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1.
Nutrient additions represent an important anthropogenic stress on coastal ecosystems. At moderate levels, increased nutrients may lead to increased primary production and, possibly, to increased biomass of consumers although complex trophic interactions may modify or mask these effects. We examined the influence of nutrient additions and interactive effects of trophic interactions (predation) on benthic infaunal composition and abundances through small-scale field experiments in 2 estuaries that differed in ambient nutrient conditions. A blocked experimental design was used that allowed an assessment of direct nutrient effects in the presence and absence of predation by epibenthic predators as well as an assessment of the independent effects of predation. Benthic microalgal, production increased with experimental nutrient additions and was greater when infaunal abundances were lower, but there were no significant interactions between these factors. Increased abundances of one infaunal taxa,Laeonereis culveri, as well as the grazer feeding guild were observed with nutrient additions and a number of taxa exhibited higher abundances with predator exclusion. In contrast to results from freshwater systems there were no significant interactive effects between nutrient additions and predator exclusion as was predicted. The infaunal responses observed here emphasize the importance of both bottom-up (nutrient addition and primary producer driven) and top-down (predation) controls in structuring benthic communities. These processes may work at different spatial and temporal scales, and affect different taxa, making observation of potential interactive effects difficult.  相似文献   

2.
The intertidal marsh community comprises both benthic and natant faunal components. The benthic components are primarily small invertebrates residing within or on the soft sediments of the vegetated marsh surface. The natant components include larger, fully aquatic organisms (e.g., fish and shrimp) that inhabit the shallow waters adjacent to the marsh at low tide but interact with the benthic components of the community when the marsh is tidally inundated. In this structurally complex and often expansive intertidal environment, patterns of invertebrate distribution and abundance are not apparent to the casual observer. Benthic core samples taken along an intertidal marsh transect on Sapelo Island, Georgia, USA show that many of the inconspicuous infaunal organisms, which numerically dominate the macrofaunal elements of this soft-substrate community, exhibit zonal distribution patterns along a tidal gradient. Patterns of invertebrate distribution in the intertidal salt marsh are often attributed to the activities of aquatic predators. The results of most predator exclusion experiments have left little doubt that predation/disturbance can be an important determinant of invertebrate abundance in soft-substrate communities; but a growing number of experiments, in both freshwater and marine environments, have produced results that apparently conflict with this, general tenet. Dismissed by some as “failed” experiments, these investigations have exposed our lack of knowledge about the effects of specific predators and the importance of complex interactions which involve more than two trophic levels. Although the importance of predation has been stressed in many recent experimental investigations, there are many other factors that, alone or in combination, may also influence the structure of salt marsh invertebrate assemblages. Included among these are: (1) various density-dependent processes (e.g., adult-larval interactions, agonistic behavior, interspecific competition), (2) selective larval settlement or mortality, (3) the influence of physical factors expressed through habitat preferences, and (4) unpredictable or cyclic physical disturbances. Many questions concerning the spatial and temporal patterns of invertebrate distribution and abundance in the salt marsh are unresolved and remain as challenges to our understanding of soft-substrate community dynamics.  相似文献   

3.
When compared with nearby unvergetated areas, seagrass meadows contain a dense and strikingly rich assemblage of vertebrates and invertebrates. Most recent literature has focused on evaluating the role of predation in structuring seagrass faunal communities; however, habitat complexity, abundance of food and sediment stability may also be important. This paper summarizes studies relating predator-prey relationships to different features of the seagrass system. This review suggests that the abundance of many species, both epifauna and infauna, is positively correlated with two distinct aspects of plant morphology: 1) the root-rhizome mat, and 2) the plant canopy. A scheme was developed that defines the conditions under which any particular species will be abundant or rare in a seagrass assemblage. This scheme is based on prey and predator characteristics (e.g., epifaunal vs. infaunal, tube-dweller vs. nontube dweller, burrowers vs. nonburrowers, and large vs. small as adult) and on characteristics of the seagrasses (e.g., leaf morphology, shoot density, shoot biomass, structural complexity of the meadow, and root-rhizome density and standing crop).  相似文献   

