Intertidal seagrass Halodule uninervis : Factors controlling its density, biomass and shoot length

The seagrass Halodule uninervis is distributed in separate patches along the coast of Kuwait but its distribution in the meadows in Kuwait bay appear to be declining. Physical, chemical and biotic factors were investigated in three contrasting locations to determine how these affect the biomass, shoot density and length of this seagrass. There are significantly longer leaves, higher biomass and shoot density in H. uninervis beds in south compared to that of Doha in Kuwait bay. At the same time, there are significantly longer leaves in lower intertidal zone compared to upper intertidal zone. The characteristics of tidal pools formed during low tide seem to determine the extent of exposure these seagrass endure during low tide. Most of the meadows in the intertidal zone were in tidal pools of loamy sand to sandy sediments. Tidal pools at the southern sites have a constant influx of seawater that significantly reduce the temperature and salinity of these tidal pools during summer. Shoot density and biomass at all three sites increased during the year, reaching maximum during July, after which these plants shed their leaves by an escape mechanism that is evident especially in Doha seagrass population. Doha meadows exist in isolated tidal pools and experience temperatures above 45oC. Turbidity at Doha is also significantly higher, hence reducing the availability of light to these seagrass. But at all sites, the concentration of heavy metals in the sediment and plant tissues were below toxic levels. The diversity and density of epiphytes on the leaves were also high from late spring to mid-summer, the period of rapid growth of the species.</p

Local bleaching thresholds established by remote sensing techniques vary among reefs with deviating bleaching patterns during the 2012 event in the Arabian/Persian Gulf

A severe bleaching event affected coral communities off the coast of Abu Dhabi, UAE in August/September, 2012. In Saadiyat and Ras Ghanada reefs ~. 40% of the corals showed signs of bleaching. In contrast, only 15% of the corals were affected on Delma reef. Bleaching threshold temperatures for these sites were established using remotely sensed sea surface temperature (SST) data recorded by MODIS-Aqua. The calculated threshold temperatures varied between locations (34.48 °C, 34.55 °C, 35.05 °C), resulting in site-specific deviations in the numbers of days during which these thresholds were exceeded. Hence, the less severe bleaching of Delma reef might be explained by the lower relative heat stress experienced by this coral community. However, the dominance of Porites spp. that is associated with the long-term exposure of Delma reef to elevated temperatures, as well as the more pristine setting may have additionally contributed to the higher coral bleaching threshold for this site