Variation in the mobilization of mercury into Black-winged Stilt Himantopus himantopus chicks in coastal saltpans,as revealed by stable isotopes

Causes of variation in mobilization of mercury into Black-winged Stilt Himantopus himantopus chicks were studied through analysis of stable isotope ratios of carbon and nitrogen. Blood and breast feathers were collected from chicks in coastal saltpans during successive breeding seasons. Detritus samples and potential prey (macroinvertebrates) were also collected. Total mercury concentrations and stable isotope signatures were measured using atomic absorption spectroscopy and isotope ratio mass spectrometry respectively. Mercury levels in Chironomidae, Corixidae and Hydrophilidae correlated with mercury levels in chick feathers. Differences of δ¹⁵N signatures between macroinvertebrate groups indicated that they belong to different trophic levels. δ¹⁵N signatures of invertebrates correlated with mercury levels in invertebrates and chicks, but not with δ¹⁵N signatures in chicks. Between-group and between-site differences of δ¹⁵N signatures and mercury levels in invertebrates suggested that they contribute differently to mercury mobilization into chicks, and their relative contribution depends on prey availability in each site. Inter-site differences in the biomagnification factor reinforced that idea. δ¹³C signatures in invertebrates marked a larger range of carbon sources than just detritus. Variation of water inflow regime and prey availability may cause between-group and between-site differences of δ¹³C signatures in prey. Discrepancies between feather and blood for δ¹³C signatures in Praias-Sado and Vaia suggested that temporal variation of prey availability may be the main factor affecting mercury mobilization into chicks in both those cases, since their water inflow regimes are the same. The lowest levels of δ¹³C signatures in Vau suggested that water inflow regime may be the main factor in this case, since no discrepancy existed in δ¹³C signatures between blood and feather.     

Stable isotope ratios in Cape gannets around the southern coasts of Africa reveal penetration of biogeographic patterns in oceanic signatures

The southern coasts of Africa are influenced by two major oceanic currents, leading to biogeographic patterns in inshore and offshore species assemblages, and in the stable isotope signatures of suspended particulate matter and filter-feeding mussels. We used the stable isotope ratios of carbon (¹³C/¹²C) and nitrogen (¹⁵N/¹⁴N) from the blood and feathers of adult and chick Cape gannets (Morus capensis) to investigate whether the geographic differences observed at the lower levels in the marine communities are deep penetrating effects that reach top predators. Additionally, we evaluated whether trophic segregation occurs between adult and reared chick gannets, and whether a shift to wintering habitat occurs in adults. The study was conducted during the 2006 breeding season on Bird Island in the Agulhas system, and on Malgas and Ichaboe Islands, in the south and north Benguela respectively. Our results showed significant differences in the isotope ratios of members of different colonies, but no intra-colony differences between tissues or age groups. These results indicate that there is neither age-related nor temporal segregation in the diet of members of the same colony. Feather isotopic values suggest that adults remain all year round in the same habitats, and do not undertake long migration after reproduction. Since all gannets tend to target similar prey, we attributed among-colony differences in isotope signatures mostly to the oceanic conditions experienced by the main prey of birds rather than substantial differences in diet composition. Overall, isotopic signatures segregate the two current systems, with depleted carbon values in the Agulhas and enriched nitrogen values in the upwelled waters of the Benguela. Within the Benguela birds from Ichaboe in the north had higher δ¹⁵N values than those from Malgas in the south, which we attributed to differences in the functioning of the upwelling cells in the vicinity of the two colonies. Finally, slight variation in the proportion of main prey and discards from fisheries may contribute to the variation in the stable-isotope signatures between colonies in the Benguela.     

