphin occupy the highest trophic position, along with ichtyophageous fishes such as the cod Gadus morhua (mean muscle values of 18.7, 17.9, 18.8 and 19.2parts per thousand respectively). The harbour porpoise occupies a slightly lower trophic position (mean delta(15)N value of 16.2parts per thousand), reflecting a higher amount of zooplanktivorous fishes in its diet (mean delta(15)N of 14.7parts per thousand); 2 suckling harbour porpoises displayed a significant delta(15)N enrichment of 2.2parts per thousand compared to adult females. Adult females are delta(15)N-enriched compared to adult male harbour porpoises. Fin whales, sperm whales and white-sided dolphins are C-13-depleted compared to southern North Sea particulate organic matter and species, suggesting that despite regular sightings, they do not feed within the southern North Sea area.
... (DeNiro and Epstein, 1978;Hobson and Clark, 1992;Thompson et al., 1995;Smith et al., 1996). Thus, carbon-13, rather than being a reliable indicator of the trophic level, is generally used to indicate relative contributions to the diet of dierent potential primary sources in a trophic network (Rau et al., 1992;Havelange et al., 1997;Dauby et al., 1998), indicating for example the aquatic vs. terrestrial, inshore vs. oshore or pelagic vs. benthic contribution to food intake (Hobson et al., 1995;Smith et al., 1996). ...
Associations of tunas and dolphins in the wild are quite frequent events and the question arises how predators requiring similar diet in the same habitat share their environmental resources. As isotopic composition of an animal is related to that of its preys, stable isotope (C-13/C-12 and (15)/N-14) analyses were performed in three predator species from the North-east Atlantic: the striped dolphin, Stenella coeruleoalba, the common dolphin Delphinus delphis and the albacore tuna, Thunnus alalunga, and compared to their previously described stomach content. Heavy metals (Cd, Zn, Cu and Fe) are mainly transferred through the diet and so, have been determined in the tissues of the animals. Tuna muscles display higher delta(15)N than in common and striped dolphins (mean: 11.4, s. 10.3 parts per thousand and 10.4 parts per thousand respectively) which reflects their higher trophic level nutrition. Higher delta(13)C are found in common (-18.4 parts per thousand) and striped dolphin (-18.1 parts per thousand) muscles than in albacore tuna (-19.3 parts per thousand) probably in relation with its migratory pattern. The most striking feature is the presence of two levels of cadmium concentrations in the livers of the tunas (32 mg kg(-1) dry weight (DW) vs. 5 mg kg(-1) DW), These two groups also differ by their iron concentrations and their delta(15)N and delta(13)C liver values. These results suggest that in the Biscay Bay, tunas occupy two different ecological niches probably based on different squid inputs in their diet.
... Variability in the isotopic signature of seagrass itself may provide an alternative explanation for the present observations. Moreton Bay is temporally and spatially variable with respect to many factors that affect 13 C values, such as carbon source, irradiance levels, water temperature, water movement and leaf age (Grice et al., 1996;Dauby et al., 1998). These factors may result in spatial variability in carbon values. ...
The stable isotope values for a range of size classes of Hyporhamphus regularis ardelio from Moreton Bay, south-east Australia were determined. There was a positive linear relationship between 613 C and standard length (L-s) (delta(13)C = 0.034 Ls - 16-23; r(2) = 0.78). delta(13)C ranged from -8.48 to - 17.29 parts per thousand with the smallest size class (50 mm Ls) being on average 1.04 parts per thousand enriched with respect to that of zooplankton (Temora turbinata) and 7.97 parts per thousand depleted compared to Zostera capricorni. delta(13)C was positively correlated with Ls (P<0.01) (more enriched with increasing Ls) with those fish of the largest size class (225mm L-S) being 9.86 and 0-84 parts per thousand enriched than T turbinata and Z. capricorni, respectively. There was no detectable trend in delta(15) N values with Ls (P > 0.0 1) with delta(15) N, ranging from 9.18 to 11.00 parts per thousand. Fish of all size classes were on average 2.32 and 7.63 parts per thousand more enriched than zooplankton and seagrass, respectively. Carbon isotope data indicate that H. r. ardelio commence life as carnivores and change to a diet in which seagrass is the primary carbon source. The dependence on animal matter, however, is always present. Due to the low percentage of nitrogen in Z. capricorni (2.5%) compared to zooplankton (9.1%) it appears that nitrogen from zooplankton is necessary throughout their life history with the carbon requirements for these fish coming chiefly from Z. capricorni. (c) 2005 The Fisheries Society of the British Isles.
