共查询到20条相似文献,搜索用时 78 毫秒
1.
Alexandra Baeta Ivan Valiela Francesca Rossi Rute Pinto Pierre Richard Nathalie Niquil João C. Marques 《Marine Biology》2009,156(10):2107-2120
In estuaries, eelgrass meadows contribute to fundamental ecosystem functions of estuaries, providing food to several predators
and buffering the negative effects of eutrophication. We asked whether the presence of the eelgrass Zostera noltii decreased the nitrogen concentration in the overlying water, affected the sources of nitrogen sequestrated by primary producers
and changed the benthic and pelagic food web structures. We also studied the importance of these food webs in providing food
to fish. We compared bare sediment to sediment covered by a Z. noltii meadow, and examined nutrient concentrations in the water column and δ15N in primary producers as indicators of anthropogenic inputs of nutrients. We then measured both δ13C and δ15N in the tissues of plants and consumers to establish food web structures. There were no differences in the concentrations
and sources of nitrogen between sites. Rather, δ15N values indicated anthropogenic inputs of N (e.g. sewage discharges, agriculture) in both sites. There were no major differences
in the structure of the planktonic food web, which was in part sustained by particulate organic matter and supported most
predator fish, and in the structure of the benthic food web. Nonetheless, there were differences in the sources of food for
omnivore consumers and for the detritivore Scrobicularia plana. Overall, the benthic food web did not use food derived from the eelgrass or macroalgae deposited on the substratum. Suspension
feeders used particulate and sediment organic matter, whereas the δ13C and δ15N values of the other consumers indicated a likely contribution of benthic microalgae. Furthermore, in both habitats we found
large variability in the isotope signatures of benthic macrofauna consumers, which did not allow distinguishing clearly different
trophic groups and indicated a high level of omnivory and a mixed diet opportunistically making use of the availability of
food in the surroundings. 相似文献
2.
J. W. Fourqurean N. Marbà C. M. Duarte E. Diaz-Almela S. Ruiz-Halpern 《Marine Biology》2007,151(1):219-232
Morphology, elemental content and isotopic composition of leaves of the seagrasses Posidonia oceanica and Cymodocea nodosa were highly variable across the Illes Balears, a Spanish archipelago in the western Mediterranean, and varied seasonally
at one site in the study area. The data presented in this paper generally expand the reported ranges of nitrogen, phosphorus,
iron and arsenic content and δ13C and δ15N for these species. Nitrogen and phosphorus content of P. oceanica leaves also showed significant seasonal variability; on an annual basis, P. oceanica leaves averaged 1.55% N and 0.14% P at this monitoring site. Both N and P were more concentrated in the leaves in winter
than in summer, with winter maxima of 1.76% N and 0.17% P and summer minima of 1.34% N and 0.11% P. There was no significant
annual pattern observed in the δ13C of P. oceanica leaves, but there was a repeated 0.6‰ seasonal fluctuation in δ15N. Mean annual δ15N was 4.0‰; δ15N was lowest in May and it increased through the summer and autumn to a maximum in November. Over the geographic range of
our study area, there were interspecific differences in the carbon, nitrogen and phosphorus content of the two species. Posidonia oceanica N:P ratios were distributed around the critical value of 30:1 while the ratios for C. nodosa were lower than this value, suggesting P. oceanica we collected was not consistently limited by N or P while C. nodosa tended toward nitrogen limitation. Nutrient content was significantly correlated to morphological indicators of plant vigor.
Fe content of P. oceanica leaves varied by a factor of 5×, with a minimum of 31.1 μg g−1 and a maximum of 167.7 μg g−1. Arsenic was present in much lower tissue concentrations than Fe, but the As concentrations were more variable; the maximum
concentration of 1.60 μg g−1 was eight times as high as the minimum of 0.20 μg g−1. There were interspecific differences in δ13C of the two species; C. nodosa was consistently more enriched (δ13C = −7.8 ± 1.7‰) than P. oceanica (−13.2 ± 1.2‰). The δ13C of both species decreased significantly with increasing water depth. Depth related and regional variability in the δ13C and δ15N of both species were marked, suggesting that caution needs to be exercised when applying stable isotopes in food web analyses. 相似文献
3.