Foraging ecology of an endemic shorebird, the African Black Oystercatcher (Haematopus moquini) on the south–east coast of South Africa

We investigated small–medium (1–300 km) scale variation in the foraging ecology of the African Black Oystercatcher during its breeding season, using traditional diet analysis coupled with carbon and nitrogen stable isotope analysis. Fieldwork was conducted between January and March 2006 and 2007, on rocky shores on the south–east coast of South Africa at East London, Kenton and Port Elizabeth. Middens of shelled prey left by adults feeding their chicks were collected from five territories and the abundances of the collected prey on the foraging areas were estimated using quadrats. Blood samples from 45 birds (16 females, 10 males and 19 chicks) and tissues from the predominant prey species on the territory of each breeding pair were collected for isotope analysis. The Manly–Chesson selectivity index revealed that adults feed their chicks preferentially with the limpet Scutellastra cochlear and the Mediterranean mussel Mytilus galloprovincialis, if available. A slight enrichment in the ¹⁵N stable-carbon isotope signature was observed towards the west in both prey and oystercatchers. Differences in isotope signatures between males and females from the same breeding pair indicate sex-related differences in the diet. Both had signatures indicating a mixed diet, but with males exhibiting a signature closer to that of limpets and females closer to that of mussels. In the single case where mussels were rare on the feeding territory, the two members of a pair showed carbon signatures which were identical and very similar to that of limpets. These results indicate dietary partitioning between genders in breeding pairs.     

Intraspecific diet shift in Talitrus saltator inhabiting exposed sandy beaches

Talitrid amphipods are the most abundant herbivores on exposed sandy beaches. Despite their important role as trophic intermediates between macrophytes and higher levels (i.e. insect and bird) of beach food webs, very little information is available on their feeding patterns. The main aim of this study was to investigate intraspecific differences in the feeding behaviour of Talitrus saltator. We tested the hypotheses that: (1) adult females and males showed different isotope signatures and therefore relied on different sources of food; and (2) patterns of variation of isotope signatures of juveniles differed from those of adult specimens, evidencing a diet shift during the development. We used stable isotope signatures and tested for differences upon the level on the shore, times of the year and beaches experiencing similar morpho-dynamic and environmental conditions. Finally, we investigated the trophic significance of macrophyte detritus in the diet of males, females and juveniles. Results showed that adult males had a more variable diet than females and juveniles (inferred from δ¹³C and δ¹⁵N values). Dual-isotope graphs suggested that Sargassum muticum and Cystoseira baccata wrack could be among the main food sources for both juvenile and adult stage.     

Field evidence of differential food utilization of phytal harpacticoids collected from Fucus serratus indicated by δC and δN stable isotopes

The present study is the first to compare trophic relationships of several co-occurring phytal harpacticoid species, in their natural habitat, using both δ¹³C and δ¹⁵N signatures. Three phytal harpacticoid species/taxa (Zaus spinatus, Tisbe spp., and Parathalestris cf. intermedia) all collected from the alga Fucus serratus, at different times of the year, were analyzed. The results indicated that the harpacticoids were utilizing food sources differently. Specific food sources of the three species/taxa could not be accurately pinpointed, but there were strong indications that F. serratus and fragments from it did contribute significantly to the diet of P. cf. intermedia and Tisbe spp. Both of these harpacticoid species overlapped in δ¹³C and δ¹⁵N values with some of the macrofaunal species, collected from the same site in Hvassahraun, Iceland, while no overlap was seen for Z. spinatus. The signatures for Z. spinatus indicated that its food sources changed seasonally.     

Effect of body size and body mass on δC and δN in coastal fishes and cephalopods

Carbon and nitrogen isotopes have been widely used in the investigation of trophic relations, energy pathways, trophic levels and migrations, under the assumption that δ¹³C is independent of body size and that variation in δ¹⁵N occurs exclusively due to ontogenetic changes in diet and not body size increase per se. However, several studies have shown that these assumptions are uncertain. Data from food-webs containing an important number of species lack theoretical support on these assumptions because very few species have been tested for δ¹³C and δ¹⁵N variation in captivity. However, if sampling comprises a wide range of body sizes from various species, the variation of δ¹³C and δ¹⁵N with body size can be investigated. While correlation between body size and δ¹³C and δ¹⁵N can be due to ontogenetic diet shifts, stability in such values throughout the size spectrum can be considered an indication that δ¹³C and δ¹⁵N in muscle tissues of such species is independent of body size within that size range, and thus the basic assumptions can be applied in the interpretation of such food webs. The present study investigated the variation in muscle δ¹³C and δ¹⁵N with body size and body mass of coastal fishes and cephalopods. It was concluded that muscle δ¹³C and δ¹⁵N did not vary with body size or mass for all bony fishes with only one exception, the dragonet Callionymus lyra. Muscle δ¹³C and δ¹⁵N also did not vary with body size or mass in cartilaginous fishes and cephalopods, meaning that body size/mass per se have no effect on δ¹³C or δ¹⁵N, for most species analysed and within the size ranges sampled. The assumption that δ¹³C is independent of body size and that variation in δ¹⁵N is not affected by body size increase per se was upheld for most organisms and can be applied to the coastal food web studied taking into account that C. lyra is an exception.     