... The isotopic composition of an animalÕs tissue therefore reflects that of its prey with a slight trophic enrichment in 13 C and 15 N of about 1& and 3.4&, respectively (De Niro & Epstein, 1978Peterson & Fry, 1987). d 15 N ratios are often used as a predictor of relative trophic level (Pinnegar, Jennings, OÕBrien, & Polunin, 2002;Post, 2002;Vander Zanden, Cabana, & Rasmussen, 1997) whereas d 13 C values can be useful in evaluating sources of primary production in marine systems : d 13 C values are typically higher (less negative) in inshore/ benthic food webs and more negative in plankton-based systems (Dauby, Khomsi, & Bouquegneau, 1998;Hobson, 1999;Hobson, Ambrose, & Renaud, 1995). Stable isotope studies provide some advantages over stomach content analysis. ...
In order to trace their feeding habits, stable carbon and nitrogen isotope ratios (delta15N and delta13C), as well as trace metal concentrations (Zn, Cd, Fe, Cu, Se and Hg) were analysed in the tissues of five commercial shark species from the Celtic Sea: the tope shark Galeorhinus galeus, the black-mouthed catshark Galeus melastomus, the starry smooth hound Mustelus asterias, the spiny dogfish Squalus acanthias and the lesser-spotted dogfish Scyliorhinus canicula. Our results were compared to previously described stomach contents and isotopic composition of potential preys. Isotopic ratio delta15N suggested that tope sharks fed at a higher trophic level (16.7 per thousand in the muscle) than the other species, reflecting its piscivorous diet. The lower values of spiny dogfish (11.6 per thousand in the muscle) might be explained, amongst other things, by either its migratory behaviour or its preference for preys from lower trophic levels. Cd and Hg were correlated with isotopic ratios delta13C and delta15N, and were shown to be diet-related whereas Zn, Fe and Cu seemed much more linked to species-specific metabolism. Although this multidisciplinary approach is revealed as a useful tool for the study of shark ecology, the lack of known trophic fractionation suggests that isotopic data be compared to traditional diet analyses.
... nitrogen-15 typically shows a stepwise increase with trophic level within a food chain (Cabana & Rasmussen, 1994;Hobson & Welch, 1992;Thompson, Furness, & Lewis, 1995). The carbon-13 value is close to that of the diet and is preferentially used to indicate relative contributions to the diet of different potential primary sources in a trophic network, indicating for example the aquatic vs. terrestrial, inshore vs. offshore, or pelagic vs. benthic contribution to food intake (Dauby, Khomsi, & Bouquegneau, 1998;Hobson, Ambrose, & Renaud, 1995;Smith et al., 1996). When using stable isotopes to assess diets of animals feeding at or near the top of the trophic web on several prey items, many of which may have similar isotopic signatures, clear distinctions about the diet are more difficult to determine. ...
The relationship between trophic position through delta13C and delta15N and trace metal concentrations (Zn, Cd, Cu and Hg) was investigated in the tissues of six marine mammal species from the Northeast Atlantic: striped dolphin Stenella coeruleoalba, common dolphin, Delphinus delphis, Atlantic white-sided dolphin Lagenorhynchus acutus, harbour porpoise Phocoena phocoena, white beaked-dolphin Lagenorhynchus albirostris, grey seal Halichoerus grypus stranded on French Channel and Irish coasts. White-beaked dolphins, harbour porpoises, white-sided dolphins, common and striped dolphins display the same relative and decreasing trophic position, as measured by delta15N values, along both the Irish and French channel coasts, reflecting conservative trophic habits between these two places. Hepatic and renal Cd concentrations were significantly correlated to muscle delta13C and delta15N values while Hg, Zn and Cu did not. These results suggest that Cd accumulation is partly linked to the diet while other factors such as age or body condition might explain Hg, Zn or Cu variability in marine mammals. Combined stable isotope and trace metal analyses appear to be useful tools for the study of marine mammal ecology.
