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1.
Sabellariid worms, such as Phragmatopoma lapidosa, are sessile suspension feeders that attach to exposed hard bottom and serve as foundation species for worm reefs which are complex, multifaceted habitats. While worm reefs are adapted to dynamic sedimentary environments, burial of these habitats by beach nourishment projects is a concern. This study determined duration and depth of burial that can be tolerated by P. lapidosa without death. Worm rock samples were buried in sand at 1–10 cm (1-cm intervals), and at 15, 25 and 40 cm for the duration of 72, 144, and 216 h and then surveyed for initial mortality after burial and one week after removal of sediment (latent effects). Initial mortality was similar across all burial depths for the 72-h duration with values ranging from 8.3% (±0.8 SE) for 1 cm to 24.0% (±8.0 SE) for 10 cm of sediment. As burial duration increased to 144 h, mortality generally increased as burial depth increased with an average mortality for 2 cm of sediment of 23.5% (±5.3 SE) increasing to 96.0% (±14.3 SE) with 40 cm of sediment. The mean percent mortality for burial samples in the 216 h treatment varied from a low of 71.2% (±3.3 SE) for 1 cm depth to a high of 100% (±0 SE) for 10, 15, 25, and 40 cm depths. Mortality for most treatments also increased over time after removal of sediment indicating latent effects of burial stress.  相似文献   

2.
A cross-system analysis of bulk sediment composition, total organic carbon (TOC), atomic C/N ratio, and carbon isotope composition (δ13C) in 82 surface sediment samples from natural and planted mangrove forests, bank and bottom of tidal creeks, tidal flat, and the subtidal habitat was conducted to examine the roles of mangroves in sedimentation and organic carbon (OC) accumulation processes, and to characterize sources of sedimentary OC of the mangrove ecosystem of Xuan Thuy National Park, Vietnam. Sediment grain sizes varied widely from 5.4 to 170.2 μm (mean 71.5 μm), with the fine sediment grain size fraction (< 63 μm) ranging from 11 to 99.3% (mean 72.5%). Bulk sediment composition suggested that mangroves play an important role in trapping fine sediments from river outflows and tidal water by the mechanisms of tidal current attenuation by vegetation and the ability of fine roots to bind sediments. The TOC content ranged from 0.08 to 2.18% (mean 0.78%), and was higher within mangrove forests compared to those of banks and bottoms of tidal creeks, tidal flat, and subtidal sediments. The sedimentary δ13C ranged from − 27.7 to − 20.4‰ (mean − 24.1‰), and mirrored the trend observed in TOC variation. The TOC and δ13C relationship showed that the factors of microbial remineralization and OC sources controlled the TOC pool of mangrove sediments. The comparison of δ13C and C/N ratio of sedimentary OC with those of mangrove and marine phytoplankton sources indicated that the sedimentary OC within mangrove forests and the subtidal habitat was mainly composed of mangrove and marine phytoplankton sources, respectively. The application of a simple mixing model showed that the mangrove contribution to sedimentary OC decreased as follows: natural mangrove forest > planted mangrove forest > tidal flat > creek bank > creek bottom > subtidal habitat.  相似文献   

3.
 Functional group analysis was used to determine the major bioturbators in the Dry Tortugas, Florida Keys. The surface community is dominated by surface deposit feeding polychaetes and burrowing bivalves capable of mixing the top 0–4 cm of the sediment on time scales of days to weeks. Bioturbation by the Notomastus sp. and Callianassa sp. deep community effectively removes primary sedimentary structures. Their fossilized burrow structures may be geologically important in this system. Surface microtopography is controlled by stabilizing and destabilizing forces that determine the potential for surface resuspension and sediment transport in the Dry Tortugas.  相似文献   

4.
Chemical concentration gradients in the interstitial waters of shallow (0–10 cm), reducing sediments are reported for four stations in the Tamar Estuary over a two-year period. The products of organic matter breakdown, sedimentary redox changes and diagenetic reactions have been determined and a multicomponent analytical approach has enabled the interactions of complementary processes to be examined. While many components show spatial and seasonal patterns related to the supply of organic matter and salinity associated sulphate distribution, the effects of temperature, sediment disturbance and river flow are also apparent.Sediment stored prior to the separation of interstitial water showed significant changes in chemical composition compared to samples processed within 24 h of collection.  相似文献   