4.
Human population growth and sea-level rise are increasing the demand for protection of coastal property against shoreline erosion. Living shorelines are designed to provide shoreline protection and are constructed or reinforced using natural elements. While living shorelines are gaining popularity with homeowners, their ability to provide ecological services (e.g., habitat provision and trophic transfer) is not well understood, and information is needed to improve coastal and resource management decision-making. We examined benthic community responses to living shorelines in two case-study subestuaries of Chesapeake Bay using a before-after control-impact study design. At Windy Hill, a bulkhead was removed and replaced by three tombolos, sand fill, and native marsh vegetation. At Lynnhaven, 25 m of eroding marsh shoreline was stabilized with coir logs, sand fill, and native marsh vegetation. Communities of large (>?3 mm) infauna adjacent to living shorelines at both locations tended to increase in biomass by the end of the study period. Community compositions changed significantly following living shoreline construction at Windy Hill, reflecting a trend toward higher density and biomass of large bivalves at living shorelines compared to pre-construction. Increasing trends in density and biomass of clams and simultaneously decreasing density and decreasing trends in biomass of polychaetes suggest a transition toward stable infaunal communities at living shorelines over time, though longer-term studies are warranted.  相似文献   

5.
Despite a recent review concluding that there is little or no reason to expect that the production of fish and other animals will increase with nutrient enrichment or eutrophication, there is a variety of evidence that anthropogenic nutrients can stimulate secondary production in marine ecosystems. Unique multiple-year fertilization experiments were carried out over fifty years ago in Scottish sea lochs that showed dramatic increases in the abundance of benthic infauna and greatly enhanced growth of fish as a result of inorganic nitrogen (N) and phosphorus (P) additions. These experiments appear to have provided a good qualitative model for the responses of the Baltic Sea to nutrient enrichment and resulting eutrophication. Historical comparisons by others have shown that the weight of benthic animals per unit area above the halocline in the Baltic is now up to 10 or 20 times greater than it was in the early 1920s and that the total fish biomass in the system may have increased 8 fold between the early part of the 1900s and the 1970s. While there are no similar data for the highly enriched central and southern North Sea, there is convincing evidence that the growth rates of plaice, sole, and other species have increased there since the 1960s or 1970s. Cross-system comparisons have also shown that there are strong correlations between primary production and the production and yield of fish and the standing crop and production of benthic macrofauma in phytoplankton-dominated marine ecosystems. Concerns over the growing nutrient (especially N) enrichment of coastal marine waters are clearly valid and deserve the attention of scientists and managers, but the recent demonizing of N ignores the fact that nutrients are a fundamental requirement for producing biomass. Decisions regarding the amount of N or P that will be allowed to enter marine ecosystems should be made with the full knowledge that there may be tradeoffs between increases in water clarity and dissolved oxygen and the abundance of oysters, clams, fish, and other animals we desire.  相似文献   

6.
Benthic microalgal biomass is an important fraction of the primary producer community in shallow water ecosystems, and the factors controlling benthic microalgal biomass are complex. One possible controlling factor is sediment grain-size distribution. Benthic microalgal biomass was sampled in sediments collected from two sets of North Carolina estuaries Massachusetts and Cape Cod bays, and Manukau Harbour in New Zealand. Comparisons of benthic microalgal biomass and sediment grain-size distributions in these coastal and estuarine ecosystems frequently showed a negative relationship between the proportion of fine-grained sediments and benthic microalgal biomass measured as chlorophylla. The highest sedimentary chlorophylla levels generally occurred in sediments with lower percentages of fine particles (diameter <125 mm). A negative relationship between the proportion of fine sediments and benthic microalgal biomass suggests anthropogenic loadings of fine sediment may reduce the biological productivity of shallow-water ecosystems.  相似文献   

7.
As a result of human activities, coastal waters can be exposed to multiple stressors that affect primary producers and their interactions with higher trophic levels. Mesocosm experiments were conducted during spring and summer 1996–1998 to investigate the responses of natural populations of primary producers to multiple stressors and the potential for these responses to be transmitted to higher trophic levels (i.e., copepods, bivalves, anemones, and fish). The effects of two stressors, elevated nutrient and trace element loadings, were examined individually and in combination. Nutrient additions had a positive effect on biomass, productivity, and abundance of primary producers (Breitburg et al. 1999; Riedel et al. 2003). Growth or abundance of consumers increased with nutrient additions, but the magnitude of the response was reduced relative to that of their prey. Responses to trace element additions varied seasonally and among taxa. The responses of zooplankton and bivalves to stressor additions were affected by the biomass and changes in species composition of phytoplankton assemblages. The presence of fish predators did not alter zooplankton responses to stressor additions. These results suggest that the extent to which nutrient and trace element effects are transmitted from primary producers to higher trophic levels depends on the capacity of consumers to respond to stressor-induced changes in abundance and species composition of prey, on the absolute abundance of prey, and on the ability of predators to feed on alternative prey. The magnitude of the effects of stressors on estuarine food webs may depend on seasonal variability in species composition of phytoplankton assemblages, whether sensitive species dominate, and whether these species are important prey for secondary consumers. Because spatial and temporal patterns in nutrient and trace element loadings to the estuary can affect species composition of primary producers, it is critically important to examine the magnitude, timing, and spatial relationships of loadings of multiple stressors to coastal waters in order to understand the impacts of these stressors on higher trophic levels.  相似文献   

