scholarly journals A Comparison of Abundance and Diversity of Epiphytic Microalgal Assemblages on the Leaves of the SeagrassesPosidonia oceanica(L.) andCymodocea nodosa(Ucria) Asch in Eastern Tunisia

2014 ◽  
Vol 2014 ◽  
pp. 1-10 ◽  
Author(s):  
Lotfi Mabrouk ◽  
Mounir Ben Brahim ◽  
Asma Hamza ◽  
Mabrouka Mahfoudhi ◽  
Med Najmeddine Bradai
Keyword(s):  
Growth Rate ◽  
Species Composition ◽  
Posidonia Oceanica ◽  
Cymodocea Nodosa ◽  
Seagrass Species ◽  
Light Penetration ◽  
Grazing Effect ◽  
Abundance And Diversity ◽  
Fast Growing Species ◽  
Host Characteristics

We studied spatial patterns in assemblages of epiphytic microalgae on the leaves of two seagrass species with different morphologies and longevity,Cymodocea nodosaandPosidonia oceanica, which cooccur in Chebba in Eastern Tunisia. Epiphyte assemblages were described for each species in summer. Epiphyte microalgal assemblages were more abundant on the leaves ofC. nodosabut more diversified on the leaves ofP. oceanica. We suggest that the differences in species composition and abundance between those seagrass species may reflect an interaction of timescales of seagrass longevity with timescales of algal reproductive biology. Short-livedC. nodosawas dominated by fast growing species such as the cyanobacteria speciesOscillatoriasp., whileP. oceanicaleaves were colonized by more mature and diversified species such as Prorocentrales. Local environmental conditions (hydrodynamics, light penetration), host characteristics (meadow type, shapes forms of leaves, life span, and growth rate), and grazing effect seem also to be responsible for these dissimilarities in epiphytic microalgae communities.

Variability of foraminifera associations in seagrass ecosystems in shallow water during winter (Kerkennah – Southern Tunisian coasts)

2017 ◽  
Vol 98 (8) ◽  
pp. 1945-1954 ◽  
Author(s):  
Raida Trabelsi ◽  
Jannet Elloumi ◽  
Asma Hamza ◽  
Najla Ayadi ◽  
Ihsen Zghal ◽  
...  
Keyword(s):  
Mediterranean Sea ◽  
Benthic Foraminifera ◽  
Statistical Study ◽  
Environmental Parameters ◽  
Posidonia Oceanica ◽  
Cymodocea Nodosa ◽  
Seagrass Species ◽  
Halophila Stipulacea ◽  
Seagrass Ecosystem ◽  
Seagrass Ecosystems

This study intends to reliably estimate the general status of the benthic and the epiphytic foraminifera community related to each studied seagrass ecosystem (Posidonia oceanica,Cymodocea nodosaandHalophila stipulacea) distributed in different shallow sites in the coastal archipelago of Kerkennah (Gulf of Gabes, Tunisia) during winter. We were able to first sort and subsequently identify some characteristics conditioning their behaviour. Twenty-four species of foraminifera were encountered. Among them, three epiphytic species identified on these seagrass leaves had a much lower abundance than those in the sediment. We were interested in highlighting the foraminiferal community related toHalophila stipulacea, since this seagrass species is newly introduced into the Mediterranean sea. Thanks to the statistical study, we were able to identify the favourable habitat for epiphytic and benthic foraminifera among the three seagrass ecosystems. A correlation between the identified foraminifera species and some environmental parameters was addressed using a variety of software.

Scales of heterogeneity in prairie and forest

1999 ◽  
Vol 77 (3) ◽  
pp. 370-376 ◽  
Author(s):  
Heather R Kleb ◽  
Scott D Wilson
Keyword(s):  
Species Composition ◽  
Small Scale ◽  
Light Penetration ◽  
Pocket Gopher ◽  
Available N ◽  
Litter Mass ◽  
Thomomys Talpoides ◽  
Mixed Grass ◽  
Below Ground ◽  
Aspen Forest