Matthew Parry 《Marine Biology》2008,153(3):249-256
From 1998 to 2001 a total of 200 Ommastrephes bartramii (27 paralarvae) and 170 Sthenoteuthis oualaniensis (14 paralarvae) were sampled from the Central North Pacific. One group of non-paralarval O. bartramii (n = 30) was sampled from farther northwest in 1996. The δ15N of mantle muscle of non-paralarval O. bartramii (
= 12.4‰) was significantly greater than that of non-parlarval S. oualaniensis ( = 8.1‰) (P < 0.001). The δ15N of whole paralarvae of O. bartramii ( = 6.4‰) was not significantly different than parlarvalae of S. oualaniensis ( = 6.1‰) (P = 0.528). There was no significant difference between the mantle muscle δ15N values of male (n = 95, = 13.3‰) and female (n = 18, = 12.9 ‰) O. bartramii greater than 300 mm mantle length (ML) (P = 0.15). There was also no significant difference between the mantle muscle δ15N values of male (n = 15, = 7.2‰) and female (n = 26, = 7.3 ‰) S. oualaniensis in the same size range (P = 0.41). Overall there was a distinct logistic increase in δ15N with mantle length for O. bartramii, whereas S. oualaniensis showed an exponential increase in δ15N with mantle length that was stronger within individual years than with all samples combined. In general, adult O. bartramii are more than a trophic level above S. oualaniensis (4.3‰, 1.3 TLs). Because of the nature of the sampling protocol, this study could not separate spatial and temporal effects
on the δ15N signals from each squid species. This study demonstrates the ability of stable isotope analyses to differentiate trophic
levels between squid species as well as track trophic changes across size ranges from paralarvae to adults. Additional research
is needed to validate these trophic changes across size within individuals. 相似文献
4.
The feeding ecology of the green tiger shrimp Penaeus semisulcatus was studied in inshore fishing grounds off Doha, Qatar, using a combination of stable isotope (δ13C and δ15N) analysis and gut contents examination. Samples of post-larvae, juvenile and adult shrimp and other organisms were collected from intertidal and subtidal zones during the spawning season (January–June). Shrimp collected from shallow water seagrass beds were mostly post-larvae and juveniles and were significantly smaller than the older juveniles and adults caught in deeper macroalgal beds. Gut content examination indicated that post-larvae and juvenile shrimp in seagrass beds fed mainly on benthos such as Foraminifera, polychaetes, benthic diatoms and small benthic crustaceans (amphipods, isopods and ostracoda), whereas larger shrimp in the macroalgal beds fed mainly on bivalve molluscs and to a lesser extent polychaetes. In shrimp from both seagrass and algal beds, unidentifiable detritus was also present in the gut (18, 32%). δ13C values for shrimp muscle tissue ranged from −9.5 ± 0.26 to −12.7 ± 0.05‰, and δ15N values increased with increasing shrimp size, ranging from 4.1 ± 0.03 to 7.7 ± 0.11‰. Both δ15N values and δ13C values for shrimp tissue were consistent with the dietary sources indicated by gut contents and the δ13C and δ15N values for primary producers and prey species. The combination of gut content and stable isotope data demonstrates that seagrass beds are important habitats for post-larvae and juvenile P. semisulcatus, while the transition to deeper water habitats in older shrimp involves a change in diet and source of carbon and nitrogen that is reflected in shrimp tissue stable isotope ratios. The results of the study confirm the linkage between sensitive shallow water habitats and the key life stages of an important commercially-exploited species and indicate the need for suitable assessment of the potential indirect impacts of coastal developments involving dredging and land reclamation. 相似文献
5.
