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1.
We examined the rhizosphere structure of 14 seagrass meadows (seven mixed, three Enhalus acoroides, two Zostera japonica, one Thalassia hemprichii, and one Halophila ovalis) in the Philippines and Vietnam and tested their effect on sediment redox potential by comparing the redox potential in vegetated vs unvegetated sediments. The effect of seagrass photosynthesis on sediment redox potential was tested in an E. acoroides meadow during a short-term (2-day) clipping experiment. In all the meadows, the centroidal depth (i.e., depth comprising 50%) of seagrass belowground biomass was within the top 15 cm sediment layer. Redox potentials in vegetated sediments tended to be higher than those in adjacent unvegetated ones; sediment redox potential anomaly ranged from −61 to 133 mV across the meadows. The centroidal depths of positive redox potential anomaly and seagrass root biomass were significantly correlated across the meadows investigated (type II regression analysis, slope = 0.90, lower confidence limit [CL] = 0.42 upper CL = 1.82, R 2 = 0.59, p < 0.01). Experimental removal of E. acoroides leaves resulted in a decrease in rhizosphere redox potential by 20 mV, further confirming the positive effect of seagrass roots and rhizomes on sediment redox potential and, thus, the general conditions for microbial processes in the coastal zone.  相似文献   

2.
We compared nekton use of prominent habitat types within a lagoonal system of the northeastern Gulf of Mexico (GoM). These habitat types were defined by combinations of structure (cover type) and location (distance from shore) as: Spartina edge (≤1 m from shore), Spartina (3 m from shore); Juncus edge (≤1 m from shore); seagrass located 3, 5, and 20 m from shore; and shallow non-vegetated bottom at various distances from shore. Although seagrass and Spartina edge sites differed little in environmental characteristics, the density and biomass of most abundant taxa, including pink shrimp (Farfantepenaeus duorarum), were higher in seagrass. Most species within seagrass and Spartina did not differ in abundance or biomass with distance from shore. Our study revealed a shift in peak habitat use in the northeastern GoM to seagrass beds from the pattern observed to the west where nekton is concentrated within shoreline emergent vegetation.  相似文献   

3.
Cedar Bayou, a natural tidal inlet, was recently dredged to allow for direct water exchange between the Gulf of Mexico and Mesquite Bay, TX, USA. We quantified changes in densities of juvenile nekton (fish, shrimps, and crabs) and community structure in Mesquite Bay after Cedar Bayou was reopened by collecting samples at both control and impact sites using an epibenthic sled 1 year before (October 2013–April 2014) and after (October 2014–April 2015) opening. Significantly higher densities of total nekton were observed at the impact sites after opening using a before-after control-impact design. Red Drum (Sciaenops ocellatus), Atlantic Croaker (Micropogonias undulatus), post-larval penaeid shrimps (Farfantepenaeus aztecus, F. duorarum, and Litopenaeus setiferus), and Blue Crabs (Callinectes sapidus) were significantly more abundant at impact sites after Cedar Bayou was opened. Multivariate analysis showed a significant change in impact site communities after opening and was driven by an increased presence of estuarine-dependent species. Overall, this study demonstrates that opening tidal inlets, such as Cedar Bayou, and reconnecting Mesquite Bay to the Gulf of Mexico increased the presence of numerous estuarine-dependent species, many of which were not present or occurred at very low densities prior to reopening. Thus, reestablishing the historical connectivity between a productive estuary and the open Gulf of Mexico via Cedar Bayou should reinstitute natural nekton recruitment processes important to the Aransas, Mesquite, and San Antonio Bay regions.  相似文献   