8.
The effects of nutrients, trace elements, and trophic complexity on benthic photosynthesis and respriation were studied in the Paxtuxent River estuary near St. Leonard, Maryland. Experiments were conducted over three years (1995–1997) in mesocosms containing riverine sediment and water. The experimental design was 2×2×3 factorial with two levels of nutrients (ambient and + nutrients), two of trace elements (ambient and + trace elements) and three of trophic complexity (plankton, plankton + fish, and plankton + fish + benthos). Trace elements included arsenic (As), copper (Cu), and cadmium (Cd). The experiment was conducted three times in 1995 and 1997 and four times in 1996. In 1995 and 1996, sediments were muddy, while in the final year sediments were sandy. In mesocoms with sandy sediments, nutrient additions increased benthic photosynthesis overall, while trace element additions increased benthic photosynthesis in two of three experimental runs. Benthic photosynthesis in these mesocosms appeared to be related to nitrogen loading. Benthic respiration increased in nutrient and trace element amended mesocosms with sandy sediments, apparently in response to higher benthic photosynthesis. Increasing trophic complexity, particularly the presence of benthic organisms, also increased benthic respiration in mesocosms with sandy sediments. There were no effects of nutrient or trace element additions on benthic photosynthesis and respiration when the sediments were muddy. The lack of consistent responses to nutrient additions was surprising given that benthic respiration rates (and presumably nutrient regeneration) were similar in all three years, regardless of sediment type. Muddy, sediments did not mask, the effects of nutrient addition by supplying more nutrients to benthic microalgae than sandy sediments. In 1996, the presence of filter feeding bivalves increased the relative heterotrophy of sediments, measured as production: respiration. Consistent with increased heterotrophy, effluxes of ammonium and soluble reactive phosphorus from sediments were greater in mesocosms containing benthic organisms. Anthropogenically-induced changes in estuaries, such as loading of nutrients and trace elements or reduced trophic complexity, can have important effects on benthic processes and potentially pelagic processes through feedback mechanisms.  相似文献   

9.
We examined the spatial extent of nitrogen (N) and phosphorus (P) limitation of each of the major benthic primary producer groups in Florida Bay (seagrass, epiphytes, macroalgae, and benthic microalgae) and characterized the shifts in primary producer community composition following nutrient enrichment. We established 24 permanent 0.25-m2 study plots at each of six sites across. Florida Bay and added N and P to the sediments in a factorial design for 18 mo. Tissue nutrient content of the turtlegrassThalassia testudinum revealed a spatial pattern in P limitation, from severe limitation in the eastern bay (N:P>96:1), moderate limitation in two intermediate sites (approximately 63:1), and balanced with N availability in the western bay (approximately 31:1). P addition increasedT. testudinum cover by 50–75% and short-shoot productivity by up to 100%, but only at the severely P-limited sites. At sites with an ambient N:P ratio suggesting moderate P limitation, few seagrass responses to nutrients occurred. Where ambientT. testudinum tissue N:P ratios indicated N and P availability was balanced, seagrass was not affected by nutrient addition but was strongly influenced by disturbance (currents, erosion). Macroalgal and epiphytic and benthic microalgal biomass were variable between sites and treatments. In general, there was no algal overgrowth of the seagrass in enriched conditions, possibly due to the strength of seasonal influences on algal biomass or regulation by grazers., N addition had little effect on any benthic primary producers throughout the bay. The Florida Bay benthic primary producer community was P limited, but P-induced alterations of community structure were not uniform among primary producers or across Florida Bay and did not always agree with expected patterns of nutrient limitation based on stoichiometric predictions from field assays ofT. testudinum tissue, N:P ratios.  相似文献   