5.
Sediment and water column data from four sites in North, Central and South San Francisco Bays were collected monthly from November 1999 through November 2001 to investigate the seasonal variation of benthic organic matter and chlorophyll in channel sediments, the composition and quality of sediment organic matter (SOM), and the relationship between seasonal patterns in benthic organic matter and patterns in water column chlorophyll. Water column chlorophyll peaked in the spring of 2000 and 2001, characteristic of other studies of San Francisco Bay phytoplankton dynamics, however an unusual chlorophyll peak occurred in fall 2000. Cross-correlation analysis revealed that water column chlorophyll at these four channel sites lead sediment parameters by an average of 2 to 3 months. Sediment organic matter levels in the San Francisco Bay channel showed seasonal cycles that followed patterns of water column production: peaks in water column chlorophyll were followed by later peaks in sediment chlorophyll and organic matter. Cyclical, seasonal variations also occurred in sediment organic matter parameters with sediment total organic carbon (TOC) and total nitrogen (TN) being highest in spring and lowest in winter, and sediment amino acids being highest in spring and summer and lowest in winter. Sediment chlorophyll, total organic carbon, and nitrogen were generally positively correlated with each other. Sediment organic matter levels were lowest in North Bay, intermediate in Central Bay, and highest in South Bay. C:N ratio and the ratio of enzyme hydrolyzable amino acids to TOC (EHAA:TOC) data suggest that SOM quality is more labile in Central and northern South Bay, and more refractory in North Bay and southern South Bay.  相似文献   

6.
Rose Bengal stained benthic foraminifera were studied from 11 cores collected along two depth transects off southern Portugal: one in the Lisbon-Setúbal Canyon and the other along the canyon edge. The total standing stocks and distribution of foraminifera were investigated in relation to sediment and pore water geochemistry. Nitrate was used as a redox indicator, sedimentary chlorophyll a and CPE (chloroplastic pigment equivalents) contents as a measure of labile organic matter, and total organic carbon as a measure of bulk organic matter availability.The canyon sediments were enriched in organic carbon and phytopigments at all water depths in comparison with the canyon edge. Water depth seemed to control sedimentary phytopigment content, but not total organic carbon. No significant correlation was seen between pigment and total organic carbon content.The abundance of calcareous foraminifera correlated with the phytodetritus content, whereas a weaker correlation was observed for the agglutinated taxa. Therefore, calcareous foraminifera appear to require a fresher food input than agglutinated taxa. The foraminiferal species composition also varied with pigment content and nitrate penetration depth in the sediment, in line with the TROX concept. Phytopigment-rich (surficial CPE content >20 μg/cm3) sediments with a shallow nitrate penetration depth (∼1 cm depth) were inhabited by generally infaunal species such as Chilostomella oolina, Melonis barleeanus and Globobulimina spp. As the nitrate penetration increased to ∼2 cm depth in sediment and the pigment content remained relatively high (>15 μg/cm3), Uvigerina mediterranea and Uvigerina elongatastriata became dominant species. With declining CPE content and increasing nitrate penetration depth, the foraminiferal assemblages changed from the mesotrophic Cibicides kullenbergi-Uvigerina peregrina assemblage to the oligotrophic abyssal assemblage, mainly consisting of agglutinated taxa.  相似文献   