4.
Subsidence and erosion of intertidal salt marsh at Galveston Island State Park, Texas, created new areas of subtidal habitat that were colonized by seagrasses begining in 1999. We quantified and compared habitat characteristics and nekton densities in monospecific beds of stargrassHalophila engelmanni and shoalgrassHalodule wrightii as well as adjacent nonvegetated substrates. We collected 10 replicates per habitat type during April, July, October, and December 2001. Most habitat characteristics varied with season. Water temperature, salinity, and dissolved oxygen were similar among habitat types. Turbidity and depth were greatest inH. engelmanni beds and least inH. wrightii beds.H. engelmanni exhibited shorter leaves and higher shoot density and biomass core−1 thanH. wrightii. Densities of almost all dominant species of nekton (fishes and decapods) were seasonally variable, all were higher in seagrass habitats than in nonvegetated habitats, and most were higher in one seagrass species than the other. Naked gobyGobiosoma bosc, code gobyGobiosoma robustum, bigclaw snapping shrimpAlpheus heterochaelis, and blue crabCallinectes sapidus, were most abundant inH. engelmanni. Brown shrimpFarfantepenaeus aztecus, brackish grass shrimpPalaemonetes intermedius, and daggerblade grass shrimpPalaemonetes pugio were most abundant inH. wrightii. PinfishLagodon rhomboides and pink shrimFarfantepenaeus duorarum were equally abundant in either seagrass. Most dominant nekton varied in size by month, but only two (L. rhomboides andC. sapidus) exhibited habitat-related differences in size. Nekton densities in these new seagrass habitats equaled or exceeded densities associated with historical and current intertidal smooth cordgrassSpartina alterniflora marsh. Continued seagrass expansion and persistence should ensure ecosystem productivity in spite of habitat change.  相似文献   

5.
We assess the sheltering effect of Posidonia oceanica meadows on drag forces exerted on shells of the fan mussel Pinna nobilis. We examine a range of shell sizes under four unidirectional flow speeds (0.05–0.34 m s−1) and two oscillating regimes. Three meadow densities are evaluated and a control without vegetation. We found that the attenuating effect of the meadow on drag forces experienced by bivalves is determined by the form of the hydrodynamic energy, e.g., as unidirectional flow or wave action. In tidal currents, the meadow protects most sizes of bivalves, with a higher efficiency for dense meadows, while in wave dominant zones the meadow reduces drag forces for bivalves with shell areas below a threshold of 0.019 m2, whereas larger animals experience increased drag forces within the meadow independent of meadow density. Reduction of shoot density in seagrass meadows might therefore not affect the effectiveness of the canopy to reduce drag forces on associated species like the fan mussel in wave-dominated areas while increased storm frequency could result into losses of larger individuals during periods of high wave action.  相似文献   

6.
The Laguna Madre of South Texas is a shallow coastal lagoon whose dominant primary producers shifted from seagrasses to phytoplankton with the onset of the Texas brown tide, which persisted from 1990 through 1997. Acartia tonsa is the dominant component of the mesozooplankton and forms an important link in both the phytoplankton and detritus-based pelagic food webs. Stable carbon isotope ratios of A. tonsa, as well as the two major primary producers: phytoplankton (as particulate organic carbon) and seagrasses, were measured from March 1989 to October 1991. Zooplankton samples were collected at four locations in the Laguna Madre: two in shallow water (c. 1 m) over seagrass beds and two in slightly deeper water (c. 2–3 m) over a muddy bottom in a secondary bay without seagrasses. We found seasonal trends in the isotopic composition of A. tonsa collected within both habitats as well as distinct differences between the average {ie995-1} values of individuals collected in the two regions. Isotopic ratios of animals collected during the summer months were generally 4–8‰ enriched in 13C compared with those collected in the winter, at all stations. A. tonsa collected over seagrass beds were 2–5‰ more enriched in 13C than those collected over muddy bottoms. These observations suggest carbon derived from seagrasses can be an important source of nutrition for these copepods in summer, especially for copepods living over seagrass beds. The effects of the persistent brown tide decreased the contribution of seagrasses as a carbon source for A. tonsa during the summer of 1991. The pathway by which seagrass carbon enters the diet of A. tonsa is unclear, but the two pathways considered most likely are through copepods feeding on microzooplankton that have fed on bacteria nourished on seagrass carbon, or by copepods feeding directly on particles of seagrass detritus.  相似文献   

