Riyad Manasrah

Coral calcification: Use of radioactive isotopes and metabolic inhibitors to study the interactions with photosynthesis and respiration

In order to characterize the process of calcification in scleractinian corals, a series of laboratory experiments were conducted using radioactive isotopes. Labelled calcium, bicarbonate and glucose were used and the fates of the labelled tracers were followed in the skeleton and the tissue fractions of the coral Galaxea fascicularis. In addition, a variety of metabolic inhibitors were used to test the effects of various enzymes and processes on the incorporation rates. The incorporation rate of 45Ca into the coral skeleton decreased to about one-fifth upon inhibition of metabolic respiration by the specific inhibitor NaCN suggesting a major role of metabolic respiration in coral calcification, and decreased to one-half upon inhibition of carbonic anhydrase by the specific inhibitor acetazolamide indicating a role of the enzyme in the process. The results obtained have also shown that corals are able to incorporate carbon from seawater bicarbonate and added glucose in both skeleton and tissue fractions. The process of incorporation was influenced by light conditions, carbonic anhydrase, respiration and photosynthesis. The incorporation rate of 14C-HCO was reduced to about one-tenth in the skeleton, and one-fifth in the tissue, upon inhibition of carbonic anhydrase suggesting a major influence of the enzyme in the incorporation process. The inhibition of photosynthesis had more influence on the tissue incorporation rate of the tracer than the skeleton suggesting that photosynthesis is the main process responsible for tissue use of seawater bicarbonate in the coral. 14C-glucose incorporation into the skeleton was mainly affected by NaCN addition and to a lesser extent by dichlorophenyldimethylurea (DCMU) addition, while the tissue fraction was mainly affected by NaCN addition. It was concluded that respiration and photosynthesis, in addition to the enzyme carbonic anhydrase, are limiting factors for the process of calcification in the coral, and that various forms and sources of carbon can be used in coral calcification and tissue growth.

Seasonal changes of water properties and current in the northernmost gulf of aqaba, red sea

Seasonal changes of tide signal(s), temperature, salinity and current were studied during the years 2004-2005 in the northernmost Gulf of Aqaba, which is under developmental activities, to obtain scientific bases for best management and sustainability. Spectrum analysis revealed permanent signals of tide measurements during all seasons, which represented semidiurnal and diurnal barotropic tides. The other signal periods of 8.13, 6.10-6.32, 4.16 and 1.02-1.05 h were not detected in all seasons, which were related to shallow water compound and overtides of principle solar and lunar constituent and to seiches generated in the Red Sea and the Gulf of Aqaba. Spatial and temporal distribution of temperature, salinity and density showed significant differences between months in the coastal and offshore region and no significant differences among the coastal sites, between the surface and bottom waters and between coastal and offshore waters. Therefore, the temporal and spatial variation of water properties in the northernmost Gulf of Aqaba behave similarly compared to other parts. The coastal current below 12 m depth was weak (3-6 cms-1) and fluctuated from east-northeastward to west-southwestward (parallel to the shoreline), which may be related to the effect of bottom topography and/or current density due to differential cooling between eastern and western parts in the study area, and windinduced upwelling and downwelling in the eastern and western side, respectively. The prevailing northerly winds and stratification conditions during summer were the main causes of the southward current at 6 and 12 m depths with average speed of 28 and 12 cms-1, respectively.

Sea-water seasonal changes at a heavy tourism investment site on the Jordanian northern coast of the Gulf of Aqaba, Red Sea

The Gulf of Aqaba exhibits a strong seasonality due to convective mixing during winter and stratification during summer. The present study provides a detailed appraisal of summer and winter sea-water characteristics at the northern coast of the Gulf of Aqaba, that is witnessing rapid development and increasing changes in its geomorphological characteristics. Sea-water temperature, salinity, nutrients, and chlorophyll a concentrations were measured biweekly at five coastal and four cross-sectional stations during the periods February to April and July to September 2004. Meteorological conditions were continuously recorded at the Marine Science Station. The coastal study sites included four open coastal stations and a marina with one-way exchange with the open water. The effect of convective mixing was clearly apparent on the sea-water characteristics. Natural seasonal characteristics of higher nutrients and chlorophyll a concentrations were recorded during winter at most of the open coastal stations. In the cross-sectional stations, the concentrations of nutrients and chlorophyll a were not different between the surface and the bottom during winter, but the bottom waters had generally higher concentrations during summer. Some deviations from the natural seasonal cycle were recorded at the marina and other coastal stations. Here, higher nutrient and chlorophyll a concentrations were recorded in summer than in winter. These deviations that are most likely due to anthropogenic effects are discussed.

Community structure of the family Pomacentridae along the Jordanian coast, Gulf of Aqaba, Red Sea

Abstract The spatial distribution and community structure of the family Pomacentridae were studied at different depths and sites along the coast of the Gulf of Aqaba in seagrass and coral reef habitats. Sixteen coastal sites along the Jordanian coast were studied by the visual census technique. A total of 151,134 pomacentrid fishes representing 23 species were observed during 188 visual censuses at 96 belt transects, and 4 additional species were observed outside the transect lines. Six species accounted for 85% of all individuals. Results from cluster analysis of the studied sites based on percentage of benthic cover revealed two main groups: the seagrass and the coral reef dominated sites. Fishes were most abundant at 12 m depths in the coral dominated sites, while fewer numbers were found at reef flat and seagrass sites. This was attributed to the shelter, structural complexity and food availability in the coral reef sites. Pomacentrus trichourus and Amphiprion bicinctus were the most common pomacentrid fishes. Teixeirichthys jordani was restricted to the northern coast of the Gulf of Aqaba. Multivariate analysis of the pomacentrid community revealed certain associations of fishes with different habitats. Within the large group of coral reef associated fishes we could distinguish the following three groups: a group of species that occur at 12 m deep transects such as Chromis weberi and C. pembae; a group of species that occur only in the reef flat such as Plectroglyphidodon leucozonus and P. lacrymatus; a group of the most dominant and most common species such as Neopomacentrus miryae and Pomacentrus trichourus.

Impact of artificial lagoons on seawater quality: evidence from 7 years of physicochemical seawater monitoring

Seven years (2010–2016) of data on the basic physicochemical properties of seawater, temperature, salinity, dissolved oxygen (DO), nutrients, chlorophyll a (Chl a), and hydrocarbons from two lagoons were used to evaluate the impact of the anthropogenic activities inside the lagoon on the water quality and to explore the relationship of any impact from the lagoons’ design. Statistical analysis shows the modification in water quality inside the lagoon compared to the ambient seawater is particularly evident for nitrate, silicate, and Chl a. The modification is attributed to the extensive boat activities in the lagoons and the limited water exchange between the lagoons and ambient seawater. However, the impact to both lagoons is generally limited to inside the lagoons. The oligotrophic state of the two lagoons was evaluated and it was found that the most marked code violations were found in DIN inside both lagoons. In order to explore the design importance, the water exchange and overall water quality was compared between the two lagoons. This study highlights the importance of an environmental design study before the construction of any lagoon project. Proper design would maintain acceptable water quality inside the lagoons, critical for environmental health and supporting continued recreational activities.