7.
The annual total and organic mercury bioaccumulation pattern of Scrobicularia plana and Hediste diversicolor was assessed to evaluate the potential mercury transfer from contaminated sediments to estuarine food webs. S. plana was found to accumulate more total and organic mercury than H. diversicolor, up to 0.79 mg kg−1 and 0.15 mg kg−1 (wet weight) respectively, with a maximum annual uptake of 0.21 mg kg−1 y−1, while for methylmercury the annual accumulation was similar between species and never exceeded 0.045 mg kg−1 y−1. The higher organic mercury fraction in H. diversicolor is related to the omnivorous diet of this species. Both species increase methylmercury exposure by burrowing activities and uptake in anoxic, methylmercury rich sediment layers. Integration with the annual biological production of each species revealed mercury incorporation rates that reached 28 μg m−2 y−1, and to extract as much as 11.5 g Hg y−1 (of which 95% associated with S. plana) in the 0.4 km2 of the most contaminated area, that can be transferred to higher trophic levels. S. plana is therefore an essential vector in the mercury biomagnification processes, through uptake from contaminated sediments and, by predation, to transfer it to economically important and exploited estuarine species.  相似文献   

8.
The response of a sub-arctic, deep-sea macrofaunal community to a simulated food sedimentation event was studied by means of a stable isotope “pulse-chase” experiment. A food pulse was simulated by adding 500 mg C m−2 of 13C-labelled diatoms, Chaetoceros radicans, to sediment cores retrieved from 1080 m in the Faroe-Shetland Channel. Carbon uptake by specific macrofaunal groups was quantified after 3 and 6 days of incubation. The carbon uptake of the dominant taxon (Polychaeta) was quantified at the genus-, and where possible, species-level, representing a data resolution that is rare in deep-sea tracer studies. The macrofaunal community reacted rapidly to the diatom addition, with 47% and 70% of the animals illustrating 13C-enrichment after 3 and 6 days, respectively. Approximately 95% of C uptake was located in the upper 2 cm due to the particularly shallow vertical distribution of the macrofaunal community and the nonexistent tracer subduction by burrowing species. Polychaetes of the families Ampharetidae and Cirratulidae were among the most heavily labelled with above background enrichment reaching 1300‰. Approximately 0.8 and 2.0 mg C m−2 were processed by the macrofauna after 3 and 6 days, representing 0.2% and 0.4% of the added carbon, respectively. It was not possible to differentiate sub-surface deposit-feeding polychaetes from predator/scavenger- and omnivorous polychaetes using their natural ??15N signatures. However, the combination of natural abundance ??15N data and 13C-labelling experiments proved to be useful for elucidating trophic relations in deep-sea food webs. This study confirms that macrofauna play an active role in the short-term carbon cycling at bathyal depths even at sub-zero temperatures and highlights the need for detailed knowledge of the community structure in understanding carbon processing patterns and early diagenesis of organic matter in marine sediments.  相似文献   

9.
Bioturbation is one of the major processes influencing ecosystem functioning. Population parameters such as species density, burrow density and species-specific life modes, determine the impact of bioturbation on the ecosystem. A laboratory experiment was developed, using microcosms mimicking a marine intertidal sediment–water interface which allowed for quantification of different population parameters. The vertical redistribution, bioturbation rate and maximum penetration depth of two sizes (41 and 129 μm) of luminophores were measured in five treatments (control, low density of burrows with and without Corophium (1989 ind./m2), and high density of burrows with and without Corophium (14,921 ind./m2)) after 1, 7 and 14 days. Results indicate that the behavioural activities of Corophium are of the utmost importance in sediment reworking, since they contributed to a five-fold increase in bioturbation rate compared to the passive transport induced by the static structure of the burrows. Furthermore, density is an important parameter because only high densities play a prominent role in particle transport and hence in organic matter processing, while the role of low Corophium densities is limited in sediment reworking. No evidence for differentiation in sediment size fractions was observed. Finally, bioturbation rates in this study were low compared to other studies, and these results suggest an influence of the tidal rhythmicity in the behavioural activity of Corophium on the bioturbation rate.  相似文献   