7.
Large-scale marsh restoration efforts were conducted to restore normal salt marsh structure and function to degraded marshes (i.e., former salt hay farms) in the mesohaline lower Delaware Bay. While nekton response has been previously evaluated for the marsh surface and subtidal creeks in these marshes, little effort has been focused on intertidal creeks. Nekton response in intertidal creeks was evaluated by sampling with seines to determine if restored (i.e., former salt hay farms restored in 1996) and reference (i.e., natural or relatively undisturbed) salt marshes were utilized by intertidal nekton in a similar manner. The overall nekton assemblage during June–October 2004–2005 was generally comprised of the same species in both the restored and reference marshes. Intertidal creek catches in both marsh types consisted primarily ofFundulus heteroclitus andMenidia menidia, with varying numbers of less abundant transient species present. Transient nekton were more abundant at restored marshes than reference marshes, but in insufficient numbers to cause differences in nekton assemblages. In both marsh types, low tide stages were characterized by resident nekton, dominated byF. heteroclitus, while high tide stages were characterized by a variable mix of transient and resident nekton. Assemblage level analyses indicated that intertidal creeks in restored and reference marshes were generally utilized in a similar manner by a similar nekton assemblage, so restoration efforts were deemed successful. This is in agreement with multiple comparative studies from the ame marshes examining fish, invertebrates, and vegetation in different marsh habitats.  相似文献   

8.
Direct census of shoots tagged in permanent plots was used to assess the present (2000–2002)Posidonia oceanica population dynamics in 25 meadows along the Spanish Mediterranean Coast. Shoot density ranged from 154±8 to 1,551±454 shoots m−2, absolute shoot mortality from 5±0 to 249±53 shoots m−2 yr−1, and absolute shoot recruitment from <5 ±1 to 62±42 shoots m−2yr−1. Specific shoot mortality and recruitment rates, which are mathematically and statistically (p>0.05) independent of shoot density, varied from 0.015±0.006 to 0.282±0.138 yr−1 and 0.018±0.005 to 0.302±0.093 yr−1, respectively. Absolute shoot mortality rate was scaled to shoot density (Pearson correlation, r=0.78, p<0.0001), and variability in specific shoot recruitment rate was partially due to differences in the percentage of growing apexes, which produce most of the recruits within the population (Pearson correlation, r=0.50, p<0.001), demonstrating the existence of structural constraints on shoot demography. Shoot half-life was estimated to range from 2.5 to 60.4 yr and meadow turnover times between 6.7 yr and more than a century, provided current estimates of shoot mortality, recruitment rates, and density remain uniform. There were differences in shoot mortality and recruitment at the regional scale, with the meadows developing along the coast of the Spanish mainland experiencing the highest shoot mortality (Tukey test, p<0.05) and tending to exhibit the highest shoot recruitment. The low shoot recruitment did not balance shoot mortality in most (60%) of the meadows, showing a prevalence of declining populations among the 25 meadows studied (Wilcoxon ranked sign test, p<0.0005). This study demonstrates the power of direct census of seagrass shoots in permanent plots to evaluate the present status of seagrass meadows, to detect on-going population decline, and to provide some insight onto the possible factors involved. The incorporation of direct census of seagrass meadows to monitoring programs will help provide the early-warning signals necessary to support management decisions to conserve seagrass meadows.  相似文献   

9.
To test whether invasive Spartina alterniflora marshes were functionally equivalent to native Scirpus mariqueter marshes, the present study used bottomless lift nets (20 m2) during 12 high-tide events from August to October 2008 to compare nekton densities and biomass between the two marsh types in the Dongtan wetland. A total of eight species of fish, two species of shrimp, and three species of crab were collected. So-iny mullet Chelon haematocheilus, keeled mullet Liza carinata, Asian freshwater goby Acanthogobius ommaturus, and ridge-tail prawn Exopalaemon carinicauda dominated samples from the two marsh types and accounted for over 90% of the total catch. There were significantly greater densities and biomass (p < 0.05) of total nekton (all species combined) and two mullets (C. haematocheilus and L. carinata) in S. alterniflora marshes than in S. mariqueter marshes in August 2008, while no significant differences (p > 0.05) between the two marsh types were observed for densities and biomass of any species or total nekton in September and October 2008. Non-metric multidimensional scaling ordination did not show clear separation of samples between the two marsh types (r = 0.071, p = 0.159). Furthermore, there were no habitat-specific differences (p > 0.05) in the size distributions of the three numerically dominant species (C. haematocheilus, L. carinata, and A. ommaturus). We concluded that S. alterniflora marshes were utilized by nekton in a fashion similar to their utilization of native S. mariqueter marshes under similar physical conditions.  相似文献   

