High Shoot Density Research Articles

Morphological variation and habitat modification are strongly correlated for the autogenic ecosystem engineerSpartina anglica (common cordgrass)

We explored to what extent morphological variation and habitat modification are correlated for an autogenic ecosystem engineer, which is an organism that modifies its habitat via its own physical structures. The intertidal salt marsh species Spartina anglica is well known for its capacity to enhance sediment accretion within its canopy by reducing hydrodynamic energy. Sediment accretion is favorable to Spartina, as it reduces inundation stress, enhances soil drainage, and enhances nutrient availability. Shoot density and clonal architecture showed a large variation that was strongly correlated with the marsh elevation and sediment type. This correlation showed that at the lowest elevations at the muddy site, Spartina tussocks had the highest shoot density, which is known to be favorable for sediment accretion by reduction of hydrodynamic energy. There was also a strong positive correlation between the amount of sediment that accumulated within a tussock and gully formation around that Spartina tussock. The tussocks at the lowest elevations at the muddy site had the lowest lateral tussock growth. At the highest elevations at the sandy site, stem densities were lower and there was a relatively high rate of clonal expansion and marsh formation. At this location, we also observed tussock mortality due to erosion of several of these openly structured tussocks. Based on the observed correlations, we hypothesize that the morphology of Spartina represents trade-offs between the capacity to maximize habitat modification through sediment trapping by having a high shoot density versus the capacity to maximize clonal expansion by spreading shoots widely and the capacity of maximal clonal expansion by spreading shoots widely versus the risk of tussock mortality due to insufficient modification of the habitat that makes the tussock vulnerable to erosion. Our results indicated that morphological variation and habitat modification are strongly correlated for the autogenic ecosystem engineer S. anglica.

Rapid shear wave velocity imaging with seismic landstreamers and surface wave inversion

Surface wave data acquisition by landstreamer with flat baseplates produces nearly identical dispersion curves to those from planted geophones. Dependence on geophone frequency and good coupling is negligible and repeatability is lair. The primary application of landstreamers is to produce 2D shear wave velocity profiles through ID inversion of a number of dispersion curves at high shot density, and numerical modelling shows that this workflow provides accurate subsurface images. However, in the vicinity of a shallow, soft-layer termination, its lateral extent can be overestimated by about 10% of the recording spread length. Shorter spreads show less wavefield scattering hut more dependence on source-receiver geometry, and the response is dominated by the material under the nearer-offset channels.

Surface waves and landstreamers: Testing and results

Surface wave data acquisition by landstreamer with flat baseplates produces nearly identical dispersion curves to that from planted geophones. Dependence on geophone frequency and good coupling is negligible and repeatability is fair. `Pseudo' 2D profiling using 1D inversion at high shot density produces accurate subsurface images. However, `pushing' a spread over the termination of a soft-layer pinchout can lead to overestimation of its lateral extent by up to 20% of the spread length. Shorter spreads show less lateral scattering but large shot-geometry dependence, and the response is dominated by the material under the shot / nearer-offset channels.

Nekton of new seagrass habitats colonizing a subsided salt marsh in Galveston Bay, Texas

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.

A small-scale analysis of the spatial structure of a Posidonia oceanica meadow off the Island of Ischia (Gulf of Naples, Italy): Relationship with the seafloor morphology

Posidonia oceanica L. (Delile), an endemic species of the Mediterranean, forms extensive meadows which are continuously endangered by anthropic impacts. The availability of up-to-date information about interannual changes in shoot density of meadows and the knowledge of its expansion capabilities are crucial elements for the development of effective protection plans. Conversely, spatial ecology is becoming an increasingly important component of resource management, and the use of quantitative data for constructing prognosis maps of the dynamics of ecosystem degradation and restoration by nonlinear simulation methods is a topical field of landscape ecology. Unfortunately, little is known on spatial patterns of shoot density of P. oceanica on a small scale, despite their increasing use as indicators of the status and/or trends of meadows. The spatial structure of a continuous P. oceanica meadow, extending from 1 to 33 m depth in Lacco Ameno (Gulf of Naples, Italy), is investigated here by the “kriging” technique, a method widely used for geostatistical purposes. The analysis detected peculiar spatial patterns of shoot density and facilitated a small-scale (square meters) model of the distribution of P. oceanica. The highest shoot densities were found at the shallow stand (430 shoots m −2, on the average, with a peak of 1000 shoots m −2 in a relatively small area, at 1 m depth) and the lowest at the deep stand (average density <300 shoots m −2 below 15 m depth). A high degree of patchiness was found in the shallow stand, down to 10 m depth. Nestlike patterns with a rounded shape, characterized by shoot density radially decreasing from the center, were demonstrated mainly in the shallow stand. An opposite trend was detected in one case, where the main nestlike pattern was characterized by a decrease of density towards the center. Nestlike patterns may be generated by the confluence and overlap of stolons expanding from proximal areas. The comparison of density and depth models indicated that the shape of the seafloor influences the density structure of meadows and the growth patterns of P. oceanica.

