Alpha and Beta Diversity of Marine Seaweeds as Indicators of Climate Change: A Case Study on Selected Areas Along the Egyptian Red Sea Coast

The Red Sea is recognized as one of the world`s most diverse marine ecosystems. As a semi-enclosed basin, it is characterized by extensive coral growth, limited rainfall, and the absence of river inflows. The Egyptian coastline of the Red Sea stretches approximately 968 km, from Suez in the north to South Halayeb. Its biodiversity, particularly marine macroalgae, has been extensively documented. However, ongoing climate change is expected to alter species distribution and community composition.

The current study employs both morphological and molecular tools to monitor the alpha (species diversity within a site) and beta diversity (species diversity between various sites/ seasons) of seaweeds in 5 selected locations along the Red Sea Coast (Zaafarana, Hurghada, Makadi, Quseir and Marsa Alam) over a two-year study. Seasonal sampling was conducted between January 2023 and December 2024. Algal Samples were collected from 10 randomly selected quadrats in each site, from tidal and subtidal zones. Weather conditions such as temperature, wind speed and UV index were retrieved from NASA Power website for the given sites and time periods.

A total of 64 genera were recorded, of which 33 were identified as rhodophytes, 15 chlorophytes, 13 phaeophytes and 3 unknowns. Algal cover varied among sites and seasons, reflecting fluctuations in temperature, ultraviolet radiation, and wind conditions. Alpha diversity showed the decline of ~50% of algae as UV radiation elevated. The influence of Ebb tides on algal distribution was also observed and underreported genera, such as Predaea sp., Asterocladon sp. and Rhodachlya sp. were reported.

The predominance of rhodophytes across the study sites suggests the high resilience to tolerate both extreme high and low temperatures Species such as Digenea simplex and Valonia aegagropila occurred at all sampling sites throughout the study period, indicating broad environmental tolerance. Invasive species such as Acanthophora sp. showed remarkable acclimatization and normal distribution along the coasts. These findings highlight the importance of long-term monitoring of macroalgal communities as indicators of ecological change along the Egyptian Red Sea coast.