Monitoring the Effect of Seasonal Variation on Macro-Benthic Invertebrates’ Fauna in Timsah Lake and Western Lagoon, Ismailia, Egypt

Macroinvertebrates (MBI) serve as a food source for various animals in both aquatic and terrestrial environments. Consequently, they are important indicators of ecosystem health and functionality. This paper investigated the macroinvertebrate fauna of Lake Timsah and the western lagoon seasonally, exploring variations in community distribution and physicochemical parameters to correlate these factors with macroinvertebrate abundance and seasonal changes. A total of 43 species were collected, belonging to six groups. The most abundant group was Arthropoda, comprising 48.23% of the total MBI, with an annual average of 22,412 individuals per square meter (ind./m²). Mollusca contributed 38.25% of the total MBI, averaging 17,776 ind./m² annually. Annelida and Chordata had annual averages of 4,544 and 1,491 ind./m², respectively. From June 2022 to May 2023, approximately 24 water samples were taken from both the lake and the western lagoon on a seasonal basis. Higher levels of dissolved oxygen were observed in the tested samples during spring compared to other seasons, ranging from 11.2 to 6.96mg/ L. The pH levels varied from 7 to 9.5, with the maximum mean value (9.5) recorded in autumn, while the average salinity in summer was 30.5‰. The MBI displayed spatial distribution variations across the study sites, with Timsah Lake exhibiting the highest number of species and individuals (41 species, 40,275 ind.) compared to the western lagoon (20 species, 6,198 ind.). The highest seasonal density at Timsah Lake occurred in summer (12,579 ind./m²), while the western lagoon recorded its highest density in winter (11,862 ind./m²). Principal component analysis (PCA) revealed a strong positive correlation with the most prevalent MBIs, particularly Bivalvia and Crustacea, across all seasons. Canonical correspondence analysis (CCA) indicated that the physicochemical parameters tested in Lake Timsah during summer, autumn, and spring had a strong positive association with MBIs, including Polychaeta, Cnidaria, and Crustacea.