The feeding ecology of Merluccius hubbsi was investigated in 2 regions of SE Brazil. The major food sources for the hakes were fish, crustaceans, and squid. In the
upwelling system of Cabo Frio, the diet was very similar in the summers of 2001/2002 and spring 2002; fish were the most important
prey followed by crustaceans. In Ubatuba, euphausiids were an important prey during the winter 2001 (100 m), while in the
summer 2002, fish and amphipods predominated in the diet in the shallower site (40 m) and squid in the deeper site (100 m).
The hakes showed temporal differences in stable isotope signatures in both regions, while C:N ratios varied only in Cabo Frio.
δ15N and δ13C (bulk and corrected for lipid content) increased with fish length, which seems to be related to the increasing importance
of fish and decreasing importance of euphausiids and amphipods in the diet of larger hakes. The mean trophic level of 3.7
for M. hubbsi was estimated using δ15N of bivalves as baseline and the fractionation of 3.4‰ between trophic levels. 相似文献
6.
Diet of the social groups of long-finned pilot whales (<Emphasis Type="Italic">Globicephala melas</Emphasis>) in the Strait of Gibraltar 总被引:1,自引:1,他引:0
R. de Stephanis S. García-Tíscar P. Verborgh R. Esteban-Pavo S. Pérez L. Minvielle-Sebastia C. Guinet 《Marine Biology》2008,154(4):603-612
The Strait of Gibraltar is inhabited throughout the year by a group of pilot whales (Globicephala melas), but their spatial distribution varies between Summer and Autumn. In this paper, we have used carbon (13C/12C) and nitrogen (15N/14N) stable isotope signatures to investigate the differences in diet amongst seasons, sex and stable social units. Skin samples
were collected from 56 individually photo-identified pilot whales during Autumn 2005 and Summer 2006. These individuals were
genetically sexed and their isotopic signature determined. The level of inter-individual association both within and between
stable social units were compared to Euclidean distances between individual isotopes signatures. No differences in either
δ15N or δ13C were found according to the sex of individuals, but significant seasonal differences were found in δ15N, although not in the δ13C values. This suggests that pilot whales are resident year round in the Strait, a finding supported by independent photo-identification.
The variation in δ15N could reflect a shift in pilot whale diet through the year, with pilot whales feeding at a higher trophic level in Autumn
compared to Summer. This could also represent a change in the diet of pilot whale prey species. The δ13C values were significantly different amongst the four stable social units sampled and individual δ13C values were significantly related to the level of inter-individual association, while no relationship was found for δ15N. These results suggest that within the same general area (i.e. the Strait of Gibraltar), there is some level of specialisation
in habitat or prey choice between pilot whales social units. 相似文献
7.
We conducted grazing experiments with the three marine cladoceran genera Penilia, Podon and Evadne, with Penilia avirostris feeding on plankton communities from Blanes Bay (NW Mediterranean, Spain), covering a wide range of food concentrations (0.02–8.8 mm3 l–1, plankton assemblages grown in mesocosms at different nutrient levels), and with Podon intermedius and Evadne nordmanni feeding on the plankton community found in summer in Hopavågen Fjord (NE Atlantic, Norway, 0.4 mm3 l–1). P. avirostris and P. intermedius showed bell-shaped grazing spectra. Both species reached highest grazing coefficients at similar food sizes, i.e. when the food organisms ranged between 15 and 70 µm and between 7.5 and 70 µm at their longest linear extensions, respectively. E. nordmanni preferred organisms of around 125 µm, but also showed high grazing coefficients for particles of around 10 µm, while grazing coefficients for intermediate food sizes were low. Lower size limits were >2.5 µm, for all cladocerans. P. avirostris showed upper food size limits of 100 µm length (longest linear extension) and of 37.5 µm particle width. Upper size limits for P. intermedius were 135 µm long and 60 µm wide; those for E. nordmanni were 210 µm long and 60 µm wide. Effective food concentration (EFC) followed a domed curve with increasing nutrient enrichment for P. avirostris; maximum values were at intermediate enrichment levels. The EFC was significantly higher for P. intermedius than for E. nordmanni. With increasing food concentrations, the clearance rates of P. avirostris showed a curvilinear response, with a narrow modal range; ingestion rates indicated a rectilinear functional response. Mean clearance rates of P. avirostris, P. intermedius and E. nordmanni were 25.5, 18.0 and 19.3 ml ind.–1 day–1, respectively. Ingestion rates at similar food concentrations (0.4 mm3 l–1) were 0.6, 0.8 and 0.9 g C ind.–1 day–1.Communicated by O. Kinne, Oldendorf/Luhe 相似文献
8.
