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1.
Ocean acidification results from an increase in the concentrations of atmospheric carbon dioxide (CO2) impacts on marine calcifying species, which is predicted to become more pronounced in the future. By the end of this century, atmospheric pCO2 levels will have doubled relative to the pre‐industrial levels of 280 ppm. However, the effects of pre‐industrial pCO2 levels on marine organisms remain largely unknown. In this study, we investigated the effects of pre‐industrial pCO2 conditions on the size of the pluteus larvae of sea urchins, which are known to be vulnerable to ocean acidification. The larval size of Hemicentrotus pulcherrimus significantly increased when reared at pre‐industrial pCO2 level relative to the present one, and the size of Anthocidaris crassispina larvae decreased as the pCO2 levels increased from the pre‐industrial level to the near future ones after 3 days' exposure. In this study, it is suggested that echinoid larvae responded to pre‐industrial pCO2 levels. Ocean acidification may be affecting some sensitive marine calcifiers even at the present pCO2 level.  相似文献   

2.
A model based on that of Kishi et al. (2001) has been extended to 15 compartments including silicon and carbon cycles. This model was applied to Station A7 off Hokkaido, Japan, in the Northwestern Pacific. The model successfully simulated the observations of: 1. a spring bloom of diatoms; 2. large seasonal variations of nitrate and silicate concentrations in the surface water; and 3. large inter-annual variations in chlorophyll-a. It also reproduced the observed features of the seasonal variations of carbon dioxide partial pressure (pCO2)—a peak in pCO2 in winter resulting from deep winter convection, a rapid decrease in pCO2 as a result of the spring bloom, and an almost constant pCO2 from summer through fall (when the effect of increasing temperature cancels the effect of biological production). A comparison of cases with and without silicate limitation shows that including silicate limitation in the model results in: 1. decreased production by diatoms during summer; and 2. a transition in the dominant phytoplankton species, from diatoms to other species that do not take up silicate. Both of these phenomena are observed at Station A7, and our results support the hypothesis that they are caused by silicate limitation of diatom growth. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

3.
To understand the adaptation of euphausiid (krill) species to oxygen minimum zones (OMZs), respiratory response and stress experiments combining hypoxia‐reoxygenation exposure with warming were conducted. Experimental krill species were obtained from the Antarctic (South Georgia area), the Humboldt Current System (HCS, Chilean coast) and the Northern California Current System (NCCS, Oregon). Euphausia mucronata from the HCS showed oxyconforming pO2‐dependent respiration below 80% air saturation (18 kPa). Normoxic subsurface oxygenation in winter posed a ‘high oxygen stress’ for this species. The NCCS krill, Euphausia pacifica, and the Antarctic krill, Euphausia superba, maintained respiration rates constant down to low critical pO2 values of 6 kPa (30% air saturation) and 11 kPa (55% air saturation), respectively. Antarctic krill had low antioxidant enzyme activities, but high concentrations of the molecular antioxidant glutathione (GSH) and was not lethally affected by 6 h exposure to moderate hypoxia. The temperate krill species (E. pacifica) had higher superoxide dismutase (SOD) values in winter than in summer, which relates to a higher winter metabolic rate. In all species, antioxidant enzyme activities remained constant during hypoxic exposure at the typical temperature for their habitat. Warming by 7 °C above habitat temperature in summer increased SOD activities and GSH levels in E. mucronata (HCS), but no oxidative damage occurred. In winter, when the NCCS is well mixed and the OMZ is deeper, +4 °C of warming combined with hypoxia represents a lethal condition for E. pacifica. In summer, when the OMZ expands upwards (100 m subsurface), antioxidant defences counteracted hypoxia and reoxygenation effects in E. pacifica, but only at mildly elevated temperature (+2 °C). In this season, experimental warming by +4 °C reduced antioxidant activities and the combination of warming with hypoxia again caused mortality of exposed specimens. We conclude that a climate change scenario combining warming and hypoxia represents a serious threat to E. pacifica and, as a consequence, NCCS food webs.  相似文献   