10.
Recolonization dynamics from disturbance on a Philippine mixed seagrass meadow, containing species spanning more than 10-fold in rhizome elongation rates and reproductive effort, was examined by following the recovery of a 1,200 m2 gap over 2.5 yr. The objective was to assess the contribution of contrasting species to the recovery process and to evaluate the importance of sexual versus vegetative colonization. Large, slow-growing species,Thalassia hemprichii andEnhalus acoroides, that produce large, broadly-dispersed seeds dominated sexual colonization with a total of 2,643 and 210 seedlings, respectively, recruiting to the area. Despite very rapid turnover of sexual recruits, the high frequency of seedling establishment ensured successful development of new patches in areas devoid of vegetation, leading to a scattered and evenly distributed presence of vegetation inside the gap. The small seagrass speciesCymodocea rotundata andHalodule uninervis, characterized by fast rhizome elongation rates but low reproductive output and limited seed dispersal, were the major contributors to the overall 450 m2 increase in vegetation cover through fast lateral extension (144±6 cm yr−1) from meadow edge and surviving patches, forming a compact vegetation cover in one edge of the denuded area. We conclude that contrasting recruitment strategies in the mixed-species seagrass community examined have implications for colonization potential at different spatial scales. Fast clonal growth is only an efficient mechanism for colonization of disturbances within established meadows (small gaps), whereas the large species, which combined high reproductive output with high seed dispersal capacity, may act to accelerate the colonization process in large gaps or distant from established meadows.  相似文献   

11.
We examined the spatial and temporal variability in drift macroalgal abundance in two seagrass dominated estuarine systems on the Texas coast: Redfish Bay (in the Copano-Aransas Estuary) and Lower Laguna Madre. Measurements of benthic macroalgal variability were made in conjunction with a suite of biotic (seagrass biomass, percent cover, blade width and length, shoot density, epiphyte biomass, seagrass blade C:N ratios, and drift macroalgal abundance and composition) and abiotic (inorganic nitrogen and phosphorus concentrations, chlorophylla, total suspended solids, light attenuation, salinity, temperature, total organic carbon and porewater NH4 +) indicators. All parameters were measured at 30 sites within each estuary semiannually from July 2002 to February 2004. Principal components analysis (PCA) was used to examine relationships between drift macroalgal abundance and biotic and abiotic parameters. In both Redfish Bay and Lower Laguna Madre, drift macroalgal distribution was widespread, and during three of four sampling periods, abundance was equal to abovegro und biomass ofThalassia testudinum, the dominant seagrass. Drift macro algal abundance was highly variable within sites, between sites, and between seasons in both estuaries. No significant differences in drift macroalgal abundance were found between Redfish Bay and Lower Laguna Madre. In Redfish Bay, drift macroalgae (90.1±10.2 gm−2) tended to accumulate in bare patches within seagrass beds. In Lower Laguna Madre, drift macroalgae (72.7±10.7 gm−2) tended to accumulate in areas of dense seagrass cover rather than in bare areas. We found no relationship between drift macroalgal abundance and low (<2μM) water column nutrient concentrations, and although several of our measured parameters were related to drift macroalgal abundance, none alone sufficiently explained the variability in abundance noted between the two estuarine systems. The contrasting patterns of macroalgal accumulation between Redrish Bay and Lower Laguna Madre likely reflect differences in water circulation characteristics between the two regions as dictated by local physiography, in cluding the shape and orientation of the lagoons, with seasonal variations in macroalgal abundance related to changes in freshwater inflow and nutrient loading.  相似文献   