This study aims at describing and interpreting concentrations of arsenic (As), mercury (Hg) and vanadium (V) in seven species of fish, three species of shellfish, one species of crab and two species of shrimp from the typical estuary-bay ecosystem. Arsenic, Hg and V differed among species, and the highest As, Hg and V were observed in shellfish. The stable nitrogen (δ(15)N) and carbon (δ(13)C) isotopes were determined to investigate the trophic interactions between fluctuating environment and aquatic species. Arsenic concentrations in samples were found negatively correlated with δ(15)N, implying biodilution effect of As through the food web, while Hg concentrations in samples were positively correlated with δ(15)N, indicating their biomagnification effect. The estimated daily intake values of Hg and V in this study were all below the oral reference dose. However, elevated As intakes of some aquatic organisms suggested a potential risk for frequent consumers.
Trace elements (22) and stable isotope ratios (δ15N and δ13C) were analyzed in marine organisms from shallow (SW) and deep-water (DW) of the East China Sea to understand biomagnification and prey source of trace elements. In the benthic marine organisms from DW, δ15N values were negatively correlated with Ba, Cu, Ag, Mo, Sr, As, and Co concentrations. This may be due to the specific accumulation in lower trophic animals and/or the biodilution through the food web in DW. Relationships between δ15N and concentrations of Co, Cr, Bi, and Tl in fish and Ag, Bi, V, Hg, and Tl in crustaceans showed positive correlations, suggesting that trophic position was affecting the concentrations of those elements in phyla, with higher trophic animals retaining higher concentrations than the lower trophic animals. Positive correlations between δ13C and Rb were observed in marine organisms. Therefore, Rb may be a possible substitute of δ13C as tracer of prey source in the East China Sea although further investigation is required.
The distributions of natural stable isotopes of carbon and nitrogen have been extensively investigated in a variety of primary producers such as vascular plants and algae to provide baseline information of the trophic structure of various ecosystems (Currin et al . 1995). However, there have been few attempts to use this ecological approach to characterize lichens which frequently constitute the principal vegetation in many rocky habitats (Gilbert 2000). Rocky sea shores are characterized by a vertical zonation of biological communities which fall into three major zones: supralittoral, mediolittoral and infralittoral. The supralittoral zone is rarely submerged and is typically covered by a vegetation of lichens and cyanobacteria (Lewis 1964; Russel 1991).
Rocky shores in the North Atlantic are known for their zonation patterns of both algae and animals, which can be expected to greatly affect food availability to consumers at different height levels on the shore. We tested the hypothesis that consumers would feed on the most abundant suitable food source in their surroundings. In total 36 species/taxa of common primary producers and consumers were sampled for stable isotope analyses from a sheltered fucoid shore at Hvassahraun in south-western Iceland. A selection of these species was also collected seasonally and from different height levels. Feeding experiments, field observations and gut analyses were also conducted. Our results were in good overall agreement with pre-existing knowledge of trophic relationships in the rocky intertidal. Consumers often appeared to be assimilating carbon and nitrogen from the most common diet in their immediate surroundings. The predator Nucella lapillus was thus feeding on different prey at different height levels in accordance with different densities of prey species. When tested in the laboratory, individuals taken from low on the shore would ignore the gastropod Littorina obtusata, uncommon at that height level, even when starved, while individuals from mid-shore readily ate the gastropod. This indicated that some kind of learned behaviour was involved. There were, however, important exceptions, most noteworthy the relatively small contribution to herbivores, both slow moving (the gastropod L. obtusata) and fast moving (the isopod Idotea granulosa and the amphipod Gammarus obtusatus) of the dominant alga at this site, Ascophyllum nodosum. The recent colonizer Fucus serratus seemed to be favoured. Selective feeding was indicated both by isotope signatures as well as by results of feeding experiments. Seasonal migrations of both slow and fast moving species could partly explain patterns observed.