Morphological adaptations of emergent plants to water flow: a case study with Typha angustifolia, Zizania latifolia and Phragmites australis

Summary1. Water velocity plays an important role in shaping plant community structure in flowing waters although few authors have yet attempted to explain the adaptation of plants to flow.2. We aimed to test two hypotheses, that: (i) some emergent macrophytes reconfigure their shoot distribution in fast currents and form clumps, and (ii) the shape and morphology of such clumps minimises drag caused by the current. The study focuses on three emergent macrophytes that co‐occur along a gradient of water velocity.3. The species showed a clear zonation in response to water depth and current velocity. Phragmites australis occupied shallower and more slowly flowing water than Typha angustifolia and Zizania latifolia, which had similar preferences.4. Both T. angustifolia and Z. latifolia shoots were more clumped at high velocity, whereas they were more randomly distributed at low flow or in stagnant water. Because of the low shoot density, water flowed more easily through T. angustifolia clumps, whereas Z. latifolia clumps had a high shoot density and large amounts of trapped litter, causing stagnant water in the centre of the clump. The clumps of Z. latifolia with a high density of shoots were longer and narrower than T. angustifolia clumps. Phragmites australis was less tolerant of flow than the other two species and large amounts of litter trapped in the clumps impaired flow.5. The shoot distribution of both T. angustifolia and Z. latifolia is reconfigured at high flow and this minimises drag on the clumps.

Population dynamics in a 6-year-old coppice culture of poplar: II. Size variability and one-sided competition of shoots and stools

Coppice cultures are characterised by a high stool and shoot density. Studies on density-dependent mortality, and intraspecific competition in crowded populations have mainly focused on non-woody species. We investigated intraspecific competition in a coppice culture of poplar ( Populus spp.). A high-density plantation with 17 poplar clones was established in April 1996, coppiced (i.e. cut back) in December 1996 and subsequently grown for 4 years (1997–2000). High stool mortality was observed in the establishment year. Frequency distributions of stool and shoot size, and the relationship between shoot biomass and shoot density was determined for the different clones during the 4-year rotation. Stool mortality was not correlated with stool density. In the paper it will be argued that stool competition was probably very low, although increasing by the end of the rotation. Stool mortality was caused by Melampsora rust infections, implicating that process based yield models for poplar SRC should take into account rust infections. Skewness and inequality of shoot size distributions were very high at the start of the rotation, but progressively decreased during the course of the experiment. No self-thinning line was found, although high shoot mortality was evident for all clones. Therefore, it might be argued that shoot elimination within a stool was not due to light competition, but to another physiological mechanism within the stool/dominant shoot.

Interference between the macroalga Caulerpa prolifera and the seagrass Halodule wrightii

A field experiment was conducted to examine interactions between the seagrass Halodule wrightii and the macroalga Caulerpa prolifera in the Indian River Lagoon, FL, USA, and further if the outcome of the interactions between the two species was influenced by water depth. The experiment involved the manipulation of neighbor presence in plots established at the shallowest (50 cm) and deepest (80 cm) depths at which the two species co-existed at adequate densities to perform removal experiments. Shoot and frond densities were measured at the beginning (April), middle (July) and end (October) of the 6-month growing season, and above- and below-ground biomass values were determined at the end of the experiment (October). In the middle of the growing season H. wrightii had higher shoot densities and greater biomass in plots where C. prolifera had been removed at both water depths. This same pattern in shoot density and biomass for H. wrightii also occurred at the end of the growing season at the 80 cm depth. C. prolifera occurred at higher densities and greater biomass in the 80 cm depth range, but was generally unaffected by the presence of H. wrightii at either depth.

