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1.
We examined the effect of whole-ecosystem nutrient enrichment on herbivory in saltmarsh creek-wall habitats in the Plum Island Estuary (Massachusetts, USA). Located between the macrophyte-dominated high marsh and adjoining mudflats, creek walls are steep vertical habitats vegetated with productive filamentous algae and associated epiphytes. Annual nitrate and phosphate loading rates were increased approximately ×10–15 in creeks mimicking short-term (2-month) and chronic (6-year) eutrophication. We assessed the diets of epifaunal invertebrates (three gastropods and one amphipod species) that potentially graze on benthic algae using natural isotope abundance data and per capita grazing rate measurements derived from 13C prelabeled algae. Substantial dietary contributions from benthic algae were observed in all consumers even though previous research has indicated most rely on Spartina detritus as the principal food resource. The amphipod Orchestia grillus and the snail Melampus bidentatus grazed benthic algae in excess of 500 μg algal C g C?1 h?1, whereas the snail Nassarius obsoletus and hydrobiid snails grazed at lower rates. Few dietary changes were detected with short-term enrichment. Algal grazing rates of N. obsoletus and M. bidentatus increased with chronic enrichment probably as a functional response to increased algal productivity. O. grillus grazed at a high rate and parasitic infection did not affect its consumption of benthic algae. The abundance and frequency of occurrence of O. grillus on creek-wall habitats increased with chronic nutrient enrichment suggesting amphipods contribute to top–down control on benthic algae and slow algal growth as nutrient enrichment occurs.  相似文献   

2.
Beach-cast wrack of marine origin is considered a spatial subsidy to the marine-terrestrial transition zone. We found that the wrack line on sand and gravel beaches of Vancouver Island was frequented by intertidal purple shore crabs,Hemigrapsus nudus (Dana 1851) and densely colonized by detritivorous talitrid amphipods. Amphipods spend the day buried in sand and forage on beach wrack during the night.H. nudus were found in supratidal wrack putches immediately after nightly high tides in field censuses, but spent most of the day and ebb tides either submerged subtidally or hidden underneath intertidal rocks and boulders. In feeding trials, intertidal shore crabs were capable of preying on talitrid amphipods. We considerH. nudus an omnivore feeding on both fresh and decaying macroalgae as well as animal prey. Although living supratidally, amphipods were significantly preferred over intertidal littorine snails by foraging shore crabs. Handling time of amphipods was significantly shorter than for littorine snails. While amphipods had a reduced risk of predation byH. nudus when buried in the sand, foraging undern eath wrack patches did not reduce predation pressure on amphipods by shore crabs. Rates of amphipod consumption by shore crabs were higher at darkness than daylight. In addition to an apparent day-night rhythm, tidal height and time elapsed since previous high tide had a significant influence on shore crab density wrack. We conclude that beach-cast wrack acts as a spatial subsidy by virtue of providing a valuable food source to talitrid amphipods, which are in turn consumed by shore crabs that ride the nightly high tide into supratidal wrack patches to reduce the risk of passing bare sand on theiry way to a feeding habitat rich in valuable prey.  相似文献   

3.
Temperature acclimation influenced the desiccation tolerance of the marine snail Ilyanassa obsoleta (Nassarius obsoletus). I. obsoleta acclimated to 35‰ seawater at 18°C could survive for 116 hours, and tolerate a 57% loss of body water when desiccated at 15 °C in air with a relative humidity of 35%. In contrast, I. obsoleta acclimated to 3°C seawater survived for only 76 hours, and could not tolerate more than a 37% loss of body water. These results were used to support the proposition that freezing and desiccation tolerance are closely related in I. obsoleta.  相似文献   

4.
In summer 2009, the effects of 6 years of landscape-level experimental nutrient enrichment on the eastern mudsnail, Nassarius obsoletus (formerly Ilyanassa obsoleta), were examined. The experiment was conducted in five tidal creeks (two nutrient-enriched, three reference creeks) in the Plum Island Estuary, Massachusetts, USA. (42°44′ N, 70°52′ W). After 6 years of enrichment, N. obsoletus size structure differed between treatment creeks with adult snails on average 14 % larger in enriched creeks. N. obsoletus densities (in individuals per square meter) and biomass (in grams dry weight per square meter) were four times higher in nutrient-enriched versus reference creeks. Nutrient enrichment did not significantly affect the biomass of benthic microalgae (a N. obsoletus food resource), but snail density was significantly correlated with benthic microalgal biomass, suggesting bottom–up control of snails. N. obsoletus is abundant on the east and west coast of North America; thus, N. obsoletus density and biomass may be useful variables for monitoring eutrophication effects on North American estuaries.  相似文献   