There have been several studies where the isotopic composition of organisms has been determined seasonally, but fewer have examined separate organs. In this context, separate organs (e.g. gonad, digestive gland and muscle) of a suspension-feeder, the scallop Pecten maximus, were used to assess seasonal changes of both stable isotopes and biochemical components. Our study used multiple indicators [stable carbon and nitrogen isotope ratios, biochemical components and seston chlorophyll-a (chl a)] to track nutritive activity and energy allocation in P. maximus from the Bay of Brest (France). In addition to seasonal variation in the isotopic composition of P. maximus tissues, we found strong differences in the mean isotopic signatures of different organs. This has serious implications for interpretation of animal diets and potential use in animal physiology. Furthermore, we present evidence that seasonal variations of metabolism will cause changes in the isotopic composition not related to changes in the diet. Interpretation of isotopic data may require consideration of values from several separate organs. Finally, δ15N appears powerful to track metabolite fates in the scallop P. maximus.
The origin of carbon substrates used by in situ sedimentary bacterial communities was investigated in an intertidal mangrove ecosystem and in adjacent seagrass beds in Gazi bay (Kenya) by ?13C analysis of bacteria-specific PLFA (phospholipid fatty acids) and bulk organic carbon. Export of mangrove-derived organic matter to the adjacent seagrass-covered bay was evident from sedimentary total organic carbon (TOC) and ?13CTOC data. PLFA ?13C data indicate that the substrate used by bacterial communities varied strongly and that exported mangrove carbon was a significant source for bacteria in the adjacent seagrass beds. Within the intertidal mangrove forest, bacterial PLFA at the surface layer (0-1 cm) typically showed more enriched ?13C values than deeper (up to 10 cm) sediment layers, suggesting a contribution from microphytobenthos and/or inwelled seagrass material.
Under the assumption that seagrasses and mangroves are the dominant potential end-members, the estimated contribution of mangrove-derived carbon to benthic mineralization in the seagrass beds (16-74%) corresponds fairly well to the estimated contribution of mangrove C to the sedimentary organic matter pool (21-71%) across different seagrass sites. Based on these results and a compilation of literature data, we suggest that allochtonous carbon trapped in seagrass beds may often represent a significant fraction of the substrate for benthic mineralization - both in cases where seagrass C dominates the sediment TOC pool and in cases where external inputs are significant. Hence, it is likely that community respiration data systematically overestimate the role of mineralization in the overall seagrass C budget.
The study was performed in the English Channel, the Celtic Sea, and the Southern Bight of the North Sea in June and October 1991. SW to NE gradients of suspended matter mass and of lithogenic components (Ti and Al) linked to riverine inputs and to depth shallowing, are observed; organic carbon and nitrogen display an opposite distribution pattern and reach a maximum in the Biscay oceanic waters. Cu, Pb and Zn concentrations are highest near industrialized areas and large estuaries, showing the importance of river inputs. In contrast, Cd, Cu and Cr concentrations are markedly elevated in organic-rich suspended matter from waters in which suspended matter loadings are low, suggesting a significant biological uptake. Finally, 13C/12C analyses reveal the relative importance of coastal or continental inputs in the north-eastern Channel and in the North Sea. -from Authors
1. The stable isotopes of nitrogen (deltaN-15) and carbon (deltaC-13) were analysed in 22 species of marine birds from coastal waters of the northeast Pacific Ocean. Analyses confirm that stable nitrogen isotopes can predict seabird trophic positions. 2. Based on deltaN-15 analyses, seabird trophic-level inferences generally agree with those of conventional dietary studies, but suggest that lower trophic-level organisms are more important to several seabirds than was recognized previously. 3. Stable-carbon isotope analysis may be a good indicator of inshore vs. offshore feeding preference. 4. In general, stable-isotope analysis to determine trophic level offers many advantages over conventional dietary approaches since trophic inferences are based on time-integrated estimates of assimilated and not just ingested foods, and isotopic abundance represents a continuous variable that is amenable to statistical analysis.