Although mysids play important roles in marine food chains, studies on their production are scarce, especially for warm-water
species. We investigated life history and production of Orientomysis robusta in a shallow warm-temperate habitat of the Sea of Japan. Its spawning and recruitment occurred throughout the year; 19 overlapping
cohorts were recognizable over an annual cycle. The summer cohorts recruited in July–September exhibited rapid growth, early
maturity, small brood size, and small body size. A converse set of life history traits characterized the autumn–winter cohorts
recruited in October–March. The spring cohorts recruited in April–June had intermediate characteristics of both cohorts. Life
spans were 19–33, 21–48, and 69–138 days for summer, spring, and autumn–winter cohorts, respectively, and mortality rates
were high for spring and summer cohorts, especially during June–August but were low for autumn–winter cohorts. Production
calculated from the summation of growth increments was 488.8 mg DW m−2 year−1 with an annual P/B ratio of 21.26. The short life span seems to be responsible for such an extremely high P/B ratio. A method not requiring recognition and tracking cohorts gave similar values (534.0 mg DW m−2 year−1 and 20.49). The close agreement in production values between the two methods indicates our estimates are valid. 相似文献
9.
Simon Ducatez Sébastien Dalloyau Pierre Richard Christophe Guinet Yves Cherel 《Marine Biology》2008,155(4):413-420
Individual specialisation is widespread and can affect a population’s ecological and evolutionary dynamics. Whether intra-specific
niche differences can influence reproductive investment was examined in a marine mammal, the southern elephant seal (Mirounga leonina), whose females were known to forage in two different areas during the austral winter. The study was conducted at Kerguelen
Islands (49°21′S, 70°18′E), southern Indian Ocean, in late winter–early spring 2006. Pups were used as proxies of their mothers’
biology and combined information on their weaning mass (a proxy of females’ foraging success and short-term fitness) together
with their blood δ13C value (a proxy of female foraging zone). First, the use of isotopic signature of pups was validated to study the female
foraging ecology during their pre-breeding trip by demonstrating that δ13C and δ15N values of pups and their mothers were positively and linearly correlated. Then, blood samples were taken from a large number
of newly-weaned pups, which were also weighed, to provide information at the population level. Estimated δ13C values of female seals encompassed a large range of values (from −23.7 to −19.1‰) with an unimodal frequency distribution,
suggesting no contrasted foraging areas within the population. No significant relationship was found between pup weaning mass
and their carbon signature, indicating no link between female foraging areas and maternal foraging success and investment.
Finally, blood δ13C and δ15N values gave new insights into southern elephant seal ecology, suggesting that females mainly foraged north of the Polar
Front where they preyed upon myctophid fish in late winter. 相似文献
10.