5.
Between September 1976 and August 1978, samples of four species of sponge,Microciona prolifera (Ellis and Solander),Haliclona loosanoffi Hartman,Lissodendoryx isodictyalis (Carter) andHalichondria bowerbanki Burton, were collected from subtidal shell debris in a North Edisto River, South Carolina saltmarsh creek and associated amphipods identified. Dominant spongicolous amphipods wereColomastix halichondriae Bousfield,Leucothoe spinicarpa (Abildgaard),Corophium simile Shoemaker,Corophium acherusicum Costa,Lembos cf.L. websteri Bate andMelita appendiculata (Say). Densities of amphipods inMicroclona prolifera andHalichondria bowerbanki usually exceeded those inLissodendoryx isodictyalis andHaliclona loosanoffi. Seasonal changes in amphipod dominance were however approximately the same in all sponge species. Winter dominance byCorophium spp., and on occasionLembos spp., is followed by spring dominance byMelita appendiculata and summer dominance byColomastix halichondriae. Harsher winter conditions in 1976–77 apparently resulted in more reduced populations of various sponge species as well asColomastix halichondriae andLeucothoe spinicarpa when compared with the following winter. With some exceptions during the winter, amphipod density inMicrociona prolifera generally decreased as sponge size increased. The range of gammarid amphipod densities inMicrociona prolifera was 128–724 individuals per 5 g (40.3 cm3) of sponge.  相似文献   

6.
Although top-down control of plant growth has been shown in a variety of marine systems, it is widely thought to be unimportant in salt marshes. Recent caging experiments in Virginia and Georgia have challenged this notion and shown that the dominant marsh grazer (the periwinkle,Littoraria irrorata) not only suppresses plant growth, but can denude marsh substrate at high densities. In these same marshes, our field observations suggest that the black-clawed mud crab,Panopeus herbstii, is an abundant and potentially important top-down determinant of periwinkle density. No studies have quantitatively examinedPanopeus distribution or trophic interactions in marsh systems, and its potential impacts on community structure remained unexplored. We investigated distribution and feeding habits ofPanopeus in eight salt marshes along the Mid-Atlantic seashore (Delaware-North Carolina). We found that mud crabs were abundant in tall (4–82 ind m?2), intermediate (0–15 ind m?2), and short-form (0–5 ind m?2)Spartina alterniflora zones in all marshes and that crab densities were negatively correlated with tidal height and positively correlated with bivalve density. Excavation of crab lairs r?utinely produced shells of plant-grazing snails (up to 36 lair?1) and bivalves. Lab experiments confirmed that mud crabs readily consume these abundant marsh molluscs. To experimentally examine potential community effects of observed predation patterns, we manipulated crab and periwinkle densities in a 1-mo field experiment. Results showed thatPanopeus can suppress gastropod abundance and that predation rates increase with increasing snail density. In turn, crab suppression of snail density reduces grazing intensity on salt marsh cordgrass, suggesting presence of a trophic cascade. These results indicate that this previously under-appreciated consumer is an important and indirect determinant of community structure and contribute to a growing body of evidence challenging the long-standing notion that consumers play a minor role in regulating marsh plant growth.  相似文献   

7.
The zonation of mobile species, such as grazing snails, may be influenced by migration patterns, which often are missed if the population is not sampled within the appropriate temporal scales (i.e., tidal cycles, diurnal periods, seasons). Aspects of community ecology, especially abundance, biodiversity, and habitat preferences, are better described when the mobility of different species or group of organisms also are investigated. The effect of migration on the density and size-frequency distribution of a dominant intertidal grazer (Turbo smaragdus) was investigated across four habitats (mangrove tree, pneumatophore, algal aggregation, and seagrass bed) during emersion and immersion periods at Matapouri Estuary, northern New Zealand, in August 2004 and March 2005. Snails were marked and recaptured to identify their specific movements across the four zones during high and low tide periods. Results from the population surveys and the marked-recaptured experiments indicate that snails migrate upward during high tide and do wnward during low tide. These snail movements appear to be related to improved feeding activity during tidal inundation within macroalgal aggregations in the pneumatophore and algal zones. Large snails (up to 48 mm in width) were predominant in the highest zone among the mangrove trees, where they appear to feed on filamentous algae and microalgae that cover the sediment and plant surfaces in this area. Differences in snail density and sizes between the two sampling months were attributed to reproductive patterns of this species, which result in about 30% more snails (mostly juveniles) during peak reproduction in March.  相似文献   

