Epizoic diatom diversity and abundance of on the spider crab Hyastenus hilgendorfi from Lake Timsah, Suez Canal, Egypt

Abstract We investigated the epizoic diatoms colonizing the carapace of the spider crab Hyastenus hilgendorfi inhabiting Lake Timsah in the Suez Canal. A total of 63 individuals, free of macro-epibionts, were examined to assess the diversity, abundance, and seasonal dynamics of their associated diatom communities. A total of 61 diatom taxa belonging to 31 genera were recorded, with raphid pennate diatoms being the most dominant, particularly Navicula lanceolata . Diatom density and diversity exhibited clear seasonal variation, where Summer had the highest richness and Spring the highest cell densities. Overall, males hosted more diatom taxa than females, however, sex-specific differences fluctuated seasonally. The cluster analysis revealed distinct diatom assemblages between sexes and seasons, showing subtle but significant variation in epibiont structure. These findings provide the first detailed characterization of epizoic diatom assemblages on H. hilgendorfi . They suggest that seasonal variations in diatom communities may influence the crab’s camouflage effectiveness by altering biofilm characteristics which facilitate macro-epibiont settlement.