Ecohydrological gradients affecting the abundance and biodiversity of macro-invertebrates in the estuarine system of Sperchios River, Central Greece

The factors affecting the abundance and biodiversity of the macro- invertebrates in relation to the quality of substrate and vegetation of the estuarine system of Sperchios River, Central Greece, were examined. The reason why only the two specific seasons of winter and summer were chosen is because extreme weather phenomena take place during both seasons that affect the factors of abundance and biodiversity. Of the nine identified taxa, the main contributor to macro-invertebrate abundance in August 2001 was Hediste diversicolor, while Cerastoderma glaucum was the principal one in January 2002. The Spearman coefficient showed a positive correlation of biomass (A') with water temperature (0.39) in January, the concentration of nitrates (0.69), the clay (0.66), and the organic matter of the sediment (0.47-0.53). A positive correlation (Spearman) has also been shown between biodiversity, the percentage of sand in the sediment, and the concentrations of ammonia and nitrates. As species abundance (A) has been positively correlated (Spearman coefficient = 0.21-0.72) with sediment organic matter, vegetation in the lower inter-tidal zone seems to have affected A positively. The analyses of the used indices (A, A', Margalef, Shannon-Wiener, Pielou's evenness, Sorensen similarity) indicated a negative influence on the diversity of benthic macroinvertebrates, and a possibly causal relationship between agricultural wastes drained to the estuarine Sperchios system and its sediment quality.