4.
In this study, we examined the impact of temperature on the carbon and nitrogen trophic transfers from a macroalga to a macro‐grazer by the use of dual 13C‐ and 15N‐labeling. Using an experimental approach in mesocosms, individuals of the urchin Psammechinus miliaris were maintained for 1 month at 17°C (mean summer temperature in the Bay of Brest) and at 20°C (maximum summer temperature) and fed with 13C‐ and 15N‐labeled Solieria chordalis. The results showed that the urchins’ 13C uptake was 0.30 µg13C g dry weight (DW)?1 at 17°C and 0.14 µg13C g DW?1 at 20°C at the end of the experiment. The lower uptake at the higher temperature may be attributed to a decrease in metabolic activity at 20°C, involving lower feeding and/or respiration rates. Conversely, no significant effect of temperature was detected on 15N uptake. At the end of the experiment, the urchins’ 15N uptake was 0.04 µg15N g DW?1 at 17°C and 0.03 µg15N g DW?1 at 20°C. This suggests that temperature may affect carbon and nitrogen trophic fluxes differently. The use of dual isotope labeling offers interesting prospects and needs to be further extended in order to better understand trophic interactions in marine communities and the consequences of current environmental changes, such as global warming.  相似文献   

5.
Volatile organic compounds (VOCs) may play the role of infochemicals and trigger chemotaxis and ecologically relevant responses in freshwater and marine invertebrates. Aquatic grazers use these signals as chemical cues to trace the presence of their food or to detect their predators. However, detailed data are still needed to fully understand the role of these relationships in marine plankton. We investigated the ability of the copepod Centropages typicus to perceive the odour of three planktonic diatoms (Skeletonema marinoi, Pseudonitzschia delicatissima and Chaetoceros affinis) and a dinoflagellate (Prorocentrum minimum). This information is ecologically relevant for orientation, habitat selection, predator avoidance and communication. In addition, as the pH of the medium influences the perception of chemical cues in aquatic environments, we tested the effect of seawater acidification resulting from increasing levels of CO2, and its influences on the olfactory reactions of copepods. For this reason, our tests were repeated in normal (pH 8.10) and acidified (pH 7.76) seawater in order to simulate future ocean acidification scenarios. Using replicated chemokinetic assays we demonstrated that VOCs produced by Ps. delicatissima and Pr. minimum attract copepods at normal pH, but this effect is lowered in acidified water. By contrast, the odour of S. marinoi mainly induces a reaction of repulsion, but in acidified water and at higher concentrations this toxic diatom becomes attractive for copepods. Our experiments demonstrate, for the first time, that copepods are sensitive to the volatile compounds contained in various microalgae; VOCs prompt chemokinesis according to algal species and odour concentrations. However, seawater acidification induces changes in copepods' perception of odours. These findings highlight the sensitivity of chemically mediated interactions to global changes  相似文献   

6.
The partial pressure of CO2 (pCO2) and dissolved inorganic carbon (DIC) were monitored in shallow coastal waters located inside and outside giant kelp beds (Macrocystis pyrifera) located in the Kerguelen Archipelago (Southern Ocean). Photosynthesis and respiration by microplankton and kelp lead to marked pCO2 and DIC diel cycles. Daily variations of pCO2 and DIC are significant in the spring and summer, but absent in the winter, reflecting the seasonal cycle of biological activity in the kelp beds. If the kelp beds seem to favour the onset of phytoplankton blooms, most of the primary production inside the kelp beds is due to the kelp itself. The primary production of Macrocystis kelp beds in the Sub-Antarctic high-nutrient, low-chlorophyll (HNLC) waters off the Kerguelen Archipelago is elevated and closely linked to light availability. This production is significant from October to March and reaches its climax in December at the solar radiation maximum.  相似文献   