12.
Vegetation maps of the lower Laguna Madre prepared from surveys conducted in 1965–1967, 1974–1976, and 1988 document a >330 km2 decrease in cover byHalodule wrightii, an increase of almost 190 km2 in other seagrass species, and an increase of 140 km2 in bare bottom. Loss in seagrass cover is confined to deeper parts of the laguna; turbidity caused by maintenance dredging is the suspected cause. The species shifts are consistent with observed reductions in salinity maxima. Although the hydrological alterations and climatic shift responsible for moderating the salinity regime occurred between 1948 and 1965, the biological changes continue. Establishment of patches away from source meadows appears to be the process for displacing species that limits their rate of expansion into suitable habitat in this elongate embayment.  相似文献   

13.
Studies of fish assemblages between natural and newly recolonized (<4 yr) seagrass meadows have shown no significant differences in community composition between meadow types. However, comparison of natural and well-established (31 yr) recolonized seagrass meadows in the Indian River Lagoon, Florida, showed that, although patterns in fish assemblages are complex and not always consistent, differences were evident. Species richness was higher in natural meadows during spring and autumn while density and species richness were higher in recolonized meadows during summer. Juveniles of all but the five most abundant species were more common in one or the other meadow type. Additionally, species composition was distinctly different between recolonized and natural seagrass meadows, as indicated by UPGMA cluster analysis based on the Morisita-Horn similarity index, Spearman'sr s (r s>0.05 in all but one case), and a maximum of only 58.5% species in common. There were also significant differences in the length-frequency distribution for six of seven abundant species. Our results suggest that a well-established recolonized seagrass meadow has the potential to maintain species complements distinct from nearby natural meadows. Reasons for our differing results may include differences in seagrass morphology and collecting techniques between our study and the former studies. Additionally, species may have a longer time to establish specific habitat-use patterns in well-established compared to newly-formed recolonized meadows. Recolonized seagrass meadows appear to be as suitable a habitat as natural meadows for juvenile and small adult fishes.  相似文献   

14.
We evaluate if the distribution and abundance ofThalassia testudinum, Syringodium filiforme, andHalodule wrightii within Biscayne Bay, Florida, are influenced by salinity regimes using, a combination of field surveys, salinity exposure experiments, and a seagrass simulation model. Surveys conducted in June 2001 revealed that whileT. testudinum is found throughout Biscayne Bay (84% of sites surveyed),S. filiforme andH wrightii have distributions limited mainly to the Key Biscayne area.H. wrightii can also be found in areas influenced by canal discharge. The exposure of seagrasses to short-term salinity pulses (14 d, 5–45‰) within microcosms showed species-specific susceptibility to the salinity treatments. Maximum growth rates forT testudinum were observed near oceanic salinity values (30–40‰) and lowest growth rates at extreme values (5‰ and 45‰).S. filiforme was the most susceptible seagrass species; maximum growth rates for this species were observed at 25‰ and dropped dramatically at higher and lower salinity.H. wrightii was the most tolerant, growing well at all salinity levels. Establishing the relationship between seagrass abundance and distribution and salinity is especially relevant in South Florida where freshwater deliveries into coastal bays are influenced by water management practices. The seagrass model developed by Fong and Harwell (1994) and modified here to include a shortterm salinity response function suggests that freshwater inputs and associated decreases in salinity in nearshore areas influence the distribution and growth of single species as well as modify competitive interactions so that species replacements may occur. Our simulations indicate that although growth rates ofT. testudinum decrease when salinity is lowered, this species can still be a dominant component of nearshore communities as confirmed by our surveys. Only when mean salinity values are drastically lowered in a hypothetical restoration scenario isH. wrightii able to outcompeteT. testudinum.  相似文献   