Seagrasses of Tongsha Island, with descriptions of four new records to Taiwan

The composition, abundance, and distribution of seagrasses on Tongsha island were studied from 21 to 29 April 2004. A total of seven seagrass species from six genera and two families were identified. Among them, four species were new to Taiwan, including Cymodocea rotundata Ehrenb. et Hempr. ex Aschers., Cymodocea serrulata (R. Br.) Aschers. and Magnus, Syringodium isoetifolium (Aschers.) Dandy, and Thalassodendron ciliatum (Forsk.) den Hartog. The species number of seagrasses was 14% of the total global number. The total coverage area of the seagrass beds was estimated to be 8.2 km^2 distributed around Tongsha island and the lagoon. Mean percentage cover and shoot density were high, ranging from 20 to 95% and ＜1250 to ＞2500 shoots m^(-2), respectively. The large area of the seagrass bed, the high shoot density and coverage of seagrasses, and the diverse species of Tongsha island indicate that the seagrass resource on Tungsha island is very abundant. These seagrass beds must be conserved to ensure the sustainable management of Tongsha Island.

Productivity aspects of three tropical seagrass species in areas of different nutrient levels in Kenya

Previous work conducted in two seagrass areas of different nutrient status, along the Kenyan coast, has shown that the seagrasses were characterised by differences in the species composition and biomass of epiphytic algae. This study was undertaken to evaluate the productivity patterns of the seagrass species growing in these same sites. Studies were made on Thalassodendron ciliatum (Forskål) den Hartog, Thalassia hemprichii (Ehrenberg) Aschers and Cymodocea rotundata Ehrenberg and Hempr. ex Ascherson growing in the lagoons of Nyali and Vipingo, along the Kenyan coast, during the South East (SE) and North East (NE) monsoon periods. The results of this study revealed differences in the levels of nitrate within the water column, with Vipingo having lower levels of around 4 μM during the low tide period of the SE monsoon while nitrate levels in Nyali reached levels of 16 μM during the same period. Of the three seagrass species studied, C. rotundata had the highest shoot densities in both sites. The shoot densities of C. rotundata reached levels of 1300 shoots m −2 compared to an average of 600 shoots m −2 for both T. ciliatum and T. hemprichii. The stems of T. ciliatum were found to be 200 mm long in Nyali whereas those in Vipingo were 80 mm in length. Of the three seagrasses T. ciliatum and T. hemprichii showed significant differences in total leaf growth between the two sites. However, of these two species, only T. hemprichii showed distinct differences in leaf production and biomass when the two sites were compared. Leaves of T. hemprichii showed growth rates of 0.008 g dw shoot −1 day −1 in Nyali while the growth rate in Vipingo was 0.004 g dw shoot −1 day −1. Leaf production rates were approximately 0.005 g dw shoot −1 day −1 for T. ciliatum in both Nyali and Vipingo and that of C. rotundata was approximately 0.0015 g dw shoot −1 day −1 in the two sites. This suggests that of the three species studied, T. hemprichii may have been influenced by the nutrient input in Nyali. The abundance of epiphytes on the stems of T. ciliatum was higher in Nyali during both seasons; therefore we suggest that although the composition of epiphytic species is the main indicator of nutrient enrichment in these areas the enhanced productivity of T. hemprichii may be another indicator of the nutrient status of these study sites.

Modeling growth and carbon allocation in two reed beds ( Phragmites australis) in the Scheldt estuary