Influence of nutrients in the feeding ecology of seagrass (Posidonia oceanica L.) consumers: a stable isotopes approach 总被引:1,自引:1,他引:0
Nitrogen inputs to coastal environments can considerably alter the abundance of primary producers. However, how herbivores
modify their trophic signatures and adjust to changes in food resource conditions remains controversial. Here, we assess the
effect of nutrient availability on the diet shifts of the two main Mediterranean herbivores, the Sparid fish Sarpa salpa L. and the sea urchin Paracentrotus lividus (Lmk.) that feed mostly on the seagrass Posidonia oceanica L. (Delile), epiphytes and benthic macroalgae. To do this, we (1) investigate the patterns of isotopic composition (δ13C and δ15N signatures) of the two herbivores and their potential food sources in three areas of contrasting nutrient conditions and,
(2) we assess the diet shift along this nutrient gradient by estimating the isotopic nutrient enrichment (i.e., the contribution
of δ13C and δ15N signatures in consumers’ tissues relative to potential food sources). Food web signatures of δ13C were similar among the three study sites, and no patterns of δ13C shift were observed in their diets. In contrast, there was a consistent increase in N contents and δ15N along the nutrient gradient for all primary producers and their consumers. The rate of δ15N enrichment was also clearly distinctive between the two herbivores: in P. lividus it increased by 61% along the nutrient gradient, while in S. salpa it remained constant. Our results suggest that sea urchins behave as facultative omnivores and feed on vegetable or mixed
diets depending on the trophic status of the system. It is unclear, however, if this modification is behavioral or the consequence
of mere changes in the availability of food items, as animal epiphytes (e.g., hydrozoans, bryozoans and ascidians) can also
became more abundant on seagrass leaves under increased nutrient conditions. In contrast, adult fish appear to feed on vegetal
material independent of nutrient availability in the ecosystem. 相似文献
11.
Benoit Lebreton Pierre Richard Robert Galois Gilles Radenac Amel Brahmia Géraldine Colli Marig Grouazel Cyril André Ga?l Guillou Gérard F. Blanchard 《Marine Biology》2012,159(7):1537-1550
In an intertidal Zostera noltii Hornem seagrass bed, food sources used by sediment meiofauna were determined seasonally by comparing stable isotope signatures (δ13C, δ15N) of sources with those of nematodes and copepods. Proportions of different carbon sources used by consumers were estimated using the SIAR mixing model on δ13C values. Contrary to δ15N values, food source mean δ13C values encompassed a large range, from −22.1 ‰ (suspended particulate organic matter) to −10.0 ‰ (Z. noltii roots). δ13C values of copepods (from −22.3 to −12.3 ‰) showed that they use many food sources (benthic and phytoplanktonic microalgae, Z. noltii matter). Nematode δ13C values ranged from −14.6 to −11.4 ‰, indicating a strong role of microphytobenthos and/or Z. noltii matter as carbon sources. The difference of food source uses between copepods and nematodes is discussed in light of source accessibility and availability. 相似文献
12.
Pedro Reis Costa Sandra Lage Marisa Barata Pedro Pousão-Ferreira 《Marine Biology》2011,158(12):2805-2811
Marine toxins generated by harmful algal blooms can be transferred through the marine food web and ultimately cause massive
deaths of piscivorous predators. However, very few studies have explored the processes of accumulation and biotransformation
of paralytic shellfish toxins (PSTs) within fishes. White seabream (Diplodus sargus) were orally challenged with contaminated cockles (Cerastoderma edule) containing N-sulfocarbamoyl and decarbamoyl toxins and non-contaminated cockles afterwards. Specific PSTs that occurred
in low abundance in cockles (B1 7.6% and dcSTX 1.6% molar fraction) were the only toxins detected in fish viscera possibly
resulting from selective elimination and transformation of the various PSTs. Concentration of toxins progressively increased
in fish viscera throughout the uptake period. Toxins were then rapidly depurated (B1 0.905 day−1, dcSTX 0.467 day−1) when diet was changed to non-toxic cockles. Results indicate conversion of a precursor toxin into B1 which in turn might
be converted into dcSTX at a lower extent. Low accumulation efficiency of 1.7 and 5.0% was calculated to B1 and dcSTX, respectively.
This study contributes to a better understanding of dynamics of PSTs in fish and the fate of these compounds in the marine
food web. 相似文献
13.
