Increase In Percentage Cover Research Articles

Effect of Tourism Activities on Coral Communities at the Gulf of Suez, Red Sea

Although the rapidly expanding tourism industry is considered an extremely important economic activity, it caused increasing pressure on coral reefs of Egypt. Damage occurs from both direct and indirect impacts of tourism activities on coral communities. The Gulf of Suez has increasing of resorts from 8 at 2000 to 31 at 2014. This affected the coral communities along the area of study leads to a decrease in coral areas from 960 m2 at 2000 to 750 m2 at 2014, number of coral species from 21 species at 2000 to only 14 species at 2014, percentage cover of life coral from 46.4% at 2000 to 10.6% at 2014; on contrary, dead coral increased from 23.8% to 47.9% at the same period. This accompanied with an increase in the percentage of the algal cover from 8.6% at 2000 to 19.4% at 2014. The statistical analysis revealed a high correlation between the increased tourism activities and the coral status variables measured during the study. The data obtained showed high significant positive and negative correlation between the different variables that determined according to the effect of the different variables on each other and the relation between them. The simple linear regression statistical analyses showed a significant effect of tourism activities on the coral status, the analyses indicated that each increase in number of resorts by one resort leads to significant decrease in total coral area at the site by 0.9%, the analysis also showed that 80% of that decrease referred to the effect of tourism activities and 20% referred to other reasons. The analysis of variance (ANOVA) divided the recoded coral species into three categories, the first is soft corals which recorded significant increase in percentage cover from 2000 to 2014, the second is three species that recorded insignificant difference during the period of study, while the third category include most of the recorded species and they showed significant decrease in their percentage cover along time of study. The data obtained illustrated that all the investigated coral parameters are affected by the increasing tourism activities.

Recovery of canopy-forming macroalgae following removal of the enigmatic grazing sea urchin Heliocidaris erythrogramma

The sea urchin Heliocidaris erythrogramma (Valenciennes, 1846) is considered an ecologically important member of shallow sub-tidal reef assemblages across temperate Australia. However, defining its ecological role has remained elusive due to a paucity of evidence demonstrating the ability of this species to graze and maintain sea urchin barrens. Here we present critical evidence for a grazing effect of H. erythrogramma at typically observable densities (~ 4–6 individuals m − 2 ) by demonstrating recovery of canopy-forming brown algae following two controlled removals of the sea urchin from ostensibly barrens reef at sheltered locations in eastern Tasmania. In experimental plots where H. erythrogramma was removed, canopy-forming algae gradually recovered to demonstrate an average 5 times (ranging nil to 10 times) increase in percentage cover at 24 months post manipulation (chiefly driven by the habitat-formers Cystophora spp., Macrocystis pyrifera, Acrocarpia paniculata, and Sargassum spp.). While divergence in the overall algal community was indicated by both experiments, a statistically significant shift, based on percentage cover community data, was observed for only one location at 24 months post sea urchin removal, suggesting that a complete canopy-driven shift in community structure will be gradual and will be contingent on urchin density remaining below approximately 1.5 m − 2 in the longer term. The relatively slow and highly variable rates of algal recovery across plots suggests that seasonal coexistence of annual (chiefly filamentous algae) and some perennial macroalgae on H. erythrogramma barrens is likely due to a relatively low and variable intensity of selective grazing. We conclude that H. erythrogramma, at sufficient densities, is capable of grazing and maintaining a sea urchin barrens state however this phenomenon is observed to manifest in sheltered waters only. In contrast, H. erythrogramma occurring on exposed Tasmanian reefs achieves similar densities but here barrens are not observed and the sea urchin occurs cryptically within crevices and, consistent with experiments elsewhere in Australia, the sea urchin under these conditions appears to feed exclusively on an abundance of detached ‘drift’ macroalgae. Top–down and bottom–up factors leading to increased abundance of H. erythrogramma will be important in determining the potential influence of this enigmatic grazer on rocky reef communities, however critical tests of mechanisms controlling the switch between foraging modes are needed. Taken together, correlative patterns and results of experimental removals across the range of H. erythrogramma demonstrate that models of temperate Australian reef dynamics must account for the highly context-dependent effects of sea urchin foraging.