Trophic ecology of European sardine Sardina pilchardus and European anchovy Engraulis encrasicolus in the Bay of Biscay (north-east Atlantic) inferred from δ13C and δ15N values of fish and identified mesozooplanktonic organisms

European sardine (Sardina pilchardus) and European anchovy (Engraulis encrasicolus) are two species of economical and ecological significance in the Bay of Biscay (north-east Atlantic). However, the trophic ecology of both species is still poorly known in the area, and more generally, few studies have considered the potential trophic overlap between sardines and anchovies worldwide. This study aims to highlight the trophic links between the mesozooplankton and adults of these two pelagic fish in the Bay of Biscay, through carbon and nitrogen stable isotope analysis (SIA). Mesozooplankton and individuals of sardines and anchovies were collected during one season (spring 2010), over spatially contrasted stations within the study area. First, the potential effect of preservation (ethanol vs. freezing) and of delipidation (by cyclohexane) on mesozooplankton δ¹³C and δ¹⁵N values was assessed. Results demonstrated the necessity to correct for the preservation effect and for lipid contents in mesozooplankton for further analyses of sardines' and anchovies' diet through SIA. Next, this study highlighted the interest of working on identified mesozooplanktonic organisms instead of undetermined assemblages when unravelling food sources of planktivorous fish using stable isotopes. The inter-specific variability of isotope values within a planktonic assemblage was effectively high, probably depending on the various feeding behaviours that can occur among mesozooplankton species. Intra-specific variability was also significant and related to the spatial variations of baseline signatures in the area. To investigate the foraging areas and potential diet overlap of S. pilchardus and E. encrasicolus, mixing models (SIAR) were applied. Both fish species appeared to feed mainly in the neritic waters of the Bay of Biscay in spring and to select mainly small- to medium-sized copepods (e.g. Acartia sp., Temora sp.). However, E. encrasicolus showed a greater trophic plasticity by foraging more offshore and on a wider range of prey sizes, while S. pilchardus seemed more limited to coastal areas and the mesozooplanktonic species of these waters for feeding.     

Assessing waterbird habitat use in coastal evaporative systems using stable isotopes (δC, δN and δD) as environmental tracers

Isotopic patterns of biota across salinity gradients in man-made evaporative systems could assist in determining the use of these habitats by animals. Here we report δ¹³C, δ¹⁵N and δD measurements of a euryhaline fish, the Mediterranean toothcarp (Aphanius fasciatus), inhabiting a range of salinities in the Thyna saltworks near Sfax (Tunisia). The contribution of these salinity niches to egg formation of two typically piscivorous bird species breeding in the area and feeding within saltworks, Little Tern (Sternula albifrons) and Little Egret (Egretta garzetta), was inferred trough a triple-isotope (δ¹³C, δ¹⁵N and δD) Bayesian mixing model. Isotopic trends for fish δ¹⁵N and δD across the salinity gradient followed the equations: δ¹⁵N = e^{(1.1 + 47.68/Salinity)} and δD = −175.74 + Salinity + Salinity²; whereas fish δ¹³C increased as salinity rose (δ¹³C = −10.83 + 0.02·Salinity), after a sudden drop in fish isotopic values for salinities >60 (Practical Salinity Scale) (average fish δ¹³C for salinities <60 = −5.92‰). Both bird species fed largely on low hypersalinity ponds (salinity = 43; average contribution = 37% and 22% for Little Egrets and Little Terns, respectively), although the use of intermediate hypersalinities (salinities 63 and 70) by Little Terns also occurred (16% and 21%, respectively). Isotopic patterns across salinity gradients allow the use of isotopic measurements to inform studies of habitat occupancy within evaporative systems and provide further insights into how wildlife communities interact with them.     