Few studies have compared scales of heterogeneity among plant communities. We predicted that differences in the sizes of dominant species should allow us to detect small-scale (<256 cm) heterogeneity in mixed-grass prairie but not in adjacent aspen forest. We examined light penetration, soil moisture, available N, elevation, species composition, and plant mass at 10 locations in prairie and forest in both spring and summer. Variables were measured in 1-cm2 plots arranged in pairs separated by 0-256 cm. Several variables in prairie (elevation, litter mass, light penetration, and species composition) showed significant evidence for scale within the range examined. In contrast, only one variable in forest (light penetration in summer) showed evidence for scale in the same range. The scale of heterogeneity in prairie was consistent with the scale of two possible causes, species composition and elevation variability due to northern pocket gopher (Thomomys talpoides Richardson) activity, both of which varied significantly in prairie but not in forest. Whereas some aboveground factors (light and litter mass) varied within the range examined, belowground factors (water and N) did not, suggesting that the scale of heterogeneity differs between above- and below-ground factors. In total, the results suggest that differences in the scale of heterogeneity between prairie and forest reflect the relative sizes of the dominant plants.Key words: aspen, forest, heterogeneity, light, nitrogen, prairie, scale, soil, water.

scholarly journals Effects of grazing on plant species diversity and above ground biomass in a Trans- Himalayan Rangeland

1970 ◽  
Vol 17 (1) ◽  
pp. 25-31 ◽  
Author(s):  
Anita Pokharel ◽  
Madhu Chhetri ◽  
Chiranjibi P Upadhyaya
Keyword(s):  
Species Diversity ◽  
Species Composition ◽  
Plant Species ◽  
Diversity Index ◽  
Livestock Grazing ◽  
Above Ground Biomass ◽  
Ground Biomass ◽  
Grazing Effect ◽  
Significant Difference ◽  
Palatable Species

Limited information is available on the species composition, above ground biomass and its relations to grazing in a trans-Himalayan rangeland. Its assessment is essential for long term conservation and management. In the present study, we compared species composition, phenology, diversity index and biomass between controlled (without grazing) and open (free grazing) plots to assess the effects of grazing in the selected experimental sites of Upper Mustang during July and November 2005. Species encountered were classified as high, medium, low and non palatable and in three life form categories-grasses, shrubs and forbs. The experimental sites are dominated by forbs (80%) followed by grasses (15%) and shrubs (5%). Disturbance caused by grazing affects the phenological characteristics of the plant community. Result also reveals that species diversity, maximum possible diversity, evenness and species richness was higher in the grazed plots during July and November. A comparison of the aboveground biomass in July showed that mean percentage biomass of high, medium and low palatable species is higher in ungrazed plots. In November, the percentage biomass of only medium palatable species was higher in ungrazed plots and rest of the category is higher in grazed plots. Significant difference in July, a peak growing seasons for most of the plant species in the region reveals that the pasture has impact of livestock grazing. Keywords: Biomass, diversity, grazing effect, rangeland, species Banko Janakari: A journal of forestry information for Nepal Vol.17(1) 2007 pp.25-31

scholarly journals The rooting, survival and growth of woody species on tailing dumps in the limestone quarry “Lafarge ciment”

2021 ◽  
Vol 13 (1(22)) ◽  
pp. 34-42
Author(s):  
Petru Cuza ◽  
◽  
Corina Certan ◽  
Constantin Bulimaga ◽  
◽  
...  
Keyword(s):  
Growth Rate ◽  
Environmental Factors ◽  
Slow Growth ◽  
Woody Species ◽  
Mineral Elements ◽  
Black Pine ◽  
Limestone Quarry ◽  
Survival And Growth ◽  
High Degree ◽  
Fast Growing Species

The rooting, the survival and dynamics of growths in the height and after the diameter of the seedlings, of a range of woody species, had investigated on the freshly formed sterile dump limestone quarry „Lafarge Ciment”. The seedlings of the woody species had a relatively good rooting (69-99%). A high degree of rooting can be ensured as a result of the maintenance of forest crops. After planting, the young seedlings must be cared for by hoeing as many times as necessary in order to control the weeds and maintain moisture in the soil, which increases the survival of the seedlings. Tree species have been characterized by a different growth rate. Acacia has showed a very rapid increase in height, but the black pine has been characterized by a slow growth. Acacia being a fast-growing species and unpretentious to the mineral elements in the soil can be used to afforest the limestone quarry land. In the fi rst year after planting, the young seedlings, otherwise sensitive to the action of the environmental factors, had an increase in height and in diameter slow and uneven. In the years that followed, the seedlings became more viable and less infl uenced by local and temporal fl uctuations of environmental factors.

scholarly journals Selective top-down control of epiphytic biomass by amphipods from Posidonia oceanica meadows: implications for ecosystem functioning