7.
Studies of the trophic structure in methane‐seep habitats provide insight into the ecological function of deep‐sea ecosystems. Methane seep biota on the Chilean margin likely represent a novel biogeographic province; however, little is known about the ecology of the seep fauna and particularly their trophic support. The present study, using natural abundance stable isotopes, reveals a complex trophic structure among heterotrophic consumers, with four trophic levels supported by a diversity of food sources at a methane seep area off Concepción, Chile (~36° S). Although methanotrophy, thiotrophy and phototrophy are all identified as carbon fixation mechanisms fueling the food web within this area, most of the analysed species (87.5%) incorporate carbon derived from photosynthesis and a smaller number (12%) use carbon derived from chemosynthesis. Methane‐derived carbon (MDC) incorporation was documented in 22 taxa, including sipunculids, gastropods, polychaetes and echinoderms. In addition, wide trophic niches were detected in suspension‐feeding and deposit‐feeding taxa, possibly associated with the use of organic matter in different stages of degradation (e.g. from fresh to refractory). Estimates of Bayesian standard ellipses area (SEAB) reveal different isotopic niche breadth in the predator fishes, the Patagonian toothfish Dissostichus eleginoides and the combtooth dogfish Centroscyllium nigrum, suggesting generalist versus specialist feeding behaviors, respectively. Top predators in the ecosystem were the Patagonian toothfish D. eleginoides and the dusky cat shark, Bythaelurus canescens. The blue hake Antimora rostrata also provides a trophic link between the benthic and pelagic systems, with a diet based primarily on pelagic‐derived carrion. These findings can inform accurate ecosystem models, which are critical for effective management and conservation of methane seep and adjacent deep‐sea habitats in the Southeastern Pacific.  相似文献   

8.
We carried out a benthic survey and two experiments in runs at eight sites down the Kakanui River (South Island, New Zealand) during summer low flows, to investigate the interaction between nutrients, periphyton, and macro‐grazers. Benthic periphytic biomass was generally low (< 20 mg m‐2 chlorophyll a) at most sites, but high densities of macro‐grazers (mainly snails) were observed at six of the eight sites. Chlorophyll a and cellular P concentrations were generally higher on artificial substrates in the first‐ to third‐order tributaries, compared with downstream. Macro‐grazer densities (mainly snails) were also highest in the second‐ and third‐order tributaries. Enrichment of patches with N and P did not translate into significant increases in chlorophyll a concentrations. Instead there was a general increase in macro‐grazers, and an increase in the relative abundance of Cocconeis placentula. In a second experiment, the chlorophyll a level was five‐fold higher on the substrates where macro‐grazers were excluded and there was no significant response of chlorophyll a to nutrient addition on these substrates. On the grazed substrates, densities of snails and caddis‐larvae were two‐fold higher with N+P enrichment. These experiments provided evidence for a tight coupling between first and second trophic levels, and strong grazer control of periphyton, in this river.  相似文献   

9.
Partial pressure of CO2 (pCO2) in surface seawater has been measured in the northeastern Pacific Ocean at Station P and along Line P since 1973. These data have been divided into ‘oceanic’ and ‘coastal/transition’ zones, and the seasonal and interannual variability and the long-term trends for each zone have been examined. The oceanic zone shows little seasonality in surface seawater pCO2, with undersaturation throughout the year. A strong, biologically-driven seasonal cycle is offset by variation in temperature-dependent solubility of CO2. The coastal/transition zone shows a decline in pCO2 from winter–spring through summer and fall that is likely the result of seasonal stratification and convection rather than coastal upwelling. Interannual variability all along Line P is correlated with the multivariate ENSO index (MEI), with lower seawater pCO2 associated with El Niño conditions. Correlations with the Pacific Decadal Oscillation Index are similar but weaker, in part because there are few data prior to the 1976 regime shift. The long-term trend in seawater pCO2 in the oceanic zone is +1.36±0.16 μatm year?1, indistinguishable from the atmospheric growth rate, and varies little among the seasons. In the coastal/transition zone a slow increase in the pCO2 of surface seawater relative to that of the atmosphere has led to increasing undersaturation, particularly in spring. Aliasing of the seasonal and interannual variability due to sampling frequency may explain part of the observed trend in the coastal/transition zone, but real changes in physical or biological processes are also possible and require more detailed study.  相似文献   