10.
Grain-size distributions, total organic carbon (TOC) and total nitrogen (TN) concentrations, and TOC/TN ratios (C/N) were analysed for surface sediments from the Lower Yangtze River-East China Sea (ECS) shelf system. Hierarchical cluster analysis of grain-size parameters (mode, mean, sorting, skewness and kurtosis) has been employed to characterize grain-size compositions. The results suggest there are five grain-size compositional types (type-I–V) that fingerprint distinct depositional conditions. In areas with high sedimentation rates, hydrological sorting preferentially enriches the fraction coarser than 6.4ø (12 μm) in shallow seafloor sediments (water depth<30 m) by transporting the finer fraction to the deeper seafloor (water depth>30 m), and thus forms grain-size compositional type-I (shallow) and type-II (deep). In the open shelf, where modern sediment supply is very limited, grain-size types-III–V are identified according to different winnowing intensity. Overall TOC contents significantly correlate with mud proportions, suggesting muddy sediments are the primary control on OM accumulation. However, de-association of terrestrial OM from fine sediments in the Estuary and the occurrence of presumably relict OM in the open shelf exert additional controls on OM dispersal and carbon cycling in the ECS. By considering geography, oceanography, sediment source, and the relation between sedimentation conditions and sedimentary OM distributions, we define six depositional settings: the lower river, the estuary, the coast, the offshore upwelling area, the erosional area, and the open shelf. These settings describe the sediment dispersal and associated organic matter cycling in the Lower Yangtze River-ECS shelf system.  相似文献   

11.
Maldanid polychaetes can be important components of marine benthic communities, playing significant roles in particle subduction or sediment irrigation. Many maldanids are known to inhabit tubes consisting of sediments consolidated by mucus; the structure and composition of these tubes, and their potential impact on benthic environments, are poorly known. We examined the three-dimensional organization of Maldane sarsi tubes, using CT scanning together with analyses of sediment grain size and concentrations of Fe, Mn, organic carbon and bacteria in tube material. M. sarsi tubes consist of stacks of individual consolidated mud disks, surrounding a dense, continuous, inner tube. The tubes of M. sarsi contained fewer fine particles than surrounding sediments, and greater concentrations of Fe, Mn, organic carbon and bacteria, especially in the inner zone. These distributions suggest that tube irrigation affects Fe and Mn oxidation and precipitation in a narrow zone surrounding M. sarsi, and that mucous secretion and potential feeding activities (the hoeing of surface sediments) lead to increases in organic carbon and bacteria in the inner, and deepest parts of the tube. The finding of relict tubes, buried at up to 15 cm depth, indicates a relatively high longevity for these structures and suggests a potential importance in biogeochemical cycling.  相似文献   

12.
Biogenic bottom features, animal burrows and biological activities interact with the hydrodynamics of the sediment–water interface to produce altered patterns of sediment erosion, transport and deposition which have consequences for large-scale geomorphologic features. It has been suggested that depending on the hydrodynamic status of the habitat, the biological activity on the bottom may have a variety of effects. In some cases, different bioturbation activities by the same organism can result in different consequences. The burrowing crab Neohelice granulata is the most important bioturbator at SW Atlantic saltmarshes and tidal plains. Because of the great variety of habitats that this species may inhabit, it is possible to compare its bioturbation effects between zones dominated by different hydrodynamic conditions. Internal marsh microhabitats, tidal creeks bottoms and basins, and open mudflats were selected as contrasting zones for the comparison on a large saltmarsh at Bahía Blanca Estuary (Argentina). Crab burrows act as passive traps of sediment in all zones, because their entrances remain open during inundation periods at high tide. Mounds are generated when crabs remove sediments from the burrows to the surface and become distinctive features in all the zones. Two different mechanisms of sediment transport utilizing mounds as sediment sources were registered. In the first one, parts of fresh mound sediments were transported when exposed to water flow during flooding and ebbing tide, with higher mound erosion where currents were higher as compared to internal marsh habitats and open mudflats. In the second mechanism, mounds exposed to atmospheric influence during low tide became desiccated and cracked forming ellipsoidal blocks, which were then transported by currents in zones of intense water flow in the saltmarsh edge. Sedimentary dynamics varied between zones; crabs were promoting trapping of sediments in the internal saltmarsh (380 g m−2 day−1) and open mudflats (1.2 kg m−2 day−1), but were enhancing sediment removal in the saltmarsh edge (between 10 and 500 g m−2 day−1 in summer). The implication is that biologically mediated sedimentological changes could be different among microhabitats, potentially leading to contrasting geomorphologic effects within a particular ecosystem.  相似文献   