10.
Accurate measures of intertidal benthic microalgal standing stock (biomass) and productivity are needed to quantify their potential contribution to food webs. Oxygen microelectrode techniques, used in this study, provide realistic measures of intertidal benthic microalgal production. By dividing a salt-marsh estuary into habitat types, based on sediment and sunlight characteristics, we have developed a simple way of describing benthic microalgal communities. The purpose of this study was to measure and compare benthic microalgal biomass and production in five different estuarine habitats over an 18-mo period to document the relative contributions of benthic microalgal productivity in the different habitat types. Samples were collected bimonthly from April 1990 to October 1991. Over the 18-mo period, tall Spartina zone habitats had the highest (101.5 mg chlorophyll a (Chl a) m?2±6.9 SE) and shallow subtidal habitats the lowest (60.4±8.9 SE) microalgal biomass. There was a unimodal peak in biomass during the late winter-early spring period. The concentrations of photopigments (Chl a and total pheopigments) in the 0–5 mm of sediments were highly correlated (r2=0.73 and 0.88, respectively) with photopigment concentrations in the 5–10 mm depth interval. Biomass specific production (μmol O2 mg Chl a ?1 h?1) was highest in intertidal mudflat habitats (206.3±11.2 SE) and lowest in shallow subtidal habitats (104.3±11.1 SE). Regressions of maximum production (production at saturating irradiances) vs. biomass (Chl a) in the upper 2 mm of sediment by habitat type gave some of the highest correlations ever reported for benthic microalgal communities (r2 values ranged from 0.43 to 0.73). The habitat approach and oxygen microelectrode techniques provide a useful, realistic ranged from 0.43 to 0.73). The habitat approach and oxygen microelectrode techniques provide a useful, realistic method for understanding the biomass and production dynamics of estuarine benthic microalgal communities.  相似文献   

11.
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   

12.
We examined individual and interactive effects of two stressors—nutrients (nitrogen [N] and phosphorus [P]) and trace elements (a mix of arsenic [As], copper [Cu], and cadmium [Cd], and in a second experiment also zinc [Zn] and nickel [Ni])—on phytoplankton of the mesohaline Patuxent River, a tributary of Chesapeake Bay. Experiments were conducted in twenty 1-m3 mesocosms. Four mesocosm runs used two levels of nutrient loadings (0.7–1.0 × ambient N loading and enriched to 1.3–1.6 × ambient N loading) crossed with two levels of trace elements (ambient and enriched approximately 2–5 × higher than ambient concentrations) crossed with five progressive levels of ecosystem complexity. To examine seasonal patterns of responses to stressors, data from these experiments were combined with results of a similar experiment conducted during 1996 (Breitburg et al. 1999a). A second mesocosm experiment examined effects of individual and mixed trace elements, both alone and in combination with nutrients, to further examine which nutrient-trace element interactions were important. Nutrients consistently increased phytoplankton productivity and biomass. Most of the increased biomass was created by large centric diatoms, which increased the mean cell size of the phytoplankton community. Trace element additions decreased phytoplankton productivity and biomass, as well as the contribution of large centric diatoms to phytoplankton biomass. When both trace elements and nutrients were added, trace elements reduced nutrient stimulation. Although the magnitude of the response to nutrient additions tended to be somewhat greater in spring, the seasonal patterns of trace element effects, and nutrient-trace element interactions were far more striking with significant responses restricted to spring mesocosm runs. The second experiment indicated that both As and Cu were more inhibitory to phytoplankton in spring than in summer, but As was more inhibitory in the low nutrient treatments and Cu was more inhibitory in the nutrient enrichment treatments. The potential for strong seasonal patterns and high temporal variability in stressor effects and multiple stressor interactiosn will require close attention in the design and interpretation of management-relevant research and monitoring and may indicate the need for seasonally varying management strategies.  相似文献   

13.
A field experiment was carried out to investigate the patterns of macrobenthic recolonization and to determine the effects of biodeposition on benthic communities at an intertidal oyster culture site in New Brunswick, Canada. Total organic deposition in azoic organic-free sediment trays was generally higher within the farm compared to reference sites. Two weeks after deployment of trays, total organic content had reached 1.1%. The abundance, species number, and diversity of the macrobenthic community were positively correlated with the total organic content in the experimental trays, but the correlations between community parameters and organic content were negative in the ambient sediment. The results suggest that organic matter in sediment may have positive effects on macrobenthic infauna at low levels as an additional food source but may be harmful to benthic animals at high levels. This study also indicates that location in the intertidal zone is a major parameter affecting the community structure of macrobenthic colonization.  相似文献   