Spatial and temporal dynamics of carbon and nitrogen stable isotope signatures of the bottom-dwelling caridean shrimp Nauticaris marionis were measured during April and May between 1984 and 2000 in the vicinity of Marion Island (the Prince Edward Islands, Southern Ocean). There was one trophic-level enrichment in bulk 15N and 13C signatures between small (<20 mm long) and large (>20 mm) specimens of N. marionis, suggesting distinct trophic differentiation among major shrimp size groups. Both 15N and 13C values of N. marionis increased with the depth, reflecting changes in their diet. There were no clear temporal trends in bulk 15N signatures of N. marionis. However, compound-specific 15N measurements of amino acids indicated that N. marionis from the inter-island realm occupied the trophic level of second order carnivores, while similarly sized shrimps in the near-shore realm were at the trophic level of first order carnivores. Compound-specific measurements also identified a change in the source of inorganic nitrogen at the base of the food web between the inter-island and near-shore realms. In contrast to the bulk 15N values, a significant shift in bulk 13C values of N. marionis was observed between 1984 and more recent years. This temporal change appears to be linked to changes in the overall productivity of the Prince Edward Island inter-island system, which could be linked to global climate change.Communicated by J.P. Thorpe, Port Erin 相似文献
14.
Nicolas Goñi John Logan Haritz Arrizabalaga Marc Jarry Molly Lutcavage 《Marine Biology》2011,158(5):1057-1073
This study aims to describe the variability of albacore (Thunnus alalunga) diet in the Northeast Atlantic and Mediterranean Sea and to identify possible relationships between this variability and
the features of different feeding areas, the behavior, and the energetic needs of albacore. Stomach contents from albacore
caught in five zones of the Bay of Biscay and surrounding waters (n = 654) and three zones of the Mediterranean Sea (n = 152) were analyzed in terms of diet composition and stomach fullness. Carbon and nitrogen stable isotope and C/N ratios
were measured for white muscle and liver from albacore in the Bay of Biscay (n = 41) and Mediterranean Sea (n = 60). Our results showed a spatial, seasonal, inter-annual, and size-related variability in the diet of albacore. Albacore
diet varied by location in the Mediterranean Sea, with a particularly high proportion of cephalopods, and low δ15N values in the Tyrrhenian Sea. In the Northeast Atlantic, albacore consumed a higher proportion of crustaceans and a lower
proportion of fishes in the most offshore sampling zone than inshore. The digestion states of the major prey reflected a diurnal
feeding activity, indicative of feeding in deeper waters offshore, whereas on the continental slope, feeding probably occurred
in surface waters at night. Important seasonal and inter-annual diet variability was observed in the southeast of the Bay
of Biscay, where preferred albacore prey appeared to be anchovy (Engraulis encrasicolus). Stomach fullness was inversely related to body size, probably reflecting higher energetic needs for smaller individuals.
Albacore from the Bay of Biscay had significantly lower δ13C and higher δ15N values compared with albacore from the Mediterranean Sea, indicative of regional baseline shifts, and trophic position and
muscle lipid stores in albacore increased with body size. 相似文献
15.
Production dynamics of eelgrass, Zostera marina was examined in two bay systems (Koje Bay and Kosung Bay) on the south coast of the Korean peninsula, where few seagrass
studies have been conducted. Dramatically reduced eelgrass biomass and growth have been observed during summer period on the
coast of Korea, and we hypothesized that the summer growth reduction is due to increased water temperature and/or reduced
light and nutrient availabilities. Shoot density, biomass, morphological characteristics, leaf productivities, and tissue
nutrient content of eelgrass were measured monthly from June 2001 to April 2003. Water column and sediment nutrient concentrations
were also measured monthly, and water temperature and underwater irradiance were monitored continuously at seagrass canopy
level. Eelgrass shoot density, biomass, and leaf productivities exhibited clear seasonal variations, which were strongly correlated
with water temperature. Optimal water temperature for eelgrass growth in the present study sites was about 15–20°C during
spring period, and eelgrass growths were inhibited at the water temperature above 20°C during summer. Daily maximum underwater
photon flux density in the study sites was usually much higher than the light saturation point of Z. marina previously reported. Densities of each terminal, lateral, and reproductive shoot showed their unique seasonal peak. Seasonal
trends of shoot densities suggest that new eelgrass shoots were created through formation of lateral shoots during spring
and a part of the vegetative shoots was transformed into flowering shoots from March. Senescent reproductive shoots were detached
around June, and contributed to reductions of shoot density and biomass during summer period. Ambient nutrient level appeared
to provide an adequate reserve of nutrient for eelgrass growth throughout the experimental period. The relationships between
eelgrass growth and water temperature suggested that rapid reductions of eelgrass biomass and growth during summer period
on the south coast of the Korean peninsula were caused by high temperature inhibition effects on eelgrass growth during this
season. 相似文献
16.
