TITLE:
Ecological Status and Phytoplankton Structure of a Coastal Lagoon in South-Western Benin Prior to Dredging of the Mono-Aheme-Couffo Complex
AUTHORS:
Kolawolé Boni, Rafiatou Bamisso, Ahouansou Montcho Simon, Cédric Woito, Domiho Japhet Kodja, Firmin Adandedji, Ernest Amoussou, Christian Comlan Viaho, Martin Nani Gbedey
KEYWORDS:
Coastal Lagoon, Phytoplankton, Dredging, South-Western Benin
JOURNAL NAME:
Journal of Geoscience and Environment Protection,
Vol.14 No.7,
July
27,
2026
ABSTRACT: The lack of recent data on the ecological status and phytoplankton structure of the coastal lagoon of south-western Benin is a major obstacle to assessing the impacts of dredging on the Docloboué-Avlo section. This study characterises that status from physico-chemical parameters and the phytoplankton community, measured in February 2025 (before the start of dredging work) at eight stations (P1 - P8). Water quality was assessed against SEQ-EAU thresholds; phytoplankton structure was analysed by microscopy, diversity indices (Shannon H', Pielou J', Simpson D), the Diatom/Cyanophyte ratio (D/C) and Principal Component Analysis (PCA). The results reveal poor to critical water quality: widespread hypoxia (DO: 0.03 - 3.19 mg/L), high organic loads (BOD5: 184 - 318 mg/L; COD: 248 - 409 mg/L) and variable salinity (5.66 - 19.33 PSU). The PCA reveals a gradient of mineralisation and oxygenation. The inventory records 46 taxa (4 classes, 24 families), dominated by cyanophytes (71.8%); diversity is low to moderate (H': 1.22 - 4.01 bits) and the D/C ratio indicates critical eutrophication at P8 (D/C = 0.07). This study confirms an advanced state of degradation and justifies rigorous environmental monitoring throughout the dredging works.