10.
A quasi-two dimensional model of the carbon and nitrogen cycling above the 70m isobath of the southeastern Bering Sea at 57°N replicates the observed seasonal cycles of nitrate, ammonium, ΣCO2, pCO2, light penetration, chlorophyll, phytoplankton growth rate, and primary production, as constrained by changes in wind, incident radiation, temperature, ice cover, vertical and lateral mixing, grazing stress, benthic processing of phytodetritus and zooplankton fecal pellets, and the pelagic microbial loop of DOC, bacteria, and their predators. About half of the seasonal resupply of nitrate stocks to their initial winter conditions is derived from in situ nitrification, with the rest obtained from deep-sea influxes. Under the present conditions of atmospheric forcing, shelf-break exchange, and food web structure, this shelf ecosystem serves as a sink for atmospheric CO2, with storage in the forms of exported DOC, DIC, and unutilized POC (phytoplankton, bacteria, and fecal pellets).As a consequence of just the rising levels of atmospheric pCO2 since the the Industrial Revolution, however, the biophysical CO2 status of the Southeastern Bering Sea shelf may have switched over the last 250 years, from a prior source to the present sink, since this relatively pristine ecosystem has unergone little eutrophication. Such fluctuations of CO2 status may thus be reversed by the physical processes of : (1) reduction of atmospheric pCO2, (2) increased on welling of deep-sea ΣCO2, and (3) warming of shelf waters. Based on our application of this model to the Chukchi Sea and the Gulf of Mexico, about 1.0–1.2 gigatons C y-1 of atmospheric CO2 may now be sequestered by temperate and polar shelf ecosystems. When tropical systems are included, however, a positive net sink of only 0.6–0.8. × 1015g C y−1 may prevail over all shelves.  相似文献   

11.
The influence of the coastal ocean on global net annual air-sea CO2 fluxes remains uncertain. However, it is well known that air-sea pCO2 disequilibria can be large (ocean pCO2 ranging from ∼400 μatm above atmospheric saturation to ∼250 μatm below) in eastern boundary currents, and it has been hypothesized that these regions may be an appreciable net carbon sink. In addition it has been shown that the high productivity in these regions (responsible for the exceptionally low surface pCO2) can cause nutrients and inorganic carbon to become more concentrated in the lower layer of the water column over the shelf relative to adjacent open ocean waters of the same density. This paper explores the potential role of the winter season in determining the net annual CO2 flux in temperate zone eastern boundary currents, using the results from a box model. The model is parameterized and forced to represent the northernmost part of the upwelling region on the North American Pacific coast. Model results are compared to the few summer data that exist in that region. The model is also used to determine the effect that upwelling and downwelling strength have on the net annual CO2 flux. Results show that downwelling may play an important role in limiting the amount of CO2 outgassing that occurs during winter. Finally data from three distinct regions on the Pacific coast are compared to highlight the importance of upwelling and downwelling strength in determining carbon fluxes in eastern boundary currents and to suggest that other features, such as shelf width, are likely to be important.  相似文献   

12.
The diet of different macrozoobenthic trophic groups was investigated in the Arcachon Bay—a semi-enclosed macrotidal ecosystem that shelters the largest Zostera noltei seagrass meadow in Europe—in early spring and late summer 2009, using stable isotopes and fatty acids. Fatty acid profiles and literature information about the biology and physiology of benthic consumers were combined to identify the main organic matter sources for the benthic primary consumers. An isotope mixing model was then run to evaluate the contribution of each organic matter source to each identified trophic group (suspension feeders, sub-surface deposit feeders, micro-and macrograzers, suspension-oriented interface feeders and deposit-oriented interface feeders). Variations in organism' diets with respect to both habitats (intertidal seagrass meadows, intertidal bare sediments and subtidal bare sediments) and study periods were also investigated. At the scale of this study, it appeared that the diet of macrozoobenthos primary consumers was based exclusively on autochthonous material (no use of terrestrial organic matter): mainly microphytobenthos, seagrasses and their epiphytes, and phytoplankton. In addition, the different trophic groups relied on different organic matter pools: for instance, suspension feeders mainly fed on microphytobenthos and phytoplankton, whereas subsurface deposit feeders fed on microphytobenthos, decayed seagrasses and bacteria, and grazers mainly fed on microphytobenthos, and seagrasses and their epiphytes. The same pattern was observed in both early spring and late summer, indicating a stability of the benthic system at a six-month time scale. Finally our results showed that, in Arcachon Bay, the seagrass meadow directly or indirectly (through detritus) plays a significant role in the diet of most benthic consumers.  相似文献   