Young green turtles (Chelonia mydas) spend their early lives as oceanic omnivores with a prevalence of animal prey. Once they settle into neritic habitats (recruitment),
they are thought to shift rapidly to an herbivorous diet, as revealed by studies in the Greater Caribbean. However, the precise
timing of the ontogenic dietary shift and the actual relevance of animal prey in the diet of neritic green turtles are poorly
known elsewhere. Stable isotopes of carbon, sulfur and nitrogen in the carapace scutes of 19 green turtles from Mauritania
(NW Africa), ranging from 26 to 102 cm in curved carapace length (CCLmin), were analyzed to test the hypothesis of a rapid
dietary shift after recruitment. Although the length of residence time in neritic habitats increased with turtle length, as
revealed by a significant correlation between turtle length and the δ13C and the δ34S of the scutes, comparison of the δ15N of the innermost and outermost layers of carapace scutes demonstrated that consumption of macrophytes did not always start
immediately after recruitment, and turtles often resumed an animal-based diet after starting to graze on seagrasses. As a
consequence, seagrass consumption did not increase gradually with turtle size and animal prey largely contributed to the diet
of turtles within the range 29–59 cm CCLmin (76–99% of assimilated nutrients). Seagrass consumption by turtles larger than
59 cm CCLmin was higher, but they still relied largely on animal prey (53–76% of assimilated nutrients). Thus, throughout
most of their neritic juvenile life, green turtles from NW Africa would be better classified as omnivores rather than herbivores.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
17.
Mikael van Deurs Jane W. Behrens Thomas Warnar John Fleng Steffensen 《Marine Biology》2011,158(8):1781-1789
The commercially and ecologically valuable sandeel (Ammodytes ssp.) make distinct vertical shifts between an inactive stage,
during which they seek refuge in the sand, and a pelagic schooling stage, during which they forage. This characteristic discontinuous
foraging pattern constitutes a challenge to fishery biologists and has consequences for a wide range of predators ranging
from birds and mammals to commercially important species. However, experimental studies that shed light on the primary drivers
of foraging activity in fish are rare. In the present study, whole schools of sandeel (A. tobianus) were caught in August in east Denmark (65°02′30N; 12°37′00E) and kept in large tanks in the laboratory. It was found that
the amount of food ingested and memory of past days feeding history are primary drivers of foraging activity at the level
of the entire school, whereas external factors such as prey concentration and temperature are merely secondary drivers. 相似文献
18.
Martin Gullström Charlotte Berkström Marcus C. Öhman Maria Bodin Mattis Dahlberg 《Marine Biology》2011,158(7):1483-1495
Although herbivorous fish form critical linkages between primary producers and higher trophic levels, the major factors regulating
their spatial structure in seagrass systems remain poorly understood. The present study examined the parrotfish Leptoscarus vaigiensis in seagrass meadows of a tropical embayment in the western Indian Ocean. Stomach content analysis and direct field observations
showed that L. vaigiensis is an efficient grazer, feeding almost exclusively on seagrass leaves. Seagrass shoot density was highly correlated to all
density variables (total, juvenile and subadult) and juvenile biomass of L. vaigiensis, while subadult biomass was predicted by distance to neighbouring coral habitat. Moreover, density and biomass of predatory
fish (piscivores) were predicted by seagrass canopy height and the distribution patterns of predators followed those of L. vaigiensis. Hence, factors at local (seagrass structural complexity and feeding mode) and landscape scale levels (seascape context and
distribution of piscivores) likely mutually structure herbivorous fish communities. The findings underscore the importance
of incorporating multiple scale-dependent factors when managing coastal seagrass ecosystems and their associated key species. 相似文献
19.