2020 ◽  
Vol 145 (2) ◽  
Author(s):  
Loïc N. Michel ◽  
Patrick Dauby ◽  
Alessandra Dupont ◽  
Sylvie Gobert
Keyword(s):  
Ecosystem Functioning ◽  
Posidonia Oceanica ◽  
Seagrass Species ◽  
Coastal Zones ◽  
Top Down ◽  
Essential Components ◽  
Mutualistic Relationship ◽  
N Enrichment ◽  
Adequate Data ◽  
Endangered Ecosystems

Mediterranean Posidonia oceanica meadows shelter an important biomass and biodiversity of amphipod crustaceans that graze on epiphytes. However, their actual significance for ecosystem functional processes is hard to estimate, due to the lack of adequate data. Here, a field microcosm-based inclusion experiment was used to test if three of the dominant taxa of the amphipod community (Apherusa chiereghinii, Dexamine spiniventris and Gammarus spp.) could exert top-down control on seagrass leaf epiphytes. Influence of amphipod activity on nutrient availability for the host species was also investigated. All grazer taxa significantly reduced biomasses of erect macroalgae and erect sessile animals present on leaves. None of them consumed encrusting epiflora or epifauna. This selective top-down control could have important implications for the structure of the epiphytic community on leaves of P. oceanica, which is one of the most diverse and abundant of all seagrass species. Grazing activity of all taxa caused higher N content of seagrass leaves, likely through amphipod excretion and/or sloppy feeding. Since P. oceanica meadows often grow in oligotrophic zones where plant growth can be nutrient-limited, this N enrichment could enhance seagrass production. Overall, the ecological interaction between P. oceanica and amphipods could be seen as a facultative mutualistic relationship. Our results suggest that amphipod mesograzers are key-elements in some of the functional processes regulating these complex and yet endangered ecosystems, which are essential components of Mediterranean coastal zones.

Effect of protozoan predation on relative abundance of fast- and slow-growing bacteria

1989 ◽  
Vol 35 (5) ◽  
pp. 578-582 ◽  
Author(s):  
James L. Sinclair ◽  
Martin Alexander
Keyword(s):  
Growth Rate ◽  
Bacterial Community ◽  
Relative Abundance ◽  
Growth Rates ◽  
Bacterial Species ◽  
Test Species ◽  
Fast Growing ◽  
Population Sizes ◽  
Slow Growing ◽  
Fast Growing Species

The survival of six bacterial species that had different growth rates was tested in raw sewage and sewage that was rendered free of protozoa. When test bacteria were added to protozoa-free sewage at densities of approximately 105 to 106 cells/mL, five of the six species did not decline below 105 cells/mL. If protozoa were present, the population sizes of all test species were markedly reduced, but bacterial species able to grow faster in artificial media had the larger number of survivors. When the same bacteria were inoculated into protozoa-free sewage at densities of less than 103 cells/mL, only the three species able to grow quickly in artificial media increased in abundance. When the six species were inoculated at the same densities into sewage containing protozoa, the three slow-growing species were rapidly eliminated, and two of the three fast-growing species survived in detectable numbers. We suggest that in environments with intense protozoan predation, protozoa may alter the composition of the bacterial community by eliminating slow-growing bacteria.Key words: growth rate, predation, protozoa, sewage.

Amphipod assemblages from an artificial reef: a long-term analysis

Crustaceana ◽  
2013 ◽  
Vol 86 (7-8) ◽  
pp. 1025-1037 ◽  
Author(s):  
M. Targusi ◽  
L. Lattanzi ◽  
L. Nicoletti
Keyword(s):  
Species Composition ◽  
Spatial Heterogeneity ◽  
Artificial Reef ◽  
Scuba Diving ◽  
Tyrrhenian Sea ◽  
Abundance And Diversity ◽  
Second Period ◽  
Term Analysis

The aim of this paper is to evaluate the long-term development of a hard bottom amphipod assemblage over a period of 12 years. Amphipod data were collected in the artificial reef of Fregene, situated in the central Tyrrhenian Sea (Italy). Amphipod samplings were carried out by scuba diving in two different periods: 1991-1992 (1st period) and 2001-2003 (2nd period). The amphipod assemblage’s structure and species composition changed over the years, as the species collected on the reef in the second period differed from those collected in the first. In addition, within the same timeframe the assemblage shows an increase in both abundance and diversity, as a result of the reef’s increase in spatial heterogeneity.

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