13.
An increase in the level of atmospheric carbon dioxide (CO2) and the resultant rise in CO2 in seawater alter the inorganic carbon concentrations of seawater. This change, known as ocean acidification, ...  相似文献   

14.
There are serious concerns that ocean acidification will combine with the effects of global warming to cause major shifts in marine ecosystems, but there is a lack of field data on the combined ecological effects of these changes due to the difficulty of creating large‐scale, long‐term exposures to elevated CO2 and temperature. Here we report the first coastal transplant experiment designed to investigate the effects of naturally acidified seawater on the rates of net calcification and dissolution of the branched calcitic bryozoan Myriapora truncata (Pallas, 1766). Colonies were transplanted to normal (pH 8.1), high (mean pH 7.66, minimum value 7.33) and extremely high CO2 conditions (mean pH 7.43, minimum value 6.83) at gas vents off Ischia Island (Tyrrhenian Sea, Italy). The net calcification rates of live colonies and the dissolution rates of dead colonies were estimated by weighing after 45 days (May–June 2008) and after 128 days (July–October) to examine the hypothesis that high CO2 levels affect bryozoan growth and survival differently during moderate and warm water conditions. In the first observation period, seawater temperatures ranged from 19 to 24 °C; dead M. truncata colonies dissolved at high CO2 levels (pH 7.66), whereas live specimens maintained the same net calcification rate as those growing at normal pH. In extremely high CO2 conditions (mean pH 7.43), the live bryozoans calcified significantly less than those at normal pH. Therefore, established colonies of M. truncata seem well able to withstand the levels of ocean acidification predicted in the next 200 years, possibly because the soft tissues protect the skeleton from an external decrease in pH. However, during the second period of observation a prolonged period of high seawater temperatures (25–28 °C) halted calcification both in controls and at high CO2, and all transplants died when high temperatures were combined with extremely high CO2 levels. Clearly, attempts to predict the future response of organisms to ocean acidification need to consider the effects of concurrent changes such as the Mediterranean trend for increased summer temperatures in surface waters. Although M. truncata was resilient to short‐term exposure to high levels of ocean acidification at normal temperatures, our field transplants showed that its ability to calcify at higher temperatures was compromised, adding it to the growing list of species now potentially threatened by global warming.  相似文献   

15.
Abstract. Grazing by the copepods Temora turbinata and Acartia lilljeborgii and the marine cladoceran Penilia avirostris on natural phytoplankton and cyanobacteria assemblages from Kingston Harbour. Jamaica, was examined in summer 1992. Food assemblages were often dominated by an unidentified filamentous cyanobacterium. with abundances of up to 1.16 × 104 filaments. ml-1. Other abundant phytoplankters included microflagellates and diatoms of the genus Niteschia. Mean clearance rates for the entire food assemblage ranged from 0.10 to 2.41 ml animal-1. h-1, although most mean clearance rates were between 0.5 and 1.5 ml. animal-1 h-1. Patterns of selection of different food items by various grazers on different dates were variable and inconsistent. Microscopic measurements revealed that cyanobacterial filament lengths were shorter in grazed than initial aliquots during a cyanobacterium bloom in August. This suggests that grazers reduced lengths of many filaments by biting off portions, in addition to consuming entire filaments. Such ‘filament clipping’ of cyanobacteria filaments has been recorded previously in freshwater studies and suggests that grazers impact a larger portion of the phytoplankton assemblage than is accounted for by ingestion and clearance rates based only upon removal of filaments. Grazers exhibited no adverse effects from consuming cyanobacteria. Cyanobacterkd are often considered to be toxic or of poor food quality for planktonic grazers. but due to the high abundance and dominance of filamentous cyanobacteria in Kingston Harbour. if these cyanobacteria were ungrazed. there would at times be little alternative phytoplankton food for copepods and cladocerans. Our results suggest that the trophic role of tilamentous cyanobacteria in pelagic food webs of the tropical ocean should be further investigated and possibly reconsidered.  相似文献   

