This study has allowed to classify the marine macroalgae from the intertidal zone on the Atlantic side of Cap Estérias (Gabon). This area has a rich biodiversity but very few studies in the knowledge of benthic macroalgae have been done. The first study on the knowledge of the algae of the Gabonese coast was made in February 1974 by John and Lawson. This article has been revised to transcribe books and our study would aim to update the existing collection. The algae census is spread over a year from August 2020 to August 2021 and is the first detailed study carried out over a year, with regard to this part of the Gabonese coast. This study has allowed to know the specific diversity, to determine the structure of the flora and its spread out over time. The results show a significant algal diversity of thirty five (35) identified species. Three classes of macroalgae were determined and the percentage of species in the class (%EC): Floridaophyceae at 50% EC, Phaeophyceae at 30% EC and Ulvophyceae at 20% EC. The red algae are the most common in the area with sixteen ( 16) species determined against twelve (12) species of brown algae and seven (7) species of green algae. The Phaeophyceae class presents the Dictyotaceae family which is the most diverse with 7 species found. Some species seen appear in the collection of John et al., but others are new species encountered in Gabon such as Caulerpa sertularioides, Bryopsis plumosa (two Ulvophytes), Padina arborescens which is a Pheophyte and Galaxaura filamentosa, Digenea simplex, Hildenbrandia rubra, Asparagopsis armata and Caulacanthus ustulatus which are Rhodophytes. Some species are permanently present, they are found in all seasons but with significant abundance from July to September.

This study has made it possible to link the configuration and distribution of molluscs in the Cape Estérias mediolittoral rocky foreshore area, from January 2021 to January 2022, during a one-year cycle. In fact, the intertidal area being a fragile and above all unstable, it necessitates regular and frequent monitoring. The malacofauna were then taken every two weeks during spring tides. And the temperature was measured twice a day in situ during the two tides. The Cap Estérias rocky foreshore malacofauna reveals 36 molluscs belonging to 3 families (29 gastropods, 6 bivalves and 1 cephalopod). As for the water temperature, it shows large fluctuations with average amplitude of 0.75 °C, probably due to tidal dynamics and the Mondah fresh water in flows. These temperatures vary from 32.2 to 23.5 °C, for an average of around 28.5 ± 1.5 °C year - round. To end, the highest water temperatures are recorded during the rainy seasons, while the lowest are recorded during the dry seasons; this is in accordance with the equatorial climate of the studied area.