Nutrients increase epiphyte loads: broad-scale observations and an experimental assessment

There is a global trend towards elevated nutrients in coastal waters, especially on human-dominated coasts. We assessed local- to regional-scale relationships between the abundance of epiphytic algae on kelp (Ecklonia radiata) and nutrient concentrations across much of the temperate coast of Australia, thus assessing the spatial scales over which nutrients may affect benthic assemblages. We tested the hypotheses that (1) percentage cover of epiphytic algae would be greater in areas with higher water nutrient concentrations, and (2) that an experimental enhancement of nutrient concentrations on an oligotrophic coast, to match more eutrophic coasts, would cause an increase in percentage cover of epiphytic algae to match those in more nutrient rich waters. Percentage cover of epiphytes was most extensive around the coast of Sydney, the study location with the greatest concentration of coastal chlorophyll a (a proxy for water nutrient concentration). Elevation of nitrate concentrations at a South Australian location caused an increase in percentage cover of epiphytes that was comparable to percentage covers observed around Sydney’s coastline. This result was achieved despite our inability to match nutrient concentrations observed around Sydney (<5% of Sydney concentrations), suggesting that increases to nutrient concentrations may have disproportionately larger effects in oligotrophic waters.

Expansive covers of turf-forming algae on human-dominated coast: the relative effects of increasing nutrient and sediment loads

Turf-forming algae form more extensive habitat on subtidal rock adjacent to urban than non-urban coast of South Australia. This pattern is frequently observed on the world’s temperate coasts and is variously considered to be a result of enhanced concentration of nutrients or rates of sediment deposition on urban coasts. We experimentally tested which of three components of environmental change (increased nutrients in water, increased nutrients in sediments and increased sediment deposition) best explain the expansive covers of turf-forming algae on urban coasts. All three treatments had independent and positive effects on the percentage cover of turf-forming algae. The addition of nutrients from the water column had the largest influence (ω 2=0.55), which was more than six times greater than the effect of nutrients added to sediments (ω 2=0.08). An increase in rate of deposition of sediments had substantial effects (ω 2=0.35), which were about one third less than those of water-borne nutrients. Importantly, the combined effect of all three treatments caused a 77% increase in percentage cover of turf-forming algae, which is comparable to the observed difference in covers between urban and non-urban coast in South Australia (93%). These results suggest that human activities that reduce water quality in both nutrient and sediment loads account for major change observed on human-dominated coasts. Despite this knowledge, we still lack complete information on the mechanisms that switch the primary subtidal habitat from canopy-forming algae to turf-forming algae on human-dominated coasts.

Recovery of small denuded patches of the dominant NSW coastal saltmarsh species (Sporobolus virginicus and Sarcocornia quinqueflora) and implications for restoration using donor sites

Summary Efforts to restore coastal saltmarsh habitats through transplantation of saltmarsh species from donor sites are becoming more frequent. As sections removed are generally small there is little information on the ability of these areas to recover naturally after removal. The present study provides an understanding of the potential of dominant saltmarsh species in NSW (Saltcouch, Sporobolus virginicus and Samphire, Sarcocornia quinqueflora) to regenerate naturally after such small‐scale removal (25 cm × 25 cm plots) at separate sites for each species. The increase in percentage cover of vegetation within the denuded plots was measured over 21 months along a gradient within the marsh (between the mangrove and terrestrial boundaries) and then compared to non‐denuded plots. Recovery of Saltcouch was slow with an estimate of 5–6 years to reach the surrounding cover levels. Similarly, recovery of Samphire on upper levels of the shore is estimated at 4–5.5 years. On the lower level on the shore, however, Samphire had reached a cover that was within the range of the surrounding vegetation by the end of the 21‐month study period.

Annual changes in summer patterns of mesohabitat distribution and associated macroinvertebrate assemblages

The summer distribution of distinct mesohabitats (gravel, sand, silt, Ranunculus beds and emergent vegetation patches) at four 100-m sections along the length of a lowland river was studied over 3 years, together with their associated faunal assemblages. Habitat proportions in the sections showed little change between 1995 and 1997 at the uppermost site, in contrast to major changes downstream, which included an increase in percentage cover of Ranunculus from 10% in 1995 to 50% in 1996. There did not appear to be a significant relationship between summer or winter discharge and the proportions of mesohabitat, but there were indications that stream macrophyte areas were high when the preceding winter flows were low. Multivariate analysis of the faunal/site matrix showed that the principal source of variation was the mesohabitat composition. Superimposed over this was a site component where the uppermost site was separated from the intermediate sites, which in turn were separated from the most downstream site. Annual changes in faunal composition appeared to be the least significant overall but this varied with site, with little difference at the uppermost site and clear differences between 1995 and the other two years at the other sites. Ranunculus beds showed the least change between years. The highest number of taxa was found in emergent or marginal vegetation at all sites, with Ranunculus and sand supporting the lowest number. Mean abundance was greatest in Ranunculus and gravel samples, intermediate in emergent vegetation and silt, and lowest in sand. In order to investigate the implications of habitat changes, mean abundance of taxa per mesohabitat per year was compared with total abundance in the 100-m section for which habitat information was available. The total mean abundance of macroinvertebrates per mesohabitat was greatest in 1995 but this is not reflected in the total abundance per section. Mesohabitat abundances were greatest in Ranunculus, silt and emergent vegetation in 1995 but these mesohabitats were poorly represented in the section. In 1996, Ranunculus increased in area and this was reflected in higher total abundance. In 1997, the mean number of animals per mesohabitat was less than in previous years and this resulted in low overall abundance for the reach. Thus, the changes in habitat proportions controlled annual changes in total reach abundance and composition. Such changes have implications for the interpretation of biomonitoring and river habitat survey results whereby misleading conclusions may be drawn without considering annual and spatial fluctuations in habitat proportions. Copyright © 2000 John Wiley & Sons, Ltd.