16.
In order to evaluate the respiration–photosynthesis dynamics in two contrasting North Sea estuaries, pH, temperature, alkalinity, chlorophyll-a (chl-a), and isotopic ratios of dissolved inorganic carbon (δ13CDIC) and dissolved oxygen (δ18ODO) were measured in the Tyne (July 2003) and Tweed (July 2003 and December 2003) estuaries. Using a concentration-dependent isotope mixing line, δ13CDIC values in the Tweed (July 2003) demonstrated mostly conservative behaviour across the estuary, reflecting mixing between riverine and marine sources, although some samples were slightly more 13C-enriched than predicted δ13CDIC values. Low pCO2 (less than 2 times atmospheric pressure) and 18O-depleted δ18ODO signatures below equilibrium with the atmosphere provided further evidence for net autotrophy in the Tweed estuary in summer 2003. Conversely, in the Tyne during the summer and in the Tweed during the winter higher pCO2 (up to 6.5 and 14.4 times atmospheric partial pressure in the Tweed and Tyne, respectively), slightly 13C-depleted δ13CDIC and 18O-enriched δ18ODO values indicated heterotrophy as the dominant process. The relatively large releases of CO2 observed during these two estuarine surveys can be attributed to significant oxidation of terrigenous organic matter (OM). This study therefore demonstrates the usefulness of combined δ18ODO and δ13CDIC isotopes in examining the relationship between respiration–photosynthesis dynamics and the fate of terrestrially derived OM during estuarine mixing.  相似文献   

17.
Partial pressure of CO2 in surface sea water (pCO2) was measured continuously off Sanriku in May, 1997 by a new pCO2 measurement system. We have examined the relation of pCO2 to physical factors such as temperature, salinity and density, chemical and biological factors such as nutrients and carbonate system and chlorophylla. In the Kuroshio region pCO2 was not correlated to physical, chemical and biological factors in the range of 260 to 290 μatom. In transition water (Tr1) between Kuroshio and the Oyashio second branch, pCO2 was weakly correlated to physical factors and strongly correlated to nutrients. In transition water (Tr2) between the Oyashio first and second branches, pCO2 was highly correlated to temperature (SD: 10.9 μatom) and salinity (SD: 8.6 μatom) and also to nutrients. In transition water (Tr1+Tr2), pCO2 was highly multivariately correlated to temperature (T), salinity (S), chlorophylla (CH) (or nitrate+nitrite (N)) as follows, pCO2(μatom)= 10.8×T(°C)+27.7×S+2.57CH(μg/1) −769, R2= 0.86, SD = 20.9, or pCO2(μatom)= 3.9×T(°C)+25.5×S+16.0NO3(μM) −686, R2= 0.99, SD = 6.4. Moreover, pCO2 was predicted by only two factors, one physical (S) and the other chemical/biological (N) as follows: pCO2 (μatom)=32.8×S+19.4N−908, R2=0.97, SD=8.4. The pH measured at 25°C was well correlated with normalized pCO2 at a fixed temperature. In the Oyashio region pCO2 was decreased to 160 μatom, probably because of spring bloom, but was not correlated linearly to chlorophylla. The results obtained showed the possibility of estimating pCO2 of the Oyashio and transition regions in May by satellite remote sensing of SST, but the problem of estimation of pCO2 in Kuroshio water remains to be solved.  相似文献   