8.
The salt marsh periwinkleLittoraria irrorata (Say) remains on the substratum during low tide but climbs above the water on stalks ofSpartina alterniflora Loisel during high tide. Rhythmic tidal migrations may allowL. irrorata to avoid predators such as blue crabsCallinectes sapidus Rathbun that forage when the marsh is inundated. These tidal rhythms may be driven by endogenous clocks or they may be easily entrained. Snails with flexible and entrainable climbing rhythms may be able to avoid predators in unpredictable environments (e.g., when water unexpectedly covers the substratum as in storm surges). We tested the behavioral response ofL. irrorata to different simulated tidal regimes in the laboratory, and the effect of remaining above mean high water (MHW) on snail survivorship in a smallS. alterniflora salt marsh. In laboratory mesocosms, vertical snail position was measured under constant water levels, simulated tidal cycles, and simulated tidal cycles 180° out of phase (reversed). Under constant water levels, snails ceased to migrate vertically after 1 d. When exposed to tidal and reversed tidal cycles, snails migrated in synchrony with the appropriate simulated rhythm.L. irrorata entrained quickly to differing tidal cycles and maintained their position above the water surfce when water levels were high. In a field experiment, snails were tethered toS. alteriflora plants near the substratum and above MHW in the marsh for 1 wk to assess survival. Survival of snails tethered above MHW was sigificantly greater than for snails tethered at the base of plants; no snails in control cages died. Rapid alteration of tidal vertical migrations may allowL. irrorata to avoid predators that forage when water inundates the marsh predictably or unexpectedly.  相似文献   

9.
Understanding methane emissions from natural sources is becoming increasingly important with future climactic uncertainty. Wetlands are the single largest natural source of methane; however, little attention has been given to how biota and interactions between aboveground and belowground communities may affect methane emission rates in these systems. To investigate the effects of vegetative disturbance and belowground biogeochemical alterations induced by biota on methane emissions in situ, we manipulated densities of Littoraria irrorata (marsh periwinkle snails) and Geukensia granosissima (gulf ribbed mussels) inside fenced enclosures within a Spartina alterniflora salt marsh and measured methane emissions and sediment extracellular enzyme activity (phosphatase, β-glucosidase, cellobiohydrolase, N-acetyl-β-D-glucosaminidase, peroxidase, and phenol oxidase) over the course of a year. Changes in snail density did not have an effect on methane emission; however, increased densities of ribbed mussels significantly increased the emission of methane. Sediment extracellular enzyme activities for phosphatase, cellobiohydrolase, N-acetyl-β-D-glucosaminidase, and phenol oxidase were correlated to methane emission, and none of the enzymes assayed were affected by the snail and mussel density treatments. While methane emissions from salt marsh ecosystems are lower than those from freshwater systems, the high degree of variability in emission rates and the potential for interactions with naturally occurring biota that increase emissions warrant further investigations into salt marsh methane dynamics.  相似文献   

10.
Small blue crabs (Callinectes sapidus Rathbun, 43–70 mm carapace width) can influence the size-distribution of the gastropod,Bittium varium, strongly reducing the contribution of snails >3 mm shell length in field enclosures. We test the hypothesis that these size-dependent effects are due to size-selective predation rather than size-dependent emigration from the field enclosures. In laboratory feeding trials, blue crabs showed negative selectivity for snails <2.5 mm and positive selectivity for snails >3.3 mm. When feeding, blue crabs crushBittium shells, but the opercula are deposited undamaged in the sediment. Sediment from a field enclosure experiment contained 6.5× moreBittium opercula from enclosures with blue crabs than from enclosures without blue crabs. We reconstructed the size distribution ofBittium killed by blue crabs from the opercula recovered from sediment. This distribution qualitatively matched those “missing” from the size frequency distribution of surviving snails. Estimates of selectivity from laboratory feeding trials predicted the pattern of size-selection fromBittium killed in the enclosures. We also estimated Strauss's linear index of selectivity and Chesson's α based on the size distribution of snails available during the field enclosure experiment. These indices predicted both the pattern of selectivity and the size distribution ofBittium killed in enclosures with blue crabs. We conclude that size-selective predation by blue crabs can explain the observed shifts inBittium size distributions.  相似文献   