Trophic importance of diatoms in an intertidal Zostera noltii seagrass bed: Evidence from stable isotope and fatty acid analyses

A current predominant paradigm emphasizes the role of epiphytic algae for invertebrates in most seagrass food webs. However, in some intertidal Zostera noltii beds, epiphyte biomass is very low compared to microphytobenthos and seagrass biomasses. We assessed the role of microphytobenthos in a temperate intertidal Z. noltii bed by combining stable isotope and fatty acid (FA) analyses on primary producers, composite sources — suspended particulate organic matter (SPOM) and sediment surface organic matter (SSOM) — and the main macrofaunal consumers. Z. noltii showed high δ¹³C (−9.9‰) and high 18:2(n-6) and 18:3(n-3) contents. Microphytobenthos was slightly more ¹³C-depleted (−15.4‰) and had high levels of diatom markers: 14:0, 16:1(n-7)c, 20:5(n-3). Low mean δ¹³C (−22.0‰) and large amounts of diatom and bacteria (18:1(n-7)c) markers indicated that SPOM was mainly composed of a mixture of fresh and decayed pelagic diatoms. Higher mean δ¹³C (−17.9‰) and high amounts of diatom FAs were found in SSOM, showing that microphytobenthic diatoms dominate. Very low percentages of 18:2(n-6) and 18:3(n-3) in consumers indicated a low contribution of Z. noltii material to their diets. Grazers, deposit and suspension-deposit feeders had δ¹³C close to microphytobenthos and high levels of diatom FAs, confirming that microphytobenthos represented the main part of their diet. Lower δ¹³C and higher amounts of flagellate FAs – 22:6(n-3) and 16:4(n-3) – in suspension feeders indicated that their diet resulted from a mixture of SPOM and microphytobenthos. These results demonstrate that invertebrates do not consume high amounts of seagrass and highlight the main role of benthic diatoms in this intertidal seagrass bed.     

Food-web structure and trophodynamics of mesopelagic–suprabenthic bathyal macrofauna of the Algerian Basin based on stable isotopes of carbon and nitrogen