13.
Four profiles of estuarine sediments obtained from boreholes drilled in the Algarve, Southern Portugal were studied in order to reconstruct the process of sediment accumulation driven by the postglacial sea level rise. In addition to the sedimentological analysis, the Foraminifera Index of Marine Influence (FIMI) permitted assessment of the nature and organization of sedimentary facies in the Beliche–Guadiana and Gilão–Almargem estuaries. The Beliche–Guadiana CM5 and Almargem G2 profiles accumulated in a sheltered environment, with the former presenting an almost continuous record of the sea level rise since ca 13?000 cal yr BP. The G1 and G3 profiles from the Gilão–Almargem area represent a more discontinuous record of the last 8000 years, which accumulated in the more dynamic environment of an outer estuary. The integration of all radiocarbon ages of dated levels, led to an estimate of sediment accumulation rates. Assuming a constant position of the sediment surface with respect to the tidal range and a negligible compaction of sediment, the sea level rose at the rate of 7 mm yr−1 in the period from 13?000 to 7500 cal yr BP. This process slowed down to ca 0.9 mm yr−1 from 7500 cal yr BP until the present. The marked historical change in the rate of sediment accumulation in these estuaries also occurred with the accumulation of organic matter and is, therefore, important data for global biogeochemical models of carbon. The main obstacle to obtain higher temporal resolution of the sedimentary processes was the intense anaerobic respiration of organic matter via sulphate reduction, which did not allow any accumulation of peat and, furthermore, led to erasure of the palaeontological record by acid formed from the subsequent oxidation of sulphides.  相似文献   

14.
In the sedimentary column, a combined quantification of burrows and macrobenthic community provides evidence of bioturbation features in the submarine canyon of Cap-Ferret between 2000 and 3000 m depth. An image-processing technique allows accurate quantification of burrow volumes with depth in the sedimentary column. The major bioturbation mode seems to be different in the channel compared to the interfluve. Macrobenthic activity is more inclined to mix the sediment in the channel in response to increased organic matter supplies. Sediment mixing leads to burrow destruction in the upper mixed layer of sediment in the canyon. Burrows are better preserved on the interfluve where mixing is slower. Under the mixed zone, the volume of recorded burrows is higher when sedimentation rate increases, as in the upper canyon. In this transition layer, the burrow volume is estimated to be between 3 and 64% of the total sediment volume depending on the sediment depth. The fill-down of numerous burrows with surface sediment by bioregeneration suggests that anaerobic degradation of fresh organic matter is dominant in this canyon. In the sedimentary column, the negative relationship between carbonate content and macrobenthic abundance confirms that carbonate dissolution is largely influenced by bioturbation.  相似文献   

15.
A series of experiments in Willapa Bay, Washington, indicates the degree to which the presence of spilled oil modifies the burrowing behavior of infauna and the extent to which the animals redistribute oil into interridal sediment. Small amounts of North Slope crude oil introduced at low tide directly into burrow openings (mostly made by the crustacean Callianassa) resulted in a limited and temporary reduction in the number of burrow openings. In contrast, a layerof oil-saturated sand 1 cm thick buried about 5 cm below the sediment surface sharply reduced the number of burrow openings. After a year, the few new burrows penetrated only the margins of the experimental plot, and bioturbation below the buried oil saturated sand layer declined dramatically.The experiments suggest that small amounts of oil temporarily stranded by tides in themselves have no long-range effect on burrowing behavior. The fauna, however, are capable of introducing measurable amounts of oil into the subsurface, where it is retained long after the rest of the stranded oil has washed away. A buried layer of oil-saturated sand greatly reduces infaunal activity; the oil presents an effective barrier that can persist for years.The oil incorporated into the sediment from burrow openings showed evidence of degradation after 7 months. In contrast, the layer of buried oil remained essentially undegraded after a period of two years, even though oil in lower concentrations above the layer was degraded after a period of one year. This variation in degree of dgradation of the buried oil, as well as the heterogeneity of oil distribution wherever the oil has been incorporated from the surface, emphasises the importance of careful sampling in any attempt to locate or monitor the presence of spilled oil in the substrate.  相似文献   