Katsumasa Yamada Kazutaka Takahashi Carole Vallet Satoru Taguchi Tatsuki Toda 《Marine Biology》2007,150(5):905-917
Spatial and seasonal distribution pattern, life history and production of three species of Neomysis (Mysidacea) which commonly occur in northwestern subarctic Pacific coastal waters, were investigated throughout the year
in the Akkeshi-ko estuary, northern Japan. The most abundant species Neomysis awatschensis (annual mean density: 179.8 inds. m−2, biomass: 108.8 mg DW m−2) occurred at the inner part of the estuary including low salinity areas with no clear preference for the seagrass bed. The
second most abundant Neomysis mirabilis (mean density: 95.8 inds. m−2, biomass: 90.1 mg DW m−2) occurred at relatively saline seagrass site throughout the year. Occurrence of Neomysis czerniawskii in the estuary was limited to the seagrass bed during summer when their population mainly consisted of juveniles, suggesting
that this species is a seasonal migrant between the estuary and the marine environment. Both N. awatschensis and N. mirabilis populations were composed of two generation types, a larger sized overwintering and smaller sized spring/summer generations;
however, each species had a different reproductive strategy. N. awatschensis was characterized by fast growth to maturity at a smaller size than N. mirabilis with a relatively high fecundity during warm season, suggesting that this species is an r-strategist which can utilize opportunistically
a wide variety of habitats. In contrast, the seagrass bed resident N. mirabilis was a K-strategist which matures at a larger size producing fewer but larger offspring. The annual production of N. awatschensis (0.57–0.70 g DW m−2, mean of the whole estuary) and N. mirabilis (0.58–0.68 g DW m−2, mean of the seagrass bed) at their respective habitats was comparable. Consequently, species-specific life history and distribution
pattern are concluded to allow Neomysis spp. to coexist in the estuary and the high carrying capacity of seagrass bed is suggested to contribute to maintain their
high biomass level. 相似文献
20.
Stable 13C and 15N isotope analyses of scale, bone, and muscle tissues were used to investigate diet and trophic position of North Atlantic bluefin tuna (Thunnus thynnus Linnaeus) during residency in the northwest Atlantic Ocean off the northeast coast of the United States. Adult bluefin tuna scales collected from fish between June and October 2001 were significantly enriched in 13C compared to both muscle and bone across all months, while muscle was significantly enriched in 15N compared to either bone or scale throughout the same period. In muscle tissue, there was evidence of a shift over the summer from prey with 13C values (–17 to –18) that were characteristic of silver hake (Merluccius bilinearis) to species with 13C values of –20 to –21 that were similar to Atlantic herring (Clupea harengus) and sandlance (Ammodytes americanus). Depletion of 15N values in adult scales and bone compared to muscle tissue may be explained by bone and scale samples representing juvenile or life-long feeding habits, isotopic routing, or isotopic differences in amino acid composition of the three tissue types. Adult bluefin tuna were estimated to be feeding at a trophic position similar to pelagic sharks in the northwest Atlantic Ocean, while the trophic positions of yellowfin tuna (Thunnus albacares), albacore tuna (Thunnus alalunga), and juvenile bluefin tuna were indicative of a diet of up to a full trophic position below adult bluefin tuna. The close relationship between the juvenile bluefin 15N values and those of suspension feeders suggests that nektonic crustaceans or zooplankton may contribute significantly to the diet of bluefin tuna, a food source previously overlooked for this species in the northwest Atlantic Ocean.Communicated by J.P. Grassle, New Brunswick 相似文献