11.
This paper documents horizontal and vertical dispersion patterns of a Texas population of the saltmarsh periwinkle, Littoraria irrorata, over a 15-month period. The study was conducted within a tidal marsh on the Anahuac National Wildlife Refuge in Galveston Bay. Two mark-recapture experiments demonstrated that L. irrorata rarely move more than 2 m from their release point over long periods of time and do not home to individual Spartina plants. Adult L. irrorata forage farther away from the base of Spartina stalks at low tide than do juvenile snails. Remaining near the plant base may decrease both temperature and desiccation stress on juveniles. During warm months, L. irrorata climb grass stalks with tidal inundation and forage on the substratum at low tide. Snails are inactive and aggregate in detrital debris at the base of Spartina clumps during the winter. *** DIRECT SUPPORT *** A01BY058 00016  相似文献   

12.
Macroalgal biomass and competitive interactions among primary producers in coastal ecosystems may be controlled by bottom-up processes such as nutrient supply and top-down processes such as grazing, as well as other environmental factors. To determine the relative importance of bottom-up and top-down processes under different nutrient loading conditions, we estimated potential amphipod and isopod grazer impact on a dominant macroalgal species in three estuaries in Waquoit Bay, Cape Cod, Massachusetts, that are subject to different nitrogen loading rates. We calculated growth increases and grazing losses in each estuary based on monthly benthic survey data of macrophyte biomass and herbivore abundance, field grazing rates of amphipods (Microdeutopus gryllotalpa andCymadusa compta) and an isopod (Idotea baltica) on the preferred and most abundant macroalga (Cladophora vagabunda) and laboratory grazing rates for the remaining species, and in situ macroalgal growth rates. As nitrogen loading rates increased, macroalgal biomass increased (3×), eelgrass (Zostera marina) was lost, and herbivore abundance decreased (1/4×). Grazing rates increased with relative size of grazer (I. baltica > C. compta > M. gryllotalpa) and, for two of the three species investigated, were faster on algae from the high-nitrogen estuary in comparison to the low-nitrogen estuary, paralleting the increased macroalgal tissue percent nitrogen with nitrogen load. Macroalgal growth rates increased (2×) with increasing nitrogen loading rate. The comparison between estimated growth increases versus losses ofC. vagabunda biomass to grazing suggested first, that grazers could lower macroalgal biomass in midsummer, but only in estuaries subject to lower nitrogen loads. Second, the impact of grazing decreased as nitrogen loading rate increased as a result of the increased macroalgal growth rates and biomass, plus the diminished abundance of grazers. This study suggests the relative impact of top-down and bottom-up controls on primary producers varies depending on rate of nitrogen loading, and specifically, that the impact of herbivory on macroalgal biomass decreases with increasing nitrogen load to estuaries.  相似文献   

13.
The vertical distribution of infauna was quantified in eight strata from 0–35 cm in sand and mud sediments of a lower mesohaline subestuary of Chesapeake Bay. Large numbers of small polychaetes, amphipods, and clams occurred in the upper 5 cm of both sediment types, whereas large clams (Macoma balthica in mud andMya arenaria in sand) extended down to 30 cm and comprised most of the biomass in their respective sediment types. There was extensive overlap of the species inhabiting both sediment types. Vertical stratification within and among species apparently reflected constraints on burrowing depth related to body size rather than resource partitioning among competitors. The maximal sediment penetration of 35 cm, which was exhibited byHeteromastus filiformis, was considerably less than the maximal penetration for deep burrowing species in some marine infaunal communities. Several species which burrowed deeper than 5 cm exhibited significant temporal shifts in their vertical distribution.  相似文献   