Notes the considerable regional differences in temperature, tidal fluctuation, ice scouring, wave exposure and nutrient enrichment along the predominantly rocky coastline between Cape Cod/Nantucket Shoals and Newfoundland. Species diversity is generally low compared with the NE Atlantic, but patterns of community structure and zonation are consistent with other north temperate regions, as are the mechanisms controlling them. Major sections describe: the abiotic environment; biogeography; community patterns of open coastal rocky ecosystems - littoral and sublittoral zones; organisation (largely zonation) of the same, including the role of inshore fishes and avian predators; and primary productivity of benthic communities. Appendices summarise the geography, geology, circulation patterns, tides, wave action/upwelling, temperatures, ice, salinity and nutrients of the Gulf of Maine, the Bay of Fundy, the Atlantic coast of Nova Scotia, Gulf of St Lawrence, and Newfoundland. -P.J.Jarvis
Emphasises the place of zonation in the vertical arrangement of littoral species and communities. Discussion follows on the characteristics of the supralittoral zone (including comments on the lichens, cyanobacteria, other algae, littorinid snails and other fauna); the eulittoral zone (algae, benthic plankton feeders, herbivores, species interactions); and the sublittoral zone (algae, competition and herbivory). Possible causes of zonation are mooted: while critical tide levels are important, other aspects of tidal activity must be considered, and the role of interspecific competition and predator-prey interactions must be added to discussion of the role of physical and chemical factors. -P.J.Jarvis
Marine algae have interesting characteristics relating to the transport and fixation of inorganic carbon and this chapter summarizes some of the recent findings. Researchers' understanding of the pathway of carbon metabolism in marine algae has been aided by the use of carbon isotopes. In 1952, Steeman Nielsen introduced the “C-14 technique” for measuring primary productivity in aquatic systems. This technique has its problems and many of the problems and uncertainties can be attributed to the fact that measurements are made in the absence of precise information on the transport and subsequent assimilation of inorganic carbon. Additionally, the use of carbon isotopes has helped elucidate the pathway of carbon assimilation in a number of marine algae and has shown that the photosynthetic carbon reduction cycle (PCRC) is operational with ribulose-1,5-bisphosphate carboxylase/oxygenase (RUBISCO) as the carboxylase. However, other early labeled products of photosynthesis, in particular C4 acids, have given rise to the notion that certain marine algae may have a C4 type of photosynthesis similar to that in specialized angiosperms. During recent years, certain advances have been made and various enzyme activities have been demonstrated in extracts of marine algae. Furthermore, certain enzymes have been purified but the number so far purified is extremely low. For these reasons, the contribution to the basic understanding of the processes involved in plant carbon assimilation by marine algae is comparatively small. The chapter shows some of the properties of the inorganic carbon system in seawater that are relevant to the assimilation of inorganic carbon by marine algae and cyanobacteria.
Whatever the underlying cause(s), our observations further substantiate the existence of small but progressive increases in animal tissue ¹³C/¹²C with increasing trophic level. Such a relationship has significant implications for the use of stable carbon isotope natural abundance in animal tissues or remains, in order to interpret the tropic structure and food base of past as well as present-day animal communities. The delta¹³C of the marine animal tissues analyzed ranged from -20.6 to -15.8%. The macro-fauna from the eastern tropical Pacific Ocean had higher isotope values than the net plankton collected from the same area. The average increases in delta¹³C per trophic level were 0.73 and 1.38% for the California coastal waters and for the eastern tropical Pacific, respectively. These isotopic increases approximate closely those previously reported to occur within single trophic level steps.
Additional data is presented to show that plants of genera which are known to follow the C4-dicarboxylic acid pathway in photosynthetic carbon dioxide fixation have δ 13C values in the −10 to −20‰ range. Plants which follow the Calvin cycle in photosynthesis have δ 13C values of −22 to −33‰. Plants of families which show Crassulacean acid metabolism also have many examples enriched in 13C.