14.
Acrylic panels were employed to follow fouling community development at Channel Points, Lynnhaven Bay, Virginia, from April 1977 through March 1979. Panel treatments were devised to study the effects of predator exclusion and panel area on community development. An additional panel was introduced in April 1978 to test the repeatability of initial community development. Early development was similar both years with hydroids, barnacles, and the polychaetePolydora ligni the initial macroinvertebrate colonists. Early community development in both years was dominated by the solitary tunicateMolgula manhattensis. Molgula was able to invade and rapidly overgrow all resident speices except largeBalanus eburneus. Panel area was shown to affect the community structure and development. The community on caged panels (predator exclusion) was significantly different from controls, although the differences could not be unequivocally attributed to predation.  相似文献   

15.
 Cold-seep communities have relatively low diversity, are dominated by one or two taxa present in high density and high biomass in comparison with the surrounding fauna, and are restricted to aphotic habitats. Their associated heterotrophic fauna are usually distinctive from the fauna of their surroundings. In contrast, a more commonplace chemoautotrophically based community occurs in shallow photic habitats. The associated heterotrophic fauna includes many of the species typical of the surrounding communities and typically dominates abundance, whereas the species with chemoautotrophic symbionts dominate biomass. All modern seep assemblages are deeper than 550 m. Many fossil seep assemblages occurred in water as shallow as the mid-shelf (<200 m). In contrast, communities where species with chemoautotrophic symbionts are biomass dominants, but not numerical dominants, are common in shallow waters at present but rarely reported in the geological record. We suggest that the absence of cold-seep communities on the continental shelf presently is due to a combination of predation and competitive exclusion by primary consumers limiting the presence of species dependent on chemoautotrophic symbionts. We suggest that cold-seep assemblages are more common at shelf depths in the fossil record for two reasons: (a) The biases of preservation have accentuated their distribution by transforming communities where species with chemoautotrophic symbionts dominate by biomass, but not numerically, into cold-seep-appearing assemblages. (b) The importance of predation pressure and oligotrophy has varied, with decreased predation pressure accompanying increased oligotrophy favoring cold-seep communities. We suggest that the paucity of shallow-water assemblages with species harboring chemoautotrophic symbionts as biomass dominants in the fossil record is based on the reliance of paleoecological analysis on numerical abundance data when energy flow analyses are required to identify these assemblages. The distinctiveness of the fossil seep assemblage is intensified by taphonomic processes that bias the assemblage against small individuals and epifaunal species, so that diversity declines, the small heterotrophic component of the assemblage is significantly reduced, and the epifaunal component is minimized. The final assemblage is usually dominated by the better-preserved large infaunal clams which perchance are also the species with chemoautotrophic symbionts. In contrast, preservation does not enhance the distinctiveness of these chemoautotroph-harboring species in shallow water. Received: 16 April 1998 / Accepted: 29 June 1999  相似文献   

16.
Penaeus aztecus Ives, the brown shrimp, and Penaeus setiferus (Linnaeus), the white shrimp, co-occur in Texas salt marshes as juveniles. Although their life cycles are similar, evidence indicates that the species utilize different resources for the primary faunal element of their diets. Prey selection and growth studies have shown that brown shrimp successfully remove infauna from natural sediment. Further, a diet of polychaetes, whether alone or in combination with algae, produced growth in the species. Brown shrimp appear to be trophically linked to infaunal populations, thus the structure and dynamics of the benthic community may directly affect local brown shrimp productivity. Areas dominated by surface-dwelling polychaetes as opposed to deep burrowers may provide more accessible foraging opportunities for juvenile brown shrimp. By contrast, white shrimp neither removed infauna nor grew to a significant degree when provided polychaetes or amphipods as food. White shrimp are omnivorous but do not rely on infaunal material to the same extent as brown shrimp. The primary faunal element in the diet of white shrimp has not yet been identified. The dietary differences between the two species may play a role in determining which species dominates in regions with varying marsh accessibility. Although not the only factors influencing penaeid survival and growth, prey choice and availability may greatly affect production and local success of penaeid populations. *** DIRECT SUPPORT *** A01BY081 00013  相似文献   