14.
Lead isotope ratios were used to trace the origin of Pb in a soil–plant (Urtica dioica)–snail (Cepaea nemoralis) food chain in two polluted locations in the floodplains of the rivers Meuse and Rhine (Biesbosch National Park) and one reference location in the Netherlands. Lead isotope ratios and concentrations were determined in soil, litter, plant leaves, snails, rainwater and airborne particulate matter. Anthropogenic Pb in the soils of all locations was found to be derived from deposition of Pb polluted river sediments. Discharging rivers influenced the reference location before being reclaimed from the sea. The river sediment contains anthropogenic Pb from various sources related to industrial activities in the hinterland of the rivers Meuse and Rhine. Lead in the atmosphere contributed substantially to Pb pollution and Pb transfer in plant leaves and snails in all locations. Lead pollution in plant leaves and snails can be explained from a mixture of river sediment-Pb and atmospheric Pb from various transfer routes that involve low concentrations.  相似文献   

15.
Knowledge of present‐day communities and ecosystems resembling those reconstructed from the fossil record can help improve our understanding of historical distribution patterns and species composition of past communities. Here, we use a unique data set of 570 plots explored for vascular plant and 315 for land‐snail assemblages located along a 650‐km‐long transect running across a steep climatic gradient in the Russian Altai Mountains and their foothills in southern Siberia. We analysed climatic and habitat requirements of modern populations for eight land‐snail and 16 vascular plant species that are considered characteristic of the full‐glacial environment of central Europe based on (i) fossil evidence from loess deposits (snails) or (ii) refugial patterns of their modern distributions (plants). The analysis yielded consistent predictions of the full‐glacial central European climate derived from both snail and plant populations. We found that the distribution of these 24 species was limited to the areas with mean annual temperature varying from ?6.7 to 3.4 °C (median ?2.5 °C) and with total annual precipitation varying from 137 to 593 mm (median 283 mm). In both groups there were species limited to areas with colder and drier macroclimates (e.g. snails Columella columella and Pupilla loessica, and plants Kobresia myosuroides and Krascheninnikovia ceratoides), whereas other species preferred areas with relatively warmer and/or moister macroclimates (e.g. snails Pupilla turcmenica and P. alpicola, and plants Artemisia laciniata and Carex capillaris). Analysis of climatic conditions also indicated that distributional shifts of the studied species during the Pleistocene/Holocene transition were closely related to their climatic tolerances. Our results suggest that the habitat requirements of southern Siberian populations can provide realistic insights into the reconstruction of Eurasian, especially central European, glacial environments. Data obtained from modern populations also highlight the importance of wet habitats as refugia in the generally dry full‐glacial landscape.  相似文献   

16.
A two-year trawl study of Laguna Joyuda, Puerto Rico, a small, polyhaline lagoon with restricted oceanic exchange, yielded 803 crabs belonging to sixCallinectes species.Callinectes danae was the most abundant (35.7%), followed byC. sapidus (21%),C. ornatus (12.6%),C. bocourti (12.1%),C. exasperatus (1.2%), andC. larvatus (0.4%). Abundances of different species differed more spatially than temporally despite very homogeneous salinities.Callinectes bocourti andC. sapidus were most abundant furthest from the lagoon’s inlet, whileC. danae andC. ornatus were most abundant near the inlet and in the center of lagoon. Juveniles were least abundant in the center of the lagoon. Size frequencies of most species showed common trends with high percentages of small crabs furthest from the inlet, and high percentages of larger crabs near the inlet and central parts of the lagoon. Distributional patterns appear to be a result of complex interactions of habitat preferences and intra- and interspecific interactions among the crabs.  相似文献   

17.
This paper investigates the stable isotopic composition from late Pleistocene–Holocene (~ 13 to ~ 10.5 cal ka BP) shells of the land snail Helix figulina, from Franchthi Cave (Greece). It explores the palaeoclimatic and palaeoenvironmental implications of the isotope palaeoecology of archaeological shells at the time of human occupation of the cave. Modern shells from around the cave were also analysed and their isotopic signatures compared with those of the archaeological shells. The carbon isotope composition of modern shells depicts the consumption of C3 vegetation. Shell oxygen isotopic values are consistent with other Mediterranean snail shells from coastal areas. Combining empirical linear regression and an evaporative model, the δ18Os suggest that modern snails in the study area are active during periods of higher relative humidity and lower rainfall δ18O, probably at night. Late glacial and early Holocene δ18Os show lower values compared to modern ones. Early Holocene δ18Os values likely track enhanced moisture and isotopic changes in the precipitation source. By contrast, lower late glacial δ18O could reflect lower temperatures and δ18Op, compared to the present day. Shell carbon isotope values indicate the presence of C3 vegetation as main source of carbon to late glacial and early Holocene snails.  相似文献   