15.
It has been assumed that because seagrasses dominate macrophyte biomass in many estuaries they also dominate primary production. We tested this assumption by developing three carbon budgets to examine the contribution of autotrophic components to the total ecosystem net primary production (TENPP) of Lower Laguna Madre, Texas. The first budget coupled average photosynthetic parameters with average daily irradiance to calculate daily production. The second budget used average photosynthetic parameters and hourly in situ irradiance to estimate productivity. The third budget integrated temperature-adjusted photosynthetic parameters (using Q10=2) and hourly in situ irradiance to estimate productivity. For each budget TENPP was calculated by integrating production from each autotroph based on the producers’ areal distribution within the entire Lower Laguna Madre. All budgets indicated that macroalgae account for 33–42% of TENPP and seagrasses consistently accounted for about 33–38%. The contribution by phytoplankton was consistently about 15–20%, and the contribution from the benthic microalgae varied between 8% and 36% of TENPP, although this may have been underestimated due to our exclusion of the within bed microphytobenthos component. The water column over the seagrass beds was net heterotrophic and consequently was a carbon sink consuming between 5% and 22% of TENPP, TENPP ranged between 5.41×1010 and 2.53×1011 g C yr−1, depending on which budget was used. The simplest, most idealized budget predicted the highest TENPP, while the more realistic budgets predicted lower values. Annual production rates estimated using the third budget forHalodule urightii andThalassia testudinum compare well with field data. Macroalgae and microalgae contribute 50–60% of TENPP, and seagrass may be more important as three-dimensional habitat (i.e., structure) than as a source of organic carbon to the water column in Lower Laguna Madre.  相似文献   

16.
To assess the potential for habitat isolation effects on estuarine nekton, we used two species with different dispersal abilities and life history strategies, mummichog (Fundulus heteroclitus) and pinfish (Lagodon rhomboides) to examine: (1) distribution trends among estuarine shallow-water flat and various intertidal salt marsh habitats and (2) the influence of salt marsh habitat size and isolation. Collections were conducted using baited minnow traps set within nonisolated interior marshes (interior), nonisolated fringing marshes (nonisolated), isolated island marshes (isolated), and shallow-water flat habitats (flat) that were adjacent to isolated and nonisolated marshes. Size range of individuals collected included juvenile and adult F. heteroclitus (20–82-mm standard length) and L. rhomboides (22–151-mm standard length). During high tide, F. heteroclitus exclusively used marsh habitats, particularly high marsh, whereas L. rhomboides used marshes and flats. F. heteroclitus abundance followed an interior > nonisolated > isolated pattern. L. rhomboides abundance patterns were less consistent but followed a nonisolated > isolated > interior pattern. A size-dependent water depth relationship was observed for both species and suggests size class partitioning of marsh and flat habitats during high tide. Minimum water depth (~31 cm) restricted L. rhomboides populations in marshes, while maximum water depth (~69 cm) restricted F. heteroclitus population use of marshes and movement between marsh habitats. Disparities in F. heteroclitus young of year contribution between isolated compared to nonisolated and interior marsh types suggests isolated marshes acted as population sinks and were dependent on adult emigrants. Resident and transient salt marsh nekton species utilize estuarine habitats in different ways and these fundamental differences can translate into how estuarine landscape might affect nekton.  相似文献   

17.
The presence of the pathogenic protist Labyrinthula sp., the causative agent of seagrass wasting disease and mass mortality events, was assessed in 18 seagrass meadows in the Balearic region (western Mediterranean). This protist was found in 70% of seagrass meadows investigated and in all seagrass species present in the region (i.e., Posidonia oceanica, Cymodocea nodosa, and Zostera noltii). Labyrinthula spp. cultures isolated from seven P. oceanica and one Thalassia testudinum meadows were used as inocula to perform cross-infection experiments in order to test seagrass vulnerability to Labyrinthula spp. infection. These isolates produced lesions on P. oceanica and other seagrass species (Zostera marina, Z. noltii, and C. nodosa). P. oceanica and Z. noltii, both species autochthonous to the Mediterranean Sea, were the seagrasses most vulnerable to infection by the tested isolates. One of the P. oceanica isolates of Labyrinthula sp. also infected the Atlantic seagrass Z. marina, and all of the Mediterranean seagrasses were infected by Labyrinthula sp. isolated from the T. testudinum, native to the Caribbean and Gulf of Mexico. This work confirms that Labyrinthula sp. is commonly found on seagrasses of the Mediterranean Sea and demonstrates that Labyrinthula sp. can infect seagrasses in different genera, in contrast to previous studies where Labyrinthula sp. was considered to be genus-specific. This finding points out the broadly pathogenic nature of some Labyrinthula sp. isolates. Finally, this work identifies Labyrinthula sp. as a possible detrimental agent for P. oceanica.  相似文献   