The trophodynamics of mesopelagic (macrozooplankton/micronekton) and benthic boundary layer (suprabenthos=hyperbenthos) faunas from the Algerian Basin were characterized on a seasonal scale through stable carbon and nitrogen isotopic analyses of a total of 34 species and two broad taxa (Copepoda and Cumacea). This is the first study simultaneously focused on trophodynamics of deep-sea zooplankton and suprabenthos. Samples were collected southeast of Mallorca (Algerian Basin, Western Mediterranean), on the continental slope close to Cabrera Archipelago, at 650–780 m depths, ca. bi-monthly between August 2003 and June 2004. Mean δ¹³C values of suprabenthos ranged from ?21.1‰ (Munnopsurus atlanticus) to ?16.7‰ (Cyclaspis longicaudata). Values of δ¹⁵N ranged from 2.8‰ (Lepechinella manco) to 9.9‰ (larvae of Gnathia sp.). The stable isotope ratios of suprabenthic fauna displayed a continuum of values, confirming a wide spectrum of feeding guilds (from filter feeders/surface deposit feeders to predators). According to the available information on diets for suprabenthic species, the highest annual mean δ¹⁵N values were found for the hematophagous isopod Gnathia sp. parasite on fish (represented by Praniza larvae) and carnivorous amphipods (e.g. Rhachotropis spp., Nicippe tumida) consuming copepods, and the lowest δ¹⁵N values were found for two cumaceans (Cyclaspis longicaudata and Platysympus typicus) feeding on detritus. Assuming a ¹⁵N-enrichment factor of 2.5‰ and deposit feeders as baseline, we found three trophic levels in suprabenthic food webs. δ¹³C ranges were particularly wide among deposit feeders (ranging from ?21.8% to ?17.3‰) and omnivores (from ?20.5% to ?18.8‰), suggesting exploitation of particulate organic matter (POM) of different characteristics. Our isotopic analyses revealed lower ranges of δ¹³C and δ¹⁵N for macrozooplankton/micronekton, compared with suprabenthos. δ¹³C values of zooplankton taxa ranged from ?21.1‰ (the hyperiid Phrosina semilunata) to ?19.9‰ (the decapod Pasiphaea multidentata), while δ¹⁵N values ranged from 3.9‰ (P. semilunata) to 7.5‰ (P. multidentata). Among zooplankton, more enriched δ¹⁵N values were found among carnivores (e.g. the fish Cyclothone spp. and Pasiphaea multidentata) preying on copepods, hyperiids, euphausiids and small fish. The lowest δ¹⁵N values were found for hyperiids that feed on the mucus nets of salps (e.g. Vibilia armata). After contrasting isotope analysis with dietary data, we conclude there were two trophic levels among zooplankton/micronekton. Strong correlation between the mean annual δ¹⁵N and δ¹³C values was found for zooplankton (R²=0.7), but not for suprabenthos, which suggests a single source of carbon for plankton. We found a general seasonal trend for δ¹³C enrichment from late autumn (November) to late winter–spring (February–April) for both suprabenthos and zooplankton. The δ¹³C enrichment in February–April was correlated in zooplankton with higher surface chlorophyll a concentration 1 month before sampling. As evidenced by δ¹³C–δ¹⁵N correlations, the response of zooplankton to the peak of surface primary production was almost immediate (an increase of δ¹³C–δ¹⁵N correlations in February), and stronger than for suprabenthos. The response among suprabenthos was weak, with slight increase in δ¹³C–δ¹⁵N relationships in April–June.     

Determining spatial changes in the diet of nearshore suspension-feeders along the South African coastline: Stable isotope and fatty acid signatures

Mesoscale oceanographic features, such as upwellings, are known to play an important role in regulating the structure and productivity of nearshore marine communities. Stable isotope (δ¹³C and δ¹⁵N) and fatty acid analyses were employed to assess the influence of an upwelling cell along the south-eastern coastline of southern Africa on the diet of the mussel, Perna perna. Eight sites were sampled: two upstream, three in the vicinity and three downstream of the upwelling cell. Stable isotope and fatty acid signatures indicated that the mussels consumed a diet of detritus derived mainly from macroalgae, diatoms and dinoflagellates. One-way ANOVA on the δ¹³C and δ¹⁵N signatures and the principal component analysis of the fatty acid profiles of the mussels identified distinct groups corresponding to the above mentioned regions. The proportion of diatom biomarkers in the fatty acid profiles decreased downstream of the upwelling region while the proportion of dinoflagellate biomarkers increased. Upwelling regions are typically associated with elevated levels of productivity; however, these systems usually become silicon depleted and result in the replacement of diatoms with dinoflagellates. The highest proportions of the dinoflagellate markers were recorded in the two furthest sites downstream of the upwelling cell. The spatial variation in the diet of the mussels, therefore, appears to reflect the presence of the upwelling cell in the nearshore biology of the region.     

Role of mysid seasonal migrations in the organic matter transfer in the Curonian Lagoon,south-eastern Baltic Sea

We investigated population dynamics, growth and feeding of an omnivorous mysid, Paramysis lacustris, performing seasonal horizontal migrations in the Curonian Lagoon. In autumn, increased predation pressure and deteriorated feeding conditions, due to zooplankton and phytoplankton decline in the open water, forces mysids to migrate to the shoreline, where large amounts of decaying submersed vegetation occur at the end of plant growth season. Using stable isotope analysis and mixing models, we evaluated relative importance of decaying submersed macrophytes, lagoon phytoplankton and mesozooplankton in the diet of mysids during this period. In September–November, mysids actively grew and produced three cohorts. Specific growth rates of adults (10.9 ± 1.9 mm) and subadults (6 ± 0.5 mm) were 3 and 9% DW d⁻¹, respectively, resulting in population somatic production of 36 g DW m⁻². Both δ¹⁵N and δ¹³C of mysids varied in concert with those in suspended and bottom particulate organic matter (POM) and mesozooplankton. The mixing models estimated that 45% of mysid diets were composed of bottom POM originated from the decaying macrophyte Potamogeton perfoliatus, 45% by suspended POM largely consisting of phytoplankton, while mesozooplankton contributed less than 10% of the diet. This diet composition differs from that in summer, when mysids rely mostly on zooplankton and phytoplankton. Therefore, mysid horizontal migrations and their ability to efficiently utilize littoral detritus improve the efficiency of macrophyte detritus transfer up the food chain and inshore/offshore habitat coupling in the Curonian Lagoon.     

