Tarek Youssef

Enhancement of morphological, anatomical and physiological characteristics of seedlings of the mangrove Avicennia marina inoculated with a native phosphate-solubilizing isolate of Oceanobacillus picturae under greenhouse conditions.

One hundred and twenty-nine rock phosphate (RP) solubilizing bacteria were isolated from the mangrove Avicennia marina rhizosphere sediment deficient in available phosphorus (P), in the United Arab Emirates (UAE). Among these isolates, an outstanding isolate of Oceanobacillus picturae grown in Pikovskaya’s liquid medium amended with RP, caused the highest percentage of RP solubilization (97%), the most pronounced drop in the medium pH and produced a variety of organic acids, as well as acid and alkaline phosphatases. Greenhouse experiments were carried out to investigate the effect of sediment inoculation with O. picturae (Op) with or without RP amendment on the growth, nutrient uptake, conducting tissue and photosynthetic gas exchange characteristics of mangrove seedlings. The application of Op to sediments amended with RP significantly promoted the growth of roots and shoots of seedlings compared with those grown in sediment amended with RP only. O. picturae significantly increased available sediment P, decreased sediment pH, positively enhanced nutrient uptake parameters in roots and shoots, increased stem circumference, number of xylem vessels, mean xylem diameter, and the hydraulically weighted xylem vessel diameter, compared with plants grown in non-inoculated sediment amended with only RP. Mechanistic analysis of A:Ci response curves (Assimilation versus sub-stomatal CO2 concentration) showed that photosynthetic gas exchange characteristics were significantly enhanced by Op + RP treatment compared with RP alone or control treatment. The maximal Rubisco-catalyzed carboxylation velocity (Vc,max), increased by more than two fold in plants treated with RP + Op, over the control. Application of Op + RP greatly increased the maximal electron transport rate values (Jmax) by 185%, over the control plants. In addition, the triose phosphate utilization rate (VTPU) increased three fold in plants treated with RP + Op over the control. To the best of our knowledge, this is the first published report of Op from mangrove sediments and also the first report of this organism as a phosphate-solubilizing bacterium. These results have clearly shown that Op has the potential to be applied as an effective and economical treatment in association with RP amendment for mangrove reforestation programs in arid environments such as those found in the UAE.

Mangrove zonation in Mobbs Bay - Australia

Zonation of mangrove vegetation at Mobbs Bay NSW was studied in relation to the physicochemical characteristics of the substrate and canopy cover at the season of seedling dispersal and establishment. The zonation pattern of mangrove species across such a low salinity site (4 to 14) was found to be a function of three environmental gradients, namely sulphide concentration in the sediments, canopy cover and height above the watertable. It is unlikely to be explained as a result of a single or particular gradient. It is suggested that the specific segregation of species is the outcome of the cumulative interaction between different environmental gradients on one hand and tolerance boundaries of each species to each particular gradient on the other.

Evidence for reduced post-spill recovery by the halophyte Sporobolus iocladus (Nees ex Trin.) Nees in oil-contaminated sediments

The germination behavior of Sporobolus iocladus seeds including germination percentage, accumulated germination percentage, the average incubation period to germination and germination velocity was studied under laboratory conditions. Treatments included six salinity regimes (0, 70, 140, 210, 280 and 350 mM NaCI) and three sources of oil hydrocarbons; Light Arabian Crude, polynuclear aromatic hydrocarbons (PAHs) including diaromatic or triaromatic hydrocarbons (in crude oil equivalent concentrations, COEC). The average incubation period needed for seeds to germinate was significantly longer for seeds germinated in 350 mM NaCl (6 +/- 1.16 days) compared with the control (4 +/- 00 days). The accumulated germination percentage gradually decreased with increasing salinity (control: 90 +/- 10, while 350 mM NaCl: 63 +/- 8.8). Oil hydrocarbons significantly affected all germination parameters of S. iocladus seeds regardless of salinity levels. COEC of di- and triaromatic hydrocarbons suppressed seed germination more than crude oil. Seeds exposed to diaromatic hydrocarbons failed to germinate. Hydrocarbons salinity interaction significantly reduced the number of germinated S. iocladus seeds. It is concluded that hydrocarbon pollutants adversely affect S. iocladus through reducing germination. It is also suggested that the toxic effect of hydrocarbons on seeds is not solely mediated through their interaction with salinity. The ecological implications of these findings are discussed in relation to other studies on the post-spill recovery of halophytes.

Sea Level Rise and Abu Dhabi Coastlines: An Initial Assessment of the Impact on Land and Mangrove Areas

The effects of climate change are now becoming more detectable because of the alarming rate of observed changes in our planet. One of the more devastating outcomes of climate change has been sea level rise (SLR). The present study aims at developing preliminary models of SLR and its effects on the coastlines of Abu Dhabi Emirate. A second aim has also been to develop a natural vulnerability index for decision makers and stakeholders to develop action plans in areas most vulnerable to SLR. For urban areas, the level of damage due to SLR would rise to 9.45% and 15.89% in a potential 1.5 m and 2 m SLR scenarios; respectively. The maximum damage to the urban areas would reach about 40% in case SLR attains the 3 m level. Mangrove Ecosystems affected would reach 25.54 Km2 (or about 81.5% of the study area) under a 3 m SLR scenario. The total land areas that would be affected by the different SLR scenarios reaches a staggering 528 Km2 (or 30% of the study area) at the 3 m SLR scenario. More than 3% of the impacted area (when considering any of the SLR scenarios) is classified as very highly vulnerable. More than 7% is classified as highly vulnerable. It is strongly believed that any future interventions and preparations to alleviate the impact of SLR should take into account the vulnerable areas highlighted above (i.e. 10.3%). The estimates reported here highlight the gravity of the potential mangrove and land areas affected, even under the lowest SLR level. Early planning for longer term implications will certainly save both time and resources.