16.
The cycling and oxidation pathways of organic carbon were investigated at a single shallow water estuarine site in Trinity Bay, Texas, the uppermost lobe of Galveston Bay, during November 2000. Radio-isotopes were used to estimate sediment mixing and accumulation rates, and benthic chamber and pore water measurements were used to determine sediment-water exchange fluxes of oxygen, nutrients and metals, and infer carbon oxidation rates. Using 7Be and 234ThXS, the sediment-mixing coefficient (Db) was 4.3 ± 1.8 cm2 y−1, a value that lies at the lower limit for marine environments, indicating that mixing was not important in these sediments at this time. Sediment accumulation rates (Sa), estimated using 137Cs and 210PbXS, were 0.16 ± 0.02 g cm−2 y−1. The supply rate of organic carbon to the sediment-water interface was 30 ± 3.9 mmol C m−2 d−1, of which ∼10% or 2.9 ± 0.44 mmol C m−2 d−1was lost from the system through burial below the 1-cm thick surface mixed layer. Measured fluxes of O2 were 26 ± 3.8 mmol m−2 d−1 and equated to a carbon oxidation rate of 20 ± 3.3 mmol C m−2 d−1, which is an upper limit due to the potential for oxidation of additional reduced species. Using organic carbon gradients in the surface mixed layer, carbon oxidation was estimated at 2.6 ± 1.1 mmol C m−2 d−1. Independent estimates made using pore water concentration gradients of ammonium and C:N stoichiometry, equaled 2.8 ± 0.46 mmol C m−2 d−1. The flux of DOC out of the sediments (DOCefflux) was 5.6 ± 1.3 mmol C m−2 d−1. In general, while mass balance was achieved indicating the sediments were at steady state during this time, changes in environmental conditions within the bay and the surrounding area, mean this conclusion might not always hold. These results show that the majority of carbon oxidation occurred at the sediment-water interface, via O2 reduction. This likely results from the high frequency of sediment resuspension events combined with the shallow sediment mixing zone, leaving anaerobic oxidants responsible for only ∼10–15% of the carbon oxidized in these sediments.  相似文献   

17.
A programme of mangrove planting has been undertaken around the island of Rodrigues (SW Indian Ocean) since the mid-1980’s involving the introduction of the species Rhizophora mucronata. We examined three coastal embayment sites (Baie Diamant, Anse Goeland and Anse Pansia) in which planting has been undertaken over different time periods within the past 20 years. Planting has met with variable success in the different sites, probably due to variations in fluvial and groundwater influence. At two sites (Baie Diamant – first planted in 1990, and Anse Pansia – first planted in 1995) ecological data indicates that the mangroves are becoming well-established, and sedimentary evidence suggests that relatively rapid modification of intertidal substrates has occurred. This is evident in the form of significant increases in sediment organic-matter content (especially fibrous organic-matter) and an increase in the accumulation of sediment fines inside the mangroves. A strong correlation exists between the magnitude and depth of substrate modification and mangrove forest density, especially root and sapling density. At the third site, Anse Goeland (first planted in 2001), mangrove establishment has not been successful, many of the seedlings have died and no secondary colonisation has occurred. Sediment substrates show no deviation from background levels in terms of organic content or weight % fines content, and we find no evidence for mangrove planting influencing sediment substrates. Despite evidence for the development of a distinctive mangrove facies at Baie Diamant and Anse Pansia there is, however, no evidence as yet for a marked change in substrate geochemistry such as would be demonstrated by evidence of active bioclast dissolution – a common process in many natural (mature) mangrove substrates. We infer this to be a function of the present relative immaturity of the still developing mangrove substrates, but may also be a function of the apparent paucity of burrowing crabs which play an important role in nutrient cycling and sediment geochemistry. Thus whilst the mangroves in some of the study sites are reaching a stage where they are producing distinctive sedimentary facies, the systems appear to be in a state of progressive sedimentary and diagenetic modification as the floral and infaunal components of the mangroves continue to develop.  相似文献   