18.
We examined the gut contents of mummichogs, Fundulus heteroclitus L., entering and leaving ditches in three marsh regions within the Barn Island Wildlife Management Area in Connecticut: a restored impounded valley marsh, a marsh below the impoundment dike (Headquarters Marsh), and an unimpounded valley marsh (Davis Marsh). On the Headquarters Marsh and at certain times on the other two marshes, fish entered the ditches on the flooding tide with relatively little food in their guts and left them on the following ebbing tide with considerably more food in their guts. Since the high tides did not flood the surface of the high marsh, it appears that the ditches are important foraging areas. Major components of the gut contents were detritus, algae, amphipods, tanaids, copepods, and insects. During the summer, fish in the restored impounded marsh consumed less food per unit body weight than did fish inhabiting the other marsh regions.  相似文献   

19.
为了揭示蜗牛化石壳体碳酸盐（文石）稳定同位素组成的古气候和古生态环境指示意义,对采集于河南荥阳邙山末次冰期黄土剖面上部中的粉华蜗牛（Cathaica pulveratrix）化石壳体碳酸盐进行了碳、氧稳定同位素分析,同时还对全岩有机物质（SOM）碳同位素组成以及全岩磁化率和粒度等气候替代指标进行分析,结果显示：剖面中反映蜗牛食物碳同位素组成的壳体δ13CSSA的变化,与反映古植被碳同位素组成的全岩有机物质碳同位素组成（δ13CSOM）无显著的相关关系,但是壳体13C相对于SOM的富集程度（Δδ13CSSA-SOM）的变化与石笋氧同位素记录的末次冰期东亚夏季风强度演化同步一致;   壳体δ18OSSA的变化不但与黄土磁化率、粒度等气候替代指标变化具有显著相关性,同样也与末次冰期东亚夏季风强度演化同步一致。这些特征,一方面说明受季风环流控制的气候温湿程度变化左右蜗牛夏季活动的几率和食物的类型,干冷气候条件下,相对温湿夏季成为蜗牛活动主要时期,相对富集13C苔藓、菌类和植物可能是蜗牛的主要食物;   另一方面暗示蜗牛化石壳体碳酸盐稳定同位素组成能够指示气候温湿程度和生态环境的变化。  相似文献   

20.
This paper compares stable isotope (δ18O and δ13C) records of early–middle Holocene land snail shells from the archaeological deposits of Grotta di Latronico 3 (LTR3; southern Italy) with modern shell isotopic data. No substantial interspecific variability was observed in shell δ18O (δ18Os) of modern specimens (Pomatias elegans, Cornu aspersum, Eobania vermiculata, Helix ligata and Marmorana fuscolabiata). In contrast, interspecific shell δ13C (δ13Cs) variability was significant, probably due to different feeding behaviour among species. The δ18Os values of living land snails suggest that species hibernate for a long period during colder months, so that the signal of 18O‐depleted winter rainfall in their δ18Os is lost. This suggests that δ18Os and δ13Cs values of Pomatias elegans from this archaeological succession provide valuable clues for seasonal (spring–autumn) climatic conditions during the early–middle Holocene. The δ18Os values of fossil specimens are significantly lower than in modern shells and in agreement with other palaeoclimatic records, suggesting a substantial increase of precipitation and/or persistent changes in air mass source trajectories over this region between ca. 8.8 cal ka BP and 6.2–6.7 ka ago. The δ13Cs trend suggests a transition from a slightly 13C‐enriched to a 13C‐depleted diet between early and middle Holocene compared to present conditions. We postulate that this δ13Cs trend might reflect changes in the C3 vegetation community, potentially combined with other environmental factors such as regional moisture increase and the progressive decrease of atmospheric CO2 concentration. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

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