The concentrations of dissolved CO2 dissolved oxygen and chlorophyll have been determined in the surface seawater of the English Channel and of the Southern Bight of the North Sea in June 1992, April–May 1993 and September–October 1993. The partial pressure of CO2(PCO2) displays large spatial and temporal variations ranging from 100 ppm up to 670 ppm. The relationship between seawater pCO2 and chlorophyll distribution is discussed and compared with data recently obtained in the North Atlantic by A. J. Watson, C. Robinson, J. E. Robertson, P. J. le B. Williams and J. R. Fasham (1991)Nature, 350, 50–53. Air-sea CO2 fluxes have been calculated from wind speed and pCO2 data and, due to the combined effect of both of those parameters, the flux can be as high as about 150 mmol m−2 d−1. This implies that shelves could play an appreciable role in the global C budget. Further extended C02 level measurements should be made to improve flux estimations for the coastal zone on a global basis.
Seagrasses have a wide range of δ 13C values. For 47 species from 12 genera, the values were within the range of −3.0 to −19.0%0. Only two species, Halophila tricostata Greenway and Halophila beccarii Aschers., had lower values, of −20.8 and −23.8%0, respectively. Among the 12 genera, Syringodium and Enhalus had the highest mean values and Phyllospadix and Amphibolis had the lowest mean values. The δ 13C values for most seagrasses are within the range usually associated with C4 metabolism, but the status of seagrasses as members of this photosynthetic group has not been confirmed by morphological and physiological studies. The high variability in δ 13C values may reflect a variable photosynthetic metabolism.
The stable carbon isotope composition of the biota, soils and tidal water particulate material was surveyed in a salt marsh near Sapelo Island, Georgia. Samples were taken in six intertidal zones: bare creekbank, Spartina alterniflora low marsh, S. alterniflora high marsh, Salicornia virginica high marsh, sand flat and high marsh mixed vegetation stands. The marsh plants analyzed segregated into three groups with respect to their ratios. The grasses, including S. alterniflora, had δ13C values of −12.3 to −13.6‰; the other vascular plants had values between −22.8 and −26.0‰; and benthic diatoms had intermediate values of −16.2 to −17.9‰. Marsh soils and to some extent the invertebrate fauna reflected the carbon isotope composition of the major primary producer species in the various zones.Five samples of the particulate organic carbon (POC) in marsh tidal water showed δ13C values of −19.8 to − 22.8‰. These values fell within the range of δ13C found for offshore POC, most of which is presumed to originate from phytoplankton photosynthesis. This result requires a re-examination of the assumption that the bulk of detrital carbon in Georgia estuaries is derived from S. alterniflora production.
A widely accepted view of intertidal community organizatiton in the NW Atlantic proposes that fucoid vegetation is maintained by the actions of predators which remove species competitively superior toFucus species. Herbivory is an important component of these predatory interactions, but has been studied largely with reference to the interaction betweenF. vesiculosus andLittorina littorea. There are many species of fucoids and herbivorous invertebrates on the shores of the NW Atlantic and this paper reports field and laboratory experiments performed in 1987 (in or near Halifax, Canada) on the effects of grazing by three species ofLittorina on adults and juveniles of four species ofFucus. In laboratory experiments, portions ofFucus species were presented singly (no choice) or together (multiple choice) to single species ofLittorina. AdultF. distichus was grazed to only a small extent.F. evanescens andF. vesiculosus adult tissues were heavily grazed in most laboratory experiments.F. spiralis adults were heavily grazed in no choice experiments, but were grazed only slightly in multiple choice tests. When adult fucoid tissues were exposed to a mixed suite of grazers in the field, onlyF. vesiculosus was grazed heavily. Tests done on adult tissues showed clearly thatFucus species are highly variable in their vunerability to grazers. Moreover, we found variability among periwinkle species in grazing rates on adultFucus. We also found a great disparity in the feeding rates of different periwinkle species on juveniles ofFucus. Therefore, it is not possible to extrapolate from a single periwinkle species/single fucoid species interaction when attempting to identify vegetation structuring processes.