18.
蟹类底栖动物对河口潮滩无机氮界面交换的影响   总被引：1，自引：0，他引：1  
以长江河口的沿岸及岛屿潮滩高潮滩湿地为研究区域,结合现场调查和实验室模拟分析,初步研究了大型穴居底栖动物无齿相手蟹(Sesarma denaan)活动对长江口潮滩沉积物-水界面无机氮交换以及界面处氮的生物地球化学循环的影响。结果表明,高潮滩蟹类底栖动物活动对潮滩滩面地貌施加了显著的改造作用,蟹类活动较集中的地段,蟹洞覆盖率达到2%~3%,滩面掘出沉积物高达1~1.5 kg/m2。潮水淹没情况下,小范围内高密度的蟹类活动能通过机体排泄、加强沉积物再悬浮及促进沉积物-水界面溶质交换等方式致使沉积物出现三态无机氮的巨大释放。蟹类活动造成的洞穴结构及对沉积物的翻动混合能增加沉积物中的氧气含量,促进沉积物中有机氮的矿化和NH4 的释放,造成无机氮在沉积物中的剖面分布特征发生较大变化。  相似文献   

19.
The burrowing and emergence behavior of sand worms, Nereis (Neanthes) virens Sars, in sediment contaminated with sublethal concentrations of Prudhoe Bay crude oil ranging from 74 to 5222 ppm, was studied in the laboratory. Initial burrowing in oiled sediment did not differ from that observed in unoiled sediment. Emergence of exposed worms was related to the oil concentration and the extent of weathering of oiled sediment. Sand worms buried in unoiled sediment did not emerge. Worms dug from oiled sediment after 12 hours' exposure and placed on unoiled sediment were impaired, resulting in a significant increase in time to burrow. However, after 12h, they recovered and burrowed at normal rates. Worms held in oiled sediment for 96 h also recovered. Possible causes for recovery are discussed. Results suggest that oil-induced aberrations may increase vulnerability to predation.  相似文献   

20.
Fiddler crabs are known as the most conspicuous bioturbating animals in mangrove forest, which by their burrowing activities promote nutrient cycling in ecosystems. Mangroves, crabs and bacteria are connected in the form of positive feedback loop, whereby an increase in the activity of any participant will tend to increase the activity of all others as well. Population structure, growth, mortality, recruitment, biomass and production of fiddler crabs as dominant species of deposit-feeder crabs have been investigated from May 2005 to March 2006 in the Sirik mangrove estuary in the eastern part of Strait of Hormuz. Ten 1 m2 squares of the substrate were randomly sampled during low tide. There was a significant change in organic content in the sampling area during study period. The sex ratio was significantly deviated from 1:1 ratio in large sizes, where males were dominated year around. Fiddler crabs showed seasonal growth pattern during a year, which the maximum growth was observed during autumn and early summer and ceased during winter by low temperature. Growth parameters were estimated by Appeldoorn's method and fitted with seasonalized von Bertalanffy growth models. The Kimura likelihood ratio test revealed significant differences in the overall growth curves between males and females, originated from the differences in kk and L∞L∞ between sexes. Males were found to exhibit higher growth rate and larger size than females, this could be attributed to the higher investment of energy for reproduction in females. Reproduction was restricted to spring and early summer, while recruitment occurs at the end of summer. Total annual production of males and females was 37.90 and 10.05 g dry weight/10 m2 respectively and major production took place during early summer. Because of impact of temperature on the activity of fiddler crabs in subtropical regions, density of crabs has significant positive correlation with temperature (P < 0.01), while growth rate shows significant negative correlation with organic matter of sediment (P < 0.05). In conclusion these crabs showed lower mortality and production rate with the seasonal growth and recruitment in comparison with tropical species.  相似文献   

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