18.
Increases in relative sea level are fragmenting the emergent vegetation of Louisiana’s coastal marshes. Nekton abundance is likely impacted by salinity and whether emergent vegetation is replaced by submerged aquatic vegetation (SAV) or open water. To assess these effects, we sampled nekton densities along a salinity gradient (categorized as freshwater, intermediate, and brackish marsh) in fragmented and non-fragmented areas. Total nekton density increased strongly with SAV in brackish marsh but only weakly in freshwater marsh (F 2,238 = 10.03, p < 0.0001). Freshwater and intermediate marshes had higher nekton densities when fragmented than when non-fragmented; this relationship was reversed in brackish marsh (F 2,238 = 8.89, p = 0.0002). Fragmentation, SAV, and salinity interacted to affect the densities of Gambusia affinis, Poecilia latipinna, Cyprinodon variegates, and Lucania parva. Our results suggest that the presence of both emergent vegetation and SAV was necessary for maintaining high nekton densities, with this combination being especially important in brackish marshes.  相似文献   

19.
Estuarine macrobenthos respond to a variety of environmental gradients such as sediment type and salinity, and organic enrichment. A relatively new influence, organic loading from suspended bivalve culture, has the potential to alter this response. A study on soft-bottom macrobenthic communities was carried out in the Richibucto estuary (46°40′N, 64°50′W), New Brunswick, Canada, with samples collected from 18 stations in late September and early October 2006. The site consisted of a large tidal channel originating upstream in a small river. The channel was punctuated by bag culture of oysters along its length. A total of 88 species were recorded. The mean values of abundance, species richness, and diversity (H′) of macrofauna were 11,199 ind. m−2 (ranged from 4,371 to 19,930 ind. m−2), 23.4 species grab−1 and 3.29 grab−1, respectively. In general species richness and H′ increased from the upper estuary to the estuarine mouth. Multivariate analyses clearly exhibited the spatial distribution in community structure, which coincided with the locations along the estuary (the upper, the lower and the mouth), as well as inside and outside the channel. Species richness and diversity H′ showed strong positive correlations with salinity (21.2–25.2 ppt), and abundance was positively correlated with water depth (1.0–4.5 m). Abundance and species richness were negatively correlated with both of silt–clay fraction (3.3–24.8%) and sorting (σI). Species richness was also negatively correlated with organic content (1.9–12.7%). The BIO-ENV analyses identified silt–clay fraction, σI and salinity as the major environmental variable combination influencing the macrofaunal patterns, and silt–clay fraction as the single best-correlated variable.  相似文献   

20.
We examined the distribution of nekton across the marsh landscape using a 1-m2 drop sampler to compare nekton densities across three different salinity zones (intermediate, brackish, saline), three pond sizes (diameter <40 m = small, ∼250–300 m = medium, >750 m = large), and two habitat types (pond, adjacent marsh) in the Barataria Bay Estuary, Louisiana. Nekton assemblages of ponds and the adjacent marsh appeared to be structured by the responses of individual species to the estuarine salinity gradient at the landscape scale and to pond habitat attributes locally. Our results indicate that ponds in the brackish and saline zones are more important nursery areas for most fishery species than ponds in the intermediate zone. Medium and large ponds supported higher densities of most species than small ponds. Most species of nekton were associated with vegetation structure, and individuals of these species were either concentrated among plant stems at the marsh edge or within submerged aquatic vegetation in ponds.  相似文献   

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