17.
While the ecological impacts of crude oil exposure have been widely studied, its sublethal effects on phytoplankton community structure in salt marsh estuaries have not been well documented. The purpose of this study was to simulate oil spill conditions using a microcosm design to examine short-term (2 day) changes in phytoplankton community composition and total biomass following exposure to crude oil obtained from the Deepwater Horizon oil spill and a mixture of Texas crude oils. Microcosm experiments were performed in situ in North Inlet Estuary near Georgetown, SC. A control and six replicated experimental treatments of crude oil additions at final concentrations of 10, 50, or 100 μl l−1 of either Deepwater Horizon spill oil or the Texas crude mixture were incubated under in situ conditions. Photopigments were analyzed using high-performance liquid chromatography and community composition was determined using ChemTax. Total phytoplankton biomass (as chl a) declined with increasing crude oil concentrations. Prasinophytes, the most abundant microalga in both experiments, showed no response to oil exposure in one experiment and a significant negative response in the other. Diatoms euglenophytes and chlorophytes appeared relatively resistant to oil contamination at the exposure levels used in this study, maintaining or increasing their relative abundance with increasing oil concentrations. Chlorophytes and cyanobacteria increased in relative abundance while cryptophyte abundance decreased with increasing oil concentrations. The results of these experiments suggest that low levels of crude oil exposure may reduce total biomass and alter phytoplankton community composition with possible cascade effects at higher trophic levels in salt marsh estuaries.  相似文献   

18.
Gulf sturgeon,Acipenser oxyrinchus desotoi, forage extensively in the Suwannee River estuary following emigration out of the Suwannee River, Florida. While in the estuary, juvenile Gulf sturgeon primarily feed on benthic infauna. In June–July 2002 and February–April 2003, random sites within the estuary were sampled for benthic macrofauna (2002 n = 156; 2003 n = 103). A mean abundance of 2,562 ind m−2 (SE ± 204) was found in the summer, with significantly reduced macrofaunal abundance in the winter (mean density of 1,044 ind m−2, SE ± 117). Benthic biomass was significantly higher in the summer with an average summer sample dry weight of 5.92 g m−2 (SE ± 0.82) compared to 3.91 g m−2 (SE ± 0.67) in the winter. Amphipods and polychaetes were the dominant taxa collected during both sampling periods. Three different estimates of food availability were examined taking into account principal food item information and biomass estimates. All three estimates provided a slightly different view of potential resources but were consistent in indicating that food resource values for juvenile Gulf sturgeon are spatially heterogeneous within the Suwannee River estuary.  相似文献   

19.
Examination of small-scale spatial variation in essential to understanding the relationships between environmental factors and benthic community structure in estuaries. A sampling experiment was performed in October 1993 to measure infauna association with sediment composition and salinity gradients in Nueces Bay, Texas, USA. The bay was partitioned into four salinity zones and three sediment types. Higher densities of macrofaua, were found in sediments with greater sand content and in areas with higher salinity. High diversity was also associated with high homogeneous salinity (31–33‰) and greater sand content. Macrofauna biomass and diversity were positively correlated with bottom salinity, porewater salinity, and bottom dissolved inorganic nitrogen (DIN). Furthermore, species dominance shifted along the estuarine gradient.Streblospio benedicti dominated at lower salinity, but,Mediomatsus ambiseta andMulinia lateralis were the dominant species at higher salinity. Statistical analyses revealed significant correlations for sediment characteristics (i.e., increased fine sediments, water content, and total organic carbon) with decreased total abundance and diversity. Increased salinity and DIN were correlated with increased total biomass, diversity, and macrofauma community structure. These physico-chemical variables are regulated by freshwater inflow, so inflow is an important factor influencing macrofauna community structure by indirectly influencing the physico-chemical environment.  相似文献   

20.
The benthic macroinfauna of Lagunal Joyuda, a coastal lagoon in Puerto Rico, was surveyed for two years. Seven hundred fifty core samples yielded 23 macrobenthic taxa. The oligochaeteThalassodrilides gurwitschi comprised 43.4% of the number of individuals collected. Polychaetes comprised 35.4% of the individuals, includingCapitella cf.capitata, Dasybranchus lumbricoides, andSteninonereis martini in approximately equal numbers. The amphipodGrandidierella bonnieroides made up 11.5% of the community. The lagoon yielded fewer species than other tropical estuaries in the Caribbean and Atlantic, but the trophic composition, mostly deposit feeders, was similar. Seasonal patterns in the abundance of individuals were most pronounced in the central basin, with maximum number of organisms during the wet season, and a minimum in the dry season. Responses to rainfall events, however, were variable and probably related to migration patterns in predators. Macrofaunal biomass demonstrated a high degree of annual variation at all sampling stations with a marked increase in 1987. Low macrofaunal biomass, lack of temporal association with physical-chemical conditions, and inverse relationships with predator populations suggest that patterns of macrofaunal abundance in Laguna Joyuda are mediated primarily by biotic mechanisms. *** DIRECT SUPPORT *** A01BY050 00006  相似文献   

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