New Records and Redistribution of Intertidal Mussels Brachidontes pharaonis, B. puniceus, B. exustus, and Perna perna (Mytilidae) from the Eastern Mediterranean, Egypt

Mussel populations are recognized as key components of coastal ecosystems. They are highly dynamic in response to environmental stressors and play a crucial role in understanding the effects of climate change and human activities on marine ecosystems. In Egypt, long-term environmental monitoring faces challenges due to lack of funding, leading to data discontinuity. Critically, there is a 20-year gap in registered mussel bed cover data for the study area.  This study aims to document the current occurrence, seasonal abundance, and distribution of rocky shore mussels along the eastern Mediterranean coast of Egypt, with an emphasis on detecting and quantifying invasive species. Specimens of the bivalved mussels Brachidontes and Perna (Mytilidae), were collected during a surveillance study focused on rocky shore mussels at Abu Qir Bay, Alexandria, Egypt, eastern Mediterranean Sea. Specimens were collected seasonally at depths ranging from 0.4 to 0.6 meters and were identified to the species level based on morphological characteristics of the shell. The brown mussel Perna perna and three species of Brachidontes, the native Red Sea mussel B. pharaonis, and two non-indigenous species, B. puniceus and B. exustus, were recorded. During the study period from March 2023 to January 2024, a total of 415, 2663, 2353, and 704 individuals per square meter of P. perna, B. pharaonis, B. puniceus, and B. exustus were collected, respectively. The highest mean abundances were recorded in Spring for all the collected mussels, with the highest value recorded for B.pharaonis. Among the four identified mussel species, P. perna, B. puniceus, and B. exustus are new records for the eastern Mediterranean coast of Egypt, whereas B. pharaonis is one of the successful Lessepsian immigrants previously recorded.