Shell growth and oxygen isotopes in the topshell Osilinus turbinatus: resolving past inshore sea surface temperatures

Shells of the rocky shore intertidal gastropod Osilinus turbinatus (von Born), often abundant in archaeological deposits in the Mediterranean region, are a potential source of data on palaeotemperature, palaeoseasonality and archaeological seasonality. To evaluate this species as a climate archive, investigations of annual patterns of shell growth and of monthly variations in oxygen isotopes in shell carbonates were made on different populations in NW Sicily. Mark-recapture experiments at San Vito lo Capo and Mazzaforno show that O. turbinatus grows almost continuously throughout the year but at different rates in different seasons. Around 75% of the yearly shell growth occurs in the autumn and winter. On average, larger/older shells produce narrower annual growth increments than smaller/younger ones. Conspicuous growth lines in larger/older shells show that growth stops during the hottest part of the summer. Oxygen isotope analyses on monthly collected shells of O. turbinatus from three shores (Cala Grande, Monte Cofano and Mazzaforno) show that the isotope values record temperature variations through the year. In all the datasets, surface seawater temperatures (SSTs) calculated from δ¹⁸O_SHELL mostly underestimate measured SSTs, offsets being generally greater in summer. Minimum annual offsets range from 0.0°C to 0.7°C and maximum annual offsets from 3.1°C to 8.7°C. δ¹⁸O_SHELL values fail to record temperatures higher than 25°C. Careful selection of shells to be analysed can reduce offsets between δ¹⁸O_SHELL temperature estimates and measured SSTs for many parts of the year, except the hottest. Allowing for this, shells of O. turbinatus offer good potential as climate archives and for archaeological studies of seasonal patterns of human foraging for shellfish.     

“海参-对虾”混养海水池塘的食物网结构及营养层级研究

The food sources of aquacultured Apostichopus japonicus and the trophic levels of organisms in a sea cucumber(A. japonicus) and prawn(Penaeus japonica) polyculture system in a saltwater pond in Zhuanghe, Liaoning Province were examined using carbon and nitrogen stable isotopes. Across organisms, δ13C ranged from(–25.47±0.20)‰ to(–16.48±0.17)‰(mean±SD), and δ15N ranged from(4.23±0.49)‰ to(12.44±0.09)‰. The δ13C and δ15N contents of A. japonicus, P. japonica and Fenneropenaeus chinensis were comparatively higher than those of other organisms. Values of δ13C and δ15N revealed that P. japonica, Hemigrapsus sanguineus and Neomysis japonica comprised the largest component of the diet of A. japonicus. The mean trophic level of the organisms in this saltwater pond polyculture system was(2.75±0.08). P. japonica, A. japonicus, F. chinensis,Synechogobius hasta and Neomysis japonica were in the 3rd trophic level(2–3); jellyfish, H. sanguineus and zooplankton were in the 2nd trophic level(1–2); and Enteromorpha prolifera, benthic microalgae, periphyton and suspended matter primarily consisting of phytoplankton, bacteria and humus were in the primary trophic level(0–1).     

