Meiofauna of the Red Sea Mangroves with Emphasis on Their Response to Habitat Degradation: Sudan’s Mangroves as a Case Study

Abstract

This chapter provides an overview on the meiofauna of mangroves in the Red Sea coast of Sudan, with an emphasis on the meiofaunal response to mangrove degradation. Investigations of meiofaunal response were based on comparing sites subjected to human impacts resulting in complete clearance and partial clearance of mangrove cover with a non-cleared site with intact mangrove cover in the southern coast of the Sudanese Red Sea. At the degraded mangrove sites, sediment sorting, mean grain size, water and organic contents in sediments changed significantly, and the variation between shoreward (high-and mid-intertidal) and seaward (low-intertidal, shallow subtidal) zones intensified. These changes were attributed to modification of the sediment depositional and reworking processes at the deforested sites. Correlated significant changes in the structure of meiofauna at higher taxonomic levels were indicated by ANOSIM, resulting from the different responses of the various meiofaunal groups to the deforestation impact. Changes in the meiofaunal community structure at higher taxonomic levels were mainly due to increased copepod/nauplii and decreased nematode abundances at the deforested sites. Among other groups, abundances of Ostracoda, Acari and Kinorhyncha were also reduced, but some others, for example, Oligochaetes, Platyhelminthes, Gnathostomulida, Gastrotrichs, and Cnidaria became more frequent and abundant at the partially-deforested sites. Similar changes occurred at lower taxonomic levels in the nematode community structure. While changes in the abundance of different nematode species have contributed to the community variation at the deforested sites, the decrease in the abundance of Terschellingia sp. was the most important. The nematode species Shannon-Wiener diversity became significantly higher at the partially-deforested site and lower at the completely deforested site, in comparison with the natural non-cleared mangrove site. The increased richness and diversity at the partially-deforested site, which was also indicated by species k-dominance curves, were attributed to the habitat heterogeneity of the patchy mangrove vegetation. These observations were also considered in the context of Connell's intermediate disturbance hypothesis ``with peak meifauna diversity at intermediate level of disturbance{''}. On the other hand, the results also recorded increased variability in the meiofaunal and nematode communities within the deforested sites, which was considered indicative of community stress. Seasonal variations of meiofaunal communities were also exaggerated at the deforested sites, which could be attributed to the decline of their resilience to seasonal changes due to loss of mangroves from the habitat. Among the nematode species, the relative abundance of selective deposit feeders showed a noticeable response, decreasing sharply at the deforested sites. This was related to the decline in the availability of organic/microbial food resulting from mangrove degradation. Other feeding guilds, especially non-selective deposit feeders, displayed an opposite trend, increasing in relative abundance as their feeding strategy might prove to be more energetically favourable with the decline of organic detritus and microbial contents at the deforested sites. Thus, the functional properties of the community were modified at the deforested areas, although nematode diversity was enhanced at the partially-deforested site. The overall feature of the change at the deforested sites was a shifting of ecosystem properties with consequent changes in the meiofauna, which indicated decline in the efficiency of the ecosystem function as a nursery ground for marine organisms, which represents one of the vital services provided by the mangrove ecosystem.