18.
桡足类是海洋生态系统中初级生产者和较高营养级消费者之间的关键联系环节,掌握桡足类的现场食物组成对于准确评估海洋食物网中的营养关系和能量转移至关重要。本研究中,我们以中华哲水蚤这一在中国、日本以及韩国近海具有重要生态地位的大型哲水蚤属桡足类为研究对象,应用之前开发的基于PCR的克隆技术,通过分析中华哲水蚤所摄食生物的18S rDNA序列,研究了中华哲水蚤的现场食物组成。结果揭示了南黄海（Y19站位）和渤海（B49站位）中华哲水蚤食物组成的多样性。共检测出43个操作分类单元（OTUs）,分别隶属于13个类群：硅藻（Bacillariophyta）、甲藻（Dinoflagellata）、硅鞭藻（Dictyochophyceae）、金藻（Chrysophyta）、Katablepharidophyta、浮生藻（Pelagophyceae）、无根虫（Apusozoa）、水螅水母（Hydrozoa）、栉水母（Ctenophora）、棘皮动物（Echinodermata）、被囊动物（Tunicata）、毛颚动物（Chaetognatha）以及海洋真菌。结果还表明,当发生藻类暴发时,中华哲水蚤可以摄食引发藻类暴发的藻种。当周围海域浮游植物的丰度相对较低时,中华哲水蚤可以选择摄食各种后生动物尤其是水螅水母和栉水母的卵、幼虫或者有机碎屑。我们的研究结果表明中华哲水蚤是一种杂食性桡足类,它对食物的选择依赖其生活海域中食物的可获得性。  相似文献   

19.
Stable isotopes were used to investigate contributions of autochthonous (i.e. benthic: epilithon and macroalgae) and allochthonous (i.e. pelagic: phytoplankton) organic matter sources to the diet of suspension-feeders, grazers and predators associated to small reef-pools (cuvettes) created by the reef-building species Dendropoma petraeum in the north-western coast of Sicily (Italy). Contributions of potential food sources were calculated using Bayesian mixing-models and integrated to a multivariate approach to highlight the diversity of C and N pathways within Dendropoma cuvettes. Both pelagic and benthic organic matter sources were exploited by benthic consumers, although clear differences were revealed in the various species depending on their feeding strategy. Three different trophic pathways were identified: one based mainly on phytoplankton, one based mainly on macroalgae and a third one mainly on epilithon. Suspension-feeders seemed to rely mainly on allochthonous organic matter sources, while grazers showed a wider diet spectrum. Predators revealed a high specialization in each of the three food chains and showed a distinct reliance on organic matter originated from benthic or pelagic sources. Stable isotopes evidenced here a marked differentiation of the trophic niche within the cuvette-associated community, which allows minimizing competition in very space-limited conditions.  相似文献   

20.
Although grazing is considered an essential process controlling epiphyte biomass on seagrass leaves, there is still a lack of fundamental knowledge about the species‐specific consumption rates of the most common grazers in Mediterranean meadows. This study experimentally assessed the effect of Posidonia oceanica‐associated gastropod grazing on early successional biofilm and the species‐specific relationship between biofilm consumption rates and biofilm biomass. Two biofilms on artificial substrata, both developed in situ (in a P. oceanica meadow), one under ambient conditions and the other under nutrient‐enriched conditions, were offered in aquaria assays to nine species of grazers found in P. oceanica meadows. Biofilm consumption rates and their association with biofilm biomass were assessed. It was found that: (i) there was a positive association between biofilm consumption and biofilm biomass up to 20 mg Chl a·m?2 for Bittium reticulatum, Gibbula ardens, Jujubinus exasperatus and Tricolia pullus; (ii) Alvania montagui, B. reticulatum and Jujubinus striatus showed the highest consumption rates and are thus expected to be amongst the leading consumers in early‐successional epiphytic communities; (iii) there was not an increase of consumption rate when a substratum colonized under nutrient‐enriched conditions was offered to any of the nine studied species. This study provides species‐specific consumption rates knowledge that is useful for the assessment of the strength of grazer–epiphyte interactions and trophic fluxes in P. oceanica meadows.  相似文献   

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