Trophic ecology of black scabbardfish,Aphanopus carbo in the NE Atlantic—Assessment through stomach content and stable isotope analyses

The black scabbardfish is a deep water species of high commercial interest in the NE Atlantic. Specimens were collected from commercial trawls to the west of the British Isles and from longliners operating near Madeira between September 2008 and May 2010. Stomach content analysis was confined to samples from the northern area, because of a high number of empty stomachs from Madeira. Stable isotope analyses identified that black scabbardfish feeds on species with epipelagic and benthopelagic affinities. For the west of British Isles, the δN values were significantly different between seasons suggesting a change in the diet throughout the year. Black scabbardfish have higher δN and δC values compared with other co-occurring benthopelagic feeders and lower nitrogen values than the true benthic predators and/or scavengers. Comparison with stable isotope analysis in samples from Madeira indicated that black scabbardfish feed at a similar trophic level and has the same trophic niche width in both areas, assuming similar baseline isotope compositions. The diet in the northern area comprised fish (68% N), crustaceans (22% N) and cephalopods (15% N) with blue whiting (Micromesistius poutassou) constituting 40% of the prey. Seasonal shift in diet was observed, with a predominance of blue whiting (70%) in the first quarter of the year, shifting to a more diverse diet in the remainder of the year. These results indicate that the diet of black scabbardfish is closely linked with the seasonal migration of blue whiting and that they likely select prey in proportion to availability. This study demonstrates that the combined used of both methods can elucidate the trophic ecology of black scabbardfish, in situations where conventional methods alone provide insufficient data.     

Depth habitats and seasonal distributions of recent planktic foraminifers in the Canary Islands region (29°N) based on oxygen isotopes

Seasonal depth stratified plankton tows, sediment traps and core tops taken from the same stations along a transect at 29°N off NW Africa are used to describe the seasonal succession, the depth habitats and the oxygen isotope ratios (δ¹⁸O_shell) of five planktic foraminiferal species. Both the δ¹⁸O_shell and shell concentration profiles show variations in seasonal depth habitats of individual species. None of the species maintain a specific habitat depth exclusively within the surface mixed layer (SML), within the thermocline, or beneath the thermocline. Globigerinoides ruber (white) and (pink) occur with moderate abundance throughout the year along the transect, with highest abundances in the winter and summer/fall season, respectively. The average δ¹⁸O_shell of G. ruber (w) from surface sediments is similar to the δ¹⁸O_shell values measured from the sediment-trap samples during winter. However, the δ¹⁸O_shell of G. ruber (w) underestimates sea surface temperature (SST) by 2 °C in winter and by 4 °C during summer/fall indicating an extension of the calcification/depth habitat into colder thermocline waters. Globigerinoides ruber (p) continues to calcify below the SML as well, particularly in summer/fall when the chlorophyll maximum is found within the thermocline. Its vertical distribution results in δ¹⁸O_shell values that underestimate SST by 2 °C. Shell fluxes of Globigerina bulloides are highest in summer/fall, where it lives and calcifies in association with the deep chlorophyll maximum found within the thermocline. Pulleniatina obliquiloculata and Globorotalia truncatulinoides, dwelling and calcifying a part of their lives in the winter SML, record winter thermocline (～180 m) and deep surface water (～350 m) temperatures, respectively. Our observations define the seasonal and vertical distribution of multiple species of foraminifera and the acquisition of their δ¹⁸O_shell.     

Spatial and temporal variations in food web structure from newly-opened habitat at hydrothermal vents

To highlight the spatio-temporal variability of the food web structure of hydrothermal vent fauna from newly-opened habitat, a series of Titanium Ring for Alvinellid Colonization devices (TRACs) was deployed at TICA site on the East Pacific Rise in 2006. This experiment was conducted for periods of 4 days, 13 days and one month and deployments were aligned along a gradient from the basaltic bottom to the vent openings. δ¹³C values of colonists revealed a narrower range of carbon sources in proximity to vent openings in Alvinella pompejana habitat than in Tevnia jerichonana habitat, separated by a distance of four meters. This was possibly due to a spatial change in available food sources with a possible higher contribution of particulate organic matter (POM) to the siboglinid habitat compared to a higher contribution of microbial primary producers such as Epsilonproteobacteria in the alvinellid habitat. Temporal variability was also observed during experimentation in the form of a shift in either δ¹³C and/or δ¹⁵N values for A. pompejana, Lepetodrilus elevatus, dirivultid copepods and polynoid polychaetes within a one-month window showing first of all, fast tissues turnover and secondly, a possible switch in feeding strategy or food sources. Lepidonotopodium riftense and Branchinotogluma sandersi may have to alternate between detritivorous and predatory feeding strategies. In addition, through the analysis of stable isotope composition of A. pompejana and its episymbionts, we provided evidence that these attached bacteria formed part of the worms’ diet during the course of these colonization experiments.     