1. Une prospection biologique de l'Archipel de Glénan a été réalisée en plongée par les auteurs jusqu'à 60 m de profondeur. Quatre peuplements distincts ont été mis en évidence et intégrés au système général d'étagement défini lors du Colloque de Gênes (Peres &Molinier 1957). La comparaison est faite avec les observations régionales effectuées en Manche (Cabioch 1968) et en Atlantique (Glemarec 1971). 2. Les deux premiers peuplements (3 et 4) constituent des horizons de l'étage infralittoral: ils sont caractérisés par des Algues, les Laminaires. Les deux derniers peuplements (5 et 7) constituent des horizons de l'étage circalittoral: ils sont caractérisés par un certain nombre d'espèces animales de forme arbusculaire. 3. L'inclinaison de la paroi rocheuse conditionnant l'éclairement, les espèces photophiles présentent une extension maximale sur les surfaces horizontales.Laminaria digitata (Linné)Lamouroux s'étend de + 1 à − 2,5 m sur les surfaces horizontales et de + 1 à − 1,5 m sur les surfaces verticales;L. hyperborea (Gunner)Foslie de 0 à − 26 m sur les surfaces horizontales et de 0 à − 10 m sur les surfaces verticales. 6. L'horizon à Axinellidae apparaît vers − 30 m. Il est caractérisé par la présence d'éponges dressées, en horizontale, et par la présence de Brachiopodes, en verticale. 7. Les Algues dressées disparaissent entre − 40 et − 47 m. 8. L'horizon àDendrophyllia cornigera (Lamarck) s'observe à − 55 − 60 m sur les surfaces horizontales (limite d'utilisation du scaphandre autonome).
The ratio of stable carbon isotopes (13C) in plants and animals from Malaysian mangrove swamps, coastal inlets, and offshore waters was determined. Vascular plants of the swamps were isotopically distinct ( xs.d.=-27.11.2) from plankton (-21.00.3) and other algae (-18.72.2). Animals from the swamps (-20.94.1) and inlets (-19.82.5) had a wide range of isotope ratios (-28.6 to-15.4), indicating consumption of both mangrove and algal carbon. Several commercially important species of bivalves, shrimp, crabs, and fish obtained carbon from mangrove trees. Mangrove carbon was carried offshore as detritus and was isotopically distinguishable in suspended particulate matter and sediments. Animals collected from 2 to 18 km offshore, however, showed no isotopic evidence of mangrove carbon assimilation, with ratios (-16.51.1, range-19.1 to-13.1) virtually identical to those reported for similar animals from other plankton-based ecosystems. Within groups of animals, isotope ratios reflected intergencric and interspecific differences in feeding and trophic position. In particular, there was a trend to less negative ratios with increasing trophic level.
13C undergoes modes biomagnification in the food web, apparently as a result of being respired at a slower specific rate than12C. The degree of13C enrichment at each trophic level is related to the fraction of assimilated carbon which is respired. Qualitative and semi-quantitative aspects of ecosystem carbon cycling can therefore be deduced from13C enrichments, provided that isotope enrichments arising from other causes are accounted for. Most important among these is lipid storage, which enriches animals in12C. This complication can be handled in various ways, here it was done by normalizing13C:12C ratios to a constant lipid content. Remaining variations in13C:12C ratio presumably result mainly from respiratory isotope fractionation. The Bering Sea ecosystem provided a test for this procedure. Our results illustrate certain aspects of food web structure and suggest varous functional aspects.
Carbon, sulfur, and nitrogen stable isotope ratio techniques were used in 1989 and 1990 to evaluate the relative importance of algae and of mangrove detritus in the nutrition of two penaeid prawn species on the west coast of Peninsular Malaysia. Mangrove detritus was found to contribute to the nutrition of juvenile Penaeus merguiensis de Man living within tidal creeks, but not to adult P. merguiensis and juvenile and adult Parapenaeopsis sculptilis (Heller) captured offshore. Results from radiotracer feeding studies, with refractory 14C mangrove lignocellulose as the food source, indicated that juvenile P. merguiensis from tidal creeks assimilated mangrove carbon with an efficiency of 13.4%. This did not differ significantly (P=0.05) from the assimilation efficiencies of juvenile and adult P. sculptilis living offshore (10.0 and 10.9%, respectively); these values were significantly higher (PP. merguiensis (2.1%). Thus, the differential contribution of mangrove material to the nutrition of prawns in the tidal creeks and offshore was not related to differences in the prawn's ability to utilize detritus. Instead, our analysis of C stable isotopes in sediments indicated that mangrove detritus was generally more abundant within the tidal creeks than offshore. Juvenile prawns in the tidal creeks may also utilize mangrove material indirectly by feeding on small detritivorous invertebrates. Stable isotope analyses suggest that benthic microalgae constitute the other major dietary component for prawns living in tidal creeks. Prawns offshore were utilizing mainly phytoplankton-based material.