Effects of grazing by re‐introduced Equus hemionus on the vegetation in a Negev desert erosion cirque

Abstract. Asiatic wild asses, Equus hemionus, were driven to extinction in Israel in the early 20th century. In 1983, a herd of these animals was re‐introduced to the wild in Makhtesh Ramon, a large erosion cirque in the central Negev desert, Israel. The population has grown steadily ever since and now numbers some 100 animals. In order to determine whether the wild asses are having a significant impact on the vegetation, we have monitored the plant communities in Makhtesh Ramon since 1992, using McAuliffe's log‐series survey method. Our study involves 11 pairs of plots along the length of the altitudinal gradient in Makhtesh Ramon. The altitudinal gradient results in a rainfall gradient from an average of 95 mm rain per year to an average of about 40 mm per year. Each pair of plots consists of: (1) an unfenced plot, and (2) a fenced plot that excludes wild asses but not the other large mammalian herbivore, the dorcas gazelle Gazella dorcas. The wild asses have not had a significant impact on vegetation cover, species richness, diversity or dominance. Three plant species showed significant increases in percentage cover in fenced plots, while one species showed a significant increase in percentage cover in unfenced plots. Furthermore, eight plant species invaded fenced plots, three species invaded unfenced plots and one species disappeared from unfenced plots during the study. Using Detrended Correspondence Analysis, we found that the major differences among plots are due to position along the altitudinal gradient. The Detrended Correspondence Analyses indicated that the wild asses have had no significant effect on vegetation community structure.

Short‐Term Responses of Alpine Buttercups to Experimental Manipulations of Growing Season Length

We examined the role of growing season length in regulating percentage cover and seed mass of the alpine snow buttercup, Ranunculus adoneus, in a snowbed habitat. Season length varies from °50 d in early—melting portions of the snowbed to 35 d in late—melting locations. Percentage cover and seed mass of snow buttercups decrease from early— to late—melting locations. Time available for growth was manipulated experimentally by altering the snowmelt schedule. Advancing snowmelt by 14 d in typically late—melting portions of the snowbed led to a threefold increase in percentage cover of snow buttercups (P &lt; .025). However, delaying snowmelt to the same extent in typically early melting locations had little influence on snow buttercups. These results indicate that time available for growth limits cover of snow buttercups in late—emerging vegetation, whereas other factors regulate cover of snow buttercups in early—emerging vegetation . Perturbation of snowmelt scheduled also had significant effects on seed mass (P &lt; .0055). These effects are probably mediated through changes in time available for seed maturation. Snow manipulation treatment accounted for 71% of the variation in seed maturation interval. Maturation interval, in turn, was correlated with seed mass (P &lt; .01). Reducing or increasing the seed maturation interval by 12 d caused a 33% change in seed mass. These findings show strong direct effects of growing season length on plant performance at diverse life history stages.

Disease assessment of early blight in potatoes in semi-arid zones

Five methods of assessing early blight (Alternaria solani) on potatoes were examined using field trials in Israel in 1986 and 1987. One method (Mean Days) was unrepeatable and therefore unsatisfactory; four others were repeatable and discriminated between the 16 cultivars examined. However, when relationships with natural senescence were examined, two of the methods (Best Score and Mean Percent) were highly correlated with it. Of the two methods that reflected the rate of increase in disease symptoms, the maximum increase in percentage cover observed in a 14 day period (Delta) was found to be more effective than the linear regression coefficient for the relationship between percentage disease cover and number of days from planting (Slope).