M.Sc Thesis

M.Sc StudentVdov Olga
SubjectThe Linkage between Environmental Heterogeneity and
Biodiversity in Algal Assemblages on the Rocky
DepartmentDepartment of Civil and Environmental Engineering
Supervisors PROF. Yohay Carmel
DR. Gil Rilov


This study inspected the complex relationship between algae species diversity and the environmental heterogeneity, attempting to reveal the ecological processes that shape algal intertidal community on abrasion platforms. The structure of the platforms, seasonal fluctuations, constant water flushing, and possibly rising temperatures, all affect community structure and the distribution of algae on the platforms. According to habitat heterogeneity hypothesis, a cornerstone in ecological theory, a more heterogenic environment will support higher species diversity. This theory was examined comparing species diversity and an index of structural heterogeneity on six abrasion platforms at Akhziv rocky shore. I also studied the effects of individual environmental parameters, temporal and spatial variability on species diversity and composition at the small to medium spatial scales. Field sampling was carried out in four seasons over one year. Seasonality had the strongest effect on species diversity and on community composition. Winter was the richest and most diverse season, and summer was the least diverse. The second most important factor was the different sub-habitats on each platform. Tide pools were the most diverse, and harbored some sub-tidal species. The following factors were significantly correlated to algal diversity: surface verticality and roughness, sand and water cover, presence of biogenic rim and limpets. Water flux was significantly greater at the edge of the platforms than at the center. Height above sea level played a major role in community structure and affected species distribution collaterally through other parameters as flux, water cover and grazer distribution. Lower platforms exhibited weaker differences between sub-habitats, and community structure was significantly different from higher platforms. This finding has critical implications for the intertidal habitat in case of acceleration in sea level rise. Correlation between the structural heterogeneity index and species diversity was insignificant. Nevertheless, individual heterogeneity components had high correlation to algal diversity. It seems that most community-forming processes operate at small spatial scales, suggesting that high environmental heterogeneity as recorded here, with high species densities on such a small area, might have a negative effect on diversity, contrary to the classic theory.