Association pattern among different snails and other macroinvertebrate species at certain freshwater courses in Egypt

The objective of the present work is to study the association among snail species, as well as between gastropods and other macroinvertebrates. The study was accomplished in three governorates; Giza, Damietta and Minya from spring (2009) till winter (2010). A total of 26 macroinvertebrates taxa representing 14 orders were recorded at 18 investigation sites, included Ephemeroptra, Plecoptera, Trichoptera, Diptera, Cleoptera, Odonata, Hemiptra, Gastropoda, Bivalva, Decapoda, Amphipoda, Oligochaeta, Arachnids and Hirudinea. The present data, revealed that the snails were the most dominant, comparing to other macroinvertebrates taxa in all stations of the study, which recorded 34.56% followed by shrimps (28.34%). Lanistes carinatus, Cleopatra bulimoides and Physa acuta were the most dominant snail species during the whole study. According to Diversity Index (H′) rank, the status of the present investigated sites ranged from poor to bad status. Moreover, Evenness Index (J) indicated that individuals at S5 (1.0), S4 and S17 (0.9) were distributed equally, while individuals at S3 (0.3), S10 (0.4) and S18 (0.41) were not.  Biomphalaria alexandrina was the only species which maximally associated with leeches and this indicates its higher tolerance than other snails. All sensitive taxa (Ephemeroptra, Plecoptera and Trichoptera) were negatively correlated with Hirudinea. Meanwhile, Gastropoda was negatively correlated with Cleoptera, Hemiptra and Hirudinea. Lymnaea natalensis and Bulinus truncatus snails were found highly associated with damselflies and dragonflies, which reflect the sensitivity of these snails. Cluster analysis showed a similarity level between macroinvertebrates orders. This study concluded that most snail species were associated with moderately to somewhat pollutant tolerant macroinvertebrates, which reveals that the strength of this group in different mechanisms to tolerate pollution and other stresses.