Common reed ( Phragmites australis) is a prominent species in the upstream part of the eutrophic Scheldt estuary (Belgium, The Netherlands). From 1996 till 1998, seasonal growth dynamics of the species were studied in two monospecific stands subjected to different salinity regimes (seasonal means 1.6 and 13.3 PSU, respectively). We addressed the following questions: how are these reed vegetations affected by meteorological conditions and by the growth site, what are the important growth processes and what is the fate of the annually fixed carbon. A mathematical model was developed and calibrated using the data from the oligohaline site. Subsequent application of the model to the mesohaline stand required adaptation of parameters relating to the partitioning of resources and timing of growth initiation only. At their peak, the aboveground biomass was 587–1678 g DW m −2 at the 13.3 PSU site and 1116–2179 g DW m −2 (1.6 PSU); more than 60% of the biomass was located underground. In 1996, biomasses were 2–3 times lower than in the other 2 years, caused by a retarded growth initiation. Probably due to a lower temperature in early 1996, rhizome bud burst occurred more than 1 month later compared to the other years. In addition, growth initiation was several weeks later in the mesohaline site. This appeared mainly responsible for the large difference in maximal aboveground biomass between both stations. Architecture of the plants was also affected, with a higher shoot density (about 50% more shoots), better-developed root system (15% of total belowground biomass compared to 5%) and more, but smaller leaves at the higher salinity site. Notwithstanding large differences in aboveground biomass, annual growth was similar at both stations (154 and 132 mol C m −2 per year at the oligo- and mesohaline station, respectively). Primary production accounted for about 80% of all growth processes, rhizome remobilization for almost 20%, translocation of mass before sloughing of leaves accounting about 3%. Within a year, some 44% (oligohaline) and 36% (mesohaline) of new assimilates produced by photosynthesis accumulated as dead litter. The other part was respired by the plant itself, either to provide the energy for growth (23%) or maintenance costs (33–41% at the oligo- and mesohaline station, respectively). Calculated annual turnover rates of aboveground biomass, rhizomes and roots were 100, 62 and 73%, respectively.

Modeling growth and carbon allocation in two reed beds (Phragmites australis) in the Scheldt estuary

Common reed ( Phragmites australis ) is a prominent species in the upstream part of the eutrophic Scheldt estuary (Belgium, The Netherlands). From 1996 till 1998, seasonal growth dynamics of the species were studied in two monospecific stands subjected to different salinity regimes (seasonal means 1.6 and 13.3 PSU, respectively). We addressed the following questions: how are these reed vegetations affected by meteorological conditions and by the growth site, what are the important growth processes and what is the fate of the annually fixed carbon. A mathematical model was developed and calibrated using the data from the oligohaline site. Subsequent application of the model to the mesohaline stand required adaptation of parameters relating to the partitioning of resources and timing of growth initiation only. At their peak, the aboveground biomass was 587–1678 g DW m −2 at the 13.3 PSU site and 1116–2179 g DW m −2 (1.6 PSU); more than 60% of the biomass was located underground. In 1996, biomasses were 2–3 times lower than in the other 2 years, caused by a retarded growth initiation. Probably due to a lower temperature in early 1996, rhizome bud burst occurred more than 1 month later compared to the other years. In addition, growth initiation was several weeks later in the mesohaline site. This appeared mainly responsible for the large difference in maximal aboveground biomass between both stations. Architecture of the plants was also affected, with a higher shoot density (about 50% more shoots), better-developed root system (15% of total belowground biomass compared to 5%) and more, but smaller leaves at the higher salinity site. Notwithstanding large differences in aboveground biomass, annual growth was similar at both stations (154 and 132 mol C m −2 per year at the oligo- and mesohaline station, respectively). Primary production accounted for about 80% of all growth processes, rhizome remobilization for almost 20%, translocation of mass before sloughing of leaves accounting about 3%. Within a year, some 44% (oligohaline) and 36% (mesohaline) of new assimilates produced by photosynthesis accumulated as dead litter. The other part was respired by the plant itself, either to provide the energy for growth (23%) or maintenance costs (33–41% at the oligo- and mesohaline station, respectively). Calculated annual turnover rates of aboveground biomass, rhizomes and roots were 100, 62 and 73%, respectively.

Cultivation and Topdressing Requirements for Thatch Management in A and G Bentgrasses and Creeping Bluegrass

Empirical observations suggest certain new cultivars of creeping bentgrass (Agrostis stolonifera L.) with high shoot density require more intensive topdressing and core aeration to control thatch compared to less dense cultivars such as `Penncross. In addition, a variety of Poa annua var. reptans Hausskn., `DW-184, has recently been released for putting green use but management requirements are undocumented. The objective of our project was to determine the core aeration and topdressing requirements for thatch management of creeping bentgrass cultivars `A-4, `G-2, and `Penncross as compared to `DW-184. Plots were established on a sand-based root zone and maintained as putting green turf for 3 years. A factorial treatment arrangement was used to assess the effects of core aeration and topdressing on thatch, topdressing removal, turf quality, and disease. Both `A-4 and `G-2 produced more organic matter as (thatch/mat) than `Penncross and `DW-184. Grass type, core aeration frequency, and topdressing regime affected the amount of topdressing removed by mowing. An interaction between grass type and topdressing regime showed biweekly topdressing with verticutting resulted in less topdressing removal from all grasses except `G-2 compared to monthly topdressing without verticutting. Since no more than 3% of the topdressing applied was removed from any single treatment, however, the overall impact of grass type, core aeration frequency, or topdressing regime are unlikely to affect turf response. Both `A-4 and `G-2 provided consistently better quality turf than `Penncross or `DW-184 at 3.2 mm mowing height, though `A-4 was more susceptible to dollar spot disease (Sclerotinia homeocarpa F.T. Bennett) than `Penncross or `G-2. Cultivation and topdressing methods for management of `A-4 and `G-2 bentgrasses do not differ substantially from `Penncross or `DW-184 creeping bluegrass.