Incorporation of terrestrial wetland material into aquatic food webs in a tropical estuarine wetland

Carbon and nitrogen stable isotope composition of a range of organisms collected from two intermittently connected floodplain pools in the Ross River estuary were analysed to assess the extent to which carbon fixed by terrestrial wetland producers is incorporated into adjacent aquatic food webs. The two pools differed in surrounding vegetation with one surrounded by mangroves and the other by the salt couch Sporobolus virginicus. At both pools, animals showed differences in δ¹³C, indicating differences in sources of carbon. Since δ¹³C values of C₃ mangroves (−29.7 to −26.3‰) were very different from those of the C₄ salt couch (−16.3 to −15.4‰), it was possible to determine the importance of terrestrial wetland producers by comparing isotope values of consumers between sites, in a species by species approach. Most animal species collected showed lower δ¹³C at the mangrove pool than at the Sporobolus pool, which indicates a greater incorporation of mangrove carbon at the mangrove pool. However, the animals’ isotopic shifts were also similar to that shown by epiphytes, and hence the differences in animal δ¹³C could also be a result of a dependence on these producers. The IsoSource model was useful to clarify this question, indicating that mangrove and salt marsh material was a crucial contributor to the diet of several fish and invertebrate species at both sites, indicating that carbon of terrestrial origin is incorporated in the estuarine food web.     

Seasonality and growth patterns using isotope sclerochronology in shells of the Pliocene scallop Chesapecten madisonius

Growth lines and variation in oxygen and carbon isotope ratios (δ¹⁸O and δ¹³C) in shells of the Pliocene scallop Chesapecten madisonius preserve seasonal chronologies of biological and environmental change. This study evaluated whether (1) prominent growth lines were formed annually, and (2) growth rates estimated using isotope sclerochronology were comparable to rates estimated using visual inspection (measuring the width between external growth lines). We compared both techniques for estimating growth rates and age on three late to mid-Pliocene C. madisonius shells. The first approach located prominent growth lines on the δ¹⁸O time series, and differentiated between annual and non-annual (disturbance) growth lines. The second approach assumed all prominent lines were annual. This comparison showed that visual inspection underestimated growth rates and overestimated age. Seasonal timing of annual growth line formation using isotope sclerochronology provided unexpected results. Because this region fell within the warm-temperate paleobiogeographic province, we predicted annual lines formed during summers (most negative δ¹⁸O values). Instead, annual growth lines coincided with the most positive δ¹⁸O values (winter), typical of bivalves from cold-temperate regions. Moreover, shells recorded seasonal temperatures ranging from 3.2–20.8°C, a range lower than the thermal regime defined for warm-temperate environments (8–25°C). Possibly, the Sea Slope Gyre, which mixed eddies and cold filaments of the Labrador Current and warm waters of the Gulf Stream, penetrated the warm-temperate environment in this region. Alternatively, warm-water fauna from the zoogeographic Carolinian subprovince migrated northward and endured by virtue of warm summer temperatures. Regardless of the explanation, our findings provide a glimpse of mid-latitude seasonal temperature range for a warm climate episode during the mid-Pliocene.     

Age at breeding of crowned cormorants Phalacrocorax coronatus

Between 1991 and 1995,242 crowned cormorant Phalacrocorax coronatus chicks were banded at Malgas Island with metal and colour rings. At least 10 subsequently bred before 4 April 1996. First-year birds had juvenile plumage, but when about one year old they attained the plumage of immature birds and of non-breeding adults. The youngest age at breeding was about one year, but many birds did not breed until aged 1½–2 years and some may not have bred before they were three years old.