The C:N:P ratios and stable C (δ13C) and H(δD) isotopic composition were studied in two species of marine benthic algae, Fucus virsoides J.Ag. and Ulva rigida C.Ag., collected from the Gulf of Trieste, Northern Adriatic. The mean C:N:P ratio (atomic) of Fucus virsoides was 804:58:1 and that of Ulva rigida was 579:75:1.The δ13C values of Fucus virsoides ranged between − 14.18 and − 17.72%. and between − 15.7 and − 19.45%. in Ulva rigida. The δD values ranged between − 68.53 and − 104.7%. in Fucus virsoides and between − 109.2 and − 150.3%. in Ulva rigida. Based on δ13C and δD Ulva rigida could be subdivided into two distinct groups (Ulva A and Ulva B). The variations in δ13C and δD were probably caused by different sources of inorganic carbon assimilated during photosynthesis, or by various reactions occurring prior to CO2 fixation in the cell.
The influence of diet on the distribution of carbon isotopes in animals was investigated by analyzing animals grown in the laboratory on diets of constant carbon isotopic composition.
The isotopic composition of the whole body of an animal reflects the isotopic composition of its diet, but the animal is on average enriched in δ^(13)C by about 1‰ relative to the diet. In three of the four cases examined, the ^(13)C enrichment of the whole body relative to the diet is balanced by a ^(13)C depletion of the respired CO_2. The isotopic relationships between the whole bodies of animals and their diets are similar for different species raised on the same diet and for the same species raised on different diets. However, the δ^(13)C values of whole bodies of individuals of a species raised on the same diet may differ by up to 2‰. The relationship between the ^(13)C/^(12)C ratio of a tissue and the ^(13)C/^(12)C ratio of the diet depends both on the type of tissue and on the nature of the diet. Many of the isotopic relationships among the major biochemical fractions, namely the lipid, carbohydrate and protein fractions, are qualitatively preserved as diet carbon is incorporated into the animal. However, the difference between the δ^(13)C values of a biochemical fraction in an animal and in its diet may be as large as 3‰. The δ^(13)C values of the biochemical components collagen, chitin and the insoluble organic fraction of shells, all of which are often preserved in fossil material, are related to the isotopic composition of the diet.
These results indicate that it will be possible to perform dietary analysis based on the determination of the ^(13)C/^(12)C ratio of animal carbon. Analysis of the total animal carbon will in most cases provide a better measure of diet than the analysis of individual tissues, biochemical fractions, or biochemical components. The limits of accuracy of this method will generally restrict its application to situations in which the diet is derived from sources with relatively large differences in their δ^(13)C values, such as terrestrial vs aquatic organisms or C_3 vs C_4 plants. The method should be applicable to fossil as well as to living material.
Stable isotopes of sulfur and carbon were used to trace the dominant flows of organic matter from producers to macroconsumers in Great Sippewissett Salt Marsh on Cape Cod. Spartina alterniflora and sulfur-oxidizing bacteria assimilate isotopically light sulfides produced via sulfate reduction, and this light sulfur was detected in consumers. In contrast, phytoplankton and upland plants assimilate isotopically heavier SO42- with little or no fractionation. A dual-isotope approach using both delta 13C and delta 14S showed that Ilyanassa obsoleta and Fundulus heteroclitus depend very heavily on Spartina detritus, while filter feeders such as Crassostrea virginica and Geukensia demissa depend on a mixture of plankton and Spartina detritus. Spartina detritus and plankton were both much more important as organic matter derived from terrestrial inputs.-Authors