Degree of correlation between total light interception and whole-canopy net CO2exchange rate in two grapevine growth systems

This paper shows the degree of precision by which measurement of total canopy light interception (TCLI) can estimate whole-canopy net CO2 exchange rate (NCER). The test vines comprised a single 35° NE-SW oriented hedgerow, with vertically shoot positioned grapevine canopies at either a low shoot density (10 shoots/metre of row) or a high shoot density (20 shoots/metre of row). TCLI was measured on different dates and at various times on each date (during the 2001 growing season) by a multiple line sensor equipped with 64 phototransistors (35 mm spacing). Each sensor had a spectral sensitivity in the 300-1100 nm waveband and the line of sensors was moved horizontally in steps of 10 cm. Whole-canopy NCER was recorded over successive clear days using an enclosure method. TCLI and canopy NCER were highly correlated on a seasonal basis for both the low shoot density treatment (R2 = 0.97) and the high shoot density treatment (R2 = 0.94). The correlation became less precise (R2 = 0.80 and 0.79 for low and high, respectively), when data taken at various times of day were treated separately. Canopy NCER derived from single TCLI readings taken at solar noon tended to be under-estimated, while NCER derived from single TCLI readings taken later in the afternoon tended to be over-estimated. Nevertheless, for a given training system, our method was sufficiently precise to predict seasonal increase of canopy NCER as well as the total leaf area at which NCER approached a maximum thus setting a value above which additional leaf area resulted in mutual shading without enhancing carbon assimilation.

Effects of seagrass habitat fragmentation on juvenile blue crab survival and abundance

Seagrasses form temporally dynamic, fragmented subtidal landscapes in which both large- and small-scale habitat structure may influence faunal survival and abundance. We compared the relative influences of seagrass ( Zostera marina L.) habitat fragmentation (patch size and isolation) and structural complexity (shoot density) on juvenile blue crab ( Callinectes sapidus Rathbun) survival and density in a Chesapeake Bay seagrass meadow. We tethered crabs to measure relative survival, suction sampled for crabs to measure density, and took seagrass cores to measure shoot density in patches spanning six orders of magnitude (ca. 0.25–30,000 m 2) both before (June) and after (September) seasonally predictable decreases in seagrass structural complexity and increases in seagrass fragmentation. We also determined if juvenile blue crab density and seagrass shoot density varied between the edge and the interior of patches. In June, juvenile blue crab survival was not linearly related to seagrass patch size or to shoot density, but was significantly lower in patches separated by large expanses of unvegetated sediment (isolated patches) than in patches separated by <1 m of unvegetated sediment (connected patches). In September, crab survival was inversely correlated with seagrass shoot density. This inverse correlation was likely due to density-dependent predation by juvenile conspecifics (i.e. cannibalism); juvenile blue crab density increased with seagrass shoot density, was inversely correlated with crab survival, and was greater in September than in June. Shoot density effects on predator behavior and on conspecific density also likely caused crab survival to be lower in isolated patches than in connected patches in June. Isolated patches were either large (patch area >3000 m 2) or very small (<1 m 2). Large isolated patches had the lowest shoot densities, which may have allowed predators to easily find tethered crabs. Very small isolated patches had the highest shoot densities and consequently a high abundance of predators (=juvenile conspecifics). Though shoot density did not differ between the edge and the interior of patches, crabs were more abundant in the interior of patches than at the edge. These results indicate that seagrass fragmentation does not have an overriding influence on juvenile blue crab survival and density, and that crab cannibalism and seasonal changes in landscape structure may influence relationships between crab survival and seagrass habitat structure. Habitat fragmentation, structural complexity, faunal density, and time all must be incorporated into future studies on faunal survival in seagrass landscapes.

