Litterfall production and nutrient dynamics in mangrove systems on the Red Sea coast of Saudi Arabia

Abstract

Litterfall production, decomposition and the release of chemical components were estimated in two Avicennia marina mangrove systems on the Red Sea coast, a northern site in Yanbu and a southern site in Shuaiba regions. Over a period of 2 years, monthly litterfall and litter standing stock production were estimated using litter traps and ground plots, respectively. The decomposition of leaf litter was assessed over a period of 256 days using litterbags, the changes in the chemical composition (carbon and nitrogen) and their ratios, and the chemical compound concentrations (leachable carbohydrates, cellulose, hemicelluloses and lignin) were estimated at each decomposition stage. The annual litterfall rates did not differ significantly between sites. In Shuaiba, monthly litterfall ranged from 87.7 kg ha-1 to 543.1 kg ha-1 with an annual litterfall rate of 3.68 t ha-1 y-1 while in Yanbu, the monthly litterfall ranged from 142 kg ha-1 to 539.5 kg ha-1 with an annual litterfall rate of 3.51 t ha-1. Monthly standing stock litter was significantly lower than monthly litterfall in both sites (p <0.05) indicating litter removal from the forest floor, however, the removed litter is retained within the mangrove system rather than exported owing to low tidal ranges. The litterfall lost 41% of its mass in the first 64 days with no significant differences in final mass loss between Shuaiba and Yanbu sites (p >0.05) and with a half-life value of approximately 90 days. The N concentration in the decomposing leaves was 40% lower than those of fresh leaves. In addition, the lignin concentration in litter increased over time and was negatively correlated to mass loss. These findings indicate low litter production and litter quality compared to systems in other parts of the world. Moreover, it indicates the accumulation and conservation mechanism of mangrove ecosystems in the extreme Red Sea environment.