Ecosystem Services of Avicennia marina in the Red Sea

Abstract

The Red Sea is an arid environment, without riverine inputs, oligotrophic waters and extreme temperature and salinity. Avicennia marina is the dominant vegetation in the shores of the Red Sea. However, little is known about their distribution, dynamics, and services. Therefore, the aim of this Ph.D. was to obtain the basic information needed to evaluate their role in the coastal ecosystems and quantify their services. With that objective we 1) estimated the past and present distribution of mangroves in the Red Sea, 2) investigated the growth, leave production and floration 3) examined the growth limiting factors 4) measured the nutrients and heavy metal dynamics in the leaves and 5) estimated carbon sequestration. We found an increase of about 12% in the last 41 years, which contrasts with global trends of decrease. The extreme conditions in the Red Sea contributed to limit their growth resulting in stunted trees. Hence, we surveyed Central Red Sea mangroves to estimate their node production with an average of 9.59 node y-1 then converted that number into time to have a plastochrone interval of 38 days. As mangroves are taller in the southern Red Sea where both temperature and nutrients are higher than the Central Red Sea, we assessed nutrient status Avicennia marina propagules and naturally growing leaves to find the leaves low in nutrient concentrations (N < 1.5 %, P < 0.09 %, Fe < 0.06) and that nutrients are reabsorbed before shedding the leaves (69%, 72% and 35% for N, P, and Fe respectively). As a result, we conducted a fertilization experiment (N, P, Fe and combinations) to find that iron additions alone led to significant growth responses. Moreover, we estimated their leaf production and used our previous estimates of both the total cover mangrove in the Red Sea along with plastochrone interval to assess their total nutrients flux per year to be 2414 t N, 139 t P and 98 t Fe. We found them to sequester 34 g m-2 y-1, which imply 4590 tons of carbon sequestered per year for the total mangroves covered by the Red Sea.