Root Weight, Nonstructural Carbohydrate Content, and Shoot Density of High-density Creeping Bentgrass Cultivars

Limited information is available on the performance under temperate conditions in the United States of recently released cultivars of creeping bentgrass (Agrostis stolonifera L.) with high shoot density for use on golf course putting greens. Fifteen cultivars were established in Aug. 1996 on a greens mix with high sand content to compare their seasonal weights and total nonstructural carbohydrate (TNC) contents. The cultivars were maintained at 3.1 mm height of cut. Shoot density counts were taken during Apr., July, and Oct. 1998. Root weights and nonstructural carbohydrate levels were assessed monthly from June 1997 through Nov. 1998. A cultivar group contrast between the high shoot density cultivars (`Penn A1', `Penn A2', `Penn A4', `Penn G1', `Penn G2', and `Penn G6') and the standard cultivars (`Penncross', `Crenshaw', `Southshore', `DF-1', `Procup', `Lopez', `SR1020', and `Providence') revealed that the former averaged 342.9 and 216.1 more shoots/dm2 on two of the three sampling dates. Root dry weights did not vary significantly (P ≤ 0.05) among the cultivars. Performing a contrast between new high shoot density cultivars and standard cultivars revealed greater root dry weight in the former during Mar. and May 1998. Differences (P ≤ 0.05) in TNC were observed on two of the 18 sampling dates, but no trends were evident.

Advanced excimer laser crystallization techniques

In high performance polysilicon thin film transistors (TFTs) the uniformity of electrical characteristics remain a major problem. This situation has stimulated a growing activity aiming to control the lateral growth phenomenon. However, most of the techniques require additional processing steps or a rather high shot density. We present a technique based on a two-pass excimer laser crystallization process: during the first irradiation the sample is irradiated through a patterned mask, while the second irradiation, performed without the mask, results in the homogeneous crystallization of the sample. This technique allows the possibility of forming uniform polysilicon layers, with large (∼2 micron) and aligned grains, with a reduced number of shots and a relatively large process energy window. The results of crystallization performed at different laser energy densities, sample thickness and laser pulse duration are analyzed.

Differences in morphology and C/N-balance between clones ofPhragmites australis within a plantation at a degraded fen

The morphology, productivity and C/N-balance of 9 different clones ofPhragmites australis planted in 1997 in a degraded fen area of 40,000 m2 was investigated in order to estimate the degree of variation between the genotypes. The planted reed clones showed significant differences in morphology, standing crop and stand structure at the same site. The above-ground biomass of some reed clones was due to high culms and large leaf areas, while among others it was due to high shoot densities and small culms. The productivity of the individual clones also differed. At the end of the 1998 growing season the standing crop of the clones ranged from about 700 to 2,000 g of dry matter per m2. Differences were found in the C/N-dynamics as in the standing stock of total nitrogen in the above-ground biomass (ranging from 15 to 50 g N/m2) and the relative nitrogen content of the shoots. Furthermore, seasonal changes in the amount of free amino acids and carbohydrates in the basal internodes of the different clones were compared. The patterns are discussed with respect to the nutritional status of the reed plants. In conclusion, the results suggest high genotypic variation despite the comparable site conditions and thus a strong influence of genetically determined differences in growth and resource exploitation on the characteristics of reed clones.

Ontogenetic changes in habitat use by postlarvae and young juveniles of the blue crab

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 186:227-238 (1999) - doi:10.3354/meps186227 Ontogenetic changes in habitat use by postlarvae and young juveniles of the blue crab Renee A. Pardieck, Robert J. Orth*, Robert J. Diaz, Romuald N. Lipcius The College of William and Mary, School of Marine Science, Virginia Institute of Marine Science, Gloucester Point, Virginia 23062, USA *Addressee for correspondence. E-mail: jjorth@vims.edu ABSTRACT: Changing habitat requirements are evident during the developmental cycles of many species. In this field investigation, we attempted to distinguish between depth (shallow vs deep), habitat structure (seagrass species), and study site as factors influencing the distribution and abundance of postlarvae and juvenile blue crabs Callinectes sapidus in the Chesapeake Bay. Deep (>= 70 cm mean low water [MLW]) and shallow (<= 50 cm MLW) suction samples in monospecific Zostera marina and Ruppia maritima beds were taken in the York River, a tributary of the Chesapeake Bay. Our studies revealed ontogenetic changes in habitat use, which suggested that blue crabs are influenced differently by physical and biological factors even during the earliest life stages. Postlarvae through 3rd instar distributions were not related to seagrass species, but their densities increased with distance upriver (regression, p < 0.004, n = 36 to 38, postlarvae: r2 = 0.173, 1st instars: r2 = 0.308, 2nd-3rd instars: r2 = 0.231). This suggests that the smallest instar distributions are related to larval supply and physical forces, such as currents and winds, which determine water-column transport. In contrast, 4th and greater instars were significantly more abundant in Ruppia than in Zostera (ANOVA, df = 1, p < 0.05), possibly because of the high shoot density of Ruppia beds. Habitat use by 4th and greater instars may be related to seasonal changes in seagrass shoot density. Water depth did not influence the distribution of any crab stage. We suggest that habitat selection and differential mortality among habitats influence larger instar distributions more strongly than they influence the distribution of postlarvae and the earliest instars of C. sapidus. KEY WORDS: Blue crabs · Callinectes sapidus · Ontogenetic changes · Habitat structure · Habitat use · Settlement · Recruitment · Shallow-water refuge · Seagrass beds Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 186. Publication date: September 17, 1999 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1999 Inter-Research.

Polychate distribution, diversity and seasonality related to seagrass cover in shallow bottoms of the Tyrrenian Sea (Italy)

Polychaete distribution, diversity and seasonality were studied in relation to covering of the small phanerogams Cymodocea nodosa and Zostera noltii in shallow soft-bottoms off the island of Ischia (Tyrrhenian Sea, Italy). Samples were collected bimonthly from July 1988 to May 1989 from four stations, selected for seagrass meadows of different physiognomy and shoot density, and in a bare sandy bottom nearby, selected as a non-vegetated reference habitat. Two meadow compartments were considered: the leaf stratum and the sediment. A hand-towed net was used to sample vagile organisms living in the leaf stratum, while PVC corers were utilized for the sediment fauna. Stratification within the sediment was studied considering three layers (0-5 cm, 5-10 cm and > 10 cm deep). On the whole a total of 4640 individuals of polychaetes, belonging to 119 species, were collected; 4061 individuals and 115 taxa were found in the core-samples, and 579 individuals and 35 taxa in the net-samples. Polychaete diversity and abundance was higher in both meadow compartments and in all seasons in the station located in the meadow where more sheltered conditions occurred, high silt-clay and organic matter content in the sediment were observed. In addition, this is where higher shoot density, plant Leaf Area Index (LAI) and Leaf Standing Crop (LSC) were recorded. Whereas, lower diversity and higher patchiness (differences among core replicates) were always recorded in the less vegetated stations, and on the bare sandy bottom. The polychaete populations of the sediment layers showed their lowest diversity and abundances in summer. Whereas, the populations associated with the leaf stratum showed an opposite trend with higher development (number of species and individuals) in summer (July-September), consistent with the higher values of all the plant phenological parameters recorded (shoot density, LAI and LSC). In all stations and seasons, the polychaetes were concentrated (84% of the whole abundance) in the upper sediment layer (0-5 cm) and decreased strongly in the deeper sediment layers. Faunistic differences were recorded mainly between the leaf stratum and the sediment populations. The interstitial Syllidae Exogone naidina, Parapionosyllis elegans, Sphaerosyllis thomasi, dominated in the leaf stratum; while endofaunal forms, such as Neanthes caudata, Peresiella clymenoides, Heteromastus filiformis, Notomastus latericeus and Euclymene collaris, dominated at the sediment level. The differences in polychaete community structure observed between the sites studied can be explained by the coupling of abiotic conditions (in particular the reduced hydrodynamics and sediment features) and meadow structure and habitat complexity characterized by plant phenological features (e.g., shoot density, LAI, LSC). The seasonal and microdistributional (sediment and leaf stratum) patterns within each of the meadow stations are influenced by ecology and life history of single species, and probably by the higher predation pressure occurring in some seasons. These results suggest that at least for small-sized and less mobile organisms, like polychaetes generally, meadow structure, shoot density and other phenological plant features influence species composition and abundances both at large (between-meadows